Effect of Replacing Inorganic Zinc with Lower Levels of Organic Zinc on Zinc Retention and Follicular Population in Rats

An experiment of 10 weeks duration was conducted on 48 weaned female rats (285.2 ± 1.95 g) of strain Sprague Dawley to study the effect of replacing dietary Zn (12 ppm) supplementation from inorganic (ZnCO3) to organic (Zn nicotinate; Zn-nic) source at lower (6 or 9 ppm) or equal (12 ppm) levels on Zn retention and ovarian follicular population. Higher Zn concentration (on day 42) in serum (P<0.01) and liver (P<0.05) was noticed with 9 and 12 ppm Zn supplementation as Zn-nic compared to other dietary treatments. Zn deposition in pancreas, muscle and kidney was comparable among the dietary treatments. In comparison to 12 ppm inorganic Zn, RBC catalase and glutathione peroxidase activities (42nd d) improved (P<0.05) with 9 and 12 ppm organic Zn. Significantly (P<0.05) highest and lowest serum progesterone concentration was observed with 9 or 12 ppm Zn as Zn-nic and 6 ppm as Zn-nic supplementation, respectively. Regular estrous cycle was observed with 9 or 12 ppm Zn supplementation as Zn-nic, while 30% rats fed on other dietary treatments showed irregular estrous cycle. The proportion of primary follicles was lowest (P<0.01) and that of corpus luteum was highest (P<0.01) with 12 ppm Zn supplementation from Zn-nic, compared to other dietary treatments. The study indicated that Zn concentration in diets could be reduced by 75% (9 ppm) when supplemented as Zn nicotinate without affecting estrous cycle and follicular population. In addition, replacement of 12 ppm inorganic Zn with 12 ppm organic Zn significantly improved its retention and follicular population.