Abstract
The aim of the present study was to determine the optimum time of artificial insemination after the beginning of standing estrus in buffalo. Nili-Ravi buffalo (n = 109) during breeding season were exposed to teaser bull at 12 hours interval to determine the standing heat (0 h). Buffalo were randomly allocated to different time groups and a single artificial insemination was performed either at 0 h (n = 30), 12 h (n = 27), 24 h (n = 28) or 36 h (n = 24). In a subset of buffalo (n = 38) ultrasonography was performed, twice daily from 0 h (onset of standing heat) to determine the time of ovulation. Pregnancy diagnosis was performed 35-40 days after AI. Results revealed that mean time of ovulation from onset of standing heat was 34.7 ± 0.96 h (range 30 to 42 h). Higher (P < 0.05) pregnancy per AI were achieved in buffalo when inseminated at 24 h (15/28; 53%) compared to 0 h (8/30; 26%) and 36 h (3/24; 13%). Pregnancy per AI, was in-between, in buffalo, inseminated at 12 h (10/27; 37%) and did not differ (P > 0.05) with those bred either at 24 h or 0 h. The odds ratio further confirmed that the occurrence of pregnancy per AI was two times higher in buffalo inseminated at 24 h as compared to those at 12 h. It is concluded that optimal pregnancy per AI can be achieved when buffalo are bred artificially 24 h after the onset of standing heat.
Highlights
Artificial insemination (AI) has played a major role in genetic selection, disease control and cost effectiveness of breeding in dairy cattle (Vishwanath, 2003; López-Gatius, 2012)
Minimum number of cows returned to estrus when bred artificially 12 hours after the beginning of standing estrus (Trimberger, 1948) that laid the foundation for AM-PM rule, i.e., a cow detected in standing heat in the morning should be bred artificially in the evening and vice versa
We reported that time of ovulation in buffalo was 31 h after the onset of standing heat (Warriach et al, 2008)
Summary
Artificial insemination (AI) has played a major role in genetic selection, disease control and cost effectiveness of breeding in dairy cattle (Vishwanath, 2003; López-Gatius, 2012). Minimum number of cows returned to estrus when bred artificially 12 hours after the beginning of standing estrus (Trimberger, 1948) that laid the foundation for AM-PM rule, i.e., a cow detected in standing heat in the morning should be bred artificially in the evening and vice versa. This method ensures sufficient time for sperm to capacitate and reach the proper site of fertilization in the oviduct (Yanagimachi, 1981; Bedford, 1983). Whether or not, this AM-PM rule holds true in water buffalo has not yet been systemically investigated
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