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Influence of Limestone Level in High Concentrate and High Roughage Diets on Site and Extent of Digestion in Lambs^1,2,

New Mexico State University, Las Cruces 88003

Abstract

Two digestion and slaughter trials were conducted to evaluate the influence of limestone level on site and extent of digestion and rumen fermentation in lambs. In trial 1, 11 wether lambs (avg wt 40.7 kg) were fed 75% concentrate diets supplemented with .6, 1.5 or 3.0% limestone (.6, 1.2, 1.7% dietary Ca, respectively) in a completely randomized design. Dry matter intake increased linearly (P<.10) with limestone level; therefore, other data were analyzed with dry matter intake as a covariate. Total tract organic matter digestion decreased linearly (P<.05) with increasing limestone but dry matter and fiber digestion were not affected by limestone. Ruminal digestion of dry matter and organic matter declined linearly (P<.05) with increasing limestone. Ruminal neutral detergent fiber (NDF) digestion was higher with the 1.5 than the .6 and 3.0% limestone diets (quadratic effect, P<.05) but ruminal digestion of other fiber components was not affected by limestone. Ruminal volatile fatty acids were not affected by limestone level; however, rumen ammonia concentrations decreased linearly (P<.05) with increasing limestone level. In trial 2, 12 wether lambs (avg wt 43.3 kg) were fed a 35% concentrate diet with .1, 1.5 or 3.0% limestone (.5, 1.2 and 1.6% dietary Ca, respectively) in a completely randomized design. Dry matter intake was not affected by limestone level, but digestibility of dry matter, organic matter and starch (P<.10), energy, crude protein, acid detergent fiber (ADF) and cellulose (P<.05) responded quadratically to limestone level, with increases at the 1.5% limestone level. Ruminal dry and organic matter (P<.05), NDF (P<.10), ADF (P<.01), cellulose (P<.05) and starch (P<.05) digestion responded quadratically to limestone level with higher values at the 1.5% limestone level. Proportions of ruminal propionate increased linearly (P<.01) with increasing limestone level and acetate:propionate ratio declined linearly (P<.01) with limestone level.

¹ Journal article 1018 of the New Mexico Agr. Exp. Sta. Portions of the data have been reported in the Proc. Western Sec. Amer. Soc. Anim. Sci., Vol. 34, 1983.

² Dept. of Anim. and Range Sci. Dr. El Tayeb's current address is University of Khartoum, Sudan.