Lipid supplementation with macadamia by-product reduces methane emissions by sheep

Macadamia cake (MC) is a waste product from the macadamia nut industry with high nutritional value for animal nutrition. It has the potential to modify rumen fermentation, increase the efficiency of rumen microorganisms, and reduce methanogenesis. This study aimed to evaluate how the dietary lipid supplementation with MC modulates the methane (CH4) emission and nutrients digestibility of finishing lambs. Thirty-one lambs, approximately 90 days old and mean initial body weight of 26 ± 3.4 kg, were allocated to individual metabolic cages and subjected to in vivo digestibility assays for 24 days (17 days of adaption and 7 days of data collection). The four treatments included a Control group with no MC addition, and three groups with varying amounts of MC inclusion in the diet: 4.5%, 8.5%, and 14% on a dry matter basis. The ruminal content was collected individually at the last day of the digestibility assay 2 to 3 h after the morning feed, to measure pH, protozoan count, and short-chain fatty acids. The animals were then moved to semi-open respirometry chambers for the in vivo measurement of CH4 emission. A completely randomized design was used in the study assuming MC intake (MCI) as fixed effect and each animal as random effect. The variables were submitted to tests of normality and homoscedasticity. The data was submitted to analysis of variance at a 5% significance level using the F test (P < 0.05) and polynomial regression analysis. Pearson’s correlation coefficient test was also applied to all variables. Daily dry matter intake or apparent total tract digestibility parameters were not affected by MCI (P > 0.05), while ether extract and gross energy intake showed the widest range of values, from 0.01 to 0.09 (kg/day) and 9.3 to 22.5 (MJ/day), respectively, increasing (P > 0.05) according to MCI. In addition, total digestible nutrients increased linearly with MC supplementation (P = 0.037). MCI had a significant suppressive effect on enteric CH4 production from 21.9 to 8.6 (L/day) (P < 0.05) and protozoan count (P < 0.001) from 291875 to 69500 (n/mL), while a cubic (P = 0.03) and linear (P = 0.05) effect was observed for ammonia nitrogen and butyric acid, respectively. Macadamia cake may be used as an ingredient in sheep diets and its inclusion up to 14% has shown promise in reducing daily emissions of enteric CH4 without compromising nutrient digestibility and ruminal fermentation, in addition to contributing to reducing the environmental impact by avoiding the disposal of this industrial by-product.