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Palatability improves young piglets’ feed intake

Feed intake is determined by the piglet’s health status and the diet’s palatability.Optimising feed intake of young piglets is a real challenge and requires a lot of knowledge and expertise of dietary palatability. The taste of feed is not only determined by the nature of its ingredients, but also by its composition. All this has to be taken into account when formulating prestarter diets that improve feed intake and the zootechnical performance of young piglets.

By Dr Jan Vande Ginste, nutritionist-product developer pigs, Vitamex, Belgium

A low feed intake in (pre)weaning piglets will unavoidably lead to retarded growth performance associated with economic losses throughout the whole further rearing period. As generally known, a longer time to first feed ingestion will significantly increase the negative impact of post weaning anorexia on the development and maintenance of a healthy gut and thus on piglet performance. Therefore, optimisation of feed intake in the earliest stage of growth is one of the most important challenges for piglet nutritionists.

Besides by the piglet’s health status, feed intake will also be determined by the palatability of the diet. The pig’s sense of taste differs to a great extent from the one of humans due to a higher number of taste buds. Since the number of taste buds is positively correlated with the ability to taste, it can be concluded that the pig’s sense of taste is superior to the one of humans. It is therefore of considerable importance that nutritionists have an extremely accurate knowledge of the different dietary factors that can affect the palatability of (pre)starter diets for young piglets.

An accurate selection of feed ingredients with a high preference at the most preferred inclusion rate is one of the nutritional strategies to improve the palatability of (pre)starter diets. Freechoice preference studies have been carried out over the years to assess the palatability of cereals in piglet diets. From these studies it was not only concluded that piglets have a pronounced preference for certain cereals, but also the processing of the cereals have a considerable influence on their palatability. Processing techniques were shown to significantly improve the palatability and thus preference of certain cereals.

Protein sources
Protein rich materials can contain antinutritional compounds (e.g. tannins, glucosinolates, glycoalkaloids, lectins) which, depending on their content, may be responsible for a substantial decrease in palatability. Therefore, piglet nutritionists must have outstanding knowledge and experience to select only those protein sources with sufficiently reduced levels of antinutritional compounds. For instance, toasting or extrusion will substantially reduce the antinutritional factors which are present in soybeans (i.e. trypsin inhibitors, lectins, antigens), but heat treatments will affect rather the nutrient digestibility than palatability.

Relative ranking of different protein sources based on feed intake of weaning piglets (Vitamex data, expressed relative to feed intake with micronised soybean meal).A more significant increase in palatability can be expected after a further removal or inactivation of the residual antinutritional factors through fermentation or solvent extraction processes. The resulting products are therefore known to be more suitable for application in young piglet diets (see Table 1). Depending on the level of bitter tasting glycoalkaloid compounds, potato protein may have a very low palatability. However, processing techniques can be applied to reduce these bitter tasting compounds. As has been shown in Vitamex trials potato protein sources with a low residual level of total glycoalkaloids will be preferred by young piglets to increase feed intake.

Furthermore, potato protein has an appropriate amino acid profile with an excellent digestibility.

It is also known from literature that highly preferred protein sources like fishmeal or spray-dried porcine plasma at adequate doses encourage feed intake around weaning. Other vegetable protein sources, including wheat gluten meal and rice protein are rather suitable protein sources for application in young piglet diet formulations.

Feed flavours
Feed flavours are preparations which provide (pre)starter diets with a particular odour and taste. The odorous part of the feed flavour can be categorised in different families. Some feed flavours have excellent masking properties for sharp-smelling off-odours, where smoother feed flavours are used to mask long lasting background offodours or to mimic the odour of milk and related products. The tasty part of the feed flavour can be sweet, sour, salty, bitter or umami but in many cases combinations are used. Young piglets mainly prefer sweetness or sweet/sour tastes. Recent studies also indicate some preference for umami flavours. The total flavour impression can only be obtained by sensorial experience of both odour and taste at the same time. Furthermore flavours can be strongly altered by the properties of the feed (matrix effects). As a result the final impression of the flavour of a feed, can be modified in a virtually unlimited way.

Feed flavours - multiple possible purposes.Feed flavours can be applied for multiple purposes (Table 2). The strictly commercial and technical advantages of these flavours can be combined with truly zootechnical effects. The search for these zootechnical effects requires both knowledge of flavour science as well as nutritional science in conjunction with practical experience with the piglet’s behaviour. Therefore only a real multidisciplinary approach involving nutritionists, veterinarians, flavour scientists and people experienced with elevating young piglets, can lead to a higher level of success.

Organic acids
Organic acids are widely used in (pre)starter diets for their antibacterial and/or pH reducing activity in the stomach in a way that the gastrointestinal health status of the piglet can be ensured or increased. However, high dietary levels of certain organic acids can substantially reduce diet palatability and thus negatively affect piglets feed intake. Therefore, over the years a series of trials were conducted by the Belgian company to determine what type and what dietary levels of organic acids can be used in piglet diets to optimise intestinal health without reducing their feed intake. It was observed in these trials that different organic acids, at commonly used dietary levels, obviously decrease feed intake. In some cases, this effect was even more pronounced with the calcium salts of the organic acids. For this reason, an outstanding knowledge and experience regarding the application of organic acids in (pre)starter diets is required.

Nutritionists must be aware of the fact that a selection of organic acids can be applied in piglet diets for their antibacterial and/or pH reducing activity, but only at dietary levels that do not impair feed intake of young piglets. It is advised to use in piglet diets a synergistic combination of these organic acids with medium chain fatty acids (like, e.g. Aromabiotic, by Vitamex). Moreover, medium chain fatty acids are much more effective at a lower inclusion rate.

Nutritional composition
For nutritionists, it is not only a matter of choosing highly preferred raw materials and additives; they must also have the competence to estimate the effect of nutritional composition on feed intake. Inadequate dietary levels or imbalances of amino acids or minerals can also have a detrimental effect on feed intake. It has been clearly demonstrated in different piglet trials that optimum dietary levels of the amino acid tryptophan enhance feed intake in young piglets. The possible implication of dietary tryptophan in appetite regulation and feed intake can be explained in different ways, such as its regulating role in the production of the appetite stimulating hormones serotonin and ghrelin.

Because Large Neutral Amino Acids (phenylalanine, tyrosine, isoleucine, valine and leucine) and tryptophan share the same transport route through the blood brain barrier (i.e. competition between LNAA and tryptophan for uptake in the brains), the production of the appetite stimulating hormone serotonin in the brain does not only depend on dietary tryptophan levels, but also on the dietary balance between LNAA and tryptophan.

More recently, piglet performance trials have also shown a possible stimulating effect of adequate dietary valine levels on feed intake of newly weaned piglets. It is clear from all mentioned piglet trials that a correct dietary balance between different amino acids is absolutely necessary to ensure an optimum feed intake in young piglets.

Besides amino acids, also a correct balance and level of minerals must be applied in piglet diet formulations. High dietary levels of for instance limestone, phosphates or sulphates may have a detrimental effect on diet palatability and may thus reduce feed intake.

Hygienic and physical aspects
Also the hygienic status of the feed is considerably important. A possible contamination with bacteria, mycotoxins and/or unpalatable metabolites resulting from the degradation of nutrients during storage (i.e. rancidity) will certainly reduce feed intake in young piglets. Finally, the physical form of the diet (i.e. pellet, crumble, mash or liquid feeding) as well as the supply, quality and composition of the drinking water will have an important influence on the feed intake of young piglets.