EFFECTS OF ORAL INTAKE OF NITRATES ON REPRODUCTIVE FUNCTIONS OF BULLS

Effects of oral intake of nitrates on selected biochemical and endocri nological indices and its impact on reproductive functions were invest igated in five feeder bulls aged 16-18 months. The bulls were tested p rior to (30 days), during (30 days) and after (35 days) the period of the nitrate administration. The initial dose of 100 g potassium nitrat e per day was increased at weekly intervals by 50 g up to 250 g per da y. The administration of nitrates resulted in a highly significant (P < 0.01) increase in methaemoglobin concentration and a non-significant decrease in the concentration of beta-carotene and highly significant (P < 0.01) decrease in the concentration of E vitamin in blood serum. A significant (P < 0.01) increase in brood serum concentration of bil e acids and prolonged biological half-life of progesterone were sugges tive of an impairment of liver metabolism Prolonged intake of excessiv e doses of nitrates resulted in a significant (P < 0.05) increase in c ortisol concentration during and after the administration period, whil e depressed thyroid gland activity was evident from a significant (P < 0.05) decrease in thyroxin concentration during the administration pe riod. A suppression of hypothalamic functions after the administration period was documented by non-detectable levels (< 0.001 mu g/ml) of t hyrotropin in TRH test. Depressive effects of nitrates on the function of Leydig cells during and particularly after the administration peri od were apparent from weakening testicular responses to a treatment wi th GnRH. Biochemical analyses of seminal plasma revealed a highly sign ificant (P < 0.01) increase in total acid phosphatase activity and a s ignificant (P < 0.05) decrease in the concentration of fructose. No ot her significant changes in seminal plasma components were observed. Ad verse effects of excessive intake of nitrates were also evident from r educed sperm motility in the 120-min thermal test. While no difference was found in the frequency of primary morphological abnormalities, th e number of secondary abnormalities rose by 115% in the post-administr ation period and was suggestive of damaged membrane integrity. Histolo gical examinations revealed degenerative lesions in cells of the sperm iocyte and spermatid layers.