author(s)
Ramajayan P, SN Sivaselvam, SMK Karthickeyan, R Venkataramanan and A Gopinathan

abstract
The present study aims to determine the effect of non-genetic factors on post-thaw evaluation traits and estimate the traits repeatability and correlation coefficients in Murrah buffalo bulls. The data on post-thaw incubation survival (n=1745), hypo-osmotic swelling (n=1745), and acrosome integrity (n=1402) collected from 73 bulls maintained during the period 2005 to 2015 were used for analyses. Single trait univariate analyses under General Linear Model were performed to study the non-genetic effects. The repeatability was estimated by Restricted Maximum Likelihood Method (REML) using WOMBAT programme while the correlation coefficients were calculated using Pearson's correlation coefficient. The overall least-squares means for post-thaw incubation survival (at four-time intervals), hypo-osmotic swelling, and acrosome integrity were 52.42% at 0 h, 45.44% at ½ h, 37.87% at 1h and 29.82% 1½ h; 61.71% and 69.81%, respectively. Similarly, the repeatability estimates were 0.03 at 0 h, 0.02 at ½ h, 0.03 at 1 h, and 0.03 at 1½ h; 0.44 and 0.64, respectively. The ejaculate number, period, season, and age showed a significant effect (P<0.01) on all traits, besides the non-significant effect of ejaculate on acrosome integrity and age on hypo-osmotic swelling. The performance of traits was relatively better in the second ejaculate and bulls in the age group of 68 months and above. However, a significant minimal variation was observed among the periods and seasons. The correlation coefficients were highly significant (P<0.01) and positive for all traits except the negative correlation between hypo-osmotic swelling and acrosome integrity. Thus, this would be helpful to determine the breeding efficiency of the bulls and plan suitable improvisation strategies in the semen station.