Reproductive performance of beef cattle females (Bos taurus x Bos indicus) in intensive grazing areas with or without the presence of trees

Abstract

The cattle industry is extremely important to the national economic development and the global demand for cattle meat is constantly increasing. The use of Bos indicus x Bos taurus cows is recommended to increase productivity in modern beef cattle production systems, as well as the use of composite breeds. The Canchim breed, a genotype developed in Brazil, is an important option for crossbreeding programs. Furthermore, the use of livestock-forest systems is being suggested as a way to develop more sustainable production systems in Brazil as well as an alternative to promote better thermal comfort for animals raised in tropical areas. Its use is expected to improve the productive and reproductive performance of the herd. Specific line of credit for the implementation of these systems are available for the producers, however, many technical questions and information gaps still remain regarding the impacts of their adoption. Therefore, there is recurring demand from both the productive sector and funding agencies regarding which levels of improvement in productive and reproductive performance can be achieved when integrated livestock production systems are used. Therefore, this project aims to evaluate the impact of livestock-forest systems on the thermal comfort and animal welfare of female Canchim cattle, determining the effect of the microclimate provided by the natural shade on the physiological variables related to thermolysis, endocrine and metabolic profile of the animals, as well as the establishment of puberty in young females and the potential in vitro production of embryos by mature cows. The project was design to be carried out during a 24 months period, in an intensive production system with rotational grazing, with or without the presence of trees, at Embrapa Southeast Livestock, São Carlos, SP, Brazil. The project will consist of two sequential trials. Experiment 1 - will have its field phase between February and August - 2016, when contemporary pre-pubertal heifers will be evaluated during 210 days in order to determine whether the shading of pastures is able to increase the thermal comfort of the heifers, reducing their level of stress and therefore anticipating the age at puberty. Experiment 2 - the field phase will be carried out from February to May-2017 to study the effect of grazing shaded areas on oocyte quality and in vitro production rates of embryos from adult cows. Thus, it is expect to be proved that beef cows kept in areas with natural shade availability have lower metabolic changes, greater linearity in the physiological profile, needing less frequently to activate their physiological thermolytic mechanisms. If there is a lower demand for body heat dissipation, it is expected that the animals kept in the shaded areas will be more productive, younger at puberty and present an increase (quantitative and qualitative) in embryo production, which will greatly elevate their reproductive efficiency. If the positive relationship between higher thermal comfort and increased reproductive efficiency is proved, the information may contribute for the indication of integrated production systems as a viable alternative to livestock production, and help in the development of public policies aiming at stimulating the use of livestock-forest systems. (AU)