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The objective of this study was to investigate the association between mastitis events occurring during the previous lactation, the dry period, and the peripartum period on the incidence of early lactation mastitis in cows receiving ceftiofur hydrochloride or penicillin dihydrostreptomycin as intramammary dry cow antibiotic therapy. Cows (n = 402) from 2 large dairy farms in Central Florida were enrolled in the study at the time of dry-off processing and were randomly assigned to 1 of 2 dry cow therapies: ceftiofur hydrochloride or penicillin dihydrostreptomycin. Composite milk samples were collected at dry-off and after calving for bacteriological examination and somatic cell count. Peripartal health disorders were monitored during the first 30 d of lactation and included calving difficulty, metritis, ketosis, and left displaced abomasum. Milk production and individual somatic cell scores (SCS) were recorded monthly by the Dairy Herd Improvement Association. The main outcome variables were the risk of clinical mastitis during the first 30 and 60 d of lactation, and the risk of subclinical mastitis at the first 2 monthly Dairy Herd Improvement Association tests after calving (up to 70 d in milk). Additionally, the SCS and the presence of mastitis pathogens in milk at dry-off and at calving were analyzed. Explanatory variables consisted of events occurring during the previous lactation, at dry-off and during the dry period, at calving, and with-in the first 30 d after calving. Multiple events occurring during the previous lactation had a significant effect on the incidence of mastitis in the subsequent lactation. These events included low milk yield, intermediate lactation length, clinical mastitis, and lactation SCS average. Similarly, intramammary infections with environmental bacteria at dry-off increased the chances of clinical mastitis the first month after calving. Dry-off therapy had a significant effect on mastitis incidence; cows treated with ceftiofur hydrochloride had lower odds of having clinical and subclinical mastitis in the subsequent early lactation compared with cows treated with penicillin dihydrostreptomycin. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of altering autumn pasture availability and farm system intensity on the productivity of spring-calving dairy cows during autumn. A total of 144 Holstein-Friesian and Holstein-Friesian × Jersey crossbred dairy cows were randomly assigned to 2 whole farm system (FS) intensities and 3 autumn pasture availability (PA; measured above 3.5 cm) treatments in a 2 × 3 factorial arrangement. The 2 farm systems consisted of a medium intensity (MI: 2.75 cows/ha, target postgrazing sward height of 4.0–4.5 cm) and high intensity system (HI: 3.25 cows/ha, target postgrazing sward height of 3.5–4.0 cm, + 1.8 kg of concentrate dry matter [(DM)/cow per day]. Within each farm system treatment, cows were further subdivided into 3 different PA management strategies: high PA (HPA), medium PA (MPA), and low PA (LPA). The experimental period lasted for 11 wk from September 1 to housing of all animals on November 20 (±2 d) over 3 yr (2017–2019, inclusive). To establish the different average pasture covers for each PA treatment during autumn and in particular at the end of the grazing season, grazing rotation length was extended by +13 and +7 d for HPA and MPA, respectively, beyond that required by LPA (37 d). There were no significant FS × PA interactions for any of the pasture, dry matter intake, or milk production and composition variables analyzed. There were also no differences in pregrazing sward characteristics or sward nutritive value between FS with the exception of daily herbage allowance, which was reduced for HI system (12.2 vs. 14.2 kg of DM/cow). Milk and milk solid yield were greater for HI groups (15.9 and 1.55 kg/cow per day, respectively) compared with MI (15.4 and 1.50 kg/cow per day, respectively). Mean paddock pregrazing herbage mass was significantly higher with increased PA ranging from a mean of 1,297 kg of DM/ha for LPA to 1,718 and 2,111 kg of DM/ha of available pasture for MPA and HPA, respectively. Despite large differences in pregrazing herbage mass, there was no difference in cumulative pasture production and only modest differences in grazing efficiency and sward nutritive value between PA treatments. On average, closing pasture covers were 420, 650, and 870 kg of DM/ha for LPA, MPA, and HPA, respectively, on December 1. In addition to maintaining similar grazing season lengths and achieving big differences in availability of pasture on farm into late autumn, PA treatment had no significant effect on dry matter intake, milk production, and body condition score during the study period. The results of this study indicate that greater cow performance and pasture utilization can be achieved through a greater daily concentrate allocation along with an increased stocking rate. Moreover, the potential to adapt grazing management practices to increase the average autumn pasture cover in intensive grazing systems is highlighted. In addition, a high dependence on high-quality grazed pasture during late autumn can be ensured without compromising grazing season length while also allowing additional pasture to be available for the subsequent spring. [ABSTRACT FROM AUTHOR]

The objective of this experiment was to evaluate the effect of stocking rate (SR) and animal genotype (BR) on milk production, body weight (BW), and body condition score (BCS) within intensive pasture-based systems. A total of 533 lactation records, from 246 elite genetic merit dairy cows were available for analysis; 68 Holstein-Friesian (HF) and 71 Jersey × Holstein- Friesian (JxHF) crossbred cows in each of 4 consecutive years (2013-2016, inclusive). Cows from each BR were randomly allocated to 1 of 3 whole-farm comparative SR treatments, low (LSR; 1,200 kg of BW/ha), medium (MSR; 1,400 kg of BW/ha), and high (HSR; 1,600 kg of BW/ha), and remained in the same SR treatments for the duration of the experiment. The effects of SR, BR, and their interaction on milk production/cow and per hectare, BW, BCS, and grazing characteristics were analyzed. Total pasture utilization per hectare consumed in the form of grazed pasture increased linearly as SR increased: least in LSR (10,237 kg of dry matter/ha), intermediate in MSR (11,016 kg of dry matter/ha), and greatest in HSR (11,809 kg of dry matter/ha). Milk and milk solids (MS) yield per hectare was greatest for HSR (15,942 and 1,354 kg, respectively), intermediate for MSR (14,191 and 1,220 kg, respectively), and least for LSR (13,186 and 1,139 kg, respectively) with similar trends evident for fat, protein, and lactose yield/ha. At higher SR (MSR and HSR), MS yield per kg of BW per ha was reduced (0.85 and 0.82 kg of MS/kg of BW, respectively) compared with LSR (0.93 kg of MS/kg of BW/ha). Holstein-Friesian cows achieved fewer grazing days per hectare (-37 d), and produced more milk (+561 kg/ha) but less fat plus protein (-57 kg/ha) compared with JxHF cows; the JxHF cows were lighter. At similar BW per hectare, JxHF cows produced more fat plus protein/ha during the grazing season at low (1,164 vs. 1,113 kg), medium (1,254 vs. 1,185 kg), and high (1,327 vs. 1,380 kg) SR. In addition, JxHF cows produced more fat plus protein per kg of BW/ha (0.90 kg) compared with HF cows (0.84 kg). The results highlight the superior productive efficiency of high genetic potential crossbred dairy cows within intensive pasture-based production systems. [ABSTRACT FROM AUTHOR]

The production and utilization of increased quantities of high quality pasture is of paramount importance in pasture-based milk production systems. The objective of this study was to evaluate the cumulative effects of alternative integrated grazing strategies, incorporating alternative stocking rate (SR) and grazing severities, on pasture productivity and grazing efficiency over multiple years within farm systems using perennial ryegrass dominant pastures. Three whole-farm SR treatments were compared over 4 complete grazing seasons (2009 to 2012 inclusive): low (2.51 cows/ha; LSR), medium (2.92 cows/ha; MSR), and high (3.28 cows/ha; HSR). Each system had its own farmlet containing 18 paddocks and remained on the same treatment for the duration of the study. Stocking rate had a significant effect on all grazing variables with the exception of soil fertility status and sward density. Increased SR resulted in increased total annual net pasture accumulation, improved sward nutritive value, and increased grazed pasture utilization. Total annual net pasture accumulation was greatest in HSR [15,410 kg of dry matter (DM)/ha], intermediate for MSR (14,992 kg of DM/ha), and least for LSR (14,479 kg of DM/ha) during the 4-yr study period. A linear effect of SR on net pasture accumulation was detected with an increase in net pasture accumulation of 1,164.4 (SE = 432.7) kg of DM/ha for each 1 cow/ha increase in SR. Pregrazing pasture mass and height and postgrazing residual pasture mass and height were greatest for LSR, intermediate for the MSR, and lowest for the HSR. In comparison with the LSR, the imposition of a consistently increased grazing severity coupled with increased whole farm SR in MSR and HSR treatments arrested the decline in sward nutritive value, typically observed during mid-season. Incorporating the individual beneficial effects of SR on pasture accumulation, nutritive value, and utilization efficiency, total proportional energy (unite fourragere lait) utilization per hectare increased significantly with increasing SR (+0.026 and +0.081 for MSR and HSR, respectively). These results quantify the significant effect of grazing management practices on the feed production capability of modern perennial ryegrass pastures for intensive grazing dairy production systems. Furthermore, these results highlight the importance of consistently imposing grazing treatments over multiple years, and within integrated whole farm systems, to accurately assess the longer term effects of alternate grazing management practices on pasture productivity. [ABSTRACT FROM AUTHOR]

To fill the feed deficit in the autumn/late lactation period in a seasonal grazing system, supplementation is required. This study aimed to investigate the use of baled grass silage or concentrate as supplementation to grazing dairy cows in late lactation. Eighty-four grass-based spring-calving dairy cows, averaging 212 d in milk, were allocated to 1 of 6 treatments [high grass allowance (HG), low grass allowance (LG), grass with a low concentrate allocation (GCL), grass with a low grass silage allocation (GSL), grass with a high concentrate allocation (GCH), and grass with a high grass silage allocation (GSH)] to measure the effects of using baled grass silage or concentrate as supplements to grazed grass. Effects on intake, milk yield, milk composition and N fractions, and N utilization efficiency were measured. Treatments HG and LG received 17 and 14 kg of dry matter (DM) grass/cow per d, respectively. Treatments GCL and GSL were offered 14 kg of DM grass/cow per d and 3 kg of DM of supplementation/cow per d. Treatments GCH and GSH were offered 11 kg of DM grass/cow per d and 6 kg of DM of supplementation/cow per d. Milk yield was greatest in the GCH treatment and milk solids yield was greatest in both concentrate-supplemented treatments. The HG and LG treatments excreted a greater quantity of N as a proportion of N intake than the supplemented treatments. The HG treatment also excreted the greatest total quantity of N. This indicates an improvement in N utilization efficiency when supplementation is offered compared with grazing only. Offering 6 kg of DM of either grass silage or concentrate as supplementation decreased milk true protein concentration compared with offering a grass-only diet. This suggests that increasing the proportion of supplementation relative to grass may negatively affect milk processability, which is associated with milk true protein concentration. [ABSTRACT FROM AUTHOR]