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Serum collected from multiparous Holsteins (n = 73) in a previous experiment was used to determine the effect of prepartum plane of energy intake on metabolites related to inflammation and liver function in periparturient cows. Prepartum diets were in a 3 × 2 factorial arrangement over the far-off (d -65 to -26 before expected parturition) and close-up (d -25 relative to parturition until parturition) dry periods. During the far-off period, 2 diets were fed for ad libitum intake (ADLIB) to supply either 100% (100E) or 150% (150E) of National Research Council recommendations for net energy for lactation for mature cows in late gestation. For the third dietary far-off treatment, the 150E diet was fed at restricted intake (REST) to supply 80% (80E) of recommendations. During the close-up period, cows were fed a diet either at ADLIB or REST to supply 150% of net energy for lactation or 80% of net energy for lactation requirements, respectively. Beginning at parturition, all cows were fed a lactation diet through 56 d in milk. Cows fed 150E tended to accumulate more liver lipid postpartum; peak lipid accumulation occurred in all groups on d 14 postpartum. Cows fed 150E tended to have lower serum Ca on d 1 after calving, and cows fed REST had higher Ca than those fed ADLIB. Cows fed 150E tended to have higher serum bilirubin prepartum compared with other groups. Feeding REST in the close-up period resulted in higher bilirubin prepartum compared with ADLIB; bilirubin was positively associated (r = 0.34) with lipid accumulation postpartum. Feeding REST resulted in lower serum vitamin A (an indirect measure of retinol binding protein) prepartum compared with ADLIB, especially when coupled with 80E. Postpartum paraoxonase was negatively associated (r = -0.27) and ceruloplasmin was positively associated (r = 0.21) with liver lipid accumulation postpartum. A larger spike in haptoglobin was observed on d 1 and 7 postpartum for cows fed 100E and 150E during the far-off period followed by REST during the close-up period. The ratio of albumin to globulin in serum was higher for cows fed 100E than for those fed 150E both prepartum and postpartum. Liver activity index indicated poorer liver function for cows fed 150E in the far-off period regardless of close-up diet. Negative liver function was also noted for cows fed 80E and REST. Cows in the 100E group fed ADLIB or REST had positive liver activity index postpartum. Avoidance of gross overconsumption of energy prepartum, particularly during the far-off period, appears best to reduce systemic inflammatory signals and improve liver function.

Our objective was to evaluate the effect of metabolizable protein (MP) supply on milk production, blood metabolites, and health in dairy cows during early lactation. Three experimental diets were formulated to contain 114, 107, 101 g of MP/kg of dry matter (DM; 114MP, 107MP, and 101MP, respectively) with crude protein contents of 17.0, 16.2, and 15.3% of DM, respectively. One hundred multiparous Holstein cows were fed 1 of these 3 diets during wk 1 to 3 and wk 4 to 13 of lactation in one of the following sequences: (1) 114MP and 107MP (114MP/107MP), (2) 114MP and 101MP (114MP/101MP), or (3) 101MP and 101MP (101MP/101MP). During wk 1 to 3, the 114MP and 101MP treatments were 20 and 27% deficient in estimated MP, respectively. From wk 4 to 13, the 114MP/107MP, 114MP/101MP, and 101MP/101MP treatments were 8, 12, and 13% deficient in estimated MP, respectively. Data were analyzed separately for wk 1 to 3, 4 to 13, and 1 to 13. Dry matter intake and energy-corrected milk (ECM) yield were not affected by treatment during wk 4 to 13 or wk 1 to 13; however, ECM yield decreased for 101MP versus 114MP from wk 1 to 3. Similarly, feed efficiency was not affected by treatment from wk 4 to 13 or wk 1 to 13, and was reduced with 101MP versus 114MP during wk 1 to 3. Milk N efficiency tended to increase for 101MP versus 114MP for wk 1 to 3 and increased with 101MP/101MP and 114MP/101MP relative to 114MP/107MP during wk 4 to 13 and wk 1 to 13. Treatment had no influence on yields and concentrations of milk components from wk 4 to 13 or wk 1 to 13; however, compared with 114MP, feeding 101MP tended to decrease milk fat yield and decreased yields of milk true protein and lactose for wk 1 to 3. Both milk and blood urea N concentrations decreased for 101MP/101MP and 114MP/101MP relative to 114MP/107MP during wk 4 to 13 and wk 1 to 13, and were reduced with feeding 101MP versus 114MP from wk 1 to 3. Treatment had no effect on the incidence of diseases in cows throughout the study. Serum concentrations of total fatty acids, albumin, and aspartate aminotransferase did not differ between 101MP and 114MP; however, serum β-hydroxybutyrate concentration was lower in cows receiving 101MP during the first 3 wk of lactation. Compared with 114MP, feeding 101MP during wk 1 to 3 increased plasma concentrations of creatinine and 3-methylhistidine (3-MHis) but did not change the ratio of plasma 3-MHis to creatinine. We found no differences in plasma creatinine or the ratio of 3-MHis-to-creatinine among treatments from wk 4 to 13; however, 101MP/101MP and 114MP/101MP had elevated plasma 3-MHis compared with 114MP/107MP. Treatment had no effect on body weight and body condition score over the duration of the study. Collectively, despite reduced milk production for the first 3 wk of lactation, feeding the 101MP/101MP treatment sustained lactational performance and improved milk N efficiency without negatively affecting the frequency of diseases in dairy cows during the first 13 wk postpartum.

The effect of neutral detergent fiber (NDF) degradability of corn silage in diets containing lower and higher NDF concentrations on lactational performance, nutrient digestibility, and ruminal characteristics in lactating Holstein cows was measured. Eight ruminally cannulated Holstein cows averaging 91 ± 4 (standard error) days in milk were used in a replicated 4 × 4 Latin square design with 21-d periods (7-d collection periods). Dietary treatments were formulated to contain either conventional (CON; 48.6% 24-h NDF degradability; NDFD) or brown midrib-3 (BM3; 61.1% 24-h NDFD) corn silage and either lower NDF (LNDF) or higher NDF (HNDF) concentration (32.0 and 35.8% of ration dry matter, DM) by adjusting the dietary forage content (52 and 67% forage, DM basis). The dietary treatments were (1) CON-LNDF, (2) CON-HNDF, (3) BM3-LNDF, and (4) BM3-HNDF. Data were analyzed as a factorial arrangement of diets within a replicated Latin square design with the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) with fixed effects of NDFD, NDF, NDFD × NDF, period(square), and square. Cow within square was the random effect. Time and its interactions with NDFD and NDF were included in the model when appropriate. An interaction between NDFD and NDF content resulted in the HNDF diet decreasing dry matter intake (DMI) with CON corn silage but not with BM3 silage. Cows fed the BM3 corn silage had higher DMI than cows fed the CON corn silage, whereas cows fed the HNDF diet consumed less DM than cows fed the LNDF diet. Cows fed the BM3 diets had greater energy-corrected milk yield, higher milk true protein content, and lower milk urea nitrogen concentration than cows fed CON diets. Additionally, cows fed the BM3 diets had greater total-tract digestibility of organic matter and NDF than cows fed the CON diets. Compared with CON diets, the BMR diets accelerated ruminal NDF turnover. When incorporated into higher NDF diets, corn silage with greater in vitro 24-h NDFD and lower undegradable NDF at 240 h of in vitro fermentation (uNDF240) allowed for greater DMI intake than CON. In contrast, for lower NDF diets, NDFD of corn silage did not affect DMI, which suggests that a threshold level of inclusion of higher NDFD corn silage is necessary to observe enhanced lactational performance. Results suggest that there is a maximum gut fill of dietary uNDF240 and that higher NDFD corn silage can be fed at greater dietary concentrations.

The effects of source of corn silage and trace mineral on rumen fermentation, turnover, and particle passage rates were evaluated with 8 ruminally cannulated Holstein cows averaging 83 (standard error = 5) days in milk in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments and 28-d periods. The diets consisted (dry basis) of 55% conventional (CON) or brown midrib-3 (BM3) corn silage, 2% chopped wheat straw, and 43% grain mix with either sulfate (STM) or hydroxy (HTM) source of Cu, Zn, and Mn trace minerals. The targeted supplemental amount of Cu, Zn, and Mn was 194, 1,657, and 687 mg/d, respectively. The dietary treatments were (1) CON-STM, (2) CON-HTM, (3) BM3-STM, and (4) BM3-HTM. Dietary nutrient composition of BM3 diets averaged 32.1% amylase neutral detergent fiber on an organic matter basis (aNDFom) and 6.9% undigested neutral detergent fiber at 240 h of in vitro fermentation (uNDF240om; % of dry matter), and CON diets averaged 36.2% aNDFom and 8.6% uNDF240om (% of dry matter). Data were summarized by period and analyzed as a replicated Latin square design with fixed model effects for corn silage, trace mineral, corn silage and trace mineral interaction, period within replicated square, and replicated square using the MIXED procedure of SAS (version 9.4, SAS Institute Inc., Cary, NC). Cow within replicate was a random effect. Daily mean, standard deviation, minimum, and maximum for rumen pH were unaffected by corn silage or trace mineral source. Cows fed the CON diets had greater rumen acetate percentage than cows fed the BM3 diets (65.7 vs. 64.7 molar %). In contrast, cows fed the BM3 diets had greater rumen propionate percentage than cows fed the CON diets (21.4 vs. 20.4 molar %). Total volatile fatty acid concentration was lower for cows fed STM versus HTM in BM3 diets, but not for the cows fed the CON diets. Cows fed the BM3 diets had faster turnover rate and shorter turnover time for uNDF240om than cows fed the CON diets (3.12 vs. 2.86%/h and 33.3 vs. 36.5 h, respectively). Cows fed the BM3 diets had a faster passage rate of small and medium corn silage neutral detergent fiber particles than cows fed the CON diets (5.73 vs. 5.37%/h and 4.74 vs. 4.31%/h, respectively). We observed a corn silage by source of trace mineral interaction on organic matter and uNDF240om rumen pool size and organic matter turnover. Overall, source of corn silage had a pronounced influence on rumen dynamics presumably related to greater in vitro neutral detergent fiber digestibility and lower uNDF240om content of BM3 corn silage that allowed for faster turnover of indigestible neutral detergent fiber and greater passage rate of corn silage particles. In contrast, the source of trace mineral had much less significant effects on rumen fermentation, turnover, and particle passage rates. Corn silage-based diets intended to enhance rumen fiber fermentation, turnover, and passage are more affected by source and digestibility of neutral detergent fiber than source of dietary trace minerals.

The objectives of this study were to (1) describe the calving location of dairy cattle given access to a pasture and barn; (2) identify factors associated with calving location; and (3) compare the lying and exploratory behavior of cows in the 24 h before calving and a previous day. Seventy-two Holstein dairy heifers and cows (n = 36 nulliparous and n = 36 primiparous and multiparous combined) were housed in a covered bedded-pack barn (167.4 m2) with free access to 2.1 ha of pasture. The composition of the group was dynamic, because cows were moved in weekly at 19 ± 6 d [mean ± standard deviation (SD)] before their calving date, and were removed immediately after calving. To facilitate data collection, we divided the environment into 9 sections, including the barn (section 1; 167.4 m2), 7 sections of open pasture (sections 2 to 8; 2,402 ± 60 m2), and 1 section of pasture surrounded by natural forage cover (section 9; 3,593 m2). We then collapsed these 9 sections into 3 distinct areas for further analysis: the barn, open pasture, and natural forage cover. Animals were fitted with accelerometers to measure lying time, lying bout duration, lying bouts, and steps for the 24 h before calving (calving day) and a similar 24 h period 4 to 11 d (median = 7) before calving (baseline day). We included parity (nulliparous vs. primiparous and multiparous) and heat stress [no heat stress = temperature-humidity index (THI) ≤68 vs. heat stress = THI >68 and ≤79] in all analyses; we included time of day and group composition as additional factors that may have affected calving location. We determined exploratory behavior using 10 min instantaneous scan sampling collected from video. At each scan, we recorded the section (1 to 9) the cow or heifer was located in, and then calculated the minimum number of sections that could be crossed between successive scans. Of the total sample, 39% calved in the barn, 26% calved in the open pasture, and 35% calved in the area with natural forage cover. Nulliparous heifers and those calving when heat stress was low (THI ≤68) selected the area with natural forage cover more frequently than the barn. On the calving day, cows spent more time lying down with more short bouts of lying, and crossed more sections compared with the baseline day. Steps were affected by an interactive effect of day, parity, and heat stress; nulliparous heifers took more steps on the calving day during conditions of heat stress compared with no heat stress. Results indicate that cows and heifers had different preferences for their environment at calving, and when provided access to pasture, both changed their lying and exploratory behavior on the day of calving compared with a previous day.

We evaluated the effects of source of corn silage and trace minerals on lactational performance and total-tract digestibility (TTD) of nutrients in 16 Holstein cows averaging 82 (standard error = 3) days in milk in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments with 28-d periods. The diets consisted [dry matter (DM) basis] of 55% conventional (CON) or brown midrib-3 (BM3) corn silage, 2% chopped wheat straw, and 43% grain mix with either sulfate (STM) or hydroxy (HTM) sources of copper, manganese, and zinc trace minerals. The targeted supplemental concentrations of copper, zinc, and manganese were 194, 1,657, and 687 mg/d, respectively. The dietary treatments were CON-STM, CON-HTM, BM3-STM, and BM3-HTM. The dietary nutrient composition of the BM3 diets averaged 32.1% amylase neutral detergent fiber on an organic matter basis (aNDFom) and 6.9% undigested neutral detergent fiber at 240 h (uNDF240om; % of DM), and CON diets averaged 36.2% aNDFom and 8.6% uNDF240om (% of DM). The average supplemental concentrations of copper, zinc, and manganese for the STM diets were 10, 41, and 64 mg/kg, respectively, and the average supplemental concentrations of copper, zinc, and manganese for the HTM diets were 10, 40, and 62 mg/kg, respectively. The average total dietary concentrations of copper, zinc, and manganese for the STM diets were 17, 104, and 60 mg/kg, respectively, and the average total dietary concentrations of copper, zinc, and manganese for the HTM diets were 17, 91, and 66 mg/kg, respectively. Data were summarized by period and analyzed as a replicated Latin square design with fixed model effects for corn silage, trace minerals, corn silage × trace mineral interaction, period within replicated square, and replicated square using the MIXED procedure of SAS. Cow within replicated square was a random effect. Cows fed the BM3 diets had greater dry matter intake (DMI) and milk yield (28.1 and 47.0 kg/d) than cows fed the CON diets (27.5 and 44.7 kg/d). We found no significant interaction between corn silage and trace minerals for DMI and milk yield. Cows fed the HTM diets (28.1 kg/d) had a greater DMI than cows fed the STM diets (27.5 kg/d). Cows fed the BM3 diets had greater TTD of DM and OM (72.8 and 74.1% of DM) than cows fed the CON diets (71.1 and 72.3% of DM). Cows fed the HTM diets had a tendency for greater TTD of aNDFom than cows fed the STM diets (56.8 vs. 54.9% of DM). Cows fed the CON diets ruminated longer during the day than cows fed the BM3 diets (524 vs. 496 min/d). Corn silage with greater NDF digestibility and lower uNDF240om enhanced DMI, milk yield, and TTD of DM and OM, and hydroxy trace minerals improved DMI and tended to improve TTD of aNDFom. The source of corn silage and trace minerals should be taken into consideration when formulating diets for high-producing dairy cows.

Dry matter intake, lactation performance, and chewing behavior of multiparous Holstein cows (n = 15) fed diets containing a novel bm3 corn silage hybrid with floury kernel genetics were compared with cows fed diets containing commercially available conventional and bm3 hybrids using a replicated 3 × 3 Latin square design with 28-d periods. Cows were housed in tiestalls, milked 3 times/d, and fed a total mixed ration containing 49.0% (dry matter basis) of (1) a conventional corn silage hybrid (CONV); (2) a brown midrib bm3 hybrid (BMR); or (3) a bm3 hybrid with floury kernel genetics (BMRFL). All diets contained 6.3% hay crop silage and 44.7% concentrate. Dietary nutrient composition averaged 32.7% neutral detergent fiber (NDF) and 26.3 starch (% of dry matter). Data were analyzed by ANOVA using the MIXED procedure in SAS (SAS Institute Inc., Cary, NC). The dry matter intake was greater for cows fed BMR (28.0 kg/d) compared with CONV (26.8 kg/d), whereas dry matter intake for cows fed BMRFL was intermediate (27.6 kg/d). Energy-corrected milk (ECM) yield was greater for cows fed BMR (50.3 kg/d) and BMRFL (51.8 kg/d) compared with CONV (47.2 kg/d). Milk fat yield was higher for cows fed BMRFL (1.87 kg/d) compared with CONV (1.74 kg/d) and BMR (1.80 kg/d). Milk protein yield was greater for cows fed BMR (1.49 kg/d) and BMRFL (1.54 kg/d) compared with CONV (1.36 kg/d). Milk urea-N was reduced for cows fed BMR (11.61 mg/dL) and BMRFL (11.16 mg/dL) compared with CONV (13.60 mg/dL). Feed efficiency (ECM/dry matter intake) was higher for cows fed BMRFL (1.87) compared with CONV (1.76) and BMR (1.79). Milk N efficiency was greatest for cows fed BMRFL (40.4%) followed by BMR (38.1%) and finally CONV (35.3%). Cows fed CONV chewed 5 min more per kilograms of NDF consumed than cows fed either of the BMR hybrids. No differences were observed among diets in apparent total-tract digestibility of NDF (58.1%) or starch (99.3%). Overall lactational performance was enhanced for cows fed diets containing both BMR and BMRFL hybrids versus CONV. In addition, feeding the BMRFL corn silage improved efficiency of component-corrected milk production and milk N efficiency compared with the CONV and BMR silages.

The objective of this trial was to compare a powdered 0.5% chlorhexidine acetate-based postmilking teat dip with a foamed 1% iodine-based postmilk teat dip during winter on clinical mastitis, subclinical mastitis (somatic cell count ≥200,000 cells/mL), linear score, teat skin condition, teat end score for hyperkeratosis, and risk of developing a new intramammary infection (IMI). Holstein cows (n = 331) housed in freestall and tiestall barns on one farm were blocked by pen, parity, lactation stage, and lactation performance. They were assigned randomly to a powdered chlorhexidine postmilking teat dip (PD; Derma Soft n' Dry, IBA Inc., Millbury, MA) or a foamed iodine-based postmilking teat dip (ID; FS-103, IBA Inc.). Treatments were applied for 6 wk starting January 4, 2016, for 3 milkings per day. Milk samples were collected from each quarter at the beginning and end of the trial and analyzed for aerobic culture and somatic cell count. Cows that had a clinical mastitis event during the trial were quarter sampled for aerobic culture at the time of clinical event. Teat skin condition and teat end score for hyperkeratosis were evaluated at the beginning, middle, and end of the trial based on a 3- and 5-point scale, respectively. No treatment difference was observed for linear score or teat skin condition. Teat end score was greater for ID cows compared with PD cows (2.72 vs. 2.77) at the conclusion of the trial. At the beginning of trial 102 PD quarters and 129 ID quarters had an IMI identified on aerobic culture, 402 PD and 457 ID quarters cultured negative, and 109 PD and 125 ID samples were classified as “no significant growth.” At the conclusion of the trial, 129 PD and 101 ID quarters had an IMI. Use of PD resulted in a greater risk for developing a new IMI, based on bacteriological culture, at the conclusion of the trial as compared with ID (relative risk = 1.51; confidence interval: 1.10–2.07). Additionally, use of PD resulted in a greater risk as compared with ID of coagulase-negative staphylococci (relative risk = 1.5; confidence interval: 1.10–2.25) and Staphylococccus aureus (relative risk = 2.30; confidence interval: 1.04–5.07) to be present at the conclusion of the trial. In conclusion, use of PD led to a lower teat end score, an increase in new IMI, and an increased risk of coagulase-negative staphylococci and Staph. aureus compared with ID after 6 wk of product use.

The objective of this study was to evaluate the relationship of management practices and dietary factors with de novo fatty acid concentration in bulk tank milk from commercial dairy farms milking Holstein cows. Farms were selected based on de novo fatty acid concentration during the 6 mo before the farm visit and were categorized as high de novo (HDN; 24.61 ± 0.75 g/100 g of fatty acids, mean ± standard deviation; n = 19) or low de novo (LDN; 23.10 ± 0.88 g/100 g of fatty acids; n = 20). Farms were visited once in February, March, or April 2015 and evaluated based on management and facility design known to affect cow behavior, physical and chemical characteristics of the diet, and ration formulation and forage analyses obtained from the farm's nutritionist. We observed no differences between HDN and LDN farms in farm size, time away from the pen for milking, days in milk, or body condition score. We detected no differences between HDN and LDN farms in milk fat or true protein yield; however, milk fat and protein content and de novo fatty acid yield per day were higher for HDN farms, as was gross income per unit of milk sold. High de novo farms tended to be more likely to deliver fresh feed twice versus once per day, have a freestall stocking density ≤110%, and provide ≥46 cm of feed bunk space per cow. We observed no detectable differences in forage quality or ration dry matter, crude protein, or starch content. However, ether extract was lower and physically effective neutral detergent fiber was higher for HDN farms. Feeding management, stocking density, dietary ether extract content, and the physical characteristics of the diet are related to de novo fatty acid, fat, and protein concentration in bulk tank milk from high-producing Holstein dairy farms.

Increases in grain prices have led to renewed interest in feeding reduced-starch diets to lactating dairy cows. An experiment was conducted to determine the effects of altering carbohydrate sources and reducing dietary starch on lactational performance, feeding behavior, and ruminal measures of Holstein dairy cows. Fifteen multiparous cows (6 ruminally cannulated) were blocked and assigned to 1 of 5 squares and used in a replicated 3×3 Latin square design with 21-d periods. Cows were fed 1 of 3 experimental diets: a control diet containing 20% brown midrib corn silage, 20% conventional corn silage, and 10% hay crop silage (CON); a reduced-starch high-forage diet containing 53% brown midrib corn silage and 10% hay crop silage (HFOR); and a reduced-starch diet containing the same forages as CON with partial replacement of corn meal by nonforage fiber sources (HNFFS). The CON diet contained (% of dry matter) 26.0% starch and 34.7% neutral detergent fiber (NDF), whereas the HFOR and HNFFS diets contained 21.4 or 21.3% starch and 38.3 or 38.0% NDF, respectively. Dry matter intake tended to be greater for cows fed the CON diet (28.2 kg/d) compared with those fed the HFOR diet (27.2 kg/d). Dry matter intake for cows fed the HNFFS diet was intermediate (27.7 kg/d). Milk yield was greater for cows fed the CON diet (51.6 kg/d) compared with those fed the HFOR diet (48.4 kg/d), but milk fat content tended to increase for cows fed the HFOR diet (3.98%) compared with those fed the CON diet (3.66%). Consequently, fat-corrected and solids-corrected milk yields were unaffected by dietary treatments. Total chewing, eating, and rumination times were similar across all dietary treatments. Rumination time per kilogram of DM was greatest for the HFOR diet, intermediate for the HNFFS diet, and least for the CON diet, whereas rumination time per kilogram of NDF was greatest for the CON diet and least for the HNFFS diet. Mean ruminal pH, NH3-N (mg/dL), and total volatile fatty acid concentrations (mM) were similar across all dietary treatments. Molar proportion of ruminal acetate (mol/100 mol) was increased for cows fed the HFOR diet compared with cows fed the CON diet. Microbial N yield measured by urinary purine derivatives was unaffected by dietary treatment. Reduced-starch diets containing greater amounts of high quality, highly digestible forage or nonforage fiber sources in place of corn meal resulted in similar fat-corrected or solids-corrected milk yield for high-producing dairy cows in the short term.

The objective of this experiment was to measure ruminal and lactational responses of Holstein dairy cows fed diets containing 3 different starch levels: 17.7 (low; LS), 21.0 (medium; MS), or 24.6% (high; HS). Twelve multiparous cows (118 ± 5 d in milk) were assigned randomly to dietary treatment sequence in a replicated 3 × 3 Latin square design with 3-wk periods. All diets were fed as total mixed rations and contained approximately 30.2% corn silage, 18.5% grass silage, and 5.0% chopped alfalfa hay. Dietary starch content was manipulated by increasing dry ground corn inclusion (% of dry matter) from 3.4 (LS) to 10.1 (MS) and 16.9 (HS) and decreasing inclusion of beet pulp and wheat middlings from 6.7 and 13.4 (LS) to 3.4 and 10.1 (MS) or 0 and 6.8 (HS). In vitro 6-h starch digestibility of the diet increased as nonforage sources of fiber replaced corn grain (% of dry matter; 73.6, HS; 77.3, MS; 82.5, LS) resulting in rumen-fermentable starch content by 14.6, 16.2, and 18.1% for the LS, MS, and HS diets, respectively. Diets had similar neutral detergent fiber from forage and particle size distributions. Dry matter intake, solids-corrected milk yield, and efficiency of solids-corrected milk production were unaffected by diet, averaging 26.5 ± 0.8, 40.8 ± 1.6, and 1.54 ± 0.05 kg/d, respectively. Reducing dietary starch did not affect chewing time (815 ± 23 min/d), mean ruminal pH over 24h (6.06 ± 0.12), acetate-to-propionate ratio (2.4 ± 0.3), or microbial N synthesized in the rumen (585 ± 24 g/d). Total tract organic matter digestibility was higher for HS compared with MS and LS diets (69.2, 67.3, and 67.0%, respectively), but crude protein, neutral detergent fiber, and starch digestibilities were unaffected. As dietary starch content decreased, in vitro ruminal starch fermentability increased and, consequently, the range between HS and LS in rumen-fermentable starch (3.5 percentage units) was less than the range in starch content (6.9 percentage units). Under these conditions, dietary starch content had no measurable effect on ruminal fermentation or short-term lactational performance of high-producing Holstein dairy cows.

Forty-three multiparous Holstein cows were used in a completely randomized design to evaluate the effects of protein supplementation and the use of bovine somatotropin (bST; Posilac, Monsanto Co., St. Louis, MO) in late gestation on animal metabolism and productivity in the periparturient period. Treatments were initiated 28 d prior to expected calving date and continued through parturition. Diets contained either 13.3 or 17.8% crude protein and were formulated to be similar in profile of protein fractions. Within each dietary treatment, cows were assigned to receive either 0 or 500 mg of sustained released bST once every 14 d until parturition. Following parturition, all cows were subjected to the same management and dietary treatments, and production measurements were followed until 42 d in milk. The use of bST increased plasma glucose and decreased plasma nonesterified fatty acids and beta-hydroxybutyrate prior to calving. Despite these changes in metabolism, bST did not affect concentrations of fat and triglyceride in the liver prepartum or postpartum. Feeding the 17.8% protein diet failed to stimulate glucose metabolism and tended to elevate plasma beta-hydroxybutyrate in late gestation. Cows treated with bST produced 3.3 kg/d more milk than did controls across the first 42 d of lactation; the difference was 4.6 kg/d in wk 6 of lactation. The use of bST in late gestation has considerable promise to alter cow metabolism positively. The results of these and other possible periparturient responses to somatotropin may increase milk production in early lactation.

Dairy cattle require fibrous feedstuffs in the diet. However, defining the fiber requirements requires knowledge of many interacting components within the diet as well as how the feed is allocated and processed. To meet the demands of high producing dairy cows for energy, diets consist of large quantities of concentrates and high quality forages containing relatively low amounts of fiber. However, to maintain normal rumen function and milk fat percentage, a large portion of the fiber needs to come from forage. Current National Research Council recommendations are a minimum of 25 to 28% dietary neutral detergent fiber, 75% of which is supplied from forage. Chemical measures of fiber alone are not adequate for ration balancing; fiber varies in its effectiveness at stimulating chewing. This variation is greater when feeds contain high amounts of by-products in place of forages. The effectiveness in stimulation of chewing of fiber is variable as the particle size and retention times of indigestible and digestible fiber vary. Currently, little information exists about the fiber requirements of the cow from immediately postcalving until peak lactation. Early lactation cows are clearly more limited by physical fill than are cows in mid and late lactation. Rations based on nonforage fiber sources (>45% neutral detergent fiber on a dry matter basis) are being evaluated for early lactation cows. Information is needed to determine the variation in the amount of fermentation acids produced, chewing activity, and amount of saliva secreted as these all contribute to the physical effectiveness of fiber.