Amino Acid Imbalance in the Liquid-fed Lamb

Abstract

Eleven Poll Dorset x Merino crossbred female lambs 4 weeks of age were trained to suck liquid diets from bottles. In three separate experiments liquid diets providing 14· 2 % (expt 1) 10· 6 % (expt 2) or 8·0 % (expt 3) of gross energy as protein and amino acids were fed. Responses in voluntary intake, growth rate and changes in plasma amino acid concentrations were studied when complete or incomplete mixtures of amino acids were added to the liquid diet. These mixtures supplied either: (1) all amino acids in quantities to bring the total of protein plus amino acids to provide more than 20% of dietary gross energy, the amino acids being provided in proportions estimated to meet adequately the lamb's requirements ('complete'); or (2) as the same total amount of amino acids but with the amino acid supplement devoid of threonine ('low-threonine', expts 1 and 2) or isoleucine ('low isoleucine', expt 3).In experiment 1, there was no food intake or growth depression after feeding the amino acid mixture lacking threonine.In both experiments 2 and 3, voluntary food intake was depressed to about 50 % of that observed in lambs fed the low protein diet, when the amino acid mixture devoid of threonine or of isoleucine, respectively, was fed. Addition of the missing amino acid to the low threonine and low isoleucine diets resulted in recovery of voluntary intake in experiments 2 and 3 respectively, but no significant improvement above that found after feeding the low protein (basal) diet.In experiments 1 and 2, after feeding the low threonine diet the threonine concentration in the blood plasma decreased markedly, while concentrations of total amino acids were elevated. Although there was no improvement in growth or food intake, the feeding of the diet containing the complete amino acid mixture resulted in an elevation of all essential amino acids including threonine. Similarly in experiment 3, plasma isoleucine concentration decreased in the lambs fed the isoleucine imbalanced diet.Results indicate that the suckled, preruminant lamb exhibits sensitivity to dietary amino acid imbalance, in a manner analogous to that found in simple-stomached animals. These results also clearly illustrate a depression in food intake associated with the deletion of a specific essential nutrient from the diet of the lamb.

Effects on wool growth of the infusion of mixtures of amino acids into the abomasum of sheep

“…Reductions in feed intake in the above experiments were probably minimized by the restricted amount of feed offered. It is "well known that amino acid unbalanced diets cause reductions in feed intake in monogastric species (Harper, Benevenga & Wohlhueter, 1970;Rogers & Leung, 1973), and Rogers & Egan (1975) have observed similar effects in liquid-fed lambs deprived of threonine or isoleucine. Consequently, such effects are not surprising in adult ruminants.…”

Postingestive Feedback as an Elementary Determinant of Food Preference and Intake in Ruminants

“…Lambs acquire aversions to foods that they eat when they experience imbalances in many essential amino acids Egan 1975, Egan andRogers 1978). The neural mechanisms that enable ruminants to recognize an amino acid imbalance have not been identified.…”

Metabolic constraints on voluntary intake in ruminants.

“…If the animal cannot compensate for dietary imbalances by eating more, perhaps because it is constrained by the ability to dispose of the surplus nutrients, then production must decline, because the ability to call on reserves is exceeded. Yet further deviation from the optimal diet will cause the animal to reduce its intake (e.g., in lambs; Rogers and Egan, 1975).…”