A series of three experiments were carried out in order to demonstrate an interaction between molybdenum and selenium in broilers. Trail I investigated the interaction of selenium (0, 0.2, 0.4, and 0.8 ppm) with various toxic and subtoxic dietary levels of molybdenum (0, 0.5, 100, and 330 ppm), supplemented to a wheat based diet to broilers from one to four weeks of age. Results indicated that at 300 ppm molybdenum, increasing selenium levels resulted in progressive decline in weight gain, compared to a non-significant decline across these selenium levels when no molybdenum was supplemented. At these levels of molybdenum, selenium appeared to be acting antagonistically with molybdenum. At lower molybdenum levels, selenium exerted no apparent effects on weight gain. Selenium at toxic levels responded different from selenium at subtoxic dietary levels over molybdenum levels. Trial II, used 480 broiler chicks, assigned in a randomized block (RB) experimental design and 12 treatment combinations of selenium and molybdenum. Although the overall interaction effect was non-significant for weeks 1 to 4 inclusive, there were some definite interaction trends. Results indicated that at either basal or 3 ppm Se over basal 100, 200, or 300 ppm Mo, a non-significant difference in weight gain and feed consumption occurred. Selenium and molybdenum appeared to be interacting reciprocally. At 6 ppm dietary supplementation of selenium, however, combining increasing levels of molybdenum appeared to result in an independent toxic effect on weight gain which was additive for the two mineral toxicities, and not interactive. Using 480 broilers chicks assigned to a 3 x 4x3x3 multifactorial arrangement of 12 treatments an experiment was performed to investigate the effect on weight gain and feed consumption upon feeding toxic levels of molybdenum and selenium. Selenium levies ranged from basal, to 6, 12, and 18 ppm and molybdenum levels from basal, 400, and 800 ppm. Treatments were arranged in a RB experimental design. Results indicated that combining toxic dietary levels of selenium and molybdenum resulted in a measurable interaction in birds based on weight gain to feed consumption from one to four weeks of the experimental period. As the toxic dietary levels of selenium increased from basal to 6, 12, and 18 ppm the adverse effect of molybdenum at basal, 400 and 800 ppm became progressively reduced. At 18 ppm selenium, weight gain and feed consumption were the same irrespective of whether basal, 400, 800 ppm Mo was supplemented to the diet. The presence of toxic levels of selenium appeared to either reduce toxicity of molybdenum, or induce an increased tolerance for increasingly toxic levels of molybdenum. The nature of the interaction between selenium and molybdenum is discussed. / Land and Food Systems, Faculty of / Graduate

Thirty-six mature, nongestating, crossbred ewes were randomly allotted to three diets: basal (6 ewes); 50% basal and 50% broiler litter (24 ewes), and 50% basal and 50% broiler litter with the addition of 25 ppm molybdenum (Mo) and 5 g sulfate/kg feed. The 24 litter fed ewes were allotted to withdrawal times of 0-, 30-, 60- and 120-d. The control (basal) diet contained and the deepstacked broiler litter contained 8 and 257 ppm Cu, dry basis, respectively. The ewes were fed the diets for 140-d at which time the control, the six litter-fed ewes with 0-d withdrawal and the Mo and SO₄ supplemented ewes were slaughtered. Liver samples were obtained from these ewes by biopsy initially and at 40-, 80-, and 120-d of the trial. At slaughter liver, kidney, muscle and duodenum samples were taken. Liver Cu content was increased (P<.01) by feeding broiler litter (404 vs 1543 ppm, dry basis). Liver Cu (962 ppm) accumulation and serum Cu were depressed (P<.05) by supplementing litter containing diets with Mo and SO₄. Zinc levels of the liver and Zn and Cu levels of the kidney and muscle were not affected by additional Mo and SO₄. Duodenum Cu and Zn levels reflected the dietary metal content. During the withdrawal period liver and duodenum Cu levels were not lowered (P>.05). A linear increase (P<.001) in SGOT activity was observed with time throughout the withdrawal period, suggesting possible liver damage. Serum Cu decreased at 30-d and increased thereafter (quadratic effect, P<.05). This observation coupled with increases in muscle and kidney Cu (P<.05) indicated an apparent redistribution of Cu stores. Metallothionein (MT) increased 12-fold above control values in the litter-fed ewes (P<.05) and tended to decrease during the withdrawal period. Therefore, it appears that supplementing Mo and SO₄ to a diet containing high Cu broiler litter may reduce the accumulation of hepatic Cu. Liver Cu stores will not be dissipated upon withdrawal of the high Cu litter from the diet. / Master of Science

Feeds often contain molybdenum (Mo) and sulfur (S) in excess of recommended allowances for adequate copper (Cu) absorption by ruminant livestock. Two randomized-block experiments were conducted using lambs given a cereal-based diet (90% of dry matter (DM) intake), containing 8 mg Cu, 0.7 mg Mo and 2.1g S per kg DM, that was either unsupplemented or supplemented with ammonium molybdate or sodium sulfate alone or in combination, to determine the effects of Mo, S and Mo+S on growth, hematology, serum Cu and Mo concentrations and reproductive function. Short term intake (4 weeks) by rams, aged 18 and 20 weeks, of 26 mg Mo alone or in combination with 2g S per kg DM, had no effect on growth, hematology or the concentration of total Cu in serum (TCu). However, supplemented groups had lower (P<0.05) concentrations of serum Cu soluble in trichloroacetic acid (TCA-Cu), but the group given Mo+S had the highest (P<0.05) concentration of serum residual Cu (RCu). Luteinizing hormone (LH) peak amplitude was affected by age*diet interaction (P<0.05), because of high amplitude LH peaks in the serum of lambs, aged 24 wks, given Mo alone. Testosterone serum secretory profiles did not differ among diet groups, but testosterone peak frequency was higher (P<0.05) for older ram lambs. Long term intake (32-39 wks) by ewe, ram and wether lambs (gonadal influence) of 12 mg Mo, or 2g S alone or combined per kg DM also had no effect on hematology or TCu. Food intake and liver weights were higher (P<0.05), but TCA-Cu was lower (P<0.05) for groups given S. Serum concentrations of total Mo (TMo) were higher (P<0.05) for Mo-supplemented groups, but RCu was highest only for the Mo+S group. Growth was affected by Mo*S*gonadal influence*time interaction (P<0.05); until autumn, the body weight of Mo-supplemented groups were higher than those of ram and wether lambs given Mo+S. Ovarian or testicular functions were delayed more severely for Mo- than Mo+S-supplemented groups. Mean concentrations of LH were affected by Mo*S*gonadal influence*time interaction (P<0.05); the mean LH values of Mo-supplemented ram and ewe lambs were higher than the Mo+S-supplemented group, whereas a reverse trend was observed for wether lambs. The amplitude of LH peaks was affected by Mo*S*gonadal influence*time interaction (P<0.05); for ram lambs, LH peak amplitude was higher for Mo than Mo+S-supplemented groups, whereas for wether and ewe lambs the reverse trend was noted. Mean concentrations of serum Cortisol and Cortisol peak amplitude were affected by Mo*S interaction (P<0.05); the mean Cortisol concentration and peak amplitude for the Mo-supplemented group were higher than those for the Mo+S-supplemented group. The frequency of LH and Cortisol peaks did not differ (P>0.10) among diet groups. In conclusion, Mo supplementation of cereal-based diets containing a high concentration of Cu did not adversely affect lamb growth. However, the effect of high dietary Mo on reproductive function appears to depend on the dietary level of S and the induction of high serum RCu (thiomolybdate). Further investigations on the effects of Mo and thiomolybdate on endocrine function may provide a nutritional basis for improving reproductive efficiency in ruminants. / Land and Food Systems, Faculty of / Graduate