Effects of polyethylene glycol in concentrate or feed blocks on carcass composition and offal weight of Barbarine lambs fed Acacia cyanophylla Lindl. foliage

Abstract

The influence of concentrate or feed blocks with or without Polyethylene glycol (PEG, molecular weight 4000) on the carcass characteristics and weight of offal components of 25 Barbarine ram lambs offered Acacia cyanophylla Lindl. foliage was studied. The animals were divided into 5 equal groups and housed in individual pens for 74 days. All of the animals received 400 g oat hay and air-dried foliage of acacia ad libitum. Two groups were supplemented with 300 g concentrate with (CPEG) or without (C) 20 g PEG. The other groups had free access to urea-containing feed blocks with (BUPEG) or without (BU) PEG. One other treatment was a PEG-containing feed block without urea (BPEG). PEG was used to preferentially bind A. cyanophylla condensed tannins (CT). At the end of the growth trial, the animals were slaughtered, offal components were weighed, left half carcasses were dissected and carcass tissues were weighed. At slaughter, body weight (BW) was the highest (P < 0.01) in the group receiving concentrate and PEG (35.4 kg). The animals on diets C, BPEG and BUPEG were slaughtered at similar BW (33.4, 31.8 and 32.1 kg, respectively) and those on BU had the lowest BW (27.8 kg). Dressing percentage was not affected by diet treatments. The weights of the head, feet, lungs, heart and abomasum were not affected by the diet. The diet significantly influenced the skin, testes, liver, kidneys and rumen weights. The animals fed concentrate had heavier skin (4485 g) and rumen (812 g) than those fed blocks (3773 and 720 g for the skin and rumen, respectively). The animals receiving BU had the smallest organs. On contrasting treatments plus/minus PEG, it was observed that PEG administration significantly increased the weight of all organs. PEG supply significantly increased (P < 0.01) testis weight (196 vs. 127 g with/without PEG). Due to treatment effects on slaughter BW and hence carcass weight, muscle, bone and fat weights were lower in the BU group compared to those in the other groups. In C, CPEG, BPEG and BUPEG groups, there was no significant difference in body muscle weight. Indeed, the animals fed A. cyanophylla with feed blocks with PEG and without urea (BPEG group) produced the same amount of muscle as those produced with PEG and urea-containing feed blocks or conventional diets (concentrate). The animals given feed blocks (more protein and less energy than the concentrate) were less fat (20.0%) than those receiving concentrate (24.7%). The use of acacia foliage and feed blocks without urea but containing PEG may be a useful solution to produce lean lamb in a more economic manner.