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Effects of Long Term Zinc Deficiency on Feed Utilization, Reproductive Characteristics, and Hair Growth in the Sexually Mature Male Goat¹

Departments of Dairy Science and Medicine and Surgery, University of Georgia, Athens 30601

ABSTRACT

Ten young, sexually mature goats were fed a zinc-deficient purified diet (4 ppm Zn) ad libitum and five a control diet (deficient diet + 36 ppm Zn) in amounts restricted to maintain comparable weights for 20 weeks. Less feed was required in the control group to maintain the weight in the deficient group. Inasmuch as there was no difference in digestibility of diets, the difference in feed efficiency was due to endogenous metabolism. Feed intake of deficient goats increased sharply from the 10th to 18th week without affecting body weight. Goats given the deficient diet developed zinc deficiency symptoms, which increased in severity with time. In comparison with controls, plasma zinc was much lower; growth rate and zinc content of hair were considerably less, testicles were smaller; and libido was lower in zinc-deficient goats. After an extended period on the severely restricted feed intake, testicle size in controls also decreased. As evidenced by testicle biopsies, spermatogenesis was not severely affected by zinc deficiency until 4 weeks post-treatment. At this stage, only spermatagonia were present and tubular size was reduced. The severely restricted feed intake of controls produced similar effects. Eighty percent of zinc-deficient and 60% of control goats died during the experiment.

In a post-treatment period two goats from each group were fed the control diet ad libitum for four weeks. Feed intake of controls increased, but that of the goats which had been deficient did not increase markedly, suggesting that adaptation which appeared to have taken place was not readily reversible.

¹ Supported in part by Public Health Service Research Grant AM-07367-NTN from the National Institute of Arthritis and Metabolic Diseases.