Responses to protein plus energy supplements of pregnant ewes eating mature grass diets

Abstract

Three experiments were conducted with ewes during late gestation (last 4 weeks) to examine metabolic and lamb birth weight responses to supplements. In a metabolism experiment, 18 ewes were divided into 2 groups and offered 800 g chopped Rhodes grass (Chloris gayanu, 1.1% N) with or without a supplement of 150 g cottonseed meal + 50 g molasses, daily until parturition. Supplementation was associated with significant increases in intake of digestible dry matter (37%) and crude protein (121%). Supplemented ewes had significantly greater liveweight gain (173 v. 39 g/day), plasma glucose (2.9 v. 2.5 mmol/L), glucose entry rate (20.6 v. 12.3 mmol/h), udder measurements (e.g. circumference, 548 v. 443 mm), and milk yields (measured at day 2 post-partum, 1748 v. 627 mL/day), and had heavier lambs at birth (3.9 v. 2.9 kg). In a second experiment, 10 ewes were pen-fed chopped Rhodes grass ad libitum, and 5 received individually 150 g cottonseed meal + 100 g molasses administered daily. Supplemented ewes were significantly heavier (47.8 v. 45.0 kg) in the last week before parturition. Supplementation was associated with improved ewe liveweight change (48 v. -33 g/day) and lamb birth weight (3.4 v. 2.4 kg). In a third experiment, 42 ewes grazed a 80-ha paddock during a dry season and received daily 1 of 3 individually administered treatments: control (20 mL water drench); 7 g urea + 4 g sulfate of ammonia in a 20 mL drench; 100 g meat and bone meal + 100 g molasses + 3 g urea administered as a slurry in a single drench. Performance and metabolic parameters for the 3 groups were ewe liveweight gain (38, 80, 131 g/day), rumen ammonia concentration (7.1, 10.0, 8.6 mmol/L), plasma glucose (2.6, 2.6, 2.1 mmol/L), plasma hydroxybutyrate (0.6, 0.5, 0.4 mmol/L), and lamb birth weight (3.5, 3.7, 4.0 kg). Differences were significant between the protein-supplemented and control groups for all parameters except rumen ammonia concentration. The data support the conclusion that protein supplements provide a production response in pregnant ewes that is sufficient to improve lamb survival rates when the nutrition from grass diets is inadequate.