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Effects of Dietary Leucine, -Ketoisocaproate and Isovalerate on Antibody Production and Lymphocyte Blastogenesis in Growing Lambs¹

Gail Kuhlman^*, James A. Roth, Paul J. Flakoll^*, Michael J. Vandehaar^* and Steven Nissen^*,2

^* Department of Animal Science Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011

The chronic effects of oral leucine and leucine metabolites on sheep immune function were determined in two experiments. In replicate experiments, 30 mixed-breed ram lambs were individually fed diets supplemented with approximately 0.05% ruminally protected limestone (control), -ketoisocaproate (KIC), isovalerate (IVA) or leucine (Leu). Serum titers of antibodies produced in response to Brucella abortus antigen and porcine red blood cells were determined. Mitogen-stimulated lymphocyte blastogenesis was determined in experiment 2 by adding phytohemagglutinin (PHA), concanavalin A (Con A) or pokeweed mitogen (PWM) to isolated lymphocytes and measuring [³H]thymidine incorporation. In both experiments, in lambs fed Leu, antibody production to porcine red blood cells was approximately 80% (P < 0.05) of that in control animals. When KIC was fed, antibody titers to porcine red blood cells were approximately 120% (P < 0.05) of that of controls. Compared to controls background lymphocyte blastogenesis was higher when KIC was fed, whereas background blastogenesis was lower when Leu was fed (KIC vs. Leu; P < 0.05). IVA did not significantly affect either measurement. These data indicate that feeding Leu may adversely affect immune function by suppressing lymphocyte activity, whereas oral administration of KIC has a positive influence on immune function in sheep by increasing lymphocyte activity.

KEY WORDS: • -ketoisocaproate • immune function • lambs • isovalerate • leucine

¹ Journal Paper No. J-12854 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project 2614. Supported in part by NIH Grant No. AM32540.

² To whom correspondence should be addressed, at the Department of Animal Science, Iowa State University, 301 Kildee Hall, Ames, IA 50011.

Manuscript received 14 January 1988. Revision accepted 8 August 1988.