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Four sheep were given three types of casein supplements (all providing c. 16 g nitrogen per day) and the effects on wool growth rate, body weight gain, and nitrogen retention were measured. The supplements were untreated casein in the diet, untreated casein per abomasum, and formaldehyde-treated casein in the diet. Untreated casein in the diet was inferior to the other casein supplements for all parameters studied. Formaldehyde-treated casein and casein per abomasum were of similar nutritional value. The average increase in wool growth rate above the basal rate was 62% for both types of supplement; nitrogen retained was about 3 g/day, of which more than half was in wool. The treated casein was 90% digestible.

Sheep receiving a diet consisting solely of wheat (500 g/day), supplemented with a mineral mixture, were given abomasal infusions of varying amounts of DL-methionine (1.5-6.0 g/day) or of L-cystine (5 g/day). Other sheep received DL-methionine as a supplement to a roughage diet. All levels of methionine infused caused a decrease in the mass of wool grown by sheep consuming the wheat diet. This effect was greatest with 6 g methionine and was due mainly to a considerable depression of fibre diameter. Smaller amounts of methionine decreased fibre diameter and increased length growth rate. The infusion of methionine caused a considerable weakening of the wool grown by most of the sheep, with the result that a 'break' was observed in the fleece after about 1 week of methionine administration. This effect occurred with all levels of methionine but was more pronounced with 6 g/day. The abomasal infusion of cystine (5 g/day) caused little change in the mass of wool grown, but fibre diameter was decreased slightly. There were no appreciable effects on the strength of wool fibres and no wool was shed. Supplementation of the roughage diet (400 g/day) with methionine at 2 g/day stimulated wool growth, whereas with 6 or 10 g/day the mass of wool grown was unchanged but fibre diameter was markedly reduced. The strength of wool fibres was not markedly influenced by methionine infusions on this diet. The levels of amino acids in blood plasma and in abomasal digesta indicated that the mixture of amino acids absorbed was similar with both the roughage and the wheat diets.