Effect of dietary lysine imbalance on the apparent digestibility of protein, organic matter, and ether extract for pigs

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Abstract
The effect of varying dietary lysine intake on apparent digestibilities of crude protein, dry matter, and ether extract for Large White pigs was examined in three trials, in which protein levels were either varied or held constant. In each of two trials, four groups of three barrows (approximately 30 kg mean live weight) were housed in metabolic cages for periods of 14 days, during the last 5 days of which estimates were made of apparent digestibilities. In the first trial, four different lysine levels were obtained by varying the amount of casein in the diet. In the second, similar effects were achieved by adding different quantities of synthetic L-lysine to a basal ration. In the third trial three groups of three pigs (52.5–55 kg live weight) were exposed to the same experimental conditions as before but were fed a ration containing only 60% of the crude protein present in the basal ration of Trial 1. Synthetic lysine was added to raise total lysine progressively from 0.37% to 0.95% of the air dry weight. At all levels of lysine deficiency, supplementation with lysine increased the digestibility of protein and organic matter, but not ether extract. It was concluded that where lysine is the first limiting amino acid, maximum digestibility of cereal-based rations depends on inclusion of sufficient lysine to satisfy pig requirements, irrespective of the level of protein in the diet.