Effects of the different levels of dietary vitamin D on boar performance and semen quality

Vitamin D plays a major role primarily in bone mineral homeostasis; however, the action of vitamin D on male reproduction of boars remains unknown. This study was conducted to evaluate the effects of dietary vitamin D3 supplementation on reproductive performance of boars. Twenty-four Yorkshire boars with eighteen months were randomly allocated to one of three vitamin D3 levels diets: 200 IU/kg (C), 2000 IU/kg (T1) and 4000 IU/kg (T2) of vitamin D3 for a 16-week period. Results showed that sperm motility, effective sperm number per ejaculate, acrosome intactness ratio, and membrane intactness ratio in T1 group were significantly higher than those in C group. The sperm membrane intactness ratio was higher in T1 group than in T2 group, whereas the deformity ratio was significantly lower in T1 than in C and T2 groups. Dietary supplementation with vitamin D3 significantly increased 25-OHD3 concentration in the blood and seminal plasma, but there was no significant difference in its concentration in the seminal plasma between T1 and T2 groups. The concentrations of blood testosterone and aromatase activity increased following vitamin D supplementation. Seminal plasma Ca2+, fructose concentration, and acid phosphatase activity were higher in T1 group than in C group, but not significantly different from the corresponding values in T2 group. Furthermore, expression of CYP19, CYP24A1, and VDR mRNAs in sperm was up-regulated in T1 group compared to that in C group. In conclusion, supplementation of boar diets with 2000 IU/kg vitamin D3 increased the sperm motility and effective sperm number, which was in line with the elevated concentrations of vitamin D, hormone secretion and gene expression.