Effect of different levels and sources of zinc supplementation on quantitative and qualitative semen attributes and serum testosterone level in crossbred cattle (Bos indicus x Bos taurus) bulls.

An experiment was conducted on 16 crossbred bulls (about 2 years of age, 316.2+/-0.77 kg average body weight), divided into groups I, II, III and IV to study the effect of different levels of Zn supplementation from inorganic and organic sources on semen quality. The animals in the first 3 groups were supplemented with 0, 35 and 70 ppm Zn from Zn sulfate, respectively and the animals in-group IV were supplemented with 35 ppm Zn as Zn propionate. Semen collection and evaluation was done in the first month (to assess semen quality at the start of the experiment) and 7th, 8th and 9th month of experimental feeding to evaluate the effect of supplemental Zn on semen attributes. We gave 6 months for Zn feeding, so that 3 sperm cycles of spermatogenesis had passed and the collected semen reflected the complete effect of Zn supplementation. Six ejaculates from each bull were collected and evaluated for semen quantitative (ejaculate volume, sperm concentration and sperm number per ejaculate) and qualitative characteristics (semen pH, mass motility, individual motility, sperm livability percent and abnormal sperm percent, percent intact acrosome, bovine cervical mucus penetration test, hypo-osmotic sperm swelling test) and activity of seminal plasma enzymes i.e., alkaline phosphatase, acid phosphatase, GOT and GPT. Testosterone level in the blood serum of crossbred bulls was also estimated. Mean values of semen quantitative and qualitative characteristics at the start of the experiment were statistically non significant (P > 0.05) in all the crossbred cattle bulls, however, there were statistically significant differences among the bulls of different groups after 6 months of zinc supplementation. Mean ejaculate volume (mL) was 2.37, 4.70, 5.86 and 6.38, respectively in groups I to IV, indicating a statistically significant (P < 0.05) higher semen volume in Zn-supplemented groups as compared to the control group of bulls. Similarly, sperm concentration (million.mL(-1)), live sperm (%) and motility (%) were significantly (P < 0.01) higher in Zn-supplemented groups as compared to the control group. The results of BCMPT and HOSST revealed a significant improvement in sperm functional ability in all the groups supplemented with Zn as compared to the control group. The activity of alkaline and acid phosphatase in seminal plasma was significantly (P < 0.05) higher in the Zn-supplemented groups, whereas GOT and GPT activities in seminal plasma were significantly (P < 0.05) lower in the Zn propionate supplemented group as compared to the control group. Testosterone concentration (ng.mL(-1)) in blood serum was significantly higher in animals of groups III and IV, as compared to control group. It may be concluded that Zn supplementation either in the inorganic or organic form in the diet of crossbred bulls improved the qualitative and quantitative attributes of semen; however, the number of sperm per ejaculate, mass motility and semen fertility test like bovine cervical mucus penetration was significantly higher in bulls given Zn in an organic form (Zn propionate) as compared to an inorganic form (Zn sulfate).