Evaluation of some reproductive traits of Pelibuey ewes under humid tropical conditions of Mexico

ABSTRACT We evaluated the effect of some environmental factors on age at first lambing (AFL) and lambing to conception interval (LCI) of Pelibuey ewes under the humid tropical conditions of Mexico. Ewes grazed on Tanzania (Panicum maximum), Bermuda (Cynodon dactylon), and Brachiaria grass (Brachiaria humidicola) and received hay in the corral in the months of grass scarcity. Reproduction was continuous during the year. Data of 839 lambings from 334 ewes registered from 2009 to 2017 were analyzed using survival analysis procedures. The statistical model for AFL included the effects of year, season, and litter size at lambing, whereas that for LCI included year and season plus parity number of ewe and litter size at weaning. The overall means ± SD for AFL and LCI were 551.6±144.8 and 145.4±113.1 days, and their medians were 510 and 98 days, respectively. Only year of lambing had a significant effect on AFL, whereas LCI was affected by year, parity number, and litter size at lambing (P&lt;0.05). Both AFL and LCI means did not show any trend with advancing years. The largest AFL and LCI means and medians corresponded to the first-parity ewes. In addition, single birth ewes had the longest LCI means and median. Therefore, year of lambing affects AFL, whereas year of lambing, parity number, and litter size at weaning affect LCI of Pelibuey ewes, indicating that these factors should be considered in the development of sound strategies to improve sheep production.摘要 本研究评估了墨西哥湿热热带环境下，部分环境因素对佩里布埃母羊初产日龄（age at first lambing, AFL）及产羔至受孕间隔期（lambing to conception interval, LCI）的影响。试验母羊在坦桑尼亚草（大黍，Panicum maximum）、百慕大草（狗牙根，Cynodon dactylon）及湿生臂形草（Brachiaria humidicola）牧场上放牧，并在牧草匮乏月份于圈舍内补饲干草。试验实行全年连续繁殖模式。本研究对2009年至2017年间登记的334只母羊的839条产羔记录采用生存分析方法进行了分析。初产日龄的统计模型包含年份、季节及产羔时产羔数的影响效应，而产羔至受孕间隔期的统计模型则包含年份、季节，外加母羊胎次及断奶时产羔数的影响效应。初产日龄与产羔至受孕间隔期的总体均值±标准差分别为551.6±144.8天和145.4±113.1天，中位数分别为510天和98天。仅产羔年份对初产日龄存在显著影响，而产羔至受孕间隔期则受产羔年份、胎次及产羔时产羔数的显著影响（P<0.05）。初产日龄与产羔至受孕间隔期的均值均未随年份推移呈现明显变化趋势。初产日龄与产羔至受孕间隔期的最大均值及中位数均对应于头胎母羊。此外，单羔母羊的产羔至受孕间隔期均值及中位数均为最高。综上，产羔年份会影响佩里布埃母羊的初产日龄，而产羔年份、胎次及断奶时产羔数则会影响其产羔至受孕间隔期，这表明在制定改良绵羊生产性能的科学合理策略时，应将上述因素纳入考量范围。