瘤胃十八碳不饱和脂肪酸氢化的研究进展

瘤胃微生物对不饱和脂肪酸的生物氢化作用,限制了其转化效率,使乳脂肪酸组成的调控难以达到理想的效果。不饱和脂肪酸对微生物生长的抑制是氢化的主要原因;氢化的程度主要由瘤胃内环境决定,如瘤胃pH、金属离子浓度等,脂肪酸来源、水平、脂肪酸之间的相互作用以及其他营养因素等均会对脂肪酸的氢化造成影响。本文主要综述了反刍动物饲料中不饱和脂肪酸氢化的过程、氢化相关瘤胃微生物以及影响氢化程度的因素,同时探讨了营养途径调控氢化的方法,为进一步调控乳脂肪酸组成提供依据。     

Effects of Turnout to Pasture and Dietary Fat Supplementation on Milk Fat Composition and Conjugated Linoleic Acid in Dairy Cows

Turnout to pasture involves considerable changes in the feed intake and metabolism of dairy cows. The aim of this study was to investigate how these changes affect milk production and milk fat composition, in cows selected for high (HFI) or low (LFI) milk fat content producing the same yield of 4% fat-corrected milk. Furthermore, two different concentrates, with high or low inclusion of soya oil, were studied. The experiment was conducted with 44 multiparous mid-lactating cows over a 4 week period. Samples of milk and blood were obtained before turnout to pasture, during transition to pasture and when cows were adapted to pasture. Milk yield decreased with 3.6 kg energy-corrected milk (ECM) on average during the first 5 days after turnout to pasture. This decrease, together with a drop in plasma insulin and increased plasma non-esterified fatty acids (NEFA), indicated nutritional insufficiency at turnout to pasture. Milk fat composition changed towards more long-chain fatty acids (LCFA) and fewer de novo synthesized fatty acids. This was probably caused by an increased supply of LCFA of feed and body origin to the udder. LFI cows showed higher levels of conjugated linoleic acid at pasture than HFI cows.     

奶牛乳脂率降低的生物学机制

乳脂是最易受日粮影响的一种乳成分,而乳脂含量可以直接影响到乳制品的等级及其加工工艺。近年,有大量的研究证明乳脂率下降的原因是由于日粮因素改变了瘤胃pH值等发酵参数,使得合成乳脂的前体物供应不足或产生了抑制乳脂合成的中间产物所造成的。本文即是对奶牛乳脂率降低的的两种主要生物机制进行了讨论。     

The scope for manipulating the polyunsaturated fatty acid content of beef: a review

Since 1950, links between intake of saturated fatty acids and heart disease have led to recommendations to limit consumption of saturated fatty acid-rich foods, including beef. Over this time, changes in food consumption patterns in several countries including Canada and the USA have not led to improvements in health. Instead, the incidence of obesity, type II diabetes and associated diseases have reached epidemic proportions owing in part to replacement of dietary fat with refined carbohydrates. Despite the content of saturated fatty acids in beef, it is also rich in heart healthy cis-monounsaturated fatty acids, and can be an important source of long-chain omega-3 (n-3) fatty acids in populations where little or no oily fish is consumed. Beef also contains polyunsaturated fatty acid biohydrogenation products, including vaccenic and rumenic acids, which have been shown to have anticarcinogenic and hypolipidemic properties in cell culture and animal models. Beef can be enriched with these beneficial fatty acids through manipulation of beef cattle diets, which is now more important than ever because of increasing public understanding of the relationships between diet and health. The present review examines recommendations for beef in human diets, the need to recognize the complex nature of beef fat, how cattle diets and management can alter the fatty acid composition of beef, and to what extent content claims are currently possible for beef fatty acids.