First Service Calving Rates In Irish Dairy Herds: Trends From 1991-1996

Abstract

In Ireland, surveys in the 1970's have shown calving rates to first service of 60-69%. Since then genetic merit and milk yield per cow have increased significantly. The objectives of this study were to determine calving rates in Irish dairy herds for the period 1991-1996 and if these had declined over time. Breeding records for 58 Spring calving commercial dairy herds maintained on the computerised DAIRYMIS System were analysed. Inseminations were categorised as either DIY AI (DIY), commercial AI (COM) or Natural Service (NAT). Between 1991 and 1996 there was a significant trend towards DIY (P<0.01) and away from NAT (P<0.01) with no consistent trend in COM usage. In 1991, roughly one third of services were to each of the three service methods but by 1996 DIY accounted for nearly 50% of all services. A subset of 34 herds, which had been present for at least five of the six years between 1991 and 1996, was used in the calving rate analysis. Calving rates to first service for DIY (48.4%) and NAT (46.0%) were not significantly different although both were significantly lower (P<0.001) than those for COM (54.5%). For small (<65), medium (65-128) and large herds (˃128) the respective proportion of services in each category were 22%, 44% and 34%. The respective calving rates of 55.2%, 51.6% and 45.7% declined significantly as herd size increased For all service types, there was a significant (P<0.001) decline in first service calving rate over time. The increased usage of DIY, combined with its lower fertility rates, would appear to be one factor responsible for the reduction in calving rate for 1991-1996 period.

Temporal trends in reproductive performance in Irish dairy herds and associated risk factors

“…The highest conception rate to first service was recorded in 1980 as 67% and it declined to 59% in 1988 [25]. Subsequent studies in commercial herds in the 1990s confirmed this phenotypic trend (Figure 1) when calving rate to first service declined significantly by 0.7% to 0.9% per year [52,43]. However, the decline in calving rate to all services was smaller (0.5% per year: [43]).…”

“…Irish data show a small increase in calving-to-service interval (68 v. 71 days) between herd surveys in 1969-70 [ 35 ] and in 1999 [ 5 ]. However, the proportion of cows first served more than three months postpartum increased from the 1980s (12%, [ 25 ]) to the 1990s (21%, [ 52 ]). The other component of calving interval, gestation length, has increased by approximately one day in Friesian cows mated to Friesian sires since records began (1979: 281 days; 2001: 282 days - Department of Agriculture, Food and Rural Development, 1979 - 2001).…”

“…In 1991, approximately one third of inseminations in DairyMIS herds were conducted by DIYAI. By 1996, this had increased to almost half of all inseminations [ 52 ]. This trend was confirmed nationally by the doubling in the number of DIYAI licences issued from 1992 to 2001 [ 30 ].…”

“…Examination of DairyMIS data from 1991 to 1996 showed that first service calving rate to DIYAI (48%) was significantly lower than that of commercial AI (55%) and overall first service calving rate declined over time. The decline in herd fertility in these herds was partially attributed to the increased use of DIYAI and the associated lower fertility [ 52 ]. However, calving rates following DIYAI may be attributed to DIYAI per se or herd characteristics such as calving pattern, herd size and milk yield [ 43 ].…”

Consequences of genetic selection for increased milk production in European seasonal pasture based systems of milk production

“…Calving intervals of less than 365 days were readily observed. A review of herds participating in the Dairy Management Information System (DairyMIS) run by Teagasc Moorepark (Crosse, 1991) showed that calving rate to first service fell over the period 1991 to 1996, from 53% to 49% (O'Farrell and Crilly, 2001). More recently, Evans et al (2002) reported a pregnancy rate to first service of 48% for 74 spring calving herds in the 1999 calving season.…”