Early lactation dairy cows: Development of equations to predict intake and milk performance at grazing

摘要

The objectives of this study were to examine the effect of parity and days in milk (DIM) on dry matter intake (DMI) and actual milk yield (MYAct) of grazing spring calving dairy cows in early lactation (<100 DIM) and to develop equations to predict DMI and milk yield for grass based systems of milk production. A dataset containing 335 observations from 134 Holstein Friesian dairy cows was assembled from two early lactation grazing studies. Observations were available for primiparous (n =130) and multiparous (n =205) cows during periods of DMI measurement using the n-alkane technique. Animal performance was divided into two classes of DIM: less than 50 DIM (<50 DIM) or between 51 and 100 DIM (>50 DIM). Parity and DIM had a significant effect on grass DMI (GDMI), total DMI (TDMI), MYAct and milk composition. TDMI increased with parity and DIM and ranged from 13.4 kg/cow per day (primiparous animals, <50 DIM) to 20.1 kg/cow per day (multiparous animals, >50 DIM). Actual MY increased with parity and decreased with DIM (range: 24.1 kg/cow per day (primiparous animals, >50 DIM) to 33.0 kg/cow per day (multiparous animals, <50 DIM)). Multiparous cows had greater bodyweight (BW) and lower BCS than primiparous cows. In the early lactation period a number of variables had a significant effect on GDMI, TDMI and milk yield. These predictor variables included BW, BCS, potential milk yield (MYPot), DIM, daily herbage allowance (DHA; >4 cm), concentrate level and parity. The equations accounted for 79%, 83% and 86% of the variation in GDMI, TDMI and milk yield, respectively. Actual milk yield was always below the MYPot of the cows, the mean difference was 5.8 kg/cow per day. As DHA and concentrate level increased, the difference between MYAct and MYPot reduced. This study supports the concept that immediately post-calving offering a grass based diet with a medium level of concentrate supplementation is sufficient to support high milk production in grazing dairy cows.