Energy requirements of growing small ruminants raised for meat production in contrasting climatic regions: a meta-analysis.

Abstract

The objective of this meta-regression was to evaluate the influence of ruminant species, sex, and climatic regions on the metabolizable energy (ME) requirements for maintenance (MEm) and weight gain (MEg) in growing small ruminants raised for meat production across different climatic regions. Data included 655 and 337 treatment means from 173 and 99 studies on sheep and goats, respectively. Metabolizable energy intake (MEI; MJ/kg^^0.75) was regressed against average daily gain (ADG; g/kg^^0.75), with the study included as a random effect. The analysis found that MEm was not affected by species (P = 0.50), but MEg (MJ/g ADG) was significantly different between species (P = 0.02), with sheep requiring 0.032 (± 0.002) and goats 0.026 (± 0.002) MJ/g ADG. Sex did not affect MEm in either species (P ≥ 0.32). However, in goats, intact males had a greater MEg (P = 0.02) than females (0.030 ± 0.003 vs. 0.013 ± 0.006 MJ/g ADG). MEm was lower (P = 0.03) in small ruminants raised in subtropical regions (0.497 ± 0.046 MJ/kg^^0.75) compared to those in semi-arid (0.600 ± 0.038 MJ/kg^^0.75) and tended to be lower than those in arid regions (0.529 ± 0.050 MJ/kg^^0.75). However, these differences disappeared when adjusting for maturity, diet composition, digestibility, or altitude. MEg was significantly higher (P < 0.05) in animals raised in arid regions (0.032 ± 0.006 MJ/g ADG) compared to those in Mediterranean (0.009 ± 0.004 MJ/g ADG) or semi-arid regions (0.009 ± 0.004 MJ/g ADG) after adjusting for diet composition and digestibility. Similarly, ruminants in Mediterranean regions had lower MEg (0.019 ± 0.004 and 0.009 ± 0.004 MJ/g ADG) than those in tropical regions (0.033 ± 0.002 and 0.024 ± 0.002 MJ/g ADG), respectively after adjusting for maturity, diet composition, and digestibility. MEg in semi-arid regions was consistently lower than in tropical regions, regardless of the covariates tested. For predictive purposes, the global model exhibited the best accuracy (CCC = 0.57 and RSR = 0.79), comparable to the model derived specifically for the tropical region (CCC = 0.58 and RSR = 0.80). This meta-analysis provides a comprehensive evaluation of species-specific differences in ME requirements in small ruminants while recognizing the challenges posed by confounding effects and climatic variability inherent in global datasets. The analysis suggests that animals raised in tropical conditions may have lower MEm than current feeding systems that use data from temperate climates.