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 0·96% per year (55 to 44%;P< 0·001), calving rate to first and second service (CALV12) reduced by 0·84% per year ( 77 to 70%;P< 0·001) and herd average parity number reduced by 0·10 lactation per year (4·3 to 3·5;P<0·001). The proportion of North American Holstein Friesian (NAHF) genes in the cows increased by 5·5% per year (8 to 63%;P<0·001), while pedigree index for milk yield (PIMILK) of the cows increased by 25 kg per year (P<0·001). The predicted difference of the sires of the cows for calving interval and survival increased by 0·5 days (P<0·001) and reduced by 0·12% (P<0·001) per year, respectively. A negative association was found between increased phenotypic milk yield, NAHF and PIMILKand reduced calving rates as assessed by CALV1 and CALV12. Increased proportion of NAHF genes exhibited a negative effect on survival (P<0·001) whereas increased levels of heterosis had a positive impact on survival (P<0·001). 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.