Influence of the reuse of progesterone implants in a fixed-time artificial insemination protocol on the conception rates of lactating cows during two different seasons

Abstract

This study aimed to evaluate the influence of reusing progesterone intravaginal implants using a fixed-time artificial insemination (FTAI) protocol on the conception rates of 593 primiparous and multiparous lactating cows during two different seasons. The cows were divided into two categories: multiparous and primiparous. The experiment was conducted during seasons with high and mild temperatures. To compare the conception rates during both seasons, the animals were randomly divided into three groups according to use progesterone implant (1^st use, 2^nd use and 3^rd use) on the first day of the synchronization protocol for FTAI within each category. A pregnancy diagnosis was performed at 30 days following FTAI. The temperature and humidity index was higher (P<0.01) during the season with higher temperatures (74.4 ± 0.26) than during the season with mild temperatures (67.5 ± 0.34). The different categories (multiparous and primiparous) did not influence the conception rate in terms of the seasonal temperatures or the reuse of progesterone implants. Nevertheless, a 3^rd use implant administered during the season with high temperatures was 1.98 times less likely to result in a pregnancy compared with a 1^st use implant  (P=0.01) and 2.83 less likely to result in a pregnancy than the other implants used during the season with mild temperatures (P=0.005). The results indicate that during the season with mild temperatures, the conception rates at 30 days are not influenced by reusing the P₄ implant in any of the categories analyzed. However, during the season with high temperatures, the reuse of the P₄ implant can influence the conception rates of dairy cows.

Key words: Heat stress, Holstein cows, pregnancy.