Utilization of wheat stubble pastures by gestating ewes

Abstract

A 4-month field trial was conducted with 48 mature Sardi ewes on the effects of stocking rate and supplementation on wheat stubble availability, biomass, chemical composition, dry matter (DM) intake and diet quality, and to test the effectiveness of supplementation in late gestation on ewes and lamb live weights (LW). Animals on treatments A (12 ewes ha −1) and B (24 ewes ha −1) grazed stubble alone for 10 weeks; animals on treatment C (24 ewes ha −1) received alfalfa hay at 0.5% LW (as-fed basis) after 4 weeks of grazing. At the start of the 11th week of grazing (last 5 to 6 weeks of gestation) alfalfa supplementation was discontinued and animals from each plot received a high (200 g cottonseed meal and 300 g whole barley) or a low (200 g cottonseed meal and 50 g whole barley) daily concentrate supplement. At lambing, all ewes were removed from the stubble and given an identical pen-fed ration of 1250 g chopped alfalfa hay, 400 g dried sugar beet pulp and 500 g whole barley. Stocking rate had no effect on biomass throughout the trial. Amount of wheat stubble and weeds did not differ up to the fourth week of grazing but declined sharply thereafter ( P< 0.05). Residual grain totally disappeared during the same initial period. Crude protein (CP) and fiber fractions of weed-free stubble were similar first but then CP decreased ( P<0.05) and fiber fractions increased ( P<0.05), except for acid detergent lignin which remained constant. Crude protein and ash content of esophageal extrusa samples decreased ( P<0.05) and neutral detergenber increased ( P<0.05) with increasing stocking rate. In vitro digestibility of extrusa and ewe DM intake tended to be lower at the higher stocking rate. Stocking rate had no effect on ewe performance on treatments A and C whereas animals on treatment B initially gained but then lost weight. Concentrate supplementation during the last 4 weeks of gestation tended to double LW gain of ewes on treatment A, compared to C. Lamb birth weight averaged 4.0 kg. Weight gains of A lambs were higher than of C lambs ( P<0.01), suggesting that ewes on treatment A had been fed adequately and produced enough milk for normal lamb growth rate, but ewes on B had not.