Effect of nutrition, genotype, lactation and wool cover on response by grazing sheep to methionine esters and polymer-encapsulated methionine

Esters of methionine added to the diet of penned sheep have been reported to increase wool growth. Four experiments were undertaken in which grazing sheep were drenched with methionine derivatives. In experiment 1 methyl methionine hydroxy analogue (MeMHA) and ethyl methionine hydrochloride (EMHCl) increased wool growth similarly, by about 30% (P < 0.001) on native pasture and 4% (P > 0.05) on improved pasture. Dosing three times per week was as effective as dosing six times per week. In experiment 2, wool growth of unsupplemented sheep on improved pasture in spring was c. 12 g/d and was not increased by the administration of MeMHA to fine- or strong-wool sheep whether lactating or dry. Daily weight gain by young lambs declined from 258 to 215 g/d when their dams were given MeMHA at 4 g/d 5 days per week (P < 0.05). Administration of methionine as MeMHA or EMHCl or in a polymer-encapsulated form at 1.25 gld gave c. 1 g/d additional wool in experiment 3; 2.5 g/d increased wool growth by c. 1.5 g/d (P < 0.001). In experiment 4, MeMHA doses of 1.25 and 2.5 g methionine equivalent per day produced no response in sheep in full wool. In shorn Merinos wool growth increased by 1.2 and 0.4 g/d, and Dorset Horn x Merinos showed a decrease of 0.5 and an increase of 1 .3 g wool/d at the two dose levels (P < 0.01). Wool growth was increased by c. 1 g/d by 1.25 g MeMHA in sheep that had received 10 mg selenium but not in control sheep. These responses are less than those reported from pen experiments in which methionine derivatives were incorporated in the diet. It is concluded that at current prices it would not be profitable to supplement grazing sheep with any of these forms of methionine.