Frequency of narasin intake affects ruminal metabolism and growth of lambs

Abstract

Context Ionophores improve rumen fermentation efficiency, average daily gain (ADG) and feed efficiency. However, the effects of providing ionophores to grazing animals are extremely variable, primarily due to infrequent supplement intake. Aim This study aimed to evaluate the effect of frequency of narasin intake on ruminal fermentation, nutrient digestibility and growth of lambs. Methods In Experiment I (metabolism assay), four rumen-cannulated wethers (1/2 Dorper × 1/2 Santa Inês) were assigned to a 4 × 4 Latin square design. The four treatments included a control, where animals were fed a diet without ionophore, and the following three treatments where animals were fed narasin at different intervals: 13 mg/kg of narasin every 24 h (N24), 26 mg/kg of narasin every 48 h (N48) and 39 mg/kg of narasin every 72 h (N72). All animals were fed with 95% Tifton-85 hay and 5% ground corn that was used as a vehicle for narasin. In Experiment II, 44 lambs (1/2 Dorper × 1/2 Santa Inês; 33.3 ± 0.5 kg (mean ± s.e.m.) and 180.5 ± 8 days of age) were used in a randomised complete-block design to assess performance. All treatments and management were similar to those in Experiment I. Key results Experiment I, dry-matter intake and apparent digestibility of nutrients were not affected by the treatments. The treatments N24 and N48 increased (P < 0.01) the total molar concentration of short-chain fatty acids compared with control and N72, and increased (P < 0.01) the concentration of propionate compared with control. In Experiment II, the treatments N24 and N48 increased the liveweight gain (P = 0.03) and feed efficiency (P = 0.02) compared with control and N72. Conclusion Effectiveness of narasin was reduced when offered at intervals greater than 48 h. Implication Frequency of narasin intake affects lamb production, and feeding systems are required where animals consume supplements on a regular basis.