Influence of lipids on the intestinal health of piglets

Historically, interest in lipids for swine nutrition has emphasized the effects of dietary fat on performance during various stages of production.

Several studies were conducted on the influence of n-3 polyunsaturated fatty acids (PUFAs) in the diet in relation to boar sperm quality, as reviewed in NRC (2012).

For nulliparous sows and sows during late gestation and lactation, attention has been paid to the influence of lipid supplementation on milk production, lipid content in milk, and piglet yield and viability (Verstegen et al. , 1998).

Producers have dedicated their efforts to improving the digestibility and energy value of lipids (Jørgensen and Fernandez, 2000). As well as manipulating the nutritional quality of pork,  with special emphasis on FA  composition, to meet human health recommendations (Wood et al., 2004).

• The impacts of dietary levels, type and rate of oil inclusion on the quality of finished pigs have also been studied (Lauridsen et al. , 2000;  Wisemann et al., 2000).

Short-chain fatty acids (SCFAs, i.e., acetate, propionate, butyrate), which can be added as feed additives, are produced through microbial fermentation of non-digestible carbohydrates and starch in the hindgut. These represent an energy source for the host (Sciascia et al. , 2016).

• It should be noted that the energy absorbed from glucose is much higher than that which is obtained from SCFAs (Bach Knudsen, 2011). However, SCFAs are a bioavailable energy source for colonocytes.

Digestion, absorption and metabolism of dietary lipids are affected by the fatty acid composition of the  diet. Especially by the degree of saturation and chain length, as well as the position of fatty acids in the TG molecule.

In general, unsaturated lipids are more digestible in pigs than saturated lipids, which can be attributed to  greater facility with which lipase can access the TG molecule(Ravindran et al., 2016).

Therefore, long-chain saturated fatty acids (LCFAs) may exert inhibitory effects and unsaturated LCFAs may increase lipase activity and influence lipid digestion as a result.

Fatty acids with a chain length of 12 carbons (C) or less will be absorbed through portal blood, while fatty acids with a chain length of 14 C or greater will be absorbed through lymph.

• Therefore, saturation of MCFA and FA with 6 to 12 C, which are naturally found in the form of MCTs in milk fat and some vegetable fat sources, such as coconut and palm kernel oils, represent immediately available energy sources.

The digestibility  of dietary lipids can be assessed by determining apparent or true digestibility by assessing the difference between lipids ingested in food and lipids excreted in faeces.

• This gives an estimate of the amount of digestible lipids coming from the diet due to the exclusion of endogenous fat losses.

Endogenous loss occurs due to excretion of:

• bile acids
• flaky cells
• structural lipids of the mucosa
• cholesterol

and may vary not only with dry matter intake but also with the source and level of dietary lipids (Kil et al. , 2010). The apparent digestibility of total tract lipids varies between 25% and 77% (Noblet and Van Milgen, 1994) and is limited to total digestibility of the actual tract rather than ileal digestibility, which ignores microbial synthesis of FAs in the gut.

Lipid inclusion in diets can improve protein digestibility as it slows down the passage rate within the gut, which contrasts with the effects of fiber (Kil et al., 2010).

Lipid contribution in piglet diets