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Effect of Dietary Lactic Acid on Rumen Lactate Metabolism and Blood Acid-Base Status of Lambs Switched from Low to High Concentrate Diets¹

University of Nebraska³, Lincoln 68583

Abstract

Two experiments were conducted with ruminally fistulated wether lambs to determine the effect of lactic acid addition to a hay diet on rumen lactate metabolism, blood acid-base status and subsequent adaptation to a high concentrate diet. In Exp. 1, lambs were fed mature brome hay (H), H plus 5% (w/w) D,L lactic acid (H5L) or H plus 10% lactic acid (H10L) (three lambs per treatment) for 14 days (phase I) then switched to a 90% concentrate diet for 2 days (phase II). In Exp. 2, lambs were fed alfalfa-brome hay (H) (six lambs), H plus 2.5% lactic acid (H2.5L) (six lambs) or H plus 5% lactic acid (H5L) (four lambs) during phase I, then switched to a 70% concentrate diet (3 days) followed by a 90% concentrate diet (10 days) (phase II). During both experiments rumen fluid samples were taken periodically for pH and lactate analyses and in vitro L- or D-lactate disappearance (IVLD) studies. Blood samples were taken to measure acid-base status, serum lactate, and serum calcium, magnesium and phosphorus.

Dietary lactic acid enhanced IVLD during phase I of both experiments. L and D isomer IVLD rates were similar and followed zero-order kinetics. In Exp. 2, IVLD increased rapidly during phase II in response to increased concentrate level in the diet; the enhanced rates of H2.5L and H5L lambs were sustained for the first 3 days of phase II.

Blood data from both experiments indicated a deleterious effect of dietary lactic acid on blood acid-base balance; however, this treatment effect was not manifested in any symptoms of acute acidosis. There was a decrease (P<.05) in serum calcium during phase II of both experiments. In Experiment 1, serum calcium increased linearly (P<.05) in response to dietary lactic acid level.

In Exp. 1, rumen fluid total lactate and L-lactate were lower (P<.05) for H5L vs II lambs during phase II. However, all lambs in Exp. 1 experienced acute acidosis; four of the nine lambs subsequently died.

There was evidence of acidosis in Exp. 2, but there were no clear treatment effects during phase II on rumen fluid pH or lactate, or feed intake. All lambs adapted to the high concentrate diets as evidenced by rumen lactate levels and feed intakes. In both experiments, the proportion of L-lactate in rumen fluid decreased from almost 100 to about 50% of total lactate by the end of phase II.

¹ Published with the approval of the Director as Paper No. 5774 Journal Series, Nebraska Agr. Exp. Sta., Lincoln.

² Present address: Ruminant Nutrition Laboratory, USDA, SEA, NEA, Bldg. 200 BARC East, Beltsville, MD 20705.

³ Animal Science Dept.