The reproductive performance of two genetic lines of Holstein-Friesian cows bred for heavy (H) or light (L) mature live weight (LW) was evaluated from 1992 to 1997. The interval calving to ovulation was shorter (P<0.05) for H cows (28 ± 3.2 days) than for L cows (L: 31 ± 2.5 days), but the difference between the lines in the interval calving-first heat was not significant (H: 50 days; L: 43 days). However, in the cows older than 2 years old, the H cows had a lower conception rate at first service than the L cows (H: 58% vs. L: 70%) which extended the conception and calving pattern of the H cows. The possible reasons for those differences in the reproductive performance are discussed as topics for further research.
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 73-75, 1998
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