Effect of age upon retention of mercury in chickens with a different growth rate

Retention of total mercury was examined in groups of 95 slowly-growing laying type chickens and 52 fast-growing broiler hybrids in 47 subsequent balance periods from 1 to 100 days of age. Chickens were fed ad libitum on a diet containing 5.41 µg of Hg per kilogram. Until Day 4 the values of coefficients of apparent retention of Hg were negative or very low. They were influenced by excretion of endogenous nutrients originating primarily from the yolk sac. When evaluating the period of 4 to 100 days of age, the dependence of Hg retention coefficients upon age was highly significant (P < 0.01). The course of this dependence was expressed by parabolas for laying type chickens with the maximum value at Day 61 of age and for broilers with the minimum value at Day 53. In fast growing chickens, Hg content in body gain decreased until Day 14 and then increased while in slow growing chickens it was linearly increasing for the whole experimental period. The average coefficients of Hg retention from the feed mixture were 48.18 ± 0.719 (mean ± SEM) and 47.90 ± 1.057% and Hg retained per g of live body gain were 7.494 ± 0.4682 and 6.775 ± 0.6233 ng in laying and meat type cockerels, respectively. The difference between hybrids was insignificant (P > 0.05). The growth rate of total amount of Hg in the body was lower (P < 0.01) than that of body weight of chickens, allometric coefficients were 0.706 and 0.747 for slow and fast growing chickens, respectively.