**2. The fat and the feeding of ruminants**

Fats are important in ruminant nutrition because of its high energy content. In this regard, the complete combustion of one gram of fat produces around 9.45 Kcal of net energy, while a typical carbohydrate generates around 4.4 Kcal. So, lipids, in general, provide 2.25 times more energy than traditional sources. Also, it is important to consider the intake of fatsoluble vitamins and essential fatty acids (Mayes, 1988).

Fats are part of a group of organic molecules called lipids, which accomplish many functions in the animal body: structural functions (part of cell membranes), hormonal functions (some hormones are of lipidic nature: estradiol, progesterone, testosterone, among others) and immunological functions. Some vitamins (A, D, E and K) are of lipid nature.

Fatty acids (FA) are fundamental molecules in the structure of a lipid, with hydrogenated carbon chains which contain an acidic or carboxyl group in one end and a methyl group in the other end (Jenkins, 2004). The length of the chains of the FA goes from 2 to 24 or more carbon atoms. It is common to name them according to the number of atoms and the number of double bonds, which serves to classify them as saturated or unsaturated fatty acids.

Animal tissues do not synthesized linoleic and linolenic acids (Omega 6 and Omega 3, respectively); they should therefore be incorporated within the diet (Jenkins, 2004). Both FA are known as essential in animal nutrition because they are required for many metabolic processes. Omega fatty acids belong to one of the three Omega families (ω): ω-6, ω-3 and ω-9 (Table 1). Each family has a parental fatty acid, which can be converted into other biologically active acids within the same ω family (Jenkins, 2004).

#### Effect of Rumen-Inert Fat Enriched with High Levels


(Adapted from Jenkins, 2004.)

88 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

health and reproductive performance.

mobilization of its body reserves, particularly energy, generating a state known as the Negative Energy Balance (NEB), which can cause deleterious effects on milk production,

A practical way to control this NEB is through the increase of the food consumption by animals and/or the increase of the energy density of the diet. Thus, various food technologies have been developed for this purpose: energy banks, the use of strategic crops such as sugar cane, liquid diets with high levels of energy, multi-nutritional blocks and energy supplementation with rumen-inert fat. Increasing the fat content of the ration is a way to decrease the NEB, because of fats have double the energy than sugars. However,

If rumen-inert fat is used to feed ruminants, some undesirable effects of active fats at

On the other hand, if the fat is rich in polyunsaturated faty acids (PUFA; linoleic, linolenic, docosahexanoic [DHA], or eicosapentaenoic acid [EPA]), the rumen-inert fat enriched not only supplies energy, but allows the incorporation of the beneficial effects that these fatty acids have on the animal body and in the productive and reproductive response, therefore having a nutraceutical effect, i.e., producing meat and milk with high levels of these fatty

Fats are important in ruminant nutrition because of its high energy content. In this regard, the complete combustion of one gram of fat produces around 9.45 Kcal of net energy, while a typical carbohydrate generates around 4.4 Kcal. So, lipids, in general, provide 2.25 times more energy than traditional sources. Also, it is important to consider the intake of fat-

Fats are part of a group of organic molecules called lipids, which accomplish many functions in the animal body: structural functions (part of cell membranes), hormonal functions (some hormones are of lipidic nature: estradiol, progesterone, testosterone, among others) and immunological functions. Some vitamins (A, D, E and K) are of lipid nature.

Fatty acids (FA) are fundamental molecules in the structure of a lipid, with hydrogenated carbon chains which contain an acidic or carboxyl group in one end and a methyl group in the other end (Jenkins, 2004). The length of the chains of the FA goes from 2 to 24 or more carbon atoms. It is common to name them according to the number of atoms and the number of

Animal tissues do not synthesized linoleic and linolenic acids (Omega 6 and Omega 3, respectively); they should therefore be incorporated within the diet (Jenkins, 2004). Both FA are known as essential in animal nutrition because they are required for many metabolic processes. Omega fatty acids belong to one of the three Omega families (ω): ω-6, ω-3 and ω-9 (Table 1). Each family has a parental fatty acid, which can be converted into other

double bonds, which serves to classify them as saturated or unsaturated fatty acids.

biologically active acids within the same ω family (Jenkins, 2004).

there are limitations on their use, particularly if the fat is not a rumen-inert fat.

ruminal level, would be avoided, and higher amount of fat could be used.

acids, which may have a beneficial effect on human health.

soluble vitamins and essential fatty acids (Mayes, 1988).

**2. The fat and the feeding of ruminants** 

**Table 1.** Parental fatty acids and its main metabolites within each Omega family.

The sources of lipids in ruminant feeding systems are forages, cereals, oleaginous seeds, byproducts of the industry, such as the tallow, yellow fats, mixtures of vegetable and animal fats, hydrogenated fat, oil palm and calcium soaps. Tropical forages are relatively low in their content of lipids; the concentration of fatty acids in forages rarely exceeds 1.5% of the dry matter of the diet.

Both oils and fats, belong to the group of lipids, but differ in that the first are liquids at ambient temperature, while fats are solid. Another difference is that fats are usually from animal origin (tallow) while most of the oils are from vegetables (excluding fish oil). Fats have high levels of saturated fatty acids, while the oils contain more PUFA.

Fats and oils have limitations to be incorporated in the feeding of ruminants. It has been reported that levels >5% of dry matter produced a decrease in food consumption of the animal. In this regards, Jenkins (1993) and Palmquist (1996) mention some of the possible ways of how fats can affect the microorganism action in the rumen:


The above generates a reduction in the ruminal microbial growth, which translates into a change in the production of volatile fatty acids in the rumen, with consequences to the acetic:propionic ratio and a decrease in the amount of acetic acid available for the production of fat in the mammary gland. In the particular case of unsaturated fatty acids, once they are free in the rumen, they suffer a massive hydrogenation process known as biohydrogenation (Jenkins, 1993), which consists in the addition of hydrogen atoms on the double bonds, thus transforming the unsaturated fatty acids into saturated fatty acids. Thus, PUFA as oleic (C18:1), linoleic (C18, ω-6) and linolenic acid (C18, ω-3), are transformed into

of Poly-Unsaturated Fatty Acids on the Productive and Reproductive Response in Ruminants 89

the stearic FA (C18:0). Eicosapentaenoic acid (C20:5, ω-3) and docosahexaenoic acid (C22:6, ω-3) undergo very little hydrogenation in the rumen (Mattos *et al.,* 2000). These two fatty acids are commonly found in oil and fishmeal.

When we use a source of fat, not protected or not a rumen-inert fat, with high levels of PUFA, most is lost due to the biohydrogenation, which is particularly important for PUFA ω-6 and ω-3, which are considered as essential in the diet and which have an important role on reproductive, immunological, metabolic and hormonal functions. Therefore, this type of susceptible fat to interact in the rumen, are known as active fat and its use is limited in ruminants.

New technologies have generated chemically modified fats that allow its use at higher levels and with a lower level ruminal interaction, which reduces the deleterious effects of lipids on the ruminal bacteria activity. This kind of fats is known as inert fat, by-pass fat, or protected fat. In this regard, Jenkins (2004) defines the inert greases as those fats that have been specifically designed to have very little, or no negative effect on the digestibility of foods in ruminants. Rumen-inert fats are often carboxylate calcium salts (calcium soaps), saturated fatty acids or hydrogenated fats.

The use of calcium soaps allows the incorporation of a higher level of unsaturated fatty acids in the diet of ruminants. This is particularly important in the case of essential fatty acids (ω-6 and ω-3) which not only provide an energy effect *per se*, but may have specific effects on the metabolism of tissues and organs (Staples *et al.,* 1998). The melting point of rumen-inert fats, is usually above 100°C and solubility occurs at pH levels below 5.5. These values of temperature and pH are present in the rumen, which allows the fat to by-pass the rumen. However, at the level of the abomasum and first portion of the duodenum pH levels are much lower, allowings the dissociation of the carboxylate salt, leaving the fatty acids available for absorption. Therefore, it can be concluded that supplementation of rumen-inert fats to ruminants generates an increase in the availability of unsaturated fatty acids at the intestinal level, and therefore may increase the absorption and their incorporation into tissues (Table 2).


(Adapted from Staples *et al*., 1998)

**Table 2.** Estimated amount of linoleic acid that reaches the small intestine in cows, depending on the source of fat.
