Oestrus response and pregnancy rate after oestrus synchronization with exposure to light and heavy handling in Nelore cattle

This study was conducted to evaluate the effects of oestrus synchronization protocol on oestrus response, pregnancy rate, progesterone (P4) and cortisol concentrations in Nelore cattle under two different types of handlings. In Experiment I (heavy handling), 27 cows were selected and subdivided into four groups, namely the Control, Groups 1, 2 and 3. The Control group was treated with only CIDR inserts for 15 days. Cows in Groups 1, 2 and 3 were treated with CIDR inserts for 15 days and given 500 μg of synthetic prostaglandin F2α  (PGF2α) at 9, 14 and 19 days post CIDR removal, respectively. Oestrus was observed for all cows in the four groups. Forty-eight hours after treatment, Artificial Insemination (AI) was carried out for cows that displayed oestrus, twice at 12 hours interval. Blood samples were collected twice per week beginning on the day of CIDR insertion until after AI and continued for the next 30 days. Ultrasonography was carried out after CIDR removal for the Control group and after PGF2α treatment in other groups to determine the ovulation time. In Experiment II (less handling), 30 cows were subdivided into four groups. The protocol for all the four groups in Experiment II followed that of Experiment I and the only difference was the number of blood samples and that there was no ultrasound examination. The difference between Experiment I (11; 40.7 %) and Experiment II (20; 66.6 %) for the expression of estrus were not significant, similarly for the number of pregnant cows (2; 7.4 % and 9; 30 %). The mean P4 concentrations after AI were higher at Days 7 and 14 in all groups in Experiment II compared with all groups in Experiment I. The mean cortisol concentration on the day of first AI, Days 7 and 14 post AI was higher in all groups in Experiment I than all groups in Experiment II. The results from this study showed a negative correlation between the P4 and cortisol concentrations (r= -0.267, P<0.01) after AI in Experiment I thus, indicating an inverse relationship between P4 and cortisol concentrations.  The normal P4 profile was observed in cows from different groups in both experiments, but delayed P4 production was recorded only in G3 of Experiment I. In conclusion, heavy handling may have altered the expression of oestrus, reduced the pregnancy rate and altered the P4 profiles. On the other hand, less handling and gentle interaction with animals could improve the reproductive performance.