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Effects of Limestone, Monensin and Feeding Level on Corn Silage Net Energy Value and Composition of Growth in Cattle¹

Ohio Agricultural Research and Development Center, Wooster 44691

Abstract

A growth and energy balance study was conducted to investigate the effects of limestone and monensin on corn silage net energy value. One-hundred and thirty Hereford steer calves (average initial weight, 240 kg) were allotted to 13 groups; an initial slaughter group ("initial" cattle) and 12 groups fed in a 2 x 2 x 2 factorial design ("fed" cattle). Factors were: (1) untreated or 1% limestone (CaC0₃)-treated corn silage, (2) no monensin or added monensin and (3) ad libitum or 70% of ad libitum intake, with two groups fed ad libitum and one group limit-fed each treatment. Where indicated, 1% CaCO₃ was mixed with chopped corn plant material at ensiling, and monensin was provided in the protein mineral supplement. Body composition, energy and tissue balance were calculated from measurements of carcass specific gravity taken on "initial" cattle and "fed" cattle at slaughter. Recovery of silage wet matter in barrel silos was similar whether silages were treated or not. While neither limestone nor monensin altered rate of gain, dry matter intake was reduced (P<.01) 7.8, 12.2 and 18.7% with monensin, limestone and the combination, respectively. Concurrent improvements (P<.05) in dry matter to gain ratio were 5.8, 9.1 and 14.3% for monensin, limestone and both, respectively. Monensin, limestone and the combination increased average net energy value [NE_m + NE_g]/2 by 8.8, 9.6 and 15.4%. Restricting energy by limit feeding, even on this forage diet, reduced daily rates of protein deposition by less than 14% while decreasing (P<.01) fat accretion by over 43%. As a result, cattle fed ad libitum were 21% fatter (P<.01) than limit-fed cattle (30.87 vs 25.48% fat) at 352 kilograms. Level of nutrition regulated composition of growth, and the effects of limestone treatment and monensin supplementation on corn silage net energy value were additive.

¹ Approved for publication as journal article no. 170-78 of the Ohio Agr. Res. and Develop. Center, Wooster.

² Dept. of Anim. Sci.