Meta‐analysis of the energy and protein requirements of hair sheep raised in the tropical region of Brazil
At present, the recommendations of the United States’ National Research Council (NRC, 2007) are used in Brazil to formulate diets. However, the equations proposed by the NRC (2007) were primarily developed from wool sheep raised in temperate climate regions. Salah, Sauvant, and Archimède (2014) performed a meta‐analysis of 590 publications to estimate energy and protein requirements of sheep, goats and growing cattle raised in areas of tropical climate and concluded that energy and protein requirements of ruminants raised in tropics are greater when compared to international systems like NRC, ARC, INRA and AFRC. One of the reasons to justify this difference is that, under conditions of high temperatures, the energy required to dissipate body heat significantly increases (CSIRO, 2007). The changes in energy requirements for maintenance and dry matter intake are the primary effects of the interaction between an animal and its environment, while the effects on energy requirements for production is a secondary effect (Fox & Tylutki, 1998). According to NRC (2007), the effects of extreme cold or heat conditions on metabolizable protein requirements are not well understood. Tropical genotypes were not selected for muscle deposition, thereby depositing more fat than temperate genotypes and therefore, the energy cost per kg of gain might be greater (Early, Mahgoub, & Lu, 2001). Therefore, we understand that nutrient requirements of hair sheep raised in the tropics differ from those of wool sheep raised in temperate regions. Thus, there is a critical need to assess the energy and protein requirements of these animals for production under tropical conditions worldwide.
Independent studies of nutrient requirements of hair sheep have primarily been performed in tropical regions. However, there are, in general, significant differences among studies (Azevêdo, Valadares Filho, Pina, Chizzotti, & Valadares, 2010), resulting in inconclusive results. Thus, only through meta‐analysis, it is possible to control the various effects observed across studies and to develop equations for prediction of general requirements of these animals.
Therefore, the objective of this study was to estimate energy and protein requirements for maintenance and gain of hair sheep raised in the tropical region of Brazil from a meta‐analysis of studies conducted with hair sheep until the present moment. We hypothesize that nutrient requirements of hair sheep raised in tropics differ from those recommended by traditional committees on nutrient requirements for sheep (AFRC, 1993; NRC, 2007).