Effects of enteric methane mitigating strategies on growth and carcass characteristics of lambs fed high forage diets

Abstract

This study formed part of a greater departmental research project on methane mitigation strategies in livestock, fed poor quality feeds or kept under extensive grazing conditions. Globally, livestock represents a large source of methane (CH4) from anthropogenic activities, mostly from enteric fermentation by ruminants. The aim of this project was to study the effects of dietary methane mitigation interventions on growth and carcass characteristics, due to changes in the composition of adipose tissues in livestock. Feasible methane mitigation technologies can only be adopted once the effect on the entire production cycle has been evaluated, including the potential adverse effects of such technologies on product composition and quality. Although previous research has focused on the manipulation of carcass composition by dietary oil and fat supplementation, the novelty of the present study is to investigate the possible consequences of supplementing fibrolytic enzymes and palm oil on the fatty acid composition and the related effects on carcass and meat quality of livestock. In this study 40 South African Mutton Merino (SAMM) ram lambs were stratified according to their initial body weight and randomly assigned to one of the following four treatment groups with ten lambs as a sampling unit for each treatment. The lambs were fed high-forage based total mixed rations (TMR) that consisted of a TMR diet supplemented with Megalac as bypass oil (C); TMR supplemented with 3% palm oil (PO); TMR with cellulase and xylanase enzymes (1:1) (ET) and TMR supplemented with 3% palm oil and cellulase and xylanase enzyme (O*E), for approximately 120 days. After approximately 100 days and target weight of ca. 42kg, all lambs were slaughtered at a commercial abattoir, carcasses were electrically stimulated (21V, 60Hz, 120s) and chilled at 4?C for 24 hours. Hot carcass weight (HCW), cold carcass weight (CCW) and pH of carcasses were recorded, followed by collection of three rib-cut samples to determine carcass composition and fatty acid profiles of subcutaneous and intramuscular adipose tissue. Lambs fed treatment ET and C gained 20g more per day than those in the PO and O*E treatments. Lambs in treatment PO took 8 days longer to reach target slaughter weight. HCW and CCW were higher in treatments C and ET than in treatments PO and O*E. The average HCW 19.24±1.5kg was within the industry norm. Dressing percentages in this study were in line with industry averages of 45%, even though treatments PO and O*E had a ± 3% lower dressing percentage compared to other treatment groups. Supplementation of palm oil increased meat % of carcass composition by more than 4%. A lower percentage carcass fat was observed in treatment PO and O*E. The proportion of fatty acids from this study was similar across all four treatments groups; numerically these values were so small, even negligible in some cases. Interaction effects were detected between oil and enzyme treatments for SFA’s, MUFA’s and the UFA’s in subcutaneous adipose tissue. Oil treatment groups in the present study differed from the other treatment groups and generally reduced the PUFA concentration. Palm oil supplementation affected the subcutaneous fatty acid profiles of lambs, which include C14:0, C16:0, C17:0, C18:0, C18:2n6c, C20:3n6 and C20:4n6. A general decrease in SFA concentration was observed for oil treatments in all of the SFA where oil supplementation had a significant effect, except for stearic acid (C18:0) where PO treatment increased the fatty acid concentration by almost 3%. Palm oil supplementation decreased linoleic acid (C18:2n6c) concentration, but tended to increase the EPA (C20:3n6) in subcutaneous tissue. Similar effects were observed in fatty acids of intramuscular adipose tissue. Fatty acid concentration for treatments PO and O*E were lower in concentration of myristic acid (C14:0) and palmitic (C:16) fatty acid. Palm oil supplementation had a negative effect in stearic acid (C18:0) and arachidic acid (C20:0) and increased the fatty acid concentrations compared to treatment C and ET. Interestingly ET treatment had an increasing effect on margaric (C17:0) fatty acid concentration compared to treatment PO and O*E. Overall where oil treatment groups were of significance a reduction in fatty acid concentrations was observed in PO treatment. A decrease in fatty acid concentration was observed in PO treatment that were highly significant in linoleic acid (C18:2n6) and ?-linolenic acid (C18:3n3). If methane mitigation strategies through dietary interventions are successful in lowering the carbon footprint it can be concluded that although palm oil and/or enzyme treatment groups showed significant effects in some of the evaluated parameters, mentioned above, numerically these values were minor, and probably negligible. Although lambs in treatment groups supplemented with oil took a few days longer to reach target weight, differences between treatment groups for all other parameters, ADG, HCW, CCW, pH at 24 hours and D% (dressing percentage) were small. With no negative effects on carcass characteristics or fatty acids consumer resistance should not be at risk.