Trends in milk production, calving rate and survival of cows in 14 Irish dairy herds as a result of the introgression of Holstein-Friesian genes

Trends in milk production, calving rates, and survival were monitored on a potential 5580 primiparous and multiparous Holstein-Friesian dairy cows across 14 Irish seasonal spring-calving dairy farms between the years 1990 and 2001. Over this period calving rate to first service (CALV1) reduced by 0 center dot 96% per year (55 to 44%; P < 0 center dot 001), calving rate to first and second service (CALV12) reduced by 0 center dot 84% per year (hairsp77 to 70%; P < 0 center dot 001) and herd average parity number reduced by 0 center dot 10 lactation per year (4 center dot 3 to 3 center dot 5; P < 0 center dot 001). The proportion of North American Holstein Friesian (NAHF) genes in the cows increased by 5 center dot 5% per year (8 to 63%; P < 0 center dot 001), while pedigree index for milk yield (PIMILK) of the cows increased by 25 kg per year (hairspP < 0 center dot 001). The predicted difference of the sires of the cows for calving interval and survival increased by 0 center dot 5 days (hairspP < 0 center dot 001) and reduced by 0 center dot 12% (hairspP < 0 center dot 001) per year, respectively. A negative association was found between increased phenotypic milk yield, NAHF and PIMILK and reduced calving rates as assessed by CALV1 and CALV12. Increased proportion of NAHF genes exhibited a negative effect on survival (hairspP < 0 center dot 001) whereas increased levels of heterosis had a positive impact on survival (hairspP < 0 center dot 001). The results of the present study indicate that in seasonal calving herds in Ireland a need for direct selection on traits related to fertility and survival is required to arrest and reverse the declining trends in calving rates and survival.