17 EFFECT OF A PROGESTERONE INTRAVAGINAL DEVICE ON PREGNANCY RATE IN CROSSBREED DAIRY COWS UNDER TROPICAL CONDITIONS

The objectives of these experiments were to evaluate the effect of intravaginal progesterone device on crossbreed Holstein × Carora on pregnancy rate under 2 conditions: cycling and noncycling cows. The first experiment was conducted on 135 noncycling cows (45 ± 3 days postpartum) divided in 2 groups. The first group was treated with a timed AI procedure using a progesterone device for 9 days with an eCG injection on Day 6 and estradiol benzoate after progesterone device removal followed by AI 48 h later. The second group was not treated and they were checked until they came in heat and were inseminated. The second experiment was performed on 123 cycling cows and they were divided in 2 groups. The first group was submitted to a time AI treatment similar to that in experiment 1, and the second group was not treated and they were inseminated upon heat detection. Pregnancy rate on Day 120 postpartum was recorded and pregnancy rate was compared among the different proportion of Holstein (H) × Carora (C) crossbreed cows. For the first experiment, differences (P < 0.05) were observed between ¾ Carora ¼ Holstein (46.15%) compared with the other crossbreed groups (10% 7/8 H 1/8 C, 21.42% 5/8 H 3/8 C, 29.16% ½ H ½ C). In the second experiment, differences (P < 0.05) were observed between ¾ Carora ¼ Holstein (57.14%) compared with the other crossbreed groups (6.66% 7/8 H 1/8 C, 30.76% 5/8 H 3/8 C, 33.33% ½ H ½ C). For the variable pregnancy rate at 120 days postpartum, significant differences (P < 0.05) were observed in cycling cows (39.2%) treated with the progesterone device v. nontreated cows (21%). In noncycling cows, there were no differences between treated and nontreated cows. In conclusion, the use of progesterone device did not improve pregnancy rate in the noncycling cows, which could be related to the negative energy balance that cows undergo during the first part of gestation. However, the use of the progesterone device in cycling cows did improve the pregnancy rate compared with nontreated, cycling cows. We demonstrated that this dairy farm has a serious problem in detecting estrous, which was help by use of the progesterone device and timed AI. Also, the Carora blood included in dairy animals help them to perform better under tropical conditions and they can became pregnant much faster than animals with a high level of Holstein blood.