• Milk production per cow and per hectare of spring-calving dairy cows grazing swards differing in Lolium perenne L. ploidy and Trifolium repens L. composition

      McClearn, B.; Gilliland, T.J.; Delaby, L.; Guy, C.; Dineen, M.; Coughlan, F.; McCarthy, B.; Dairy Research Ireland; Teagasc Walsh Fellowship Programme (American Dairy Science Association, 2019-09)
      Grazed grass is the cheapest feed available for dairy cows in temperate regions; thus, to maximize profits, dairy farmers must optimize the use of this high-quality feed. Previous research has defined the benefits of including white clover (Trifolium repens L.) in grass swards for milk production, usually at reduced nitrogen usage and stocking rate. The aim of this study was to quantify the responses in milk production of dairy cows grazing tetraploid or diploid perennial ryegrass (Lolium perenne L.; PRG) sown with and without white clover but without reducing stocking rate or nitrogen usage. We compared 4 grazing treatments in this study: tetraploid PRG-only swards, diploid PRG-only swards, tetraploid with white clover swards, and diploid with white clover swards. Thirty cows were assigned to each treatment, and swards were rotationally grazed at a farm-level stocking rate of 2.75 cows/ha and a nitrogen fertilizer rate of 250 kg/ha annually. Sward white clover content was 23.6 and 22.6% for tetraploid with white clover swards and diploid with white clover swards, respectively. Milk production did not differ between the 2 ploidies during this 4-yr study, but cows grazing the PRG-white clover treatments had significantly greater milk yields (+596 kg/cow per year) and milk solid yields (+48 kg/cow per year) compared with cows grazing the PRG-only treatments. The PRG-white clover swards also produced 1,205 kg of DM/ha per year more herbage, which was available for conserving and buffer feeding in spring when these swards were less productive than PRG-only swards. Although white clover is generally combined with reduced nitrogen fertilizer use, this study provides evidence that including white clover in either tetraploid or diploid PRG swards, combined with high levels of nitrogen fertilizer, can effectively increase milk production per cow and per hectare
    • Pasture allowance, duration, and stage of lactation—Effects on early and total lactation animal performance

      Claffey, A.; Delaby, L.; Lewis, E.; Boland, T.M.; Kennedy, Emer; Dairy Levy (American Dairy Science Association, 2019-10)
      Pasture availability in early spring can be limited due to climatic effects on grass production, increasing the likelihood of feed deficits in early lactation of spring-calving pasture-based systems. We hypothesized that restricting pasture allowance (PA) when animals are at peak milk production will have more negative implications on milk production compared with restricting animals before this period. A total of 105 cows were assigned to 1 of 7 grazing treatments from March 14 to October 31, 2016 (33 wk). The control treatment was offered a PA to achieve a postgrazing sward height > 3.5 cm and mean pasture allowance of 15.5 kg of dry matter per cow. The remaining treatments were offered a PA representing 60% of that offered to the control for a duration of 2 or 6 wk from March 14 (mid-March; MMx2 and MMx6), March 28 (end of March; EMx2 and EMx6), or April 11 (mid-April; MAx2 and MAx6). Within grazing treatment, animals were also assigned to 1 of 2 calving dates (early and late) based on days in milk (DIM) on March 14. Early calved (EC) cows were ≥36 DIM, while late calved (LC) were ≤35 DIM. Restricting PA for 2 and 6 wk reduced daily milk yield (−1.6 and −2.2 kg/cow, respectively), cumulative milk protein yield (−4.0 and −6.3 kg/cow, respectively), and cumulative milk solids yield (−5.8 and −9.5 kg/cow, respectively) in the first 10 wk of the experiment. Daily milk yield was similar across the treatments at the end of the 33-wk period (16.8 kg/cow, average of all treatments), as was daily milk solids yield (1.40 kg/cow). Cows in the EC group produced less milk over the first 10 wk of the experiment (20.0 kg/cow per day) compared with the LC animals (22.1 kg/cow per day). However, body weight was greater (+15 kg/cow) in the EC animals compared with the LC, while body condition score was similar (2.85). This outcome indicates that animals that are restricted later in early lactation (circa onset of peak milk production) partition a greater proportion of available energy to maintenance, resulting in greater losses in milk production. These data indicate that despite the immediate reduction in milk production, restricting intake of grazing cows to 80% of that required to achieve spring grazing targets for postgrazing sward height for up to 6 wk may be used as a method of managing short-term pasture deficits on farm with minimal effects on total lactation performance.