The effect of lactation number, milk yield and days in milk on hormonal support following insemination in repeat breeder cows

Aim: To investigate the effect of number of lactations, milk yield and days in milk on hormonal support following insemination in repeat breeder cows. Materials and Methods: 169 Holstein cows that gave birth at least once, had regular sexual cycles and did not get pregnant although inseminated at least 3 times were used in the study. PGF2α+ovsynch estrus synchronization protocol was applied to cows included in the study. Fixed time inseminated cows (Day 0) were divided into 4 groups. In the first group (Group I, progesterone group, n=42), progesterone releasing intravaginal device (PRID) was placed in the vagina at the 84th hour and removed from the vagina on the 9th day. hCG was administered intramuscularly to the cows included in the second group (Group II, hCG group, n=40) on day 7. In the third group (Group III, progesterone+hCG group, n=45), progesterone and hCG applications were combined. No application was made to the animals in the fourth group (Group IV, control group, n=42). Results: The conception rate on the 30th day after insemination was determined as 40.47% in Group I; 37.50% in Group II; 44.44% in Group III and 30.95% in Group IV (p>0.05). According to the number of lactations, no statistical difference was found in the conception rates in the groups except Group I (p>0.05). However, when all repeat breeder cows were evaluated, the conception rate of animals with a lactation number of ≥ 3 was found to be lower than those with a lactation number of 1 and 2. In addition, as the milk yield of cows in the control group increased, the conception rate decreased (p<0.05). There was no statistical difference between the groups according to the days in milking (p>0.05). Conclusion: Although the conception rate did not increase statistically in hormone applied cows; it was found higher in hormonal support groups than control group. In addition, it was determined that the number of lactation and the days in milk did not affect the conception rate in repeat breeder cows, but the conception rate decreased as the milk yield increased.