Supplementation of vitamin A to local chicken diets in tropical environment enhances seminal quality and blood testosterone concentration.

There is insufficient information on the role of micronutrient supplementation on the productivity of local breeder cocks in a tropical environment. The target of this research, thus, was to deduce the impact of dietary vitamin A incorporation on semen traits and testosterone concentration of local breeder cocks in a tropical environment. One hundred twenty-eight-matured Nigerian local breeder cocks aged 10-12 months were alloted to 4 groups (n = 32): a control group (A) was fed experimental diet supplemented with vitamin A at 0 IU/kg feed and supplemented groups (B-D) fed commercial poultry diet supplemented with vitamin A at 250, 500 and 750 IU/kg feed for 16 weeks. Every group was replicated 4 times with 16 birds in every a replicate. A quadratic typed optimization function was employed to determine the optimum vitamin A supplementation that statistically improved serum testosterone and semen quality indices in local breeder cocks. Semen profiling and serum testosterone concentration were analysed at week 4 (pre-supplementation period), and thereafter at weeks 4, 8 and 12 (supplementation period). Serum testosterone and semen quality indices at pre-supplementation period were similar (p < 0.05) among the groups. Birds on 500 IU vitamin A/kg diet produced sperm with highest (p < 0.05) active motile cells and normal morphology compared to birds on the other 3 diets. Local breeder cocks fed diets having 500 and 750 IU vitamin A/kg diet produced sperm with lowest (p < 0.05) sluggish motile cells compared with those fed the control diet. Semen pH, volume, sperm concentration (SC), acrosome morphology defects and serum testosterone concentration were not affected by vitamin A supplementation. The result of the quadratic optimization model revealed that sluggish motile sperm (Y = 41.098-10.230x + 0.903x2; r2 = 0.943, p = 0.039) and normal sperm morphology (Y = 82.665 + 8.834x - 1.500x2; r2 = 0.965, p = 0.001) was optimized (p < 0.05) at 5664 and 2945 IU/kg feed, respectively. However, other parameters estimated were not significantly influenced. It is concluded that vitamin A supplementation enhanced sperm quality in local breeder cocks.