Abstract
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.
Highlights
Lobato & Mielitz Netto (2001) reported that the birth rate of breeding animals is the variable that causes the greatest impact on profitability within a production system
This study aims to analyze the reproductive performance of Nellore cows in an extensive system in the Cerrado/Pantanal ecotone, evaluating the effect of the breeding season and the relationship of temperature and humidity (THI) on pregnancy and birth rates
The only significant effect (p < 0.05) in the results was the relationship of cow category on pregnancy rates (Table 3), with nulliparous cows having the highest pregnancy rate
Summary
In a beef cattle production system, the reproductive performance of females is essential for maximum profitability (Santos et al, 2011). Beretta, Lobato & Mielitz Netto (2001) reported that the birth rate of breeding animals is the variable that causes the greatest impact on profitability within a production system. In a beef cattle production system, the reproductive performance of females is essential for maximum profitability (Santos et al, 2011). Beretta, Lobato & Mielitz Netto (2001) reported that the birth rate of breeding animals is the variable that causes the greatest impact on profitability within a production system. Animal Sciences when the birth rate increases from 65 to 70%, it raises the number of sold animals by 16.3% on average. Several authors have presented results on the reproductive and productive performance of Nellore herds subjected to different production systems, identifying and evaluating biological rates in different Brazilian regions Few studies on pure or crossed Nellore cattle are related to how pregnancy and birth rates are affected by temperature and humidity and breeding season
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