The effect of mid-cycle insemination on subsequent conception rates of cattle

Abstract

Extract

Sir,—The proportion of return intervals after first insemination of less than 18 days' duration is between 16 and 20% in New Zealand dairy cattle (Macmillan, 1970) whereas the comparable figure in American herds is 3.5% (Moeller and VanDemark, 1951; Flerchinger and Erb, 1954). Since the incidence of these short cycles tends to increase with increasing: herd size, these short return intervals after first insemination may be the result of errors made by the farmer identifying or diagnosing oestrous cows. Such errors will arise because (1) the farmer correctly submits a cow in the first instance but then unnecessarily resubmits the same cow because of incorrect identification or diagnosis; (2) the initial incorrect submission is followed by correct diagnosis and submission; or (3) errors in detection and diagnosis are made on consecutive occasions.