Efficacy of monensin for beef cows.

Monensin fed to beef cows at levels of 50, 200 or 300 mg daily during late gestation and early lactation induced feed savings of 3.2, 10.5 and 13.5%, respectively, when feed intakes were regulated to produce similar changes in cow weights, condition scores and weight to height ratios during the 168-day feeding period. Feed dry matter intakes were different (P < .05) for the orthogonal single degree of freedom comparisons that were made. The monensin treatments and the adjustments in feed intake associated with them had no apparent effect on (1) calf birth weights, (2) adjusted 205-day weaning weights or (3) first-service conception rates for the cows. Monensin increased (P < .05) the proportion of propionate and the ratio of acetate to propionate in rumen samples taken prepartum, but not in samples taken postpartum. Blood samples obtained at the same time that rumen samples were obtained showed no treatment effects on serum creatinine, lactic dehydrogenase, alkaline phosphatase, inorganic phosphorus, calcium, creatine phosphokinase, glutamic-pyruvic transaminase or total protein.