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Utilization by Growing Goats of Diets that Contain Monensin and Low or Excess Crude Protein: Comparative Slaughter Experiment¹

University of Kentucky⁴, Lexington 40546-0215

Abstract

Monensin was added at 0 or 23 mg/kg dry matter to low (8.3%) or high (17.5%) crude protein diets (2 x 2 factorial arrangement) that were fed to 28 growing wether goats for 194 to 256 d. Average daily gain increased 24% with monensin and 20% with higher crude protein (P<.05), Feed conversion was improved by both monensin and higher crude protein (P<.001). During the experiment, digestion and metabolism trials were conducted twice (Periods I and II) with each goat. Apparent dry matter and gross energy digestibility coefficients were not affected by monensin in either period. Digestibility of dietary N was enhanced 7% by monensin in Period II (P<.01) and tended to be improved in Period I. Higher dietary protein increased all digestibility coefficients (P<.001). Nitrogen retention was not affected by monensin but was greater (P<.001) for high-protein-fed goats. Potential changes in empty body composition were assessed by comparative slaughter balance. No effects of dietary treatments on percentage composition of empty body were noted, except a trend for higher protein in monensin-fed goats compared with controls (P<.1). Empty body protein gain as a percentage of protein intake improved 41% with monensin and decreased 37% with higher dietary protein content (P<.05). Monensin increased conversion of dietary energy to body ether extract energy (12%, P<.05), to protein energy (35%, P<.001) and to total body energy (23%, P<.001). Magnitude of improvement tended to be greater with low than high dietary protein treatments, suggesting a protein-sparing effect of monensin as determined by comparative slaughter method. However, N retention, measured by intake-excreta balances, was not affected by monensin, suggesting that these point estimates are less than adequate to evaluate true body protein gain.

¹ Paper No. 84-5-165, published with approval of the Director, Kentucky Agr. Exp. Sta.

² Present address: Dairy Sci. Dept., Univ. of Florida, Gainesville 32611.

³ Present address: Dept. Anim. Sci., Texas A&M Univ., College Station 77843.

⁴ Anim. Sci. Dept.