INFLUENCE OF FOOD NITROGEN-SOURCE ON LEVE LS OF PLASMA-FREE AMINO-ACIDS IN PONIES

During this study, the effects on concentrations of plasma free amino acids (PFAA) in ponies were assessed in five diets, each containing a different source of nitrogen. A 3 x 3 latin square design was used wit h nine adult male Shetland ponies (average weight 201 +/- 19 kg). In a first experiment (E1), the ponies were fed a diet of molassed straw a nd maize, in quantities corresponding to maintenance levels, complemen ted by horse bean meal (R1), soya bean meal (R2) or fish meal (R3). In a second experiment (E2), the complements were rapeseed meal (R4), so ya bean meal (R5; identical to R2) or cotton meal (R6). Samples of jug ular blood were taken at 0800 hours (T), 1000 hours (T+2), 1200 hours (T+4), 1400 hours (T+6), and 1600 hours (T+8) for determination of PFA A. In F1, R1 (horse bean) led to nonsignificantly higher average daily concentrations of PFAA than R2 (soya bean meal) (+7%) and R3 (fish me al) (+4%). Peak values were reached at T+2 with R1 and R2. With R2, th e peak was followed by a sharp decline from T+4 onwards, whereas with R1, the decline was not observed until T+8. With R3, the peak occurred later, at T+4, but showed less variation. Daily average concentration s of lysine were higher with R1 and R3 than R2. However, concentration s of methionine were higher with R3 than with both R1 and R2. In E2, R 5 (soya bean meal) contained larger quantities of nitrogen; average da ily concentrations were higher than in E1 (2 773 and 2 480 mu mol/L re spectively). Peak values were reached at T+2 for each of the diets R4, R5 and R6. Daily average concentrations of lysine were higher with R4 (rapeseed meal) and R5 than with R6 (cotton meal). Concentrations of methionine were higher with R4 than both R5 and R6. For the quantity o f MADCi/kg P-0,P-75, as cotton meal and rapeseed meal are respectively , good sources of methionine and lysine, fish meal would make up a goo d source of both. Horse bean meal is low in methionine. Soya bean meal is a middle nitrogenous source for lysine and methionine compared wit h other nitrogenous sources.