Effect of abomasal infusions of methionine, casein, and starch plus methionine on the wool production of Merino wethers fed on lucerne or wheaten chaff

Abstract

Merino wethers received daily abomasal infusions of (a) 2.6 g DL-methionine, (b) 80 g casein protein or (c) 2.6 g DL-methionine plus 87 g maize starch, while consuming either lucerne chaff or wheaten chaff. Responses in wool growth, nitrogen metabolism and body weight were measured.

Sheep fed on lucerne chaff had a higher urinary nitrogen excretion and nitrogen retention than those fed on wheaten chaff regardless of the presence or type of infusion. The infusion of methionine did not markedly alter these parameters from their original levels on either diet. On both diets, casein infusion led to increased urinary nitrogen excretion and nitrogen retention. Compared with sheep given starch plus methionine infusions, those given casein had higher urinary nitrogen excretion and nitrogen retention. Changes in fleece-free body weight gain followed a similar pattern. There were no pronounced differences in faecal nitrogen excretion.

Regardless of the presence or type of infusion, sheep fed on lucerne grew more wool than those on wheaten chaff. On both diets, all infusions were accompanied by higher wool growths than on the basal diet alone. The effect of the casein infusion, compared with methionine infusion, was apparent only in sheep on wheaten chaff. Wool growth rates in sheep infused with starch plus methionine were not higher than the rates in the same sheep infused with methionine alone.

The results suggest that the wool production of sheep will show a greater response to abomasal supplements of sulphur amino acids or casein if they are consuming a high quality diet such as lucerne chaff, compared with a low quality diet such as wheaten chaff. The apparent failure of starch infusion to stimulate wool growth above the level obtained with methionine infusions alone is discussed in relation to the interaction of protein and energy in the growth of wool.