Heterosis in cattle crossbreeding schemes in tropical regions: meta-analysis of effects of breed combination, trait type, and climate on level of heterosis

The aim of this study was to investigate the effects of animal trait, breed combination, and climate on the expressed levels of heterosis in crossbreeding schemes using tropical cattle. A meta-analysis of 42 studies was carried out with 518 heterosis estimates. In total, 62.5% of estimates were found to be significantly different from zero, the majority of which (89.8%) were beneficial for the studied trait. Trait and breed combination were shown to have a significant effect on the size of heterosis (P < 0.001 and P = 0.044, respectively). However, climate did not have a significant effect. Health, longevity, and milk production traits showed the highest heterosis (31.84 +/- 10.73%, 35.13 +/- 14.35%, and 35.15 +/- 3.29%, respectively), whereas fertility, growth, and maternal traits showed moderate heterosis (12.02 +/- 4.10%, 12.25 +/- 2.69%, and 15.69 +/- 3.26%, respectively). Crosses between breeds from different types showed moderate to high heterosis ranging from 9.95 +/- 4.53% to 19.53 +/- 3.62%, whereas crosses between breeds from the same type did not express heterosis that was significantly different from zero. These results show that heterosis has significant and favorable impact on productivity of cattle farming in tropical production systems, particularly in terms of fitness but also milk production traits.