Abstract
The everted gut sac technique has been used to measure in vitro the absorption of amino acids by the intestine of broiler chicks, representing avian species, and of rats, representing mammalian species. Measurements of rates of absorption and concentrations gradients have been made in the chick at various ages from 5 to 56 days of age and in the rat from 21 to 60 days of age. Attempts have been made to correlate the findings with the amino acid requirements of the two species over these age ranges. During the growth of the rat the rate of absoiption of L-cysteine fell progressively to 60 days of age and that of methionine fell to 30 days whilst that of alanine changed little over the age range studied. At all ages the rate of absorption of cysteine was higher than that of methionine or alanine. The concentration gradient for cysteine was also always higher than that of either alanine or methionine. The changes during growth in the rate of absorption of these three amino acids were similar in the chick to those in the rat. However, whilst the relationship between the concentration gradients of the different amino acids were similar, those in the chick changed little in their actual values during growth. When rates of absorption of L-alanine were compared at various ages in rats and chicks it was found that the value in the rat fell gradually from 20 to 60 days but was at all ages higher than in the chick. In the latter species, the rate of absorption fell markedly between 5 and 11 days and by 30 days had fallen to a still lower value. The rate of absorption of methionine was always higher in rats then in chicks and fell markedly between 5 and 11 days of age. In contrast, the concentration gradient for methionine rose sharply in the chick from 8 days of age to 19 days of age and from 11 days was always higher than in the rat. In the rat the gradient rose slightly between 21 and 30 days but changed little thereafter. In contrast to the values for the absorption of methionine, those for cysteine were higher in the chick than in the rat. This was particularly true of the concentration gradient in which at maturity there was a three-fold difference. This species difference in particular may reflect the greater dietary requirement for cysteine in broiler chicks. Oral use of antibiotics demonstrated no detectable difference in the rate of absorption and concentration gradient for methionine when these were offered for three consecutive days only. Results confirmed that a competitive relationship existed between glucose and methionine absorption for chicks. The rate of absorption for methionine was found to increase when glucose was absent from the perfusion medium. During growth rate studies the addition of further free sulphur amino acid to a diet containing only half the requirement of sulphur amino acid from natural ingredients demonstrated no effect on body weight and food utilization. The total amount of crude protein in this diet was 13. 6% and metabolizable energy was 3007 Kcals/kg. In addition, when methionine or cysteine were offered separately, again no effect on body weight and food utilization was observed. Basic studies indicated that active transport occurred throughout the whole hour of the incubation period, and that histological damage of the intestinal cells was insignificant.