## 1 Introduction  
Lipids have multidirectional effects on the body, and this fact has contributed to the interest in evaluating alternative lipid sources as ingredients of ruminant diet. The quality of a lipid source is directly associated with its fatty acid profile. Palmitoleic and oleic acids, the main fatty acids present in macadamia oil [1], are highlighted in this study for their effects on energy metabolism. A previous study showed no difference in insulin and glucose levels when feedlot lambs received diets containing macadamia oil as a source of palmitoleic and oleic, in the proportion of 0.1% of live weight [2]. However, when sheep were supplemented with palmitoleic and oleic acids, increased insulin sensitivity was observed, which improved the efficiency of glucose uptake by tissues [3]. The same effect was observed on insulin sensitivity in humans and mice [4]. The discrepancies observed between the findings of [PERSON] et al. [2] and [PERSON], [PERSON], [PERSON], [PERSON] [5] highlight the need for further research aimed at understanding the effects of palmitoleic acid supplementation in ruminant feed, since the changes in energy metabolism may favor the use of the energy present in the diet and lead to increased animal performance.  
Palmitoleic and oleic acids supplementation has also been linked to reduced body fat deposition in cattle [6; 7], sheep [3], mice, and humans [4], which has been associated with the effect of fatty acids in modulating the expression of genes involved in lipogenesis [3; 4; 5]. Supplementation with macadamia oil for lambs in a feedlot system has been shown to favor the expression of the gene responsible for the synthesis of the enzyme stearoyl-CoA desaturase (SCD1) [2]. The same authors related this result to a significant increase in linolenic acid (C18:3 n3) in the meat. In turn, palmitoleic and oleic acids supplementation for sheep has also been related to increased polyunsaturated fatty acids (PUFA) in meat, including eicosapentaenoic acid (EPA, C20: 5 n3) and docosapentaenoic acid (DPA, C22: 5 n3) [3], the main long-chain fatty acids in a human diet [8; 9]. On the other hand, lipid oxidation is more prominent in products with greater content of PUFAS, with detrimental effects on shelf life, as well as nutritional and sensory quality [10]. Vitamin E has been widely used as a supplementation to overcome oxidation due long-chain fatty acids in meat [2; 11].  
From a sensory point of view of the meat, [PERSON] et al. [2] reported that supplementation with macadamia oil for lambs improved the flavor and tenderness, providing better sensory acceptability of feedlot lamb meat. This is extremely positive since meat from feedlot lambs is often characterized by its pronounced flavor [12].  
In view of the promising results of macadamia oil supplementation for finishing lambs, receiving diets with a high inclusion concentrate on performance and qualitative and quantitative aspects of the meat. In this study, it is hypothesized that supplementation with macadamia nut oil for lambs on a pasture system can improve performance without compromising nutritional, sensory, and meat quality parameters. It is worth mentioning that this is the first study associating macadamia oil supplementation to a diet with high forage inclusion. The results obtained in this research will guide future studies in identifying whether the diet can alter the results already highlighted in the literature for supplementation with palmitoleic and oleic sources in livestock feeding systems.  
Thus, this study aimed to evaluate the effect of macadamia oil as a source of palmitoleic and oleic acids associated with vitamin E, in the form of supplements for lambs grazing Tifton-85 (_Cynodon_ spp.), on performance, carcass characteristics, blood parameters, meat quality, fatty acid profile of the meat, and expression of genes related to lipid metabolism in muscle tissue.