Pregnancy and repeat breeding rate of high producing dairy cows for morning, evening or night artificial insemination

Resumo

The study aimed (1) to verify if artificial insemination (AI), performed in the morning, evening or nighttimehas influence on the pregnancy rate on high production dairy cows, and (2) to determine the repeat breedingrate after the AI at intervals of 01-21, 22-43 and 44-65 days. We analyzed 1980 AI data from HolsteinFriesian cows from years 2004 to 2008. The average milk production on this period was 39 kg/milk/day/cow (305 days of lactation). The AI was performed 12 hours after the first detection of estrus. For the dataanalysis one AI was computed. The AI was done based on conventional method. The incidence of the AI in themorning, evening and night was 29.8; 50.4 and 19.8% respectively; and the pregnancy rate 45.7; 44.9 and48.4%. The frequency of the repeat breeding rate at the interval of 1-21 days on morning, evening and nightafter failed AI was 28.0; 22.3 and 19.8% respectively; at the interval of 22-43 days was 52.0; 52.2 and 55.2%,respectively and at interval of 44-65 days was respectively 20.0; 25.5 and 25.0%. Comparing the three timesof the day each other, the cows showed greater repeat breeding on 22-43 days (P<0.05) after the AI. It wasconcluded that times of the day has no influence on the on pregnancy rate; the highest repeat breeding ratetook place between 22 and 43 days after AI, resulting significant delaying of the open period.