EFFECTS OF DIETARY ZINC-DEFICIENCY ON THE REPRODUCTIVE-SYSTEM OF YOUNG MALE SHEEP - TESTICULAR GROWTH AND THE SECRETION OF INHIBIN AND TESTOSTERONE

The effects of dietary zinc deficiency on testicular development in yo ung Merino rams (initial live mass, 22 kg) were tested. Four groups of five rams were fed ad libitum with diets containing 4, 10, 17 or 27 m u g Zn g(-1). To control the effects of loss of appetite caused by zin c deficiency, a fifth group (pair-fed control) was fed the diet contai ning 27 mu g Zn g(-1) but the amount of feed offered was restricted to that eaten voluntarily by the zinc deficient (4 mu g Zn g(-1)) rams t hey were paired with. After 96 days on the diets, epididymal and testi cular masses did not differ significantly between the animals fed 10, 17 or 27 mu g Zn g(-1) ad libitum, but were significantly lower in pai r-fed controls, and lowest in the zinc-deficient animals. Testicular r esponsiveness to LH, as measured by testosterone production, increased substantially in most rams as the experiment progressed, the only exc eption being the zinc-deficient group, in which the response to LH was lower than in any of the other groups. Testicular concentrations of z inc and testosterone were lower in the zinc-deficient animals than in all the other groups. Plasma inhibin concentrations fell as the experi ment progressed in rams fed 17 and 27 mu g Zn g(-1) ad libitum, but no t in the other groups. The pair-fed control rams had smaller seminifer ous tubules and less lumen development than did the controls fed ad li bitum (27 mu g Zn g(-1)), which were similar to the animals fed 10 or 17 mu g Zn g(-1). In zinc-deficient rams, the tubule development was f urther retarded and the interstitial regions were more extensive than in the other groups. We conclude that the overall effect of zinc defic iency on testicular development is due to a combination of a non-speci fic effect (low gonadotrophin concentrations caused by the low feed in take) and a specific effect due to the lack of zinc. The zinc-specific effect is localized within the testis where it reduces the developmen t of the capacity to produce testosterone, leading to low intratesticu lar concentrations of testosterone, a critical factor for the growth, development and function of the seminiferous tubules.