Replacement of mustard oil cake by urea in short-term strategic feeding of cull ewes to improve body condition and carcass traits

Abstract

Strategic short-term feeding of culled Malpura ewes (age >6 years, average liveweight 26.8 ± 0.96 kg) was aimed at improving their body condition and increase marketability of their carcass following slaughter. Randomly, 8 out of 40 ewes were slaughtered to study initial (Day 0) carcass traits and the remaining ewes were equally divided into two groups: mustard cake (Control) and urea. They were stall fed with ad libitum guar straw (Cyamopsis tetragonoloba) and concentrate mixture at 25 g/kg liveweight after 4 h of morning grazing in the pasture. The Control group was offered concentrate with solvent extracted mustard cake whereas it was replaced on an equivalent nitrogen (N) basis with urea in the concentrate offered to the other group. Daily feed intake and weekly change in ewe liveweight and body condition score were measured during the 91 days of the experiment. There was no significant (P > 0.05) difference in digestibility of nutrients between the groups. Both groups had similar dry matter and metabolisable energy intake, but the mustard cake group recorded higher (P < 0.05) cumulative weight gain and body condition score. Ruminal fluid samples and blood biochemical measurements were analysed periodically (0, 45 and 91 days), with ruminal fluid samples during the post-feeding hours also analysed. There was periodic variation in rumen pH (P = 0.013), volatile fatty acid (P = 007), total N (P = 0.001) and ammonia-N (P = 0.025) concentration in both groups. Higher post-feeding volatile fatty acid (P = 0.031) and total N (P = 0.003) values were observed in the mustard cake group. Ruminal ciliate protozoal population showed a quadratic response over time after feeding with an initial decline post-grazing, but was not affected by treatment. Similar significant (P < 0.05) improvements in haemoglobin, glucose, total protein, urea and cholesterol levels were evident in both groups at 91 days. Both treatments showed similar improvement in carcass composition, distribution of fat and chemical composition of Longissimus dorsi after 91 days of realimentation compared with initial values. Short-term pre-slaughter feeding of cull ewes improved body condition, carcass traits and composition. Replacement of costly mustard cake with urea in the diet of cull ewes could be a means to improve profitability of this strategic feeding protocol, as well as enhancing their market value.