Environmental effects on reproductive performance of Nellore cows widely raised in the Cerrado/Pantanal ecotone

We analyzed the pregnancy rate (PR) and birth rate (BR) of Nellore cows raised extensively in the Cerrado/Pantanal during 4 mating seasons (2009-2012), assessing the relationship with the temperature and humidity index (THI) and the effect of the year and breeding season. We used information from 2,116 cows, which were categorized as either multiparous (n = 1430), primiparous (n = 338), or nulliparous (n = 348). In the months of the breeding season (December-February), temperature and relative humidity data were collected to calculate the temperature and humidity index (THI). An ANOVA was performed with a model that included sources of variation from the fixed effects of category of cow and year on PR and BR; and a linear regression analysis and correlation between THI and PR and BR. We observed a significant effect (p < 0.05) on PR. We classified the average across breeding seasons as a moderate THI. The THI of the breeding seasons showed high and significant (p < 0.05) effects only on the nulliparous BR, and low values in other categories. It is concluded that the seasonal THI was not related to the performance of cows, except BR in nulliparous cows.

本研究针对2009-2012年4个配种季内，塞拉多/潘塔纳尔（Cerrado/Pantanal）地区粗放饲养的内洛尔牛（Nellore cows）的妊娠率(pregnancy rate, PR)与出生率(birth rate, BR)展开分析，探究其与温湿度指数(temperature and humidity index, THI)的关联，以及年份与配种季对繁殖性能的影响。本研究共纳入2116头母牛，按产次分为经产牛（n=1430）、初产牛（n=338）及未产牛（n=348）三组。在配种季（12月至次年2月）期间，研究人员收集温湿度数据以计算温湿度指数(THI)。本研究采用包含母牛产次类别与年份对PR、BR的固定效应变异来源的方差分析(analysis of variance, ANOVA)模型，并通过线性回归分析探究THI与PR、BR之间的相关性。结果显示，温湿度指数对妊娠率存在显著影响（p<0.05）。研究将各配种季的平均温湿度指数归类为中等水平。配种季的温湿度指数仅对未产牛的出生率存在显著且较强的影响（p<0.05），对其余产次母牛的影响程度较低。综上，季节温湿度指数与母牛的整体繁殖性能无显著关联，仅未产牛的出生率为例外。