title: The influence of heat symptoms and the time of insemination of cattle on the early and late returns.
abstract: In a material comprising 95,085 inseminations, the non-return rate and the frequency of late returns, measured as the frequency of returns, measured as the frequency of returns between 29 and 56 days, have been studied with respect to the time of insemination within the heat period and to the intensity of heat. Both these factors have effected the NR result in that insemination late in the oestrus period--2 days after heat has been observed--gives the poorest result, 60.5% 56 days NR in comparison with 68.5 one day after observation and 71.4 the same day. Weak heat symptoms give a bad result, 60.1 compared to 68.7 for fair and 72.7 for strong heat symptoms. The differences are significant. The number of late returns is also influenced by the time of insemination as well as by the intensity of heat. However, insemination in heats with weak symptoms leads to a higher frequency of late returns than what can be expected from the frequency of early returns. This might partly indicate an increased rate of early embryonic death.
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004971:Estrus; D005260:Female; D007315:Insemination, Artificial / Q000662:veterinary*; D011247:Pregnancy; D013997:Time Factors