Effects of exogenous enzymes on the nutritive value of macadamia spp. nut oil cake as a protein source for growing pigs

Abstract

The current high cost and scarcity of the conventional stock feeds, and the predicted long-term impact of climate change on their production are major risks to sustainable animal production in the smallholder sector in South Africa. The present study investigated the nutritive value of Macadamia (Macadamia spp.) nut oil cake (MOC), and the efficacy of exogenous enzymes to enhance its value as an alternative protein source in growing pig diets. In an enzyme-screening in vitro study (experiment 1), 3-step (pepsin + pancreatin + Viscozyme) porcine digestion was employed to compare the digestive efficacy on MOC of a custom enzyme cocktail containing 3000 FTU g -1 6-phytase (IUB 3e1.3.26), 7270 U g -1 endo-1,4-Beta-Xylanase (EC-3.2.1.8), 300 U g -1 alpha amylase (EC-3.2.1.1), 6000 g -1 subtilisin protease (EC-3.4.21.62), 532 U g -1 endo-1,4-beta-glucanase (IUB 3.2.1.6), and Ronozyme® WX 2000 CT (UB 3.2.1.8 endo‐1,4‐β‐xylanase, 200FXU/g) . The experiment was performed in a completely randomized design with six replicates per treatment. In experiment 2, the experimental diets were a balanced, standard commercial maize-soybean diet, and an iso-nutrient, 10% MOC-maize-growing diet, each with a duplicate supplemented with 500g/tonne of the custom enzyme cocktail. Eight F1 Large White X Landrace piglets (15.3 ± 1.91 kg live weight (LW) were assigned to diets in a 2 x 2 factorial arrangement, in a duplicated, balanced 4 × 4 Latin square design. An 8-day feeding period was used in the Latin squares, consisting of 3 days adaptation, and 5 days of feed intake measurement, and the total collection of faecal and urine excreta. In vitro, the enzymes did not affect DM digestibility(P>0.05). Neither of the enzymes altered the partial gastric-small intestine (19.9-22-8), colon (21.3-22.8) and the total (41.2-44.4) IVDMD of MOC (0.05). In vivo, the 10% MOC diet had low (p<0.05) digestibility of crude protein, with no (p>0.05) effect on the digestibility of other chemical components. Scaled to the LW, 10% MOC dietary inclusion reduced (p<0.05) the NR. The NR was higher (p<0.05) on the 0%, compared to the 10% MOC diets only when the diets contained the exogenous enzymes. Scaled to the LW0.75, the 0% MOC dietary inclusion reduced (p<0.05) the NR. Dietary inclusion of MOC at 10% marginally reduced the digestibility of CP, and the NR. In v conclusion, the IVDMD of MOC was low, and not improved by fortification with fibrolytic exogenous enzyme cocktails. In vivo nutrient digestibility, and N balance responses to the 10% MOC diet were similar to a standard diet, which supported the 10 % dietary inclusion of MOC as an alternative protein source for weaned, fast-growing Large White pigs. A more potent exogenous proteinase and or carbohydrase enzymes could be effective tools to improve dietary efficacy and protein efficiency