The effects of breed, month of parturition and sex of progeny on beef cow fertility using calving interval as a measure

This study aimed to evaluate levels of beef cow fertility using calving interval (CI; measured in days) as a measure, and investigate the effects of breed, season, year and progeny gender on CI. The CI data included 273 764 records collected between 1997 and 2012 and included the seven most common breeds (and their crosses) in Northern Ireland (Charolais, Limousin, Belgian Blue, Simmental, Blonde d’Aquitaine, Aberdeen Angus and Hereford), accounting for 94.1% of beef dams recorded. Mean CI for all cows was 395 days, 30 days longer than the optimum 365 days. Charolais and Belgian Blue dams had the longest CI (P<0.05). Cows older than 144 months had a longer CI (P<0.05) compared with cows younger than 144 months. Charolais sires had a shorter subsequent CI of 392 days (P<0.05) compared with the other breeds. Cows calving in June had the shortest subsequent CI (376 days; P<0.05), whereas cows calving in November had the longest subsequent CI (410 days). Progeny gender did not significantly affect CI. This study establishes the level of beef cow fertility using CI as a measure in Northern Ireland is sub optimal and there are opportunities for improvement. Factors identified as influencing CI included dam breed, sire breed and month of parturition. This knowledge can be used to direct breeding programmes and inform knowledge transfer protocol to improve sustainability of beef production.