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Abstract
1. The net absorption and the biological efficacy of DL‐methionine and of DL‐methionine hydroxy analogue free acid (MHA‐FA) were evaluated in chickens under heat stress.
2. In a growth assay, finishing broilers 21 to 42 d of age were fed on diets containing graded amounts of the two supplements; the basal diet was composed of practical ingredients.
3. From slope‐ratio analysis, equimolar efficacy of MHA‐FA relative to DL‐methionine was determined to be 83% (confidence limits 61 to 115%) from weight gain responses, and 67% (47 to 91%) from food conversion responses. This indicates that the relative efficacy of MHA‐FA is close to previous estimates of about 75% obtained under thermoneutral conditions.
4. In a balance study with caecectomised cockerels, net absorption (intake—excretion in faeces and urine) of DL‐methionine and of MHA‐FA, respectively, were determined to be 97.2 and 90.8%. The net absorption of MHA‐FA was significantly lower than that of DL‐methionine.
