Effects of level of feeding of concentrates during early lactation on the yield and composition of milk from grazing dairy cows with varying body condition score at calving

Abstract

An experiment was undertaken to establish the influence of body condition at calving on milk production and composition using diets typical of those currently used in Victoria. Seventy-two cows were fed differently from April 2001 to achieve target body condition scores (BCS) by 1 month before calving of about 4 (3.5–4.5), 5 (4.5–5.5) or 6 (5.5–6.5) units on an 8-point scale. The actual mean BCS at calving for the 3 treatments were 3.8, 5.2 and 5.7 units (P<0.05). After calving, cows grazed at pasture allowances of about 35 kg DM/cow.day and received 1 of 2 levels of supplementation (1 or 6 kg DM of pelleted concentrates per day) for about the first 10 weeks of lactation. The low BCS cows lost less body condition (0.35 v. 1.27 units; P<0.05) for a shorter period (4.8 v. 7.9 weeks; P<0.05) than did the medium and high BCS cows. The low BCS cows also ate more pasture than the other 2 BCS groups, but only when expressed as a percentage of liveweight (2.91 v. 2.73%; P<0.05). Improvements in BCS at calving resulted in higher milk fat percentages in early lactation (3.31% for low BCS cows v. 3.60% for the 2 higher BCS groups; P<0.05), while milk protein and lactose were not affected (P>0.05). At the lower level of feeding in early lactation, milk production increased (P<0.05) linearly as BCS at calving increased, by 1.0 kg milk per unit of body condition per day. However, when energy intake was increased by feeding 6 kg of concentrates, milk production increased as body condition increased (P<0.05) from the low to medium BCS, but there was no significant benefit beyond the medium BCS. Therefore, the hypothesis, that providing that cows are fed well with grazed pasture supplemented with high-energy concentrates in early lactation, BCS at calving will have no effect on subsequent milk production, was at least partially disproved, and it may be that it is never possible for cows at pasture to be sufficiently well fed.