Effects of feeding fresh citrus pulp to Merino wethers on wool growth and animal performance

Abstract

Two studies were conducted to determine the effects of replacing lupins with fresh citrus pulp in Merino wethers diets: (i) an in vitro study, which measured ruminal fermentation; and (ii) an in vivo study in which 18 mature Merino wethers were fed dietary treatments (n = 3) over 56 days to evaluate effects on performance [i.e. DM intake, average daily gain and wool growth]. In both the in vitro and in vivo studies, the control treatment consisted (in diet DM) of lucerne chaff (69.9%), lupins (30.1%) and phosphate (0.3%), whereas the citrus pulp treatments (n = 2; replacing lupins on 20 and 30% DM basis, respectively) consisted of lucerne chaff (61.7 and 63.3%), lupins (18.5 and 6.3%), phosphate (0.34 and 0.33%) and fresh citrus pulp (19.5 and 30.1%). Data were analysed using the MIXED model of SAS and orthogonal polynomial contrasts were used to determine linear (L) and quadratic responses to the level of citrus pulp. In the in vitro study, gas production, net total volatile fatty acid production as well as in vitro DM digestibility were similar (P > 0.05) among the dietary treatments. Ammonia production in citrus pulp treatments were twofold lower compared with the control (L, P < 0.01). The addition of citrus pulp to the diet increased the molar proportions of acetic acid and decreased that of butyric, branched-chain volatile fatty acids, and valeric acids (all L, P < 0.01) compared with the control diet. In the in vivo study, DM intake, average daily gain and feed conversion were similar among treatments (P > 0.52). Wool production parameters including clean fleece weight, yield and staple length were not different between diets (P > 0.30). Hence, fresh citrus pulp can be included up to 30% on a DM basis replacing lupins without detrimental effects on wool production and animal performance.