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Metabolism of fat in sheep diets
Most fats are hydrolyzed by lipase in the sheep rumen to form free fatty acids and glycerol, and can be further fermented by microorganisms to produce volatile fatty acids. The rumen of sheep is similar to the basic function of the rumen of cattle, and its internal environment is highly reducing, so fat can also be hydrogenated in the rumen, and UFA can also be hydrogenated by microorganisms to SFA, which are mainly stearic acid
Incomplete hydrogenation produces a variety of isomers of cis-trans-monoallyl free fatty acids and isomers of PUFA such as CLA. microbial activity in the rumen results in a substantial increase in the level of fatty acids absorbed by the sheep compared to the saturated level in the diet. The rumen of lactating lambs does not have a digestive function and digests fat differently from adult sheep.
The liver is the organ with the most complex and comprehensive metabolic functions. Nutrients absorbed from the intestinal tract first enter the liver for transformation, and the liver is also an important hub for the transportation and interchanges of energy substances in the body. Most of the substances ingested by the liver are not used as their own energy sources, but as energy substances exported to extrahepatic tissues.
LCFA in the liver are mainly derived from NEFA in the blood.In the liver, LCFA can be both esterified and oxidized. The high flow of LCFA in the liver can lead to a series of metabolic changes, culminating in the activation of peroxisome proliferator-activated receptors. Activated receptors can affect the expression of specific genes involved in metabolic regulation. In general, the expression of genes encoding enzymes involved in fatty acid oxidation and ketogenesis is increased, and the expression of genes encoding enzymes involved in fatty acid synthesis is decreased. The inhibition of gene expression regulation appears to be limited to the liver and is affected only by PUFA.
The predominant energy substances in the myocardium are fatty acids. Myocardial enzymes for oxidizing ketone bodies are highly active and are important tissues for the utilization of ketone bodies. The myocardium is the most mitochondria-rich tissue and has the highest oxygen consumption of all tissues in the body. As a result, almost all of the energy material is completely oxidized when there is an adequate supply of oxygen.
Skeletal muscle weighs about 50% of the body weight and most of its energy is used for muscle fiber contraction. Fatty acids are stored as triglycerides in adipose tissue within myocytes, in myofibers or in myofiber peroxisomes and mitochondria. The biochemical pathways in cardiac and skeletal muscle are similar to those in the liver.
Acetic acid and ketone bodies utilized by muscle are linearly related to the level of acetic acid in arterial blood. Muscle uptake of NEFA is directly dependent on the level of NEFA in arterial blood. The mechanism of NEFA uptake by muscle cells is similar to that of the liver.
Lipids in sheep production
As an important and indispensable nutrient in sheep diets, the theoretical value and production significance of lipids have been continuously recognized and explored. However, the research on the application of lipids in sheep has just begun in China, and this part will focus on the application of lipids in the nutrition and diets of lambs, fattening sheep and breeding ewes, so as to provide a technical basis for the formulation of diets in production.
Lipid nutrition in lambs
Lamb lipid nutrition consists of two aspects, namely milk replacer and starter. More research has been done nationally and internationally on milk replacer and starter alone. In lambs with intrauterine growth restriction, the fat-promoting effect of feeding a high-fat milk replacer compared to a low-fat milk replacer is more pronounced in the viscera than in the carcass.
The basic components of early weaned lamb diets are milk replacer and starter, which can be studied as a whole. The study showed (see the inside of this book for details) that lambs in the high-fat group tended to have significantly higher pre-slaughter live weights than the normal-fat group, and that eye muscle area and carcass weights were significantly higher than those of the normal-fat group.
Lipid nutrition for growing and fattening sheep
1.The effect of fat addition on growing and fattening sheep
Adding solid fat meal or liquid oil to the diet of growing and fattening sheep can improve performance, and have an effect on meat quality, especially meat color and fatty acids in the meat. The amount of fat to be added is a key consideration and when added above 3% will affect dry matter intake and hence weight gain.
Research data (see the inside cover of this book Animal Lipid Science for details) show that as the fat meal addition to fattening sheep diets increases, there is a tendency for muscle fat content to increase, and a tendency for fattening sheep to have a higher slaughter rate.
2, the impact of different sources of fat on the growth of fattening sheep
Dietary fat source is also an important factor affecting the growth of fattening sheep. Based on the same amount of fat added, solid fat powder on the growth of fattening sheep fattening effect is better than the liquid fat, and in the production of practical and easy to operate and apply.
The study showed (see the inside of this book Animal Lipid Science for details) that 10% of rapeseed, sunflower seed and caraway seed were added to the diet of crossbred rams. The results found that the addition had no significant effect on the growth performance of sheep, but caraway seed can significantly increase the ω-3 PUFA content in subcutaneous adipose tissue, reduce the ω-6/ω-3 PUFA ratio, and improve the fatty acid composition of adipose tissue.
Lipid nutrition in breeding ewes
Energy is one of the most important factors affecting the reproductive performance of ewes, and breeding ewes, especially periparturient ewes, require higher levels of energy to meet their own and lactation needs.
Research has found (see the inside of this Animal Lipid Science book for details), flaxseed and its oil have nutritional properties that can significantly improve the omega-3 PUFA in lactating lambs, with cooked flaxseed having the best effect. This shows that lipids have great potential for use in breeding ewes and provides some direction for researchers.
