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Twelve ruminally cannulated lambs (average weight, 31.1 kg) were used to determine the effects of monensin and K on apparent absorption of Mg in lambs. Lambs were assigned randomly to two groups and fed a basal high concentrate diet containing .44% K with or without 20 mg/kg monensin for 19 d of dietary adjustment. During adjustment, lambs were housed by treatment group and given ad libitum access to their diets. Following dietary adjustment, lambs were placed in individual metabolism stalls and fed 450 g of their respective diet twice daily. Within each monensin group, lambs were infused ruminally with 0, 7.6 or 31.6 g K/d (equal amounts at each feeding in 158 ml of distilled-deionized water) during three periods in a 3 X 3 Latin-square arrangement of K treatments. Each period consisted of a 10-d preliminary phase and a 7-d collection phase followed by a 3-d D2O infusion phase to determine water turnover. Addition of monensin to the diet decreased (P less than .05) fecal Mg excretion 15.9%. Apparent absorption and retention of Mg were increased (P less than .05) with the addition of monensin. Increasing K level increased (P less than .05) fecal Mg excretion. Apparent absorption of Mg decreased (P less than .05) from .93 to .80 g/d when either level of K was infused into the rumen. Monensin decreased the acetate:propionate (A:P) ratio. There was a significant interaction between monensin and K level for acetate and propionate (molar %), and A:P ratio. In the presence of higher K concentrations, monensin appears to be more effective in decreasing the A:P ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

A study consisting of two trials was conducted to determine the effects of monensin on the apparent absorption and retention of sodium (Na) and potassium (K) and to examine changes in tissue and ruminal fluid concentrations of these minerals in lambs. Eight lambs (39 kg) were used in trial 1 and 10 lambs (37 kg) were used in trial 2. Animals were used in randomized block designs, blocked by weight, and fed a high concentrate diet with or without 20 mg/kg monensin. Trials began with a dietary adjustment period lasting 18 d in trial 1 and 21 d in trial 2. Animals were then placed in metabolism stalls for a 10-d stall adjustment period followed by a 12-d collection period. Collections for mineral balance were made during the first 10 d of the collection period. Blood and ruminal fluid samples were obtained on d 11 of the collection period. Lambs were slaughtered on d 12 of the collection period and tissue samples were collected. Sodium retention decreased (P less than .05) 86.2% when monensin was fed. Apparent K absorption increased (P less than .05) 16.7%, while K retention increased (P less than .10) 52.6% when monensin was fed. In lambs fed monensin, ileal Na decreased (P less than .10) 13.8%. These results indicate that dietary monensin alters the metabolism of Na and K in lambs.

A study consisting of two trials was conducted to determine the effects of monensin on the apparent absorption and retention of magnesium (Mg), phosphorus (P), calcium (Ca) and zinc (Zn) and to determine mineral changes in tissue and ruminal fluid. Eight lambs (39 kg) were used in trial 1, and 10 lambs (37 kg) were used in trial 2. Animals were blocked by weight and fed a high concentrate diet with or without 20 mg/kg monensin. Trials began with a dietary adjustment period lasting 18 d in trial 1 and 21 d in trial 2. Animals were then placed in metabolism stalls for a 10-d stall adjustment period followed by a 12-d collection period. Collections to determine mineral balance were made during the first 10 d of the collection period. Blood and ruminal fluid samples were taken on d 11 of the collection period. Lambs were slaughtered on d 12 of the collection period and tissue samples were collected. Monensin supplementation increased (P less than .05) Mg retention 42.0%. Urinary Ca excretion decreased (P less than .05) 60.0% when monensin was fed. Monensin supplementation decreased (P less than .05) liver Ca and bone Ca, 45.5 and 2.9%, respectively. Apparent P digestibility increased (P less than .05) 40.0% and P retention increased (P less than .10) 26.8% due to monensin supplementation. Both apparent absorption and retention of Zn increased (P less than .01) 50.0 and 45.0%, respectively, with monensin supplementation. Ruminal fluid Zn concentrations decreased (P less than .05) 33.0% with the addition of monensin.(ABSTRACT TRUNCATED AT 250 WORDS)

Two metabolism trials were conducted to determine the effect of altering dietary Na and K on Mg availability. Three dietary treatments (normal K-normal Na, high K-normal Na and high K-high Na) were imposed upon nine crossbred wether lambs in a randomized block design. Each trial consisted of a 5-d diet adjustment, a 10-d preliminary period and a 5-d collection of feed, feces and urine. Increasing K and Na intake increased the percentage of Mg excreted in feces. Both elevated K and K-Na depressed (P less than .10) urinary Mg excretion, primarily a reflection of depressed Mg absorption in animals fed these diets. Apparent K absorption and retention increased when animals were supplemented with K. Addition of Na to the diet did not alter absorption or retention of K. Apparent K and Na availability increased when K and Na supplements were included in the diet. This increased availability resulted from increased total absorbed K and Na compared with a fixed endogenous excretion. Calcium balance in lambs was not affected by addition of K or Na. Lambs were able to absorb enough Mg from their respective diet to maintain normal serum Mg levels. Addition of Na to a diet high in K did not enhance Mg absorption in lambs.