Could Selecting For Fertility Result in Increased Uterine Health?13 May 2014
If more emphasis is put on fertility in genetic selection, veterinarians' time can be saved, say Irish researchers.
For several decades, genetic selection programmes focused primarily on milk production traits. Unfortunately, genetic merit for fertility traits deteriorated during this period, write Teagasc experts Stephen Moore and Stephen Butler.
Research at Moorepark set out to investigate the specific effects of genetic merit of fertility traits on reproduction in lactating dairy cows.
Heifers with similar genetic merit for milk production, but with either good (Fert+) or poor (Fert-) genetic merit for fertility traits were identified from within the national herd in collaboration with ICBF.
These animals were representative of the top 25 per cent of the national herd in genetic merit for milk production. The Fert+ and Fert- groups represented the top 20 per cent and bottom 5 per cent of the national herd in genetic merit for calving interval respectively.
During the breeding season, Fert- cows had poorer submission rates (72 per cent vs 83 per cent ); poorer conception rate to first service (33 per cent vs 56 per cent ); required more services per pregnancy (2.2 vs 1.4); and, as a result, required 28 days longer to become pregnant, compared with Fert+ cows.
Uterine health was also assessed. Based on uterine cytology, a smaller proportion of Fert+ cows were classified as having endometritis at weeks three (42 per cent vs 78 per cent ) and six (25 per cent vs 75 per cent ) than Fert- cows. Milk progesterone analysis indicated that a greater proportion of Fert+ cows had resumed cyclicity by six weeks after calving (86 per cent vs 20 per cent ), compared with Fert- cows.
Improvements to fertility traits were achieved without antagonising milk production. Cows with a high EBI fertility sub-index have a faster recovery from uterine infection and resume ovarian cyclicity earlier after calving.
As a result, the need for veterinary intervention can be reduced and fertility improved by selecting sires with a high fertility sub-index to generate replacement heifers with superior genetics for fertility traits.