Influence of monensin and lasalocid on mineral metabolism and ruminal urease activity in steers.

Growing steers were used in a replicated 3 X 3 Latin square to study the influence of ionophores on mineral metabolism and ruminal urease activity. Treatments consisted of: 1) basal high energy diet; 2) basal plus 33 ppm lasalocid and 3) basal plus 33 ppm monensin. Each period was 33 days and apparent absorption and retention of macrominerals were measured during the last 5 days of each period. Mineral intake during the collection period was not affected by treatment. Both ionophores increased apparent absorption of sodium, magnesium and phosphorus. Retention of magnesium and phosphorus were higher for steers receiving either lasalocid or monensin. Potassium and calcium absorption were not significantly affected by treatment. Serum concentrations of macrominerals were similar for all treatments. Zinc and copper concentrations in serum were higher in animals fed monensin or lasalocid. Steers fed either ionophore had lower concentrations of soluble potassium and calcium in rumen fluid. Both ionophores also decreased ruminal osmolality. Bacterial urease, a nickel-dependent enzyme, was decreased by 28 and 66% in animals that received lasalocid and monensin, respectively. These findings indicate that lasalocid and monensin affect metabolism of certain minerals in ruminants.

Interaction between nickel and protein source in the ruminant.

Eighty growing steers were used to determine the effect of nickel supplementation on performance and metabolic parameters of steers fed corn silage-based diets supplemented with different crude protein sources. Crude protein sources examined included: (1) soybean meal, (2) blood meal, (3) urea, and (4) blood meal-urea (two-thirds of supplemental nitrogen from blood meal and one-third from urea). The protein sources differed in ruminal degradability, nitrogen solubility, and nickel content. Nickel was added within each protein treatment to supply either 0 or 5 ppm of supplemental nickel. The experiment was 84 d in duration and rumen fluid and blood samples were collected on days 42 and 80. Average daily gain and feed efficiency were not affected by nickel supplementation. The addition of 5 ppm supplemental nickel greatly increased rumen bacterial urease activity regardless of protein source. When samples were collected prior to feeding on day 80, nickel increased serum urea nitrogen concentrations in steers fed urea, but decreased circulating urea concentrations in animals fed blood meal or the blood meal-urea combination.Ad libitum intake of trace mineral salt was greatly reduced in steers receiving 5 ppm supplemental nickel. The present study suggests that the source of protein may influence ruminant responses to dietary nickel.