Search

The metabolism of a single oral zinc-65 dose was studied in young dairy calves fed two concentrations of added A1 (0 and .20% A1) and two concentrations of added P (0 and .22% P) for 7 wk. The four treatments were 1) normal P-low A1, 2) low P-low A1, 3) normal P-high A1 and 4) low P-high A1. The basal diet (low P-low AL) contained, by analysis, .132% P, .74% Ca, .021% A1 and 59 ppm Zn. Zinc-65 absorption was greater (66.5 vs 63.2% of dose, P less than .10) with the low-P diet; added A1 reduced (P less than .05) 65Zn absorption. Calves fed low-P diets had higher (P less than .10) concentrations of 65Zn in liver, kidney, spleen, heart, small intestine and testicle than those fed normal-P diets. Zinc-65 was reduced (P less than .10) in pancreas, heart, testicle and muscle of calves fed high A1. Iron was increased in liver and kidney (P less than .10), Zn (P less than .10) and Mn (P less than .01) were increased in liver, but Fe in small intestine and Cu in muscle and tibia shaft were decreased (P less than .10) in calves fed the low-P diets compared to those fed adequate-P diets. High A1 reduced (P less than .10) Cu in small intestine and tibia shaft. The results suggest that zinc metabolism may be moderately affected in calves fed either low-P or high-A1 diets.

The metabolism of Mg was studied in young dairy calves fed two levels of added Al (0 and .20% Al) and two levels of added P (0 and .22% P) for 7 wk. The four treatments were 1) normal P - low Al, 2) low P - low Al, 3) normal P - high AI and 4) low P - high AI. The basal diet (low P - low Al) contained, by analysis, .132% P, .021% Al and .17% Mg. Added AI did not affect (P > .lo) serum Mg. An AI x P interaction on bone Mg was detected (P c .01). Magnesium was reduced in tibia shaft (.34 vs .44%) and in tibia joint (.43 vs .53%) in calves fed high Al in the presence of normal dietary P, but Mg was not reduced in the calves fed low-P diets. Apparent absorption of Mg was reduced by approximately five-fold (.I8 g/d vs -.84 gld, P c .Ol): urinary Mg excretion was reduced 31% (1.12 g/d vs .77 g/d, P < .Ol); and Mg retention declined 41% (-95 g/d vs -1.61 g/d, P e .01) in calves fed added Al. Compared with calves fed low-P diets, calves fed normal levels of P had a higher Mg concentration in tibia shaft (P < .01) and tibia joint (P < .05). The data indicate that supplemental AI may adversely affect Mg metabolism in calves. (Key Words: Dairy Cattle, Calves, Aluminum, Phosphorus, Magnesium, Metabolism.)

SUMMARY The role of bile in manganese metabolism and homeostasis was studied in Holstein bull calves fed diets containing 32 ppm manganese (normal) (control) or 1,000 ppm supplemental manganese (high-manganese) for 2 weeks before and 1 week after intravenous (IV) and duodenal S4Mn dosing. After dosing, all the bile was collected at 15 and 60 minutes, hourly to 12 hr and daily to 7 days. All calves were sacrificed 7 days after dosing to determine the tissue S4Mn distribution. High-Mn-fed calves secreted 48% of the IV S4Mn dose in bile over the 7-day period; which was 12 times that in bile of control calves. In contrast, after duodenal dosing, only a very small amount of S4Mn was secreted in bile by either control (.32%) or high-Mn-fed (.30%) calves over the 7-day period. With both methods of dosing, calves fed the high-Mn diets had a lower average S4Mn concentration in most tissues taken than calves fed the control diet. These data from IV dosing confirm earlier work that excretion and tissue distribution of injected S4Mn is very sensitive to dietary Mn. The data from duodenally-dosed calves showed that the amount of Mn absorbed is decreased by higher dietary Mn intake. In contrast to previously held theory, enterohepatic circulation of Mn apparently plays only a minor role in homeostasis of fed Mn. Manganese homeostasis in calves appears to be the result of changes both of absorption and