VIII. Effects of non‐oestrous inseminations and return patterns after second inseminations

Abstract

The conception rate (C.R. = 49‐day % non‐return rate) for 863 605 first inseminations was 62.0% compared with 61.5% for 207 884 second inseminations. Most(135 759) second inseminations were made after a period between insemination (p.b.i.) of 18–24 days, a further 52 075 being made after a p.b.i. of 17 days or less. C.R. was 64.0% for the former proup of second inseminations and 55.5% for the latter. This lower C.R. was associated with a higher frequency of short return intervals (1–17 days) after these second inseminations and probably arose through more errors in oestrus diagnosis. Such errors will result in non‐oestrous inseminations. Results obtained in one field trial with 1712 cows showed that if the non‐oestrous intra‐uterine insemination preceded the oestrous insemination, the C.R. for the latter insemination was not affected. In contrast, a second field trial with 65 cows indicated that if the non‐oestrous second insemination was made within 3 weeks of the oestrous first insemination, the pregnancy rate to the first insemination was significantly reduced from 53.1% to 24.2%.