LAUSR

Sheep production systems in northwest China depend mostly on natural grasslands. Seasonal growth and maturity fluctuations can cause periodical restrictions in food quality and quantity. These fluctuations, in turn, result in variability in fat deposition and fatty acid profiles in different fat depots. Consequently, the study objective was to compare fat deposition, intramuscular fat (IMF) percentage and fatty acid profiles of the longissimus dorsi (LD), kidney fat (KF), tail fat (TF), and subcutaneous fat (SF) in lambs under ME restrictions similar to seasonal changes observed in the natural grasslands of northwest China. Nineteen male Dorper × Small Tailed Han lambs were assigned to 2 treatments, a control (CON) fed at 1.0 MJ / W × d and restricted (RES) by restricting ME sequentially every 30 d (0.56 MJ / W × d, 0.84 / W × d, 1.0 MJ / W × d, 0.84 MJ / W × d, 0.56 MJ / W × d, 0.28 MJ / W × d). All lambs were harvested at the end of the 180 d experimental period. Compared to CON fed lambs, restricting ME resulted in lesser IMF, fat deposition indexes ( < 0.05) except testicular and heart fat and greater ( < 0.05) SFA in LD, KF, and TF depots. The RES fed lambs had greater ( < 0.05) -3 PUFA, eicosatrienoic acid (C20:3n3), eicosapentaenoic acid (C20:5n3, EPA), and trans-linolelaidic acid (C18:2n6t) in LD muscle. The conjugated linoleic acids (CLA) content was greater in the SF depots of the CON fed lambs compared to the RES fed lambs. Fatty acid ratios (unsaturated fatty acid; USFA:SFA, MUFA:SFA, PUFA:SFA), and percentage USFA in RES fed lambs were lesser in muscle and adipose tissue compared to CON fed lambs ( < 0.05), except SF depots. In RES fed lambs, EFA were less ( < 0.05) in LD and KF depots and the ratios of functional fatty acids were lesser in LD and some adipose tissues ( < 0.05), including lesser n-6:n-3 in KF and SF ( < 0.05) depots, lesser USFA, SFA, MUFA, SFA in LD, KF, and TF ( < 0.05) depots, and lesser PUFA and SFA in LD and TF ( < 0.05) depots. Results from this research demonstrate that sequential energy restriction, as might be experience during seasonal forage quality and quantity changes in natural grasslands, result in lesser intramuscular fat with associated lesser quality, as well as, changes in fatty acid composition in different fat depots, which has implications for both meat quality and animal physiological functions.