Studies on the growth and carcass composition in Daldale wether lambs. 1. The effect of dietary energy concentration and pasture species

Abstract

Thirty-two Daldale wether lambs were randomly allocated in groups of four and were grown from 23.3 � 0.4 kg liveweight until slaughter at a final full liveweight of 37.5 kg. Eight lambs were fed on a high energy diet (HE) ad libitum, eight lambs were given a low energy (LE) diet ad libitum, eight lambs grazed Trifolium repens L. (WC) pasture and eight others grazed Phalaris aquatica L. (PH) pasture. Those on the HE diet grew at 171 g/day, the lambs on the LE diet at 105 g/day, white clover lambs at 227 g/day and lambs on phalaris at 198 g/day. The HE lambs when compared with the LE, the grazed Trifolium repens L. (WC) pasture and eight others grazed Phalaris aquatica L. (PH) pasture. Those on the HE diet grew at 171 g/day, the lambs on the LE diet at 105 g/day, white clover lambs aat 227 g/day and lambs on phalaris at 198 g/day. The HE lambs when compared with the LE, the WC and the PH lambs, had significantly greater dressing percentage (54.7 compared with 48.8, 5 1.3 and 49.4 respectively), fat thickness over the 12th rib section (8.9 mm compared with 5.5, 5.6 and 4.8 mm), more omental fat ( + 15%, + 65%, and + 57%), kidney, perinephric and pelvic fat (+ 35%, + 85%, and + 54%), a greater amount of dissectable fat from the 9-10-11th rib (+ 15%, +30% and + 33%) and from the long leg (+ 16%, +34% and +40%), and a greater amount of carcass chemical fat (+ 19%, +27% and + 35%). No differences existed among the LE and the two pasture groups in carcass composition.Digestion of two diets (HE and LE) in the stomach and intestines was studied. The flow of digesta from the rumen was higher (+ 37%); the flow of digesta from the abomasum per unit of organic matter intake was higher (+ 47%) and the mean residence time of 51Cr-EDTA in the rumen was lower (-17%) for the LE diet than for the HE diet. There was a 23% higher concentration of acetic acid, and a 33% lower concentration of propionic acid, 6.5% less butyric acid and 30% less combined valeric acids.The greater amount of fat in the carcass of the sheep fed the high energy diet appears to be associated with the higher concentration of propionic acid in the ruminal volatile fatty acids and none of the other parameters of digestion. There may also have been a more eficient utilization of metabolizabe energy on the high energy diet.