Feeding intensity of pregnant heifers Effect of feeding intensity during gestation on performance and plasma parameters of primiparous Ayrshire cows

The effect of different feeding intensity at two stages of gestation on performance of primiparous cows was studied in 40 pregnant Ayrshire cows. The feeding intensity was either medium (M) or high (H) in period 1 (2–6 months of pregnancy) or period 2 (7–9 months of pregnancy) resulting in treatments MM, MH, HM and HH. Before pregnancy all heifers were reared to gain 650 g/day. In period 1, heifers on H feeding intensity, grew significantly faster than heifers on M (844 vs. 638 g/day; SEM 5 18.9). Daily gains in period 2 were affected by feeding intensity in period 1 and were 710, 1042, 636 and 874 g on MM, MH, HM, and HH diets, respectively. The body weights at calving were 462, 498, 480 and 499 kg on MM, MH, HM and HH diet, respectively. Feeding intensity in period 1 had no effect on milk production, but H plane of nutrition in period 2 increased milk yield by approximately 11% (22.6 vs. 20.3 kg/day, P , 0.004). Medium feeding intensity in period 1 increased postpartum DMI, and decreased postpartum mobilization of body reserves. Mobilization was positively correlated with BCS at calving (r 5 0.48; P , 0.003) and with plasma free fatty acid (r 5 0.73; P , 0.0001) and b-hydroxybutyrate concentrations (r 5 0.69; P , 0.0001). Prepartum treatments had no effect on postpartum plasma growth hormone (GH) or prolactin concentration, but high feeding intensity in period 2 decreased insulin (INS) concentration postpartum. No relationships were found across treatments between milk yield and prepartum plasma hormone concentrations, but a positive correlation was found between milk yield and postpartum GH and GH/INS. The results show that high compared with medium feeding intensity during the first two trimesters of gestation does not improve milk production of primiparous cows. Instead, during the last trimester a high feeding intensity is required for maximum milk yield.  1999 Elsevier Science B.V. All rights reserved.