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Peripartum metabolism and subsequent reproductive performance of dairy cows are linked, with maladaptation over the transition period associated with poor reproductive success. A herd of seasonal calving, grazing dairy cows was established that differed in their genetic merit for fertility traits. The heifers were produced by a customized mating program to achieve a 10-percentage point divergence in the New Zealand fertility breeding value (FertBV) as follows: +5 FertBV (POS) versus −5% FertBV (NEG), while also limiting divergence in other breeding values, including body weight, body condition score, and milk production. In this study, we aimed to characterize differences in metabolic, mineral, and metabolic stress marker profiles during their first postpartum transition period as primiparous heifers and to examine if animals with longer postpartum anestrous intervals (PPAI; more than 66 d compared with less than 35 d) had greater metabolic dysfunction. Blood was sampled at −21, −14, −7, 0, 4, 7, 10, 14, 17, 21, 28, and 35 d relative to calving in 455 primiparous cows and plasma analyzed. The NEG cows had lower concentrations of both plasma nonesterified fatty acids and β-hydroxybutyrate at d 7 compared with POS cows. Detailed temporal profiling of various metabolic, mineral, and metabolic stress markers was undertaken in a subset of cows (n = 70). Cows were selected retrospectively to create 4 groups in a 2 × 2 factorial design with either a POS or NEG FertBV and either a short (19–35 d) or long (66–131 d) PPAI. The NEG cows tended, on average, to have lower nonesterified fatty acids and β-hydroxybutyrate concentrations compared with POS cows across the transition period. Mean body weight and body condition score was greatest in NEG cows when compared with the POS cows and an interaction with day demonstrated this only occurred precalving. They also had indications of improved liver health precalving, with higher albumin-to-globulin ratios and lower bilirubin concentrations. Concentrations of aspartate aminotransferase were lower, and the Na-to-Cl ratio was greater in cows with a long versus a short PPAI at d 28 and d 35 after calving, potentially because of cows with a short PPAI (19–35 d) returning to estrous during this time. Magnesium concentrations were lower in NEG cows with a short PPAI from d 21 onwards, indicating NEG cows may metabolically respond to estrous differently than POS cows. The NEG-long PPAI cows had greater gamma-glutamyl transferase concentrations from calving until d 28 and lower bilirubin concentrations throughout the transition period. Together, the results demonstrate significant effects of FertBV on peripartum metabolic status. However, most of the markers tested returned to reference intervals within 4 d after calving or remained within those intervals for the whole transition period, indicating relatively minor biological effects of FertBV on transition period adaptation. The profound differences in reproductive performance among the groups was not explained by underlying differences in metabolic responses during the transition period.

The primary aim of this prospective study was to determine the postnatal mortality risk of replacement dairy heifers from weaning until the start of their second mating period (∼27 mo of age) in seasonal-calving, pasture-based dairy herds. Data were analyzed from 24 farms from the Waikato (n = 15) and Canterbury (n = 9) regions of New Zealand. All animals included in the study had an identified weaning date. From this point onward, data on animals that were euthanized, died unassisted, were culled, or were sold were recorded by the farmer on the home farm or by the grazier, according to animal location, and validated using calving, mating, culling, and sold records in their herd improvement database (MINDApro LIC, Newstead, Hamilton, New Zealand). The mortality risk from weaning to the start of the second mating period was calculated by dividing the number of deaths by the total number of enrolled animals at weaning. Mortality rate was calculated by dividing the number of deaths over the study period by the total days at risk, and reported as the mortality rate per 100 cow years; this measure was also calculated as the mortality rate per farm. A total of 3,770 animals from 24 farms had data from weaning until the farm planned start of mating when animals were ∼27 mo old. The animal-level mortality incidence risk from weaning (∼13 wk of age) to the start of their second mating (∼27 mo old) was 2.7% (95% confidence interval: 2.2 to 3.3%; 102 deaths/3,770 animals). The median farm-level mortality incidence risk was 3.0%, with a range across farms from 0 to 7.9%. There was a total of 102 deaths over 2,429,362 cow days at risk, with the mean time at risk for the animals of 646 d. The animal-level mortality was 1.53 deaths (95% confidence interval 1.26 to 1.86) per 100 cow years from weaning to second mating start date. The range in farm-level mortality rate was 0 to 4.52 deaths per 100 cow years. The hazard of death did not change throughout the study period. The results from this study are difficult to compare with international studies due to differences in study timing and duration, reporting method (mortality risk vs. mortality rate), and concerns with data validation. However, to the best of our knowledge, the results from this study indicate that postweaning, postnatal mortality under the New Zealand seasonal-calving, pasture-based system is lower than most other reported studies.

Milking cows once daily is a management tool that has been implemented to improve physical and financial results of seasonal pasture-based dairy farms. The Molly cow model integrates physiology and metabolism of dairy cattle; however, milk production during short-term changes in milking frequency (e.g., 1× milking) is not well represented. The model includes a representation of variable rates of cell quiescence and death. However, the rate constants governing cell death and the return of quiescent to active cells are not affected by milking frequency. An empirical assessment of the problem was conducted, and it was hypothesized that changing the current representation of the rate of cell death in response to short-term 1× milking would more accurately represent active and quiescent cells and improve predictions of milk production. An extra senescent cell flux was added to account for cell loss during periods of 1× milking. Additional changes included a gradual decline in the rate of 1× stimulated senescence during 1× milking, and a structural change in cell cycling between active and quiescent cells during and after short-term 1× milking. Data used for parameter estimation were obtained from 5 studies where 1× milking or different feeding strategies were tested. Parameter estimates of cell loss indicated that 1× milking would affect a small proportion of quiescent cells to cause extra cell death. This added cell senescence was influenced by the length of 1× milking such that cell senescence peaked on d 1 of 1× milking and decayed from that point. The new structure in the model includes a variable rate of cell death in response to 1× milking and a gradual rate of return of quiescent cells back to the active pool in response to switching to 2× milking after short-term 1× milking. Root mean square errors, mean bias, and slope bias declined by at least 50% for predictions of energy-corrected milk yield and fat percent. The model showed quantitative agreement with production data from short-term 1× milking. The accuracy of predictions was improved and the error was reduced by implementing modifications in the model in response to changes in milking frequency.

Milking cows once daily (1×) is a management practice occasionally used during mid/late lactation in pasture-based systems. It has been postulated that 1× milking will reduce dry matter intake (DMI) and increase body condition score (BCS) gain; however, this has not been quantified. Lactating, pregnant Holstein-Friesian dairy cows (n=52) were allocated to either 1× or twice-daily (2×) milking in mid-January (summer, 175d in milk). To obtain accurate DMI measurements, cows underwent 4 periods in a Calan gate indoor feeding facility, interspersed with grazing outdoors. Milk production, body weight (BW), and BCS were recorded 2 wk before treatment start (-2 wk) and weekly thereafter. Blood variables were recorded at -2 wk and weekly when indoors. Liver was biopsied at -2, 2, and 10 wk, and hepatic gene expression measured using quantitative PCR. Milking cows 1× tended to lower DMI (17.8 vs. 18.2 kg of dry matter), but increased BCS gain (0.36 vs. 0.13 BCS units) and BW (546 vs. 533 kg) at wk 12 relative to 2×. The greater BCS and BW of cows milked 1× compared with 2× were reflected in lower plasma concentrations of nonesterified fatty acids and lower transcription of genes involved in the oxidation of fatty acids, indicating reduced release and processing of fatty acids. Cows milked 1× produced 20% less milk, and although milk fat and protein concentrations were increased relative to cows milked 2×, yields of fat and protein were 14 and 17% less, respectively. The reduction in milk production with 1× milking (14.1 vs. 16.8 kg/cow per d energy-corrected milk) was accompanied by increases in blood concentrations of glucose and insulin, with a concurrent decrease in the transcription of the insulin receptor and gluconeogenic genes. These results indicate a coordinated response to reduce glucose production due to decreased mammary demand. Expression of 2 genes linked to inflammation and adipokine signaling was reduced in cows milked 1× and may indicate a lower inflammatory state in the liver of cows milked 1× in late lactation. No effect was found of milking frequency during late lactation on milk production in the subsequent lactation. In summary, although 1× milking tended to reduce DMI and increase BCS in late lactation, these effects were lower than what is commonly supposed in pasture-based dairy systems. The modest BCS gains need to be considered with the reduced milk production when adopting 1× milking as a management strategy.

Because of its high yield and the ability of cows to graze it in situ, fodder beet (FB) has become a popular crop in grazing systems, particularly for nonlactating cows. Due to its high sugar content, however, the transition to FB must be managed carefully to avoid rumen acidosis and associated metabolic dysfunction. The initial consumption of FB reduces ruminal pH; however, it is unclear whether this affects liver metabolism and results in systemic inflammation, as has been reported during subacute ruminal acidosis from high-grain diets. We used a quantitative case study approach to undertake additional measurements on a project demonstrating the effects of FB on urinary nitrogen excretion. The objective of our component, therefore, was to determine whether the inclusion of high rates of FB in the diet of nonlactating cows changed indicators of hepatic metabolism relative to a standard diet for nonlactating grazing cows. During the nonlactating period, multiparous, pregnant Holstein-Friesian cows were randomly assigned (n = 15 per treatment) to either pasture (8 kg of DM/cow per day) with corn silage (4 kg of DM/cow per day; PA) or transitioning onto an FB diet (8 kg of DM/cow per day) with pasture silage (4 kg of DM/cow per day; BT) over 14 d. Blood was sampled and the liver was biopsied during the adaptation period and after 7 d of full diet allocation. The hepatic expression of genes involved in peroxisomal oxidation was increased in cows adapting to FB, whereas the expression of genes involved in mitochondrial oxidation was increased when cows were on their full allocation of FB. These results indicate changes to fatty acid metabolism with FB consumption. Expression of 2 genes involved in the unfolded protein response was greater during the adaptation period in cows consuming FB, potentially reflecting negative effects of transitioning onto the FB diet on hepatic metabolism. Interestingly, expression of genes involved in the methionine cycle was increased in the BT cows. We hypothesize that this is a result of FB betaine absorption, although it is unclear to what extent betaine escapes ruminal degradation. While on the full diet allocation, there were lower serum concentrations of markers of hepatic stress in BT cows and no difference in expression of genes involved in oxidative stress compared with pasture-fed cows. However, there was an increase in plasma haptoglobin concentrations, indicative of an acute inflammatory response in BT cows. From this case study, we conclude that the results indicate no negative effects of the FB diet on liver metabolism and, possibly, positive effects on hepatic function. It appears, therefore, that the transition of nonlactating cows onto an FB diet can be managed to minimize the negative effects of the high sugar intake. Further research on the amount of betaine that escapes ruminal degradation in cows consuming FB would be of value to better understand whether betaine reduces liver damage in dairy cows consuming FB.

The transition from pregnancy to lactation (i.e. the transition period) is a time of significant metabolic challenge, with a several-fold increase in a cow’s requirement for energy, protein and minerals within days of calving. A successful transition involves the initiation and coordination of changes in multiple tissues that facilitate the provision of these nutrients to the cow and, more specifically, to the mammary gland, often at the considerable expense of other tissues. Failure to coordinate the necessary changes effectively results in transition period maladaptation, which can broadly be grouped into three categories: (1) negative energy balance and metabolic diseases associated with energy metabolism; (2) immune dysfunction and inflammation; and (3) metabolic diseases associated with mineral deficiency. Because reinitiation of ovarian activity, follicle recruitment, ovulation, fertilisation and, potentially, even maternal recognition of pregnancy and implantation occur against the backdrop of this metabolic and immunological disturbance in early lactation, the role of nutrition in ensuring a smooth transition between the pregnant and lactating state is important. In this paper we integrate recent research findings with previous knowledge of the interaction between transition cow metabolism and nutrition and reproductive outcomes, and offer new insights into key elements of successful cow management to avoid transition ‘maladaptation’ and improve pregnancy rates.

The objective of this experiment was to determine if transcript abundance of genes involved in metabolic pathways in adipose and liver tissue could provide some explanation for the low efficiency with which ME in autumn pasture is used for BW gain. Nonlactating, pregnant (208 ± 19 d of gestation or approximately 75 d precalving) dairy cows (n = 90) were randomly allocated to either a control diet (i.e., offered fresh autumn pasture to maintenance requirements: 0.55 MJ ME/kg of measured metabolic BW [BW0.75] per day) or, in addition to the control diet, 1 of 2 supplement amounts (2.5 and 5.0 kg DM/d) of autumn pasture or 1 of 4 supplementary feeds (i.e., a control and 2 levels of feeding for each of 5 feeds: 11 groups of cows). Along with autumn pasture, evaluated feeds included spring pasture silage, maize silage, maize grain, and palm kernel expeller. Adipose and liver tissues were biopsied in wk 4 of the experiment and transcript abundance of genes involved in metabolic pathways associated with energy metabolism, lipolysis, and lipogenesis was determined. Additional feed, irrespective of type, increased BW gain (P < 0.01) and this effect was reflected in the expression of genes in adipose and liver tissue. However, autumn pasture had lower energy-use efficiency than the other feeds. Genes involved in both lipogenesis (ACACA, THRSP, GPAM, GPD1, and LPL) and lipolysis (PNPLA2) were upregulated (P < 0.05) in adipose tissue in response to increased ME intake/kilogram BW0.75. Hepatic expression of APOA1 decreased and that of APOB increased (P < 0.05) in cows offered maize grain and maize silage (i.e., starch-containing feeds). In comparison, pasture-fed cows demonstrated a degree of uncoupling of the somatotropic axis, with lower hepatic transcript abundance of both GHR1A and IGF-1 compared with cows offered any of the other 4 feeds. Changes to gene transcription indicate a possible molecular mechanism for the poor BW gain evident in ruminants consuming autumn pasture.

Lying behaviour and activity were measured in healthy grazing dairy cows during the transition from late gestation to early lactation (i.e. the transition period). Behaviour data derived from IceTag® or IceQube® (IceRobotics, Edinburgh, Scotland, UK) tri-axial accelerometers were collated from 311 cow parities of mixed age and breed (Holstein–Friesian, Jersey and crossbred Holstein–Friesian × Jersey) cows from four experiments. The IceTag and IceQube devices captured lying and step data at 1- and 15-min intervals respectively. Behaviour was recorded during the transition period (Day –21 prepartum to Day 34 postpartum) to determine daily lying time, number of lying bouts (LB), mean LB duration and number of steps. The effect of rainfall and air temperature on lying behaviour and activity during two periods, namely, prepartum (Day –21 to Day –3) and postpartum (Days 3–34) was evaluated. Multiple-regression analysis determined that decreased air temperature and increased rainfall is associated with a decline in daily lying time, number of LB and LB duration during both prepartum and postpartum periods. Exposure to both wet and cold conditions exacerbated the behavioural response. The results highlighted the importance of considering the effects of air temperature and rainfall and the interaction of these two climate variables when analysing lying behaviour and activity. Further work is required to quantify the trigger points for this activity modulation, to help understand the balance of welfare experiences in the life of a grazing cow.

This study investigated the immediate and long-term effects of temporary alterations to postpartum milking frequency (MF) on milk production, body condition score (BCS), and indicators of energy status in pasture-grazed cows supplemented with concentrates. Multiparous Holstein-Friesian cows (n = 150) were randomly assigned to 1 of 5 groups at calving: milked twice daily (2 ×) throughout lactation (control), or milked either once daily (1 ×) or 3 times daily (3 ×) for 3 or 6 wk immediately postpartum, and then 2 × for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1 × produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2 ×. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1 × milking; these animals also produced less than 1 × cows switched to 2 × milking after 3 wk. During wk 8 to 32, when all cows were milked 2 ×, those previously milked 1 × had sustained reductions in milk (-6%) and ECM (-8%) yields, which were not affected by the duration of reduced postpartum MF. In contrast, cows milked 3 × postpartum had 7% greater milk yields during wk 1 to 6 compared with 2 × controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3 ×. Nevertheless, yields of ECM were not increased by 3 × milking, because of lower milk fat and protein contents that persisted for the rest of lactation. In addition, indicators of cow energy status reflected an increasing state of negative energy balance with increasing MF. Cows milked 1 × postpartum had greater plasma glucose and lower plasma nonesterified fatty acid concentrations during the reduced MF, and plasma glucose remained lower for 2 wk after cows had switched to 2 × milking. Moreover, BCS was improved relative to 2 × controls from wk 5 to 6. In contrast, cows milked 3 × had lower plasma glucose concentrations, greater plasma nonesterified fatty acid concentrations, and greater BCS loss during wk 1 to 3; however, greater body fat mobilization was not sustained, indicating that additional energy supplements may be required to achieve better milk production responses. In conclusion, temporary 1 × milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3 × milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.

Short-term changes to milking frequency can alter the metabolic status of dairy cows depending on the duration, magnitude, and stage of lactation at which the milking frequency changes occur. Additionally, effects of altered milking frequency that are subsequent to cows returning to a normal twice-daily (2×) milking regimen are not well established. This study tested the hypothesis that plasma concentrations of key hormones and metabolites and transcription of genes involved in the somatotropic axis and lipid metabolism would be altered in liver and subcutaneous adipose tissue from cows milked with different frequencies. Multiparous Holstein-Friesian dairy cows were allocated to 2× milking for the whole lactation, or once-(1×) or 3 times-(3×) daily milking for 3 or 6 wk, immediately postpartum, and then 2× milking for the remainder of the lactation. Liver and subcutaneous fat were biopsied at wk 1 (liver only), 3, 6, and 9 postpartum, and transcription of genes involved in the somatotropic axis and lipid metabolism were measured. At wk 3, cows milked 3× had lower hepatic expression of growth hormone receptor (GHR1A) compared with cows milked 2× or 1×, and lower IGF1 expression compared with cows milked 1×, indicating greater uncoupling of the somatotropic axis. At wk 6, reduced transcription of total GHR and GHR1B occurred in the adipose tissue of cows milked 3×. Cows milked 1× had greater transcription in adipose tissue of lipogenesis genes at wk 3 and 6, and lipolysis genes at wk 6, compared with cows milked 2×, indicating a period of increased fatty acid storage, followed by increased fatty acid reesterification. At wk 9, cows previously milked 3× for 6 wk maintained lower transcription of genes involved in lipogenesis, lipolysis, and ketolysis in adipose tissue compared with cows milked 2×, indicating that the effects of 3× milking persist for at least 3 wk after switching to 2× milking. Results indicate that alterations to milking frequency affect the transcription of genes involved in lipid mobilization and storage, enabling the animal to manage the energy demands associated with the change in milk production. Some of these gene transcription changes were maintained in cows previously milked 3×, indicating that the adipose tissue gene expression changes were still required even after 3 wk of the less-demanding 2× milking regimen.

This study examined the long-term effects of failure of passive transfer of immunity (FPT; diagnosed at 1-8 days of age) on subsequent milk production, growth, reproduction, and lactation performance in dairy heifers from 12 to 36 months of age. A total of 34 farms from the Waikato and Canterbury regions of New Zealand were enrolled in 2015. Each farm was visited on three occasions during the seasonal calving period (early, middle, and late). Blood samples were collected at each visit from 20 replacement heifer calves aged between 1 and 7 days to test for FPT. These heifers (n=1879) were monitored from birth until the end of their first lactation. From 12 months of age onwards, animals were weighed at 15 and 22 months, pregnancy tested 100 days following their first mating, and milk was sampled between 3-4 times during their first lactation to determine milk volume and milk component yields. Farmers recorded any mortality events. FPT had no effect on the odds of mortality from 12 to 22 months (P=0.57) and 12 to 34 months of age (P=0.44). There was no difference in bodyweight at 15 months (P=0.17) and 22 months of age (P=0.95), no significant difference in the odds of being diagnosed pregnant (OR 1.44; 95% CI 0.82-2.69), and no effect on milk solids (fat plus protein) yields (P=0.67). No associations were observed between serum total protein (STP) concentration and milk solids yields (P=0.22) and any other milk parameters. The data from this study indicate that FPT did not adversely affect productivity, performance, or mortality beyond 12 months of age in heifers reared in pasture-based systems.

The objective of this study was to investigate if a reduced milking frequency altered the effect of dietary energy restriction on the hepatic transcriptome of grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows ( n = 120) were milked twice daily (2×) from calving until 34 ± 6 days in milk (mean ± SD). Cows were then allocated to one of four treatments in a 2 × 2 factorial arrangement. Treatments consisted of two milking frequencies [2× or once daily (1×)] and two feeding levels for 3 wk: adequately fed (AF) or underfed (UF, 60% of AF). Liver tissue was biopsied from 12 cows per treatment after 3 wk of treatment, and the hepatic transcriptome was profiled with an Agilent 4 × 44k bovine microarray. Over 2,900 genes were differentially expressed in response to the energy restriction; however, no effects resulted from changes to milking frequency. This may indicate that after 3 wk of 1× milking, any changes to the liver transcriptome that may have occurred earlier have returned to normal. After 3 wk of energy restriction, gene expression patterns indicate that glucose-sparing pathways were activated, and gluconeogenesis was increased in UF cows. Genes involved in hepatic stress were upregulated in response to the energy restriction indicative of the pressure energy restriction places on liver function. Other pathways upregulated included “cytoskeletal remodeling,” indicating that a 3 wk energy restriction resulted in molecular changes to assist tissue remodeling. Overall, 1× milking does not modify the hepatic transcriptome changes that occur in response to an energy restriction.

The objective of this study was to investigate the effect of reduced milking frequency, at 2 feeding levels, on gene expression in adipose tissue of grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n=120) were grazed on pasture and milked twice daily (2×) from calving to 34±6d in milk (mean ± standard deviation). Cows were then allocated to 1 of 4 treatments in a 2×2 factorial arrangement. Treatments consisted of 2 milking frequencies (2× or once daily; 1×) and 2 feeding levels for 3 wk: adequately fed (AF), consuming 14.3 kg of dry matter/cow per day, or underfed (UF), consuming 8.3 kg of dry matter/cow per day. After the treatment period, all cows were fed to target grazing residuals ≥1,600 kg of DM/cow per day and milked 2× for 20 wk. Adipose tissue was collected from 12 cows per treatment by subcutaneous biopsy at -1, 3, and 5 wk relative to treatment start, RNA was extracted, and transcript abundance of genes involved in lipid metabolism was quantified using a linear mixed model. At the end of the 3-wk treatment period, transcript abundance of genes involved in fatty acid (FA) uptake into adipose tissue (LPL), FA synthesis [FA synthase (FASN) and stearoyl-coenzyme A desaturase (SCD)], FA oxidation [acyl-coenzyme A synthetase long-chain family member 1 (ACSL1) and carnitine palmitoyltransferase 2 (CPT2)], glyceroneogenesis [glycerol-3-phosphate dehydrogenase 1 (GPD1) and pyruvate carboxylase (PC)], and triacylglyceride synthesis [diacylglycerol O-acyltransferase 2 (DGAT2)] were greater in AF1× cows compared with all other treatments. However, when cows were underfed, no effects of milking frequency were observed on transcript abundance of genes involved in adipose lipid metabolism. Despite increases in plasma NEFA concentrations in UF cows, no effects of underfeeding were observed on the transcription of lipolytic genes. At 5 wk, after cows were returned to 2× milking and standard feed allowance, transcript abundances of genes involved in FA synthesis [acetyl-coenzyme A carboxylase α (ACACA) and SCD)] were increased in cows previously UF. Expression of ACSL1 was decreased in UF1× cows relative to UF2× cows and CPT2 expression was greater in AF1× cows compared with AF2× cows. In conclusion, after 3 wk of reduced milking frequency during a feed restriction, transcription of genes involved in lipid metabolism in adipose tissue were not altered, possibly due to the reduced milk production in these animals. However, 3 wk of 1× milking in AF cows increased transcription of genes involved in FA synthesis, oxidation, and triacylglyceride synthesis.

The objective of this study was to determine the increase in milk production from supplementation that occurred after supplementation ceased. This portion of the total response (i.e., the deferred response), although accepted, is generally not accounted for in short-term component research projects, but it is important in determining the economic impact of supplementary feeding. Fifty-nine multiparous Holstein-Friesian dairy cows were offered a generous allowance of spring pasture [>45 kg of dry matter (DM)/cow per day) and were supplemented with 0, 3, or 6 kg (DM)/d of pelleted concentrate (half of the allowance at each milking event) in a complete randomized design. Treatments were imposed for the first 12 wk of lactation. Treatments were balanced for cow age (5.4 ± 1.68 yr), calving date (July 27 ± 26.0 d), and genetic merit for milk component yield. During the period of supplementation, milk yield and the yield of milk components increased (1.19 kg of milk, 0.032 kg of fat, 0.048 kg of protein, and 0.058 kg of lactose/kg of concentrate DM consumed), but neither body condition score nor body weight was affected. After concentrate supplementation ceased and cows returned to a common diet of fresh pasture, milk and milk component yields remained greater for 3 wk in the cows previously supplemented. During this 3-wk period, cows that previously received 3 and 6 kg of concentrate DM per day produced an additional 2.3 and 4.5 kg of milk/d, 0.10 and 0.14 kg of fat/d, 0.10 and 0.14 kg of protein/d, and 0.10 and 0.19 kg of lactose/d, respectively, relative to unsupplemented cows. This is equivalent to an additional 0.19 kg of milk, 0.006 kg of fat, 0.006 kg of protein, and 0.008 kg of lactose per 1 kg of concentrate DM previously consumed, which would not be accounted for in the immediate response. As a result of this deferred response to supplements, the total milk production benefit to concentrate supplements is between 7% (lactose yield) and 32% (fat yield) greater than the marginal response measured during the component experiment. Recommendations to dairy producers based on component feeding studies must be revised to include this deferred response.

The aim of this study was to investigate heterogeneity in tissue morphology, milk protein and immune-related gene expression, and apoptosis of epithelial cells in the lactating and involuting mammary glands of the dairy cow. Mammary tissue from different regions of the gland (alveolar, cisternal, and peripheral) was collected postmortem from nonpregnant, pasture-fed, Holstein-Friesian primiparous cows in mid-lactation that were killed at different time points postmilking: 0, 6, 12, 18, 24, 36, and 72 h (n = 6 per time point). The CSN1NS1 and LALBA mRNA was decreased in alveolar, cisternal, and peripheral tissue by 12 to 36 h postmilking. In contrast, lactoferrin (LF) and mammary serum amyloid A3 (M-SAA3) mRNA was increased in these regions by 36 to 72 h. During lactation, more variability was present in gene expression in alveolar tissue between cows and between quarters within a cow, than within quarters. Histological analysis indicated the alveolar tissue from lactating cows was mostly uniform in structure; however, in situ hybridization indicated that although most of the alveolar tissue expressed milk proteins, the level of expression varied within and between alveoli. This heterogeneity became more pronounced with involution and with increasing regions of alveoli expressing lactoferrin, indicating that alveoli enter involution asynchronously. The peripheral and cisternal tissue had more variability in gene expression between cows compared with the alveolar tissue. The M-SAA3 signal was more intense in the cisternal tissue and less intense than the peripheral compartment compared with LF particularly in the earlier time points. In addition, between cows within the later time points, differences were observed in tissue morphology, the levels of milk protein and immune-related gene expression, and phosphorylated signal transducer and activator of transcription (STAT) 5-P and STAT3-P proteins, and degree of apoptosis, indicating that involution of the mammary gland occurs at different rates between cows. Understanding the mechanisms initiating the process of involution of the mammary gland provides an opportunity for enhancing milk production of the dairy cow.

Objective: Weaning is a process that results in a reduction in milk secretion, an increase in mammary epithelial cell (MEC) apoptosis, and involution of the mammary gland. The local mechanisms initiating MEC apoptosis and involution are unclear, although the physical morphology of the MEC may influence cell-cell and cell-extracellular matrix communication and thus may alter function. This study examined the effect of physical distension of alveoli on the early molecular events that occur at the onset of involution of rat mammary glands. Methods: Mammary tissue was collected post-mortem from lactating Sprague-Dawley rats at 0, 1, 3, and 6 h (n=6 per time point) following acute physical distension of an inguinal gland with isosmotic sucrose solution (0.8 ml; equivalent to ~6 h worth of milk accumulation) via the teat canal followed by sealing with adhesive (infused). The remaining teats on each rat were either left unsealed for pups to suckle (control), or were sealed to induce milk accumulation and mammary engorgement (engorged). Results: There was a low number of positive in situ-end labeled (ISEL) nuclei in suckled control glands indicating they had a low number of cells with fragmented DNA or were apoptotic. However, there was a greater number of ISEL nuclei in sucrose-infused and milk-engorged teat-sealed glands by 1 and 6 h, respectively, such that these changes were accelerated by sucrose infusion, compared with milk accumulation alone. The timing of the decline in abundance of β1-integrin (cell-extracellular matrix protein) and occludin (tight junction protein), and increase in abundance of the activated apoptotic marker signal transducer and activator of transcription factor-3 (pSTAT3) protein were also accelerated by sucrose infusion. Conclusion: Physical distension by sucrose infusion accelerated the onset of the first stage of mammary apoptosis and involution, supporting a role for mechanotransduction during these processes.

A study was conducted to evaluate the potential effects of altering the proportion of dietary structural carbohydrate (SC) relative to nonfiber carbohydrate (NFC) pre- and postpartum on milk production and the circulating concentrations of hormones and metabolites. Dietary treatments were arranged as a 2 × 2 factorial, with 68 multiparous cows assigned to isoenergetic diets [114 MJ of metabolizable energy (ME)/cow per d] precalving; diets were either fresh pasture and pasture silage (PreP) or pasture and pasture silage supplemented with 3 kg dry matter (DM)/cow per d of a corn- and barley-based concentrate for 36 d prepartum (PreC). Final treatments were 13 or 32% DM NFC, respectively. After calving, cows within each prepartum diet were assigned to isoenergetic diets (179 MJ of ME/cow per d) differing in their SC and NFC content. Postcalving diets were either fresh pasture and pasture silage (PostP) or pasture and pasture silage supplemented with 5 kg DM/cow per d of a corn- and barley-based concentrate (PostC) until 35 d in milk. Final treatments were 18 and 38% DM NFC, respectively. Relative to day of calving (d 0), blood samples were collected at least weekly from d −28 to d 35. During the prepartum period, PreC cows had lower plasma urea, albumin, insulin-like growth factor-I, and Ca concentrations, but greater nonesterified fatty acid and Mg concentrations. There were no evident effects of prepartum diet on body weight or body condition score, milk yield, or milk composition. During the postpartum period, PostC cows had lower concentrations of plasma urea, β-hydroxybutyrate, and Ca, but greater concentrations of nonesterified fatty acids, glucose, insulin-like growth factor-I, and Mg. Postpartum metabolic differences in PostC cows were associated with increased milk protein production and reduced milk fat (yield and %). Results do not support a periparturient metabolic benefit to altering the SC to NFC ratio precalving, but imply an altered rumen fermentation, gluconeogenesis, and milk composition when dietary SC to NFC ratio is altered postcalving.

We have used cDNA microarray analysis to identify genes that play a role in bovine mammary involution. Involution was induced by termination of milking, and alveolar tissue was collected from 48 nonpregnant Friesian cows in mid lactation sacrificed at 0, 6, 12, 18, 24, 36, 72, and 192 h (n = 6/group) postmilking. The most highly upregulated genes were those associated with oxidative stress. Quantitative real-time reverse-transcription PCR analysis confirmed that mRNA expression of spermidine/spermine N(1)-acetyltransferase was increased by 24 h, superoxide dismutase 2 and metallothionein 1A by 36 h, and glutathione peroxidase by 72 h postmilking. The mRNA expression of the host defense proteins lactoferrin and lingual antimicrobial peptide were increased by 192 h postmilking. A dramatic increase in the protein expression of lactoferrin by 192 h postmilking was also detected by Western analysis. Decreased mRNA expression of the milk protein genes alpha(S1)-, beta-, and kappa-casein, and alpha-lactalbumin were early events in the process of involution occurring within 24 to 36 h postmilking, whereas beta-lactoglobulin mRNA was decreased by 192 h postmilking. Decreases in alpha-lactalbumin and beta-lactoglobulin protein levels in alveolar tissue occurred by 24 and 192 h postmilking, respectively, and the cell survival factors beta1-integrin and focal adhesion kinase were decreased by 72 and 192 h postmilking, respectively. The results demonstrate that in the bovine mammary gland, decreased milk protein gene expression and cell survival signaling are associated with multiple protective responses to oxidative stress that occur before the induction of immune responses and mammary epithelial cell apoptosis during involution.

The objective of this study was to compare the effect of milking frequency (once vs. twice-daily milking) and breed (Holstein-Friesians vs. Jerseys) on milk and milk solids (MS; milk fat + milk protein), yield per cow, milk composition, somatic cell count and lactation length; cow body weight, body condition score, and reproductive performance over a 4-yr period. Total cow numbers in each herd were 30, 35, 36, and 42 for Holstein-Friesians milked once or twice daily, and Jerseys milked once or twice daily, respectively. Forty hectares of pasture were subdivided into 4 smaller pastures of 10 ha each. Stocking rates for the once-daily herds were 16.7% greater than the twice-daily herd in their respective breed. An increased stocking rate was chosen to achieve equal milk and MS per ha from the 2 milking frequencies. Annual milk, fat, protein, and lactose yields per cow were less for once-daily than for twice-daily milking. Interactions were detected between milking frequency and breed for annual milk, fat, protein, and lactose yields per cow, because Jerseys were relatively less affected by once-daily than by twice-daily milking than Holstein-Friesians. Holstein-Friesian cows milked once daily produced 31.2% less milk and 29.4% less MS per cow than their twice-daily counterparts. In contrast, Jersey cows milked once daily produced 22.1% less milk and 19.9% less MS per cow than their twice-daily counterparts. Milk per ha was 17.7 and 9% less for the once-daily Holstein-Friesians and once-daily Jersey herds, respectively, compared with their twice-daily counterparts, because the greater stocking rate for the once-daily herds did not fully compensate for the milk loss per cow. Milking once daily increased somatic cell count throughout the year in both breeds. Cows milked once daily conceived 3 d earlier, took 5 d less from calving to conception, and needed 11% fewer controlled internal drug release devices than those milked twice daily. Milking once daily is a viable milking option for New Zealand farmers who are prepared to trade-off loss of MS income for increased time to accomplish other non-milking activities.

Forty-eight primiparous, non-pregnant, Friesian cows in mid-lactation, were used to investigate the cell–extracellular matrix (ECM) communication in mammary epithelial cell (MEC) survival during induced mammary involution and to examine cell survival and apoptotic signalling events. Cows were sacrificed and alveolar mammary tissue was obtained at 0, 6, 12, 18, 24, 36, 72 and 192 h ( n = 6 per group) after termination of milking. Tissue mRNA concentrations, measured by quantitative real-time RT–PCR, of different integrins (β1, α6 and α5), down-stream signal transduction factors FAK and 14-3-3, and cell survival members BAG-1 and Bcl-x long of the Bcl-2 family were decreased by 24 h compared to 6 h, with no further decrease to 8 days (192 h). The pro-apoptotic member of the Bcl-2 family, αBax mRNA level was increased by 8 days. Apoptosis within the epithelial cell layer surrounding the alveolar lumen, measured by in situ end-labelling (ISEL), was evident. There were a low number of ISEL nuclei, in lactating mammary tissue (6 h), which was increased by 72 h of involution. By 8 days of induced involution, there was a dramatic increase in apoptotic products within the lumen, accounting for the majority of total apoptotic cells, which was accompanied by neutrophil infiltration. In conclusion, cell–ECM communication becomes compromised in the bovine mammary gland 18–24 h after termination of milking, as indicated by a decrease in the expression of integrins and cell survival factors. The different down-regulated integrins implicate crosstalk between integrins and growth factor receptors may occur during involution of the bovine mammary gland. Pro-apoptotic factors are up-regulated by 8 days of involution.

The main objectives of this study were to establish the relative value of milk yields under twice-daily milking (TDM) as a predictor of yield and yield loss under once-daily milking (ODM), and to understand the role of residual milk and udder storage capacity-related traits in regulating yield and yield loss during ODM. A Holstein-Friesian × Jersey crossbred herd was established over 2 seasons (years), as 2 individual cohorts on the same farm, managed on a pasture-based system over 4 lactations. Short-term (1-wk) ODM studies, with a starting total of 690 cows, were undertaken in mid- and late-lactation in lactation 2 and in mid-lactation in lactation 3 for each cohort. A 10-wk study of ODM performance began in mid-lactation in lactation 3, whereas lactation 4 was a full-lactation assessment of ODM. In the short-term studies, milk yield under ODM was well predicted (R(2)=0.7 to 0.8 in 5 of 6 studies) by the daily yield under TDM in the week before ODM. Yield loss (kg/d) increased with increasing milk yield and with increasing somatic cell count (SCC), although predictions were relatively poor (R(2)=0.09 to 0.30). Yield loss (%) decreased with increasing TDM yield in 3 of the 6 studies and was positively correlated with SCC during ODM. Nevertheless, ODM yield loss, in absolute or percentage terms, was a poorly repeatable trait in grazing cows. Part of the variation in yield loss percentage (30%) was positively associated with residual milk (%), measured pretrial, during measurement of functional udder capacity in lactation 3. Total production (kg of milk) over the full-lactation ODM study in lactation 4 was correlated with total production in the 10-wk trial in lactation 3 (r=0.72 and 0.63 for cohorts 1 and 2, respectively). Identifying the highest- and lowest-producing 10% of animals during the full lactation of ODM indicated that poor production was associated with high yields of residual milk (measured in lactation 3) and, conversely, high production was associated with low yields of residual milk, relative to the other 80% of animals. These same "high" and "low" production groups from lactation 4 had similar differences in performance in the earlier short-term studies and a larger or smaller percentage yield loss associated with the residual milk measurement. Breeding strategies for ODM may benefit, therefore, from greater emphasis on selecting for a low residual milk fraction to optimize milking performance. Nevertheless, the level of milk production under TDM is a strong phenotypic predictor of milk production under ODM.

Changes to milking frequency (MF) affect the metabolic and energetic status of dairy cows. However, the duration of altered MF necessary to modify hepatic transcription during early lactation is less clear. Additionally, long-term responses to short-term alterations in MF have not been established. Holstein-Friesian dairy cows (n=120) were allocated to 3 or 6 wk of either once-daily (1×) or thrice-daily (3×) milking, immediately postpartum. Following treatment, cows were switched to twice-daily (2×) milking. These 4 treatment groups were compared with cows milked 2× (n=30) for the whole lactation. Liver tissue was collected by biopsy at 1, 3, 6, and 9 wk postpartum from 12 cows per treatment, RNA was extracted, and transcript abundance of genes involved in hepatic metabolism was quantified. Milking frequency altered the expression of most of the genes measured; however, we observed no effects caused by the length of time on the alternative milking frequency and no interactions between MF and length. During the MF treatment, mRNA expression of some, but not all, genes involved in gluconeogenesis ( G6PC , PCK1 ), fatty acid β-oxidation ( CPT1A , CPT2 ), ketogenesis ( HMGCS2 ), lipid transport ( APOA1 ), and lipolysis ( PNPLA2 ) were lower for cows milked 1× and plasma glucose and insulin concentrations were greater. Cows milked 3× had reduced mRNA expression for some of the genes involved in fatty acid synthesis ( ACACA ) and lipid transport ( APOB ) and had greater plasma NEFA concentrations at wk 1. At 9 wk postpartum, expression data indicated that cows previously milked 3× had a greater capacity for gluconeogenesis ( PCK1 ), ketogenesis ( HMGCS2 ), and urea cycling ( ASL , CPS1 ) and lower glucose concentrations than cows previously milked 1×, because some of the genes involved in these processes were still altered. Milking cows 1× relative to 2×, however, did not result in significant carryover effects on the expression of the genes measured in this study, indicating that metabolic changes are not sustained beyond the period of reduced MF. Changes to MF altered the hepatic response during early lactation; however, this was not dependent on the duration of MF change. Although we observed only minimal carryover effects on hepatic metabolism from short periods of reduced MF postpartum, there may be long-term effects on urea cycling ( ASL , CPS1 ) and ketogenesis ( HMGCS2 ) when 3× milking occurs immediately postpartum.

The objective of this study was to investigate the effect of milking frequency (MF) at 2 feeding levels (FL) on milk production, body condition score, and metabolic indicators of energy status in grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n=120) grazed pasture and were milked twice daily (2×) from calving until 34 ± 6 d in milk (mean ± standard deviation). Cows were then allocated to 1 of 4 treatments in a 2 × 2 factorial arrangement. Treatments consisted of 2 FL: adequately fed [AF; 14.3 kg dry matter intake (DMI)/cow per d] or underfed (UF; 8.3 kg of DMI/cow per d) and 2 MF: 2× or once daily (1×). Treatments were imposed for 3 wk. After the treatment period, all cows were offered a generous pasture allowance (grazing residuals >1,600 kg of dry matter/ha) and milked 2×. During the 3-wk treatment period, we observed an interaction between FL and MF for energy-corrected milk (ECM), such that the decrease due to 1× milking was greater in AF than in UF cows (20 and 14% decrease, respectively). No interactions were found posttreatment. Cows previously UF produced 7% less ECM than AF cows during wk 4 to 12; however, no subsequent effect was observed of the previous underfeeding. Cows previously milked 1× produced 5% less ECM during wk 4 to 12, and differences remained during wk 13 to 23. During the 3-wk treatment period, UF cows lost 0.2 body condition score units (1-10 scale) and this was not affected by 1× milking. During the treatment period, UF cows had lower plasma glucose, insulin, and insulin-like growth factor I, and greater nonesterified fatty acids and β-hydroxybutyrate concentrations than AF cows. Cows milked 1× had greater plasma glucose, insulin, and insulin-like growth factor I, and lower nonesterified fatty acids and β-hydroxybutyrate concentrations compared with cows milked 2×. In conclusion, energy status was improved by 1× milking; however, when UF cows were milked 1×, milk production was reduced by more than underfeeding alone. The immediate and residual responses to 1× milking need to be considered when using this management strategy during a feed deficit.

Most dairy cows throughout the world are milked twice daily. In intensive dairying systems, however, it is not uncommon to increase milking frequency to between 3 and 6 times daily to increase milk production. Reducing milking frequency is much less common; however, once-daily milking of dairy cows, practiced either strategically during certain parts of the lactation or for the entire lactation, is not uncommon in key dairying countries where less emphasis is placed on milk production per cow. The practice fits well with more extensive dairy production systems, particularly those based on grazed pasture. A feature of once-daily milking is that it reduces milk yield by approximately 22%, depending on stage of lactation, breed, and parity, and it may adversely affect lactation length and persistency. However, it can offer several positive farm management options, especially related to labor requirements and farm working expenses. In addition, it may provide a tool to better manage the metabolism and energy balance of cows during early lactation or during periods of pasture deficit, and it may help to improve reproductive performance and animal health and welfare. Once-daily milking, representing one extreme of the mammary function spectrum, has attracted considerable research interest over the years. Consequently, substantial scientific information is available on its effects on mammary function, at both the physiological and molecular levels. This review focuses instead on the management of the cow milked once daily, covering the production response in relation to breed, stage of lactation, and parity, and its effect on energy status, reproduction, health and welfare, as well as on milk composition and processability.

Supplementing pasture-fed dairy cows with concentrates in early lactation was hypothesized to result in an earlier postpartum recoupling of the somatotropic axis in New Zealand (NZ)-type Holstein-Friesian dairy cows than in North American (NA)-type cows. To test this hypothesis, NA (n=30) and NZ (n=30) cows were allocated to 1 of 3 supplementation strategies (0, 3, or 6kg of dry matter concentrate/d) for the first 12 wk of lactation in a completely randomized design and a 2 × 3 factorial arrangement. Production traits and characteristics of the somatotropic axis were studied at phenotypic, hormonal, and gene expression levels. Milk production and plasma metabolite concentrations were measured weekly, and liver was biopsied in wk 1, 4, 8, and 12 postcalving. North American cows produced more milk and displayed a larger degree of somatotropic axis uncoupling than did NZ cows. This was evident in strain differences in body condition score, blood growth hormone, and insulin-like growth factor-1 concentrations, and hepatic expression of growth hormone receptor-1a. No strain × diet interactions were observed for any characteristic of the somatotropic axis at either the blood metabolite or gene expression level; however, blood insulin concentrations during wk 7 to 11 postpartum increased with concentrate supplementation in NZ but not NA cows. These results demonstrate that feeding supplements does not result in an earlier recoupling of the somatotropic axis; however, the greater blood insulin concentrations with concentrate feeding in NZ cows from wk 7 may result in an earlier recoupling in this genetic strain, after the period investigated in this study. Further research is required to understand differences in insulin control between these genetic strains.

The working hypothesis was that postpartum anovulatory intervals (PPAI) of grazing dairy cows are shortened by inclusion of concentrates that increase the nonstructural carbohydrate content of the transition diet. Dietary treatments were arranged as a 2 × 2 factorial, with 68 multiparous cows assigned to isoenergetic diets (114 MJ of metabolizable energy/cow per day) of pasture and pasture silage (PreP) or pasture and pasture silage supplemented with 3 kg of dry matter/cow per day a corn- and barley-based concentrate for 36 d prepartum (PreC). After calving, cows within each prepartum diet group were managed on isoenergetic diets (179 MJ of metabolizable energy/cow per day) of either pasture and pasture silage (PostP) or pasture and pasture silage supplemented with 5 kg of dry matter/cow per day a corn- and barley-based concentrate (PostC) for at least 35 d and until reestablishment of ovulatory cycles. Relative to day of calving (d 0), blood samples were collected at least weekly from d −28 to 35 and milk samples were collected twice weekly for progesterone determination to diagnose ovulatory status. The main variable of interest was PPAI, defined as the interval between calving and the first detected increase in milk progesterone (>3 ng/mL), followed by a pattern of progesterone concentrations consistent with onset of an ovulatory cycle. Subsequent mating records, pregnancy testing, and recalving data were also examined. Prepartum diet did not affect reproduction. The PPAI was 8 d shorter and the 6-wk pregnancy rate was 17% greater in PostC cows compared with PostP cows. Measured indicators of metabolic state and energy balance were poorly related to PPAI. The results support the existence of nutritional signals associated with nonstructural carbohydrates in the postpartum diet, independent of energy balance; these signals benefit the physiological mechanisms underlying the timing of first ovulation and possibly subsequent breeding performance.

Reproduction and milk production responses were compared between dairy cows offered a high (HPA; n=453 in 4 replicates) or low (LPA; n=317 in 3 replicates) pasture allowance for the first 14 d after the planned start of mating (d 0 of experiment) in 2 seasonal, pasture-based dairy herds. Estimated pasture dry matter intake (DMI) between d −1 and 13 were 14.3±2.8 and 8.0±1.7kg of DM/cow per day for HPA and LPA cows, respectively. The LPA cows produced 22% less energy-corrected milk during the 14-d feeding treatment period, and milk yield remained less in LPA cows at d 53 despite all cows receiving pasture allowances to support DMI of 16kg of dry matter/cow per day from d 14 onwards. The 3-wk submission rate (percentage of cows inseminated at least once from d 0 to 20) and the 3- and 6-wk pregnancy rates of LPA cows (88, 45, and 71%, respectively) were lower than those of HPA cows (94, 53, and 78%, respectively), but conception rates to first (50%) or second (47%) service and final pregnancy rates (93%) did not differ between treatments. These results quantify the immediate and subsequent responses in reproductive performance and milk production to a severe restriction in DMI at the onset of a seasonal breeding period in pasture-grazed dairy cows.

Dairy heifer growth and liveweight at first calving are regarded as important management variables affecting profitability and animal welfare. However, the appropriateness of heifer growth rate targets for different farming systems is not clear. Retrospective assessments of the association between heifer liveweight and subsequent productivity indicate significant benefits in milk production and, even, reproduction from increasing liveweight at breeding and first calving. However, prospective interventionist experiments do not concur, with very variable effects of liveweight at breeding on milk production and with only limited evidence of a positive effect of first-calving liveweight on first-lactation milk yield. In addition, any benefit in the first lactation is not evident in subsequent lactations in the limited number of long-term studies reported. Pre-weaning nutrition and average daily weight gain are areas of increasing interest, with lifelong increases in milk production resulting from accelerated growth rates during the first 8 weeks of life, indicating a possible significant return from a short-term investment. This could be one reason for the inconsistent effects of heifer liveweight at breeding and first lactation on milk production. Although the effect of pre-weaning average daily gain on heifer liveweight is short-lived, a recent meta-analysis indicated that pre-weaning average daily gain explains 22% of the variation in first-lactation milk production. Whether these differences in animal physiology have relevance in grazing systems, wherein heifers and cows do not consume sufficient nutrients to reach their potential, requires investigation. Despite considerable extension efforts over successive decades, current evidence indicates that failure to provide the new-born calf with sufficient high-quality colostrum is common. To understand the reasons for suboptimal colostrum feeding requires social research, with appropriate extension strategies developed to elicit practice change. Although there can be little doubt regarding the importance of heifer rearing to the profitability and sustainability of the farming business, the collective literature points to a failure of retrospective analyses in determining the cause of poor heifer performance. In reality, it is likely to be a combination of factors. The objective of this review is to investigate the effect of liveweight gain at various stages of the growth cycle of the heifer on the milk-production capacity of the lactating animal.