Body weight of dairy heifers is positively associated with reproduction and stayability

摘要

This study investigated the relationships betweenbody weight (BW) and stayability, and BW and calvingpattern, of 189,936 New Zealand dairy heifers.Heifers were classified into 5 breed groups: Holstein-Friesian (F), Holstein-Friesian crossbred (FX), Jersey(J), Jersey crossbred (JX), and Holstein-Friesian ×Jersey crossbred (FJ). Body weight was predicted usingLegendre polynomials at 6, 12, and 15 mo of age, andwe analyzed their relationships with stayability, calvingrate, and re-calving rate over the first 3 calvings. Approximately92% of heifers calved for the first time atage 2 yr, 76% a second time at 3 yr, and 61% a thirdtime at 4 yr. Heifers that were heavier were more likelyto remain in the herd for first, second, and third calvingcompared with heifers that were lighter. Furthermore,we found positive curvilinear relationships between prebreedingBW and reproductive performance of dairyheifers. Heifers that were heavier at 6, 12, and 15 mowere more likely to calve early for first calving comparedwith heifers that were lighter, regardless of breedgroup. In addition, we found a large range in BW wherethe probability of calving or re-calving early was high.For example, FJ heifers that were between 255 and 396kg at 15 mo of age had 21-d calving and re-calvingrates above 75 and 70%, respectively. For second andthird lactations, however, heifer pre-breeding BWshowed only small effects on the 21-d calving and recalvingrates. For heifers that were at the heaviest endof the BW range in the current study, slight declinesin stayability and reproductive performance occurred,compared with heifers in the mid-range of BW. Consequently,for heifers that were above average in BW, thebenefit of increasing BW before first breeding wouldbe small and might even result in slight declines instayability and reproductive performance. For heifersthat were below average in BW, considerable beneficialeffects on stayability and reproductive performance arepredicted as a result of improving rearing practices toproduce heavier heifers throughout the pre-breedingrearing phase.