Timed artificial insemination and early diagnosis of pregnancy to reduce breeding season in Nelore beef cows.

The purpose of this study was conducted to evaluate the use of a system of timed artificial insemination (TAI) and early diagnosis of pregnancy in Nelore beef cows in order to reduce the breeding season (BS) from 150 to 90 days and analyze the factors affecting the conception rate of cows selected for TAI. The study included 110 Nelore cows belonging to the Experimental Farm Capim Branco, Brazil. The body condition scores (BCS) were evaluated, and those above 2.50 were included in the TAI protocol. Five groups of cows were formed at intervals of 21 days postpartum and then commenced a 9-day progesterone protocol. Progesterone devices were used three times. Statistical analysis of binary variables was performed by logistic regression in the program Proc Logistic of Sas. A 5% of significance (P < 0.05) was used to determine the presence of statistical differences and the effect of independent variables on conception rate. The TAI and early diagnosis of pregnancy reduces the BS from 150 to 90 days without changing the pregnancy rate. The conception rate was not affected by the presence of the calf (P > 0.05), the corpus luteum (P > 0.05), the BCS (P > 0.05), or the number of reuses of the intravaginal progesterone device (P > 0.05). Therefore, this technique is beneficial for breeding Nelore beef cattle and can be used in anestrous cows with a BCS above 2.50. Additionally, the progesterone devices can be reused to reduce the cost of the protocol without compromising the results.