The effect of feeding level of pre- and postpubertal heifers on their reproductive function and later milk production

Thirty-three heifers were assigned to 3 analogous groups of 11 animals each in which three different levels of feeding were used from 6.5 to 10 months (first period) and from 11 to 12 months of age (second period): the feedin g level recommended by the IZ-INRA system (1997) (group C), lower and then 20% higher in subsequent periods in relation to group C (group D), and 20% higher in both periods in relation to group C (group H). Body weight gains in different rearing periods were assumed as follows (g/day): 700 (C), 560 and 840 (D), 840 (H), and from 13 months of age to 3 weeks before calving 7 00 g/day in all the groups. Next the heifers were fed the rations specified for primiparous cows assuming maximum production at peak of lactation to b e 35 kg milk per day. The varying level (group D) of feeding prepubertal an d postpubertal heifers was found to have no adverse effect on ovarian size and status at 12 months of age and on subsequent growth and development of these animals, while having a beneficial effect on their milk performance d uring the first lactation. The high feeding level (group H) from 6.5 to 12 months of age led to increased daily weight gains and accelerated the date of reproductive performance of heifers compared with their age-mates from g roup C.