Fertility of dairy cows in Northern Ireland

Abstract

A comprehensive database was established on the milk production and reproductive performance of dairy cows in 19 selected herds in Northern Ireland, varying in size, management system and genetic merit. Data were obtained for 2471 cows, 1775 of which calved in a second year, and 693 were culled from the herd for specific reasons. The estimated mean rate of heat detection (assessed by the interheat interval during the main breeding season) in all the herds was 71 per cent, with a range from 53 to 92 per cent The average conception rate to first insemination was 37.1 per cent (range 21 to 66 per cent). The average calving interval for the retained cows was 407.2 days (range 359 to 448 days). Twenty-eight per cent of the cows that calved were culled, with infertility being the largest single reason (26.8 per cent of the cows culled). There were major differences in reproductive performance between the herds, but heat detection rate, conception rate and calving interval did not appear to be affeded by a herd's genetic merit. The herds with shorter calving intervals were characterised by better heat detection efficiency (83 v 61 per cent, P<0.01), a shorter interval from calving to first insemination (74 v 97 days; P<0.05), a higher conception rate to first insemination (45 v 34 per cent, P>0.10) and a lower removal rate (23 v 37 per cent, P<0.01). Furthermore, the cows in these herds had lower body condition scores (BCS) in the dry period (3.0 v 3.3; P<0.05) but lost less body condition in early lactation (0.3 v 0.6 BCS units, P<0.05). These results show that dairy herd fertility in Northern Ireland is generally low and similar to that previously reported for England and the USA, but that in some herds changes in herd management practices improved the cows' fertility.

Associations between genetic merit for milk production and animal parameters and the fertility performance of dairy cows

“…The decline in reproductive performance of the dairy herd has been widely reported with various studies around the world citing conception rates to first insemination of approximately 40% (Butler, 1998;Royal et al, 2000;Mayne et al, 2002), though this figure tends to be higher in grassbased production systems Grosshans et al, 1997). At herd level, decreased individual cow fertility, with more services per conception, has been reported in cows producing more than the herd average (Wicks and Leaver, 2004) but Darwash et al (1997) found no such phenotypic effects of yield on fertility.…”

“…Herds were identified by local DARD advisers as having a good track record of data recording, a willingness and enthusiasm to participate in the study and being geographically spread throughout Northern Ireland. Twenty herds were selected as representative of those throughout the region and included a wide range of herd size, concentrate input, feeding methods, genetic merit and level of milk production, details of which are provided in Mayne et al (2002). One of these herds was later omitted from the study due to farmer illness and not replaced.…”

“…While information on calving index is readily available from milk records, data analysis is problematical since it only relates to cows that conceive and calve again (Olori et al, 2002;Veerkamp et al, 2002). In the study of Mayne et al (2002), 28% of cows were removed or sold of which almost 27% were sold for infertility. Removal rates varied from 17 to 49% between herds, making the comparison of fertility performance using calving index extremely difficult.…”

“…Recent results from a fertility study in Northern Ireland have reported a mean calving index of 407 days with a range between herds from 359 to 448 days (Mayne et al, 2002). While information on calving index is readily available from milk records, data analysis is problematical since it only relates to cows that conceive and calve again (Olori et al, 2002;Veerkamp et al, 2002).…”

“…In addition to the direct financial cost, estimated at over £500 million per annum in the UK (Lamming et al, 1998), infertility can result in increased management complexity with spread calving patterns and therefore extended breeding seasons with prolonged heat observation and infertility intervention for problem and late calving cows. In Northern Ireland, there is a diverse range of milk production systems ranging from compact spring-calving systems to all-year-round calving systems, but the majority of herds are autumn/winter calving and in these herds infertility causes increased management complexity through the inability to achieve a compact calving pattern (Mayne et al, 2002).…”