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Holstein cows’ fertility has decreased in the last decade, creating a need for new management methods to improve the reproductive performance which in this case was defined by pregnancy rates and number of artificial inseminations (AI) per pregnancy. Previous studies showed that deliberately delaying rebreeding until after peak lactation can improve reproductive performance compared with the traditional rebreeding in early lactation. The objective was to compare the reproductive performance of cows in consecutive lactations of different lengths. The reproductive performance (pregnancy rate and number of insemination to pregnancy) of 62 Holstein cows involved in a 16 months extended lactation trial was recorded and compared with the reproductive performance of the previous and following 10 months lactation of the same cows. It was hypothesized that a late rebreeding (at eight months, 16 months lactation) will improve the reproductive performance compared with an early rebreeding (at two months, 10 months lactation) in the previous lactation, and it will have no negative effect on the reproductive performance in the following lactation with an early rebreeding. The results showed that the pregnancy rates were similar for the 16 months lactation and the previous and following 10 months lactations, while the number of AI to pregnancy was increased in the 10 months lactation, following by the 16 months lactation. The use of the double AI technique did not improve pregnancy rates compared with a single AI per estrus, and induced confusion, as how to report the herd reproductive performance. To conclude, the reproductive performance was similar between the heifers, primiparous and multiparous cows, and between 10 months and 16 months lactations.

Effect of Delayed Insemination on Holstein Cows’ Reproductive Performance