Effects of Replacing Lucerne (Medicago sativa L.) Hay with Fresh Citrus Pulp on Ruminal Fermentation and Ewe Performance

Two studies were conducted to determine the effects of replacing 30% (% in diet DM) of lucerne (Medicago sativa L.) hay with citrus pulp in Merino ewe diets: i) an in vitro study which measured ruminal fermentation; and ii) an in vivo study in which twelve Merino ewes pre- and post-lambing were fed experimental diets in a cross-over design over 120 days to evaluate effects on ewe performance (i.e. DM intake, average daily gain (ADG) and wool growth). In both the in vitro and in vivo studies, the control treatment consisted of lucerne (91.3% in diet DM), lupins (8.3% in diet DM) and phosphate (0.42% in diet DM), while the citrus pulp treatment consisted of lucerne (57.7% in diet DM), lupins (9.5% in diet DM), phosphate (0.48% in diet DM) and fresh citrus pulp (32.3% in diet DM). Data were analysed using the mixed model procedure of SAS. In the in vitro study, gas production, total volatile fatty acid (VFA) yield, proportion of propionic acid to total VFA and in vitro dry matter digestibility (IVDMD) were higher (p < 0.02) in the citrus pulp treatment compared to the control treatment. In contrast, in vitro ammonia production, pH and the acetate to propionate ratio were lower (p < 0.03) for the citrus pulp treatment compared to the control treatment. In the in vivo study, DM intake of ewes fed the citrus pulp diet was lower than their control ewe counterparts throughout both the pre- and post-lambing periods (928.9 vs. 1,115.0 g/d pre-; 1,285.0 vs. 1,620.3 g/d post-lambing, p < 0.01), however ADG was similar (p = 0.12). Wool growth parameters and lamb performance did not differ (p > 0.32) between treatments. In summary, the in vitro study demonstrated that the replacement of 30% of a lucerne diet with fresh citrus pulp improved total VFA yield, increased total gas production and improved IVDMD, while decreasing the production of ammonia, acetic acid and rumen pH. In addition, the in vivo study demonstrated that the replacement of 30% of a lucerne diet with fresh citrus pulp pre- and post-lambing decreased intake but did not affect ewe performance in terms of ADG and wool growth. These findings, of course, would be of significant interest to sheep producers endeavouring to control cost of feed ingredients whilst maintaining productivity. (Key Words : Citrus Pulp, Growth Performance, Merino Ewe, Ruminal Fermentation, Wool Growth)