HIGH-ROUGHAGE RATIONS WITH OR WITHOUT MONENSIN FOR VEAL PRODUCTION. II. RATION DIGESTIBILITY

Abstract

Thirty-six calves 19–20 wk old (149 ± 17 kg) and forty-eight rams (46 ± 4 kg) were used in two experiments to study the effects of two ground roughages (alfalfa and timothy), their proportion in pelleted rations (20, 40 and 60%) and addition of monensin (0 and 33 ppm) on ration digestibility. Calves and rams were fed the test rations ad libitum for a period of 8 and 5 wk, respectively, before the digestibility trial. Dry matter (DM) digestibility in both species and energy digestibility in calves were significantly higher for the rations containing alfalfa than for those containing timothy; however, digestibility of crude protein (CP) in both animal species and of cell walls (NDF) in calves was lower in alfalfa rations. The two trials revealed an increase in digestibility of acid detergent fiber (ADF) and of cell wall (NDF) fractions but a reduction in DM digestibility when the roughage content in the rations increased; the reduction in DM digestibility was larger with timothy than with alfalfa. Addition of monensin did not affect digestion coefficients of DM, ADF and NDF in calves and rams on average. However, a monensin × roughage level interaction indicated a decrease of ADF and NDF digestibility in calves fed 20% roughage and an increase of ADF and NDF digestibility in calves fed 60% roughage. Key words: Alfalfa, timothy roughage level, monensin, calf, sheep