Plasma amino acid patterns were studied in sheep receiving varying amounts of DL-or L-methionine (0'6-10·0 g/day) or L-cystine (2·0 and 8·0 g/day) as abomasal supplements or DL-methionine (10 g/day) as a dietary supplement.Total amino acids in plasma decreased when small amounts (0'6-2'5 g/day) of methionine were infused, but increased substantially with the larger amounts of methionine (4'9-10·0 g/day). However, when methionine and taurine were excluded, the remaining amino acids decreased with all amounts of methionine. Cystine supplementation caused smaller changes in total amino acids.Methionine infusions significantly increased the concentration of methionine, cystine, taurine, and cystathionine in plasma. Cystine infusions increased the concention of the latter three compounds, but not that of methionine. Infusion of small amounts of methionine (0· 6-2 . 5 g/ day) produced only small increases in plasma methionine; with the infusion of larger amounts plasma methionine increased rapidly. The relationship between plasma methionine and amount of methionine infused was described by two straight lines which intersected at about 3 . 3 g/ day of methionine. With an infusion of 10 g/day the mean plasma methionine concentration was 235 ",moles/ 100 ml, which represented 64% of the total plasma amino acids. In contrast, an equimolar amount of cystine (8 g/day) produced only a small increase in plasma cystine, and had no effect on plasma methionine.Infusions of both methionine and cystine caused considerable reductions in the plasma concentrations of the branched-chain amino acids (valine, leucine, and isoleucine), and of serine and glycine.Dietary supplements of methionine (10 g/day) caused no change in the total concentration of amino acids in plasma nor in the concentration of any individual amino acid.

SUMMARYMerino sheep were given abomasal infusions of various amino acids or mixtures of amino acids. Effects on wool growth were measured using autoradiography or a clipping procedure and changes in the concentration of amino acids in plasma were measured in some experiments.Mixtures of five (28 g/day) or ten (45 g/day) essential amino acids (both mixtures containing 3 g methionine) stimulated wool growth of sheep receiving a maintenance ration; on average, the volume of wool grown increased 48% and 86%, respectively. When cysteine completely replaced methionine in these mixtures, wool growth was markedly reduced, but two-thirds of the methionine could be replaced by cysteine without affecting wool growth. Homocysteine was partially effective in replacing methionine and, when supplemented with betaine, folic acid and vitamin B12, the mixture was still significantly inferior to that containing methionine. In contrast, abomasal supplements of methionine or homocysteine alone were equivalent as supplements for wool growth. The results indicated a specific role for methionine in the control of wool growth, other than the provision of cysteine. This role was postulated to be related to some function of S-adenosylmethionine.Infusion often essential amino acids caused appreciable increases in the concentrations of cystine, methionine, cystathionine and taurine in plasma; total essential amino acids increased threefold whereas nonessential amino acids decreased in concentration. The replacement of methionine in the infusion by cysteine or homocysteine significantly altered the concentration of cystine, methionine and cystathionine in plasma.Evidence was obtained that the adverse effects on wool growth of high abomasal doses of methionine (10g/day) could not be reduced or prevented by provision of additional glycine and were not related to the supposed toxic effects of 3-methylthiopropionic acid, a metabolite of the transamination pathway.

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.

SUMMARYMerino sheep were given abomasal infusions of either mixtures of amino acids or protein during periods of 8 or 12 days. Effects on wool growth were measured using autoradiography and a clipping procedure which allowed time for the emergence of the wool fibres. Estimates of volume growth rate, from the autoradiographic measurements, and of mass of wool grown, from clipping, were in good agreement.An infusion of a standard mixture of 13 amino acids, which included ten essential amino acids in approximately the proportions in casein, consistently stimulated wool growth. The mean increases in volume and mass of wool grown, during 30 infusions, were 66 and 67% respectively. A mixture of ten essential amino acids alone appeared to be as effective as the standard mixture for stimulating wool growth, and there were no significant differences between the effects on wool growth of casein and the standard mixture of amino acids.The omission of methionine from an infusion of the standard mixture of amino acids, or from a mixture of essential amino acids only, inhibited wool growth rate; both fibre diameter and length of wool grown per day were reduced to below the control values. In addition, the strength of the fibres was considerably reduced.Infusions of zein and of an amino acid mixture simulating the essential amino acid composition of zein both inhibited wool growth rate, due to a reduction in fibre diameter. Similar effects on wool growth were observed when any one of three essential amino acids (lysine, isoleucine or leucine) was omitted from an infusion of the standard mixture of amino acids. The omission of five other essential amino acids (arginine, histidine, phenylalanine, threonine or valine) from the infusion, or variations in the proportions of leucine, lysine or methionine, had no appreciable effects on wool growth.

Mimosine was administered orally to Merino sheep once daily for periods of 1-3 days, either as the isolated compound or in the foliage of Leucaena leucocephala. A single daily dose of mimosine of 450 or 600 mg/kg body weight was effective for defleecing sheep. A daily dose rate of 300 mg/kg was effective for defleecing sheep if given on two sucessive days.The effectiveness of a treatment for defleecing sheep was related to the concentration of mimosine in plasma following dosing; defleecing ensued when the concentration of mimosine in plasma was maintained above 0·1 mmol/l for at least 30 h.The main products excreted in urine were mimosine and 3,4-dihydroxypyridine (DHP); small amounts of mimosinamine were also excreted. During the first day following dosing, the major excretory product was mimosine; DHP was an important component during the second and third days. In the three days following the start of dosing, between 32 and 53 % of the mimosine given was accounted for as mimosine in the urine.Following an intravenous infusion of mimosine, no DHP was detected in urine; most of the mimosine was excreted intact but a small amount (c. 9%) was excreted as mimosinamine.