Seasonal and Sex Patterns in Fat Composition of Growing Lambs

Twelve Columbia ram-ewe twin lambs from two sires were obtained to study the relationship between growth and the composition of subcutaneous fat. The lambs were fat biopsied at 9 weeks of age and rebiopsied every 9 weeks until they were approximately 18 months of age. Environmental effects exerted a greater influence on fat composition than the growth effect. The maximum iodine numbers (IN) occurred in August 1962; there was a minimum through the winter and a secondary maximum in August 1963. Melting points (MP) were inversely related to IN to about December 1962, but almost paralleled IN thereafter. There was no sire difference, but a striking sex difference was observed. After the lambs became 10 to 12 months old, the sex difference began to appear. Female fat had both higher IN and MP than male fat. Female fat possessed larger amounts of all major fatty acids containing 16 carbons or more, regardless of degree of unsaturation, and had lower percents of all acids with less than 16 carbons. The female fat was also lower than male fat in all minor acids.