High intakes of l+ and d− lactic acid are efficiently metabolized by pigs and rats

Abstract

SummaryOn farms that apply the feeding of fermented, carbohydrate‐rich liquid by‐products there have been occasional cases of muscle stiffness and impaired gait in growing pigs. The hypothesis that high intakes of a racemic mixture of d− and l+ lactic acid could be the cause of the abnormalities was tested in a trial with growing pigs and rats. In the pig diet, wheat starch was replaced by racemic lactic acid on a weight basis and the control and test diets thus obtained were fed to pigs and rats. The pigs that were fed the test diet containing 107g lactic acid per kg dry matter showed no signs of muscle stiffness. The feed conversion and daily live weight gain in the test group did not differ from those in the control group. The amounts of lactic acid in the urine were < 1% of the ingested total lactic acid. These data indicate a high metabolizability of l+ and d− lactic acid and an energy value of lactic acid that was similar to that of wheat starch. The rats in the test group consumed 134g lactic acid per kg dry matter and showed normal behaviour and the results concerning daily gain and feed conversion and lactic acid excretion in urine agreed well with those found in the pigs. Three conclusions were drawn from the present experiment: (a) a racemic mixture of lactic acid up to 10% of the dietary dry matter had no negative effects on animal health and performance, at least not in the short term; (b) l+ and d− lactic acid are both utilized as efficiently as wheat starch; and (c) the cause of the muscle stiffness, as observed in practice, remains unknown.