Abstract
Two experiments were proposed to evaluate the addition of monensin for lambs fed diets containing a high level of mature ground flint corn. The experimental diets were as follows: no inclusion of monensin (M0) and inclusion of 8 (M8), 16 (M16) and 24 mg kg–1 of monensin (M24). In experiment 1, eight cannulated wethers were divided into a double 4 × 4 Latin square experimental design to evaluate nutrient digestibility, plasma parameters and rumen fermentation. The experiment lasted 112 days, divided into four periods of 28 days each. In experiment 2, ninety-two lambs were used in a randomized block design to evaluate the performance over 56 days. In experiment 1, doses of monensin had no effect on nutrient intake (p ≥ 0.07) and digestibility (p ≥ 0.09). There was a quadratic effect for acetate molar proportion (p = 0.01), acetate to propionate ratio (p = 0.04) and rumen pH (p < 0.01). However, there was no effect on the molar proportion of propionate and butyrate. The monensin decreased linearly the total SCFA concentration (p < 0.01). The inclusion of monensin increased glucose (p < 0.01) and decreased lactate concentration in plasma (p = 0.05). In experiment 2, monensin decreased dry matter intake (p = 0.04). However, there was a quadratic effect for average daily gain (p = 0.03) and feed efficiency (p < 0.01), with the greatest values observed for the M8 diet. Thus, the inclusion of 8 mg kg–1 of dry matter diet (DM) improves ruminal fermentation and plasma parameters, resulting in greater growth performance in lambs.
Highlights
In ruminant nutrition, monensin is the main additive used in high concentrate diets (Oliveira and Millen, 2014), selecting for specific bacteria groups and promoting changes fermentation, ruminal pH and, improving animal health and performance (Schelling, 1984)
There was a quadratic effect for the molar proportion of acetate (p = 0.01) and acetate to propionate ratio (p = 0.04), with the lowest values observed for the M16 diet
In meta-analysis conducted by Martins et al (2018), the author reported that the inclusion of 25 mg kg–1 of monensin in diets containing a high level of flint corn ground for wethers did not affect the molar proportion of short chain fatty acids (SCFA), rumen pH and ammonia nitrogen concentration, questioning the dosage to be used for feedlot lambs
Summary
Monensin is the main additive used in high concentrate diets (Oliveira and Millen, 2014), selecting for specific bacteria groups and promoting changes fermentation, ruminal pH and, improving animal health and performance (Schelling, 1984). The initial studies evaluating doses of monensin for lambs demonstrated that the use of lower doses, between 5 and 11 mg kg–1 in a DM diet, were able to improve rumen fermentation (Baran et al, 1986), decrease the coccidian oocyst (Calhoun et al, 1979) and increase energy retention and growth performance of lambs (Nockels et al, 1978; Joyner et al, 1979). Considering that the action of feed additives can be influenced by diet composition and ingredient processing (Meyer et al, 2013), the present study tested the hypothesis that lower doses of monensin (8 or 16 mg kg–1 of diet DM) increases the propionate in the rumen and controls ruminal pH. Monensin would increase the performance of lambs fed diets containing a high level of mature ground flint corn. The objective of this trial was to evaluate the effects of decreasing inclusion concentrations of monensin (24, 16, 8, and 0 mg kg–1 diet DM) in diets containing a high level (72.0 % of DM) of mature ground flint corn in ruminal fermentation, nutrient digestibility, plasma concentrations of metabolites, and growth performance of feedlot lambs
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