Farm animal nutrition: Fat

Fat for farm animals is important only when they are young, and receive most of their energy from the fat in their mother's milk. As adults, only fur animals (such as foxes and minks) are dependant on fats in their diet. For ruminants, poultry and pigs, carbohydrates are more important. Fats have twice as much energy as carbohydrates, approximately 39 MJ/kg. 

Fats int he body are used in electron transfer, reaction medium, cell membranes and as stored energy. Plants have fats in their leaves and cell membranes, where they are stored as oils. Fats are used as fatty acids, of which three are necessary: linolic acid, linoleic acid and arachidonic acid (animals can build this from linoleic acid). Linoleic acid is synthetized further into EPA (Eicosapentaenoic acid) and DHA (Docosahexaenoic acid). These three acids are the source for hormone-like eikosanoids. Eikosanoids participate to blood pressure regulation, muscle cell contractions, immunology, nervous system regulation and body temperature regulation.

Fatty acids have methyl group in the tail end, and a carboxylic group in the alpha end. They always have an even number of carbons. If the fat has double bonds between the carbons, it is an unsaturated fatty acid.

Unsaturated fatty acid

 Fats are builts from fatty acids, much like carbohydrates are built from saccharides. Plant fat has usually more unsaturated fatty acids than animal fat. Fats in general belong to lipids, which include also phospholipids, waces, terpens and steroids.

Volatile fatty acids
Ruminants again have a specific way to gain fats, which are rare in their diet. The bacteria in the rumen create volatile fatty acids (VFAs) with the energy they receive from reducing carbohydrates. VFAs are fatty acids with a carbon chain of six carbons or fewer. The most important three volatile fatty acids for ruminants are acetic acid, propanoic acid and butyric acid. Acetic acid is used to synthetize 50 % of the fats in milk.

Producing VFA creates methane gas as a side product, which the animal must remove from its rumen by belching.

Fats in the metabolism
Fats are broken down into triglyserides (glyserol + three fatty acids connected to it with esther bonds) by bile acid in the small intestine:

Picture from lecture material, original source unknown

Bile breaks the structure of the fats, and creates chylomicrons, which are then transformed to adipose tissues in the body. In the adipose tissue free fatty acids are attached to glycerols, formed from glucose in the same tissue. This creates a triglyseride, which then can be stored in the adipose tissue. Thus, fats are ingested as triglyserides, then broken down to chylomicrons for transfer, and finally stored again as triglyserides

Fatty acids can also be used in the liver, where triglyserides can be built and transformed further into lipoproteins. Lipoproteins may be transferred to the adipose tissue, and used as a material for triglyseride synthesis.

Deficiency symptoms
Deficiency of the three necessary fatty acids may lead to

• skin problems (the most common symptom)
• excessive drinking
• increased risk of bacterial infection
• kidney damange, bloody urine
• sterility
• eye problems, blindness
• heart muscle failure
• decrease of ATP synthesis in the liver and heart