Association and variation in performance, nutrient digestibility, carcass traits, and intestinal development of...

Despite well-documented differences in growth performance and physiology between male and female broilers, incorporating varying male-to-female ratios into research designs offers a more industry-relevant framework, enhancing the applicability and translational value of experimental findings. The objective of this study was to determine the relationship and accurate estimate changes of performance, nutrient digestibility, carcass characteristics, coefficient of variation (CV) of performance, gut weight and length, and intestinal morphological parameters due to the use of different male-to-female ratios. Birds (n = 550) were separated by sex and placed in 11 groups (treatments) according to the male-female ratios: G100 (all males), G90 (9 males + 1 female), G80 (8 males + 2 females), G70 (7 males + 3 females), G60 (6 males + 4 females), G50 (5 males + 5 females), G40 (4 males + 6 females), G30 (3 males + 7 females), G20 (2 males + 8 females), G10 (1 male + 9 females) and G0 (all females). Body weight gain (BWG) showed a significant relationship with sex ratio, with the strongest association observed during the grower period (R² = 0.47; P = 0.006), followed by the finisher (R² = 0.27; P = 0.046), while no significant relationship was detected during the starter phase. Shifting the sex ratio from all-male to all-female reduced total feed intake and BWG by 6.94% and 10.98%, respectively, and increased feed conversion ratio by 4.53%. Single-sex rearing reduced the CV of BWG compared with mixed-sex groups. Apparent metabolizable energy (AME), crude protein, ether extract, and crude fiber digestibility decreased by 5.33%, 6.16%, 3.39%, and 20.75%, respectively, as the proportion of females increased. Pearson correlation analysis showed that BW was most strongly correlated with crude fiber digestibility (r = 0.90), small intestine weight (r = 0.88), villus height (r = 0.87), digestibility of AME (r = 0.87), ether extract (r = 0.82), and crude protein (r = 0.71). In conclusion, altering the male-to-female ratio resulted in distinct and quantifiable changes in performance, nutrient utilization, and intestinal development. These findings highlight that estimating sex ratio effects may enhance the alignment of academic research with commercial production conditions without requiring complete sex segregation.