Production and glutathione responses to rumen-protected methionine in young sheep grazing dry pastures over summer and autumn

Abstract

The aims of the experiment were to evaluate, in weaner sheep grazing dry annual pastures, the production responses and changes in blood and tissue glutathione concentrations to a methionine formulation (Lactet) protected from microbial breakdown in the rumen. Two groups of 60 weaner wether sheep, weighing 32·8 kg, were supplemented with lupin grain containing either nil (control) or 9 g Lactet per day. Lactet provided 3 g of protected methionine per day. The sheep grazed dry pastures and were rotated through 2 plots every week from December to June. After June the treatment ceased and the sheep grazed as one group until shearing in September. The sheep given Lactet grew 340 g more clean wool with a greater fibre diameter (1·2 µm) than the control sheep. Lactet supplementation increased liveweights during treatment and for 3 months following treatment. Faecal dry matter output was significantly increased by Lactet supplements and the effects were maintained in the post-treatment period, indicating that Lactet supplementation increased dry matter intake. Glutathione concentrations were significantly increased in whole blood, liver, and muscle but not in skin. Changes due to season were greater than changes due to treatment. It was concluded that glutathione in blood or tissues, although responsive at times, was not a reliable indicator of sulfur amino acid intake or status. Significant increases in total body water, protein, ash, fat, and total body energy were observed relative to the control group following Lactet supplementation. We conclude that young sheep grazing dry annual pastures in summer and autumn have the potential to respond to supplements of rumen-protected methionine even at low energy intakes from low quality pastures and show improvements in wool quality and quantity as well as liveweight and intake.