Production and Reproduction of Early and Late Bred Dairy Heifers

Abstract

A total of 253 heifers bred at first estrus after 350 d of age (350-d breeding age group) and 249 contemporary heifers bred at first estrus after 462 d of age (462-d breeding age group) were used to study the effects of age at first breeding on productive and reproductive performances of first lactation heifers. Heifers of both breeding age groups were subject to similar feeding and management practices. The average age at first calving was 698 d for the 350-d breeding group and 796 d for the 462-d breeding group. Although not statistically significant, heifers of the 462-d breeding group tended to have a higher conception rate at first service (47 vs. 38%) and fewer days between first service and conception (39 vs. 44 d) than those of the 350-d breeding age group. Breeding heifers as early as 350 d of age has no adverse effects on calving ease or retained placenta but does result in calves 1.2 kg lighter at birth. Heifers of the 350-d breeding group had lower milk, protein, and fat yields at both 168 and 308 d of first lactation than those of the 462-d breeding group. A 1-d reduction in age at first calving decreased 308-d milk yield by 2.01 kg for the 350-d breeding group as compared with 4.74 kg for the 462-d breeding group.

Effect of feeding regime, growth intensity and age at first insemination on performances and longevity of Holstein heifers born during autumn

“…In a strategy with first calving at 24 mo of age, reaching puberty at a young age is of importance: growth rate has a positive effect on puberty attainment (Little and Kay, 1979). In many species, fertility is improved when animals are bred on the 3rd or 4th detected oestrus rather than at puberty (Lin et al, 1986;Byerley et al, 1987;Robinson, 1990;Le Cozler et al, 1999). In Holstein heifers where puberty occurs at an early age (8-10 months in the present study), first insemination around 15 mo of age is then favourable.…”

A comparative study of three growth profiles during rearing in dairy heifers: Effect of feeding intensity during two successive winters on performances and longevity

“…In many species, fertility generally increases when animals are bred on the third or fourth detected oestrus rather than at puberty (Lin et al, 1986;Byerley et al, 1987;Robinson, 1990;Le Cozler et al, 1999). But relationships between rearing management and fertility are not well documented (Le Cozler et al, 2008, for a review), and there is no consistency in the published results.…”

Rearing strategy and optimizing first-calving targets in dairy heifers: a review

“…When growth is slow, fertility is improved when animals are bred on the 3rd or 4th detected oestrus rather than at puberty in many species (Lin et al, 1986;Byerley et al, 1987;Robinson, 1990;Le Cozler et al, 1999). In Holstein heifers where puberty occurs at an early age, first service around 15 months of age is then favourable.…”