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Effect of Energy Level on Ruminal D(–) and L(+) Lactic Acid Metabolism^1,2,

Ohio Agricultural Research and Development Center, Wooster 44691

Abstract

Eight fistulated wether lambs were each fed four of eight diets comprising 25 to 95% concentrate in two simultaneously conducted 4 x 4 extra period Latin square design experiments. Disappearance rates of L(+) and D(–) lactic acid isomers were determined on days 14 and 21 (in vitro) and on day 15 (in vivo). In vitro disappearance rates were similar for both isomers, with essentially a 1 to 1 ratio of D(–)/L(+) on all diets. Total in vitro lactate disappearance (mg/lOOml/hr) on day 14 increased between 25 and 55% grain, changed minimally between 60 and 80% grain and increased substantially with 95% grain. On day 21, total in vitro lactate disappearance changed very little from day 14 on 25 and 95% concentrate diets, with variable responses on intermediate diets. Thus, a transitory ruminal condition existed on intermediate grain levels which was not conducive to maximal lactate utilization. The plateauing, transitional disappearance rate over the 55 to 80% concentrate range coincides with levels of grain associated with grain adaptation disturbances. In vivo L(+) lactate turnover (fraction of dose/hr) increased non-linearly in relation to concentrate level (R², .73) from .185 (25% grain) to .368 (95% grain). In vivo turnover rates of D(–) lactate were lower than L(+) on all diets, showed little relationship to grain level, but were somewhat higher on 60 to 95% (, .171) than on the 25 and 55% grain levels (, .121). Previous treatment carryover effects for in vitro lactate disappearance (L(+), D(–) and total) and in vivo (L(+)) lactate turnover were inversely related in a linear fashion to grain level, indicating greater carryover from forage than from grain diets and supporting the function of forage particulate matter in lactate utilization. Thus, level of forage fed immediately prior to switching to high grain diets was extremely important in facilitating a rapid adaptation to grain energy and utilization of associated lactic acid produced during fermentation.

¹ Approved for publication as Journal Article No. 165-77 of the Ohio Agricultural Research and Development Center, Wooster.

² The authors express their thanks to Dr. J. R. Holman for advice on matters statistical, to R. L. Preston for design suggestions and to Dr. R. L. Stone for analytical assistance.

³ Department of Animal Science.

⁴ Graduate research assistant. Present address: Department of Animal Science, Colorado State University, Ft. Collins.

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