Selecting diet ingredients

Feed is the largest cost item in any intensive livestock enterprise. Selecting the right combination of feed ingredients to provide a diet giving optimum animal production at least cost is a complex problem. When working out diets, there are over 40 individual nutrients to consider, not only their actual concentrations, but also the ratios with other nutrients.

The pig is enormously versatile in the range of feeds which it can use. This should be exploited by considering the supply and price of a wide variety of feeds.

Computer feed formulation programs are used to design diets that meet the pigs' nutritional needs at optimum cost. Nevertheless, you still need to have an understanding of pig nutrient requirements, the value of individual ingredients and ingredient tolerance levels when calculating diets, otherwise problems can quickly develop.

Composition and nutritional value of feed ingredients

There are several approaches that can help overcome the problem of variability in the composition and feeding value of ingredients. Generally, the best method is chemical analysis. Private and some government laboratories offer these services. In most cases, relatively simple measurements of e.g. protein, are performed and from these values, the levels of the more important amino acids are estimated.

Most recently, near-infrared (NIR) spectroscopy has been introduced to allow quick determination of digestible energy (DE).

Lysine is a critical nutrient but its measurement is difficult. It is known, however, that the lysine level is related to its protein level and can be predicted.

Chemical assays are not yet available to quickly measure the biological availability of nutrients and so average values must be used to estimate the amount of available nutrients in various feeds.

Ingredient constraints

The extent to which an ingredient may be used in a particular diet is subjective. Constraints on ingredient use may be associated with their specific influence on palatability, digestibility, toxicology, palatability, availability, compatibility with other ingredients, variability in quality or simply disappointment with previous involvements. Blood meal for example, is often constrained to levels of less than 4% in pig diets because of its unpalatability.

A guide to the inclusion levels of certain feed ingredients is given in Table 1.

Table 1. A guide to inclusion levels of some feed ingredients
Feed ingredient Inclusion levels and characteristics affecting inclusion levels
Wheat No limit, can be used as the only cereal grain. High in energy with average protein. The most common cereal grain used in Australia.
Barley No limit although generally not used in diets for young pigs due to low energy and high fibre. Lower energy and higher fibre than wheat.
Triticale No limit. Modern triticale varieties represent excellent value as a cereal base in pig diets.
Sorghum No specified limit, can be used as sole grain although mixture with other grains is often preferred. Some mills report difficulty pelleting when sorghum exceeds 50%.
Maize Limit to 30% of grain component. High energy grain. Unsaturated fat and pigments affect fat quality.
Soybean meal No limit. The best quality vegetable protein source used around the world. High in protein and energy, excellent source of amino acids. Antinutritional factors in-activated by heat treatment.
Sunflower meal No limit although high-fibre/low lysine content tends to be self-restricting to about 10%.
Canola meal Limit to 15% in diets for growing and finishing pigs and sows. Cost effective protein and energy source.
Cottonseed meal Limit to 10% maximum for good quality material. Contains gossypol .
Meat and bone meal Limit to 10% depending on calcium content and protein quality. High in protein, calcium and phosphorus.
Blood meal Limit to 3% due to palatability and isoleucine imbalance. Very high in protein, quality depends on processing method as excess heat reduces digestibility and thus the protein available to the pig. Made by drying blood from animal processing.
Fish meal Limit to 5% for growing and finishing pigs if a withholding period of five to seven weeks is observed before slaughter. High levels of fishmeal affects the quality of stored pork or processed pork. Highly digestible protein source with high level of amino acids. Made from fish waste.
Skim milk powder Inclusion level is determined by cost. Highly digestible energy and amino acid source. Ideal for young pigs.
Lupins - sweet Limit to 20% for growing pigs and sows and 25-30% for finishing pigs. A good quality protein source.
Field peas Use to 20% of diet. Relatively high in energy and good source of the amino acid lysine.
Lucerne meal Cost and nutritive value will limit amount to less than 10%. Not recommended for weaners and growers as high fibre and low energy content.
Lysine HCI No limit except awareness that high levels of synthetic lysine may not be used efficiently when pigs are fed restrictively.
DL methionine No limit, however, if used at high levels most likely only serves as a filler.
Limestone Limit to 2%. If more, it is most likely only serving as an energy diluent.
Dicalphos No limit other than Ca and P limits in diet. Common source of calcium and phosphorus for pig diets.
Fats and oils A concentrated energy source, with three times the energy value of cereals.
Salt Limit to 0.3%. If used beyond this limit, it is most likely serving only as energy diluent.
Vit-min premix Use level recommended by supplier.

Nutrient constraints

The requirement for some nutrients is dependent on the supply of others. This is particularly the case with amino acids and energy supply. For example, lysine needs are best expressed relative to the DE content. Similarly, the levels of other essential amino acids are considered in relation to lysine and to one another so that an optimum balance of the essential amino acids can be maintained.

Calculating diets

Working out a diet with a calculator involves a lot of trial and error. Fortunately, there are now many good computer programs which simplify least-cost diet calculations.

To work out a diet, the feed formulation program matches the combination of feeds which meets the nutrient specifications at least cost.

There are many benefits to using a computer to formulate least-cost diets. The diets can be calculated quickly and easily. This is particularly valuable where there are a large number of feed ingredients available. The program is better able to asses all nutrients when judging the value of feed ingredients and so the final cost of the feed will be lower generally than by manual formulation.

Feed calculation programs also provide information about the price sensitivity of ingredients and nutrients used in working out a diet. The price sensitivity analysis gives an indication of which ingredient or nutrient specifications cost money to meet and shows the potential saving if these were to be relaxed or alternatively the cost of tightening them further.

Information is also provided on the price an excluded ingredient would have to be before it would be included in the diet. This information is very important to have when making buying decisions.

Feed calculation programs should be used by those familiar with nutrition as unsatisfactory calculations are possible. One problem with some least-cost programs is that, in order to reach a solution, a "filler" may be included. In some cases, this can lead to unnecessarily high levels of limestone or free amino acids being included in the diet.

Swill feeding

Swill feeding is illegal in Australia because of the serious risk of introducing a devastating exotic diseases such as foot-and-mouth disease. Swill feeding includes using food (or food scraps) containing or possibly having had contact with animal matter (e.g. from restaurants, hospitals and domestic households) as feed for pigs, poultry or ruminants. Even a tiny amount of leftover meat or dairy product could contain a dangerous virus. Once a disease agent is introduced in this way, it could rapidly spread to susceptible local livestock. Countries importing Australian meat and livestock products would immediately ban further imports.

Swill feeding has been implicated in overseas outbreaks of disease including the devastating European foot-and-mouth outbreak of 2001. Many viruses are highly resistant to chilling, freezing and curing. Experience has shown that even boiling swill may not destroy all disease organisms.

If you suspect stock are being fed swill contact your local veterinarian, stock inspector or contact the toll free Disease Watch Hotline on 1800 675 888.