Replacement of Rolled Barley with Citrus Pulp in a Concentrate Supplement for Finishing Beef Cattle Offered Grass Silage

A variety of feedstuffs of varying carbohydrate composition are available to rectify deficiencies in nutrient supply for growing cattle fed grass silage-based diets. The objective was to examine the effects of replacing rolled barley (starch) with citrus pulp (digestible fibre) in a supplement on intake and performance of young growing cattle offered grass silage ad libitum for 135 days. Weaned, late-maturing breed, steers (n = 34, initial live weight 446 kg, SD 38.0) were blocked by sire breed and weight and from within block randomly assigned to one of three concentrate treatments. The control concentrate, based on rolled barley (starch), comprised of 865 g rolled barley, 60 g soya bean meal, 50 g molasses, and 25 g minerals and vitamins/kg (BAR). In the other two concentrates, barley was replaced with 400 (CIT40) or 800 (CIT80) g/kg (digestible fibre) plus 10 and 20 g soya bean meal, citrus pulp respectively. Concentrates were formulated to have similar concentrations of PDIE (true protein digestible in the small intestine when energy limits microbial protein synthesis) per kg DM (106 g). Steers were individually offered 4.0 kg DM of the respective concentrates, in two feeds daily. Data were statistically analysed using ANOVA with terms for treatment and block in the model. Supplement type did not affect (P>0.05) daily grass silage intake (5.05 kg DM). Live weight gain (kg/day) was lower (0.88) and G:F (kg/day) was poorer (10.4) for CIT 80 (P<0.01) compared to BAR (1.03 and 9.2, respectively) and CIT 40 (1.05 and 8.6, respectively), which did not differ (P>0.05). Ultrasonically assessed body fat depth or gain did not differ (P>0.05) between treatments, but muscle depth gain was higher (P<0.01) for BAR compared to CIT80, with CIT40 being intermediate (P>0.05). Carcass weight, carcass conformation and fat score, carcass fat depth, kill-out proportion, ultimate pH and temperature of M. Longissimus muscle, and drip loss did not differ (P>0.05) between treatments. Subcutaneous fat lightness (‘L’ value) was higher (P<0.01) for CIT80 than BAR, with CIT 40 being intermediate, whereas redness (‘a' value) and yellowness (‘b’ value) did not differ (P>0.05) between treatments. In conclusion, citrus pulp can replace barley at inclusion rates up to 400g/kg when offered as a supplement to grass silage without negatively affecting performance or selected meat quality traits.