Factors affecting levels of volatile 4-alkyl branched-chain fatty acids in sheep milk from 2 contrasting farming systems in New Zealand

摘要

Knowledge of factors influencing the levels of 4-alkylbranched-chain fatty acid (vBCFA), and consequentlythe “sheepy flavor” intensity of New Zealand sheep milk,is currently limited. In this study, we investigated theeffects of 2 contrasting farming systems (fully housed/mid-lactation or pasture-grazed/late lactation) on thelevels of vBCFA in sheep milk on a commercial farmin the North Island of New Zealand. Fully housed/mid-lactation ewes were housed 24 h/d and fed a totalmixed ration. Pasture-grazed/late-lactation ewes weregrazed 24 h/d and offered approximately 40% supplementsbecause of poor pasture growth resulting fromdry and hot climatic conditions. Any effects of genetics,age, lactation stage, feed composition, lambing date, orthe environment in the housing barn or outdoors wereconfounded. The results obtained in this study weredescriptive rather than definitive, because of the limitationsof the experimental design. Levels of 4-methyloctanoicacid and 4-methylnonanoic acid in milk fromfully housed/mid-lactation ewes increased during thetrial period, but remained low in milk from pasturegrazed/late-lactation ewes. Levels of 4-ethyloctanoicacid in milk from the 2 groups of ewes were comparablethroughout the trial. Increases in levels of 4-methyloctanoicacid and 4-methylnonanoic acid in sheep milkwere associated with lactation stage and the proportionof lucerne silage fed to ewes. The level of free-form4-ethyloctanoic acid was positively correlated with theproportion of soy meal in the diet and negatively correlatedwith the proportion of barley. Milk from fullyhoused/mid-lactation ewes had a higher flavor valuesthan milk from pasture-grazed/late-lactation ewes becauseof its higher total amounts of vBCFA.