Protein and Amino Acid Requirements of the Young Piglet

When formulating pig rations a nutritionist will generally consider protein simply as the vehicle to deliver either essential amino acids or nitrogen from which non-essential amino acids can be synthesized. Minimum and maximum constraints for protein and the limiting amino acids, lysine, methionine (normally considered with cysteine), threonine and tryptophan are usually defined, together with some measure of availability, such as apparent ileal or true ileal digestibility.

The means of providing this protein will to a large extent be given little consideration apart from limiting the maximum inclusion of certain raw materials that contain performance limiting anti-nutritional factors such as rapeseed meal, peas, beans and soya. The protein requirement of the weaner pig has to be considered somewhat differently. Materials used in these feeds not only supply nitrogen and essential amino acids but other proteins that have a secondary role not related to the supply of nutrients. Immunoglobulins, present in both milk protein and porcine plasma protein would be included in this category.

The inclusion of these raw materials into feed is more to do with their functional properties than their direct nutritional value. In the first part of this paper the amino balance necessary to optimise weaner pig performance will be considered. Published values on the amino acid requirements of the young pig vary, but in commercial practice feed manufacturers are generally producing weaner diets with a lysine to DE ratio of MJ DE/1 g lysine, with methionine (considered with cysteine), threonine, and tryptophan balanced to pre-determined ratios.

Typically weaner feeds have included fish meal and milk powders as the main source of dietary protein. Milk protein is available in several forms, but traditionally has been restricted to skimmed milk powder and dried whey powder. Skimmed milk powder contains in excess of 2.5 times the level of protein as whey powder (35% and 13%) and the protein is mainly in the form of casein. Whey powder mainly consists of soluble proteins of variable quality, largely as a result of the processing techniques employed in drying.

The cost of inclusion of skimmed milk powder has led many researchers to look for other cost-effective materials with which to either partially or totally replace its inclusion in starter feeds. In the second part of this paper the use of various other proteins is reviewed including soya proteins, porcine plasma, egg proteins and whey protein concentrates. The use of soya proteins in weaner feeds, in the form of toasted full fat beans or extracted concentrated soya isolates in which anti-nutritional factors have either been reduced or eliminated has been practiced for several years. In general the response to these materials has not been as consistent compared to the use of milk products.

Other vegetable protein sources including wheat gluten and potato protein (85% crude protein) have been included successfully into weaner feeds in place of traditional protein sources without compromising performance. In the late 1980’s and early 1990’s a new raw material, spray dried porcine plasma (SDPP) was introduced to the animal feed market. Its use in the UK has been limited in the wake of BSE, by the reluctance of most of the UK feed industry to practice closed loop feeding. The rest of the world has however embraced its use at levels between 3 and 5% in weaner feeds. SDPP is consistently reported to increase feed intake and daily gain when included in place of both soya bean meal and skimmed milk powder. The exact mode of action of SDPP is not clear, but several authors have intimated that the high levels of antibodies may have a role.

The UK feed industry has sought other alternatives to porcine plasma. Some researchers in the US have found that 50% of the SDPP in weaner feed diets can be replaced by those of high quality whole egg proteins. The adoption of ultra filtration techniques within the human food processing industry has led to high protein whey concentrates becoming available to the animal feed industry. These products are rich in immunoglobulins compared with both skim milk powder and traditional 13% protein dried whey powder.

The conclusion of these materials (whey protein concentrate 78% crude protein) has been shown to confer similar performance to piglets fed porcine plasma. Commercially, various grades of whey protein concentrate are available with protein levels ranging from 35% upwards. The paper will review materials available to the commercial nutritionist, their inclusion rates and costs in order to achieve formulations of commercially viable diets.

Date published: 2003-01-01

Dr Mark Cole

SCA Nutrition Ltd