Resumen
Zilpaterol hydrochloride (ZH) redistributes ingested energy and improves feed efficiency by increasing muscle mass and reducing fat in sheep and cattle carcasses in fattening; however, by increasing lipolysis and reducing intramuscular fat (IMF), it can affect meat quality in terms of the attributes of tenderness, juiciness, taste and color; in contrast, Zn methionine (ZM), due to its lipogenic effect, can improve meat marbling without affecting production efficiency. In the current study, 36 male Suffolk sheep were used (25 ± 0.58 kg live weight, LW) to evaluate the supply of ZH and ZM on growth, carcass traits, meat quality, fatty acid content and expression of genes which regulate the deposition of fatty acids (FA) in IMF. A completely randomized design was used, with factorial arrangement of 2 × 2 ZH (0 and 0.2 mg kg-1 LW) and ZM (0 and 80 mg Zn kg-1 dry matter, DM). The results showed that ZH increased (p < 0.05) carcass yield, compactness index and chop eye area and decreased greasing (p < 0.02). The content of ether extract in meat increased (p < 0.05) in sheep with ZM plus ZH, and in sheep with ZM (p < 0.01). ZH (p < 0.05) reduced (p < 0.02) the meat?s color index L*, a*, b*, C* and H*. The content in IMF of stearic (C18:0) and arachidic (C20:0) FA was reduced (p = 0.05) by the effect of ZH, but the palmitoleic (C16:1), eicosatetraenoic (C20:4n6) and conjugated linoleic FA were increased (p = 0.05) by the effect of ZH. ZM increased (p = 0.05) palmitoleic (C16:1) and conjugated linoleic FA; the ZH interaction with ZM increased (p = 0.05) linoleic (C18:2 c 9 c 12), linolenic (C18:3 c 9c12c15) and eicosatetraenoic (C20:4n6) FA. The ZH interaction with ZM influenced (p = 0.05) the total saturated fatty acids (SFA), unsaturated fatty acids (UFA) and polyunsaturated fatty acids (PFA). ZH increased (p = 0.05) the relative expression of mRNA from the enzymes lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), glycerol -3-phosphate acyltransferase (GPAT1) and diglyceride acyltransferase (DGAT1). ZM increased (p = 0.05) the relative expression of mRNA from the enzyme gene acetyl-CoA carboxylase (ACC) and HSL, monoglyceride lipase (MGL). The ZM interaction with ZH increased (p = 0.05) the relative expression of mRNA genes of the enzymes HSL and ACC. It was concluded that ZH improved feed conversion (FC), increased yield and reduced fat in carcasses; ZM increased IMF in Longissimus dorsi. ZH and ZM influenced the FA composition, reduced the SFA and increased the UFA and PFA; both additives also influenced the relative mRNA expression of genes involved in fatty acid metabolism.