Survival analysis and seasonal patterns of pregnancy outcomes in Egyptian buffaloes

The objective of this study was to analyze the survival patterns of pregnancy outcomes in Egyptian buffaloes under subtropical environmental conditions. The overall reproductive and production indices were performed on a total of 1224 records. The means of days at first AI postpartum, days open and calving interval of Egyptian buffaloes are 62.29, 83.13 and 395.1 days, respectively. The survival analysis of pregnancy outcomes in the present study was restricted to the first AI (576 first AI records). Compared to the low temperature-humidity index (THI), the conception rate (P/AI at 30 days) was significantly decreased at high THI level (OR = 0.45; p = 0.029), however, no significant variations were recorded between the referent (low) THI level and the moderate one (OR = 0.86; p = 0.673). Additionally, the pregnancy loss rate was significantly increased at a high THI level (OR = 2.43; p = 0.008). In comparison with the referent (primiparous) group, the conception rates were significantly increased in the M1 (2-5 parities; OR = 2.84) and M2 (>5 parities; OR = 4.06) multiparous groups (p = 0.007 and 0.004, respectively). The Egyptian buffaloes produce a relatively higher daily milk yield (>9 kg) have significantly lower conception rate compared with the referent (<7 kg) group (OR = 0.46; p = 0.046). However, the daylight length (continuous variable) had no significant effects on the conception (OR = 0.88; p = 0.298) and pregnancy loss (OR = 0.92; p = 0.608) rates. The Cox Proportional-hazards model for the hazard of pregnancy outcome (P/AI at 30 days) revealed that multiparous buffaloes had a higher hazard of pregnancy than primiparous buffaloes (HR = 2.37, p = 0.001). Moreover, buffalo cows calving in the summer and spring have a lower hazard of pregnancy than buffaloes calve in the winter season (HR = 0.57 and 0.76, p = 0.001 and 0.002, respectively). The current study indicates that Egyptian buffaloes have the ability to tolerate the thermal stress up to 80 THI values without deterioration of pregnancy outcomes. Moreover, primiparous or high producing buffalo cows may require more effective reproductive strategies as modulation of breeding plans to get calving in the winter and autumn seasons.