Feeding pigs a balanced diet is an essential part of the pig profit equation. Since feed accounts for 55-75% of total costs, feeding and nutrition can make a huge difference to piggery profits.
Before deciding on how to feed pigs (e.g. types of diets, specifications and amounts) you need to understand basic nutritional terms and concepts. Armed with these, you can make better decisions about your pigs’ feed requirements.
Pigs need energy to live, grow and reproduce and they require certain amounts of energy at different stages of life. What is digestible energy? Digestible energy (DE) is part of the total energy in the feed. Pigs get all their energy from feed, but not all of it is digested.
Some energy will pass through and be lost in faeces, while some will be lost as gas. So DE is the energy in the diet that is digested and available to the pig.
Some feed ingredients are more digestible than others. Growing pigs do not digest plant fibre well so feeds with high fibre will be less digestible than ingredients with low fibre. For example, wheat contains less fibre than barley, so its average DE per kg (14.1 MJ) is higher than barley (12.9 MJ DE/kg). By comparison, the digestible energy in fats and oils is very high and pigs waste very little derived from them. The DE value of tallow, for example, is about 34 MJ DE/kg (two to three times the amount in cereal grains).
Feed energy is used for maintenance and for growth and reproduction. Pigs need energy just to keep their bodily functions working. The amount of energy needed will vary according to the climate, the environment, the age and weight of the pigs, and whether they are breeding or not. For example, during cold weather, pigs use more energy keeping themselves warm. This means they must eat more if they are to keep growing as there is less energy left over for growth compared with springtime because they are using a larger portion of their feed for maintenance.
Protein is different to energy. Pigs need protein to grow and most importantly, to develop muscle tissue (muscles contain chiefly protein and water). Protein is made up of amino acids, the ‘building blocks’ of protein, linked together in chains. Amino acids contain nitrogen and this is what distinguishes them from other food groups such as fat and carbohydrates. The amino acids and their balance with each other in protein is very important in pig nutrition, more important than just the level of protein.
Amino acids can be divided into two groups: essential and non-essential. Non-essential amino acids are manufactured by pigs, while essential amino acids must be supplied in feed. Eventually the amino acids are combined to make protein in lean muscle, with each type of protein having a strict and specific arrangement of amino acids.
Each amino acid is equally important in the synthesis of protein but those that are least plentiful in pig foods assume greater importance for diet formulation. In cereal-based diets, the most common diets fed to pigs, the essential amino acids lysine, methionine, tryptophan, threonine and isoleucine are the most deficient with lysine usually in the shortest supply.
Pigs have a high requirement for lysine. Without enough lysine in the diet, the other amino acids cannot combine correctly to form muscle protein. For this reason, lysine is usually called the first-limiting amino acid. This means that the amount of protein (for example, muscle) that animals can make is limited by the amount of lysine in their diet.
Some proteins in feed ingredients contain more lysine than others. Therefore, because proteins have differing amounts of amino acids (depending on what food the protein came from) it is important to compare diets on the basis of amino acid content rather than crude protein (CP) only. For example barley, with 11% CP, contains 0.36% of available lysine. Sorghum, testing at 13% CP, contains only 0.24% of available lysine. If the two feeds are compared on CP content only, sorghum would win. However, based on lysine content, barley is a better quality grain for pigs.
This does not mean that sorghum should not be used; most grains alone cannot provide enough amino acids for pigs’ needs. However, protein sources such as soyabean meal, fish meal and meat and bone meal are available. Synthetic amino acids such as lysine and methionine can also be readily bought. Protein-rich meals (usually more expensive than grain) can be combined with the grain to give a well-balanced diet, designed specifically for pigs’ needs. In the case of a diet based on sorghum, more protein meals (higher in lysine content) need to be included. As long as the diet is correctly formulated, pigs should grow as well and as lean as they would on a barley-based diet.
When formulating diets, you need to take account of how the pigs are growing at each stage of their lives. As they grow older, they put on a proportionally greater amount of fat and less lean meat than younger pigs, i.e. lighter pigs have less fat relative to lean meat than heavier pigs. Therefore, younger pigs need a diet higher in amino acids than older pigs so they can grow proportionally more muscle tissue.
Young pigs also have a small stomach capacity and need more nutrient dense diets.
Balancing energy and amino acids.
Pigs need both energy and protein (amino acids) to grow. However, there is a correct balance between the amount of energy in a diet and the amount of protein. Usually, you will see this balance expressed as a ratio, e.g. the grams of available lysine per megajoule of energy (g lysine/MJ DE).
Pigs need enough energy to allow the lysine and amino acids to be used in building muscle tissue. If there is too much energy in the diet and it is not balanced with lysine, pigs will convert the oversupply of energy into fat, which can reduce the market pig price.
On the other hand, too much lysine can be just as costly. Excess protein can be broken down into non-essential amino acids or be lost in urine. In heavier female pigs, too much lysine may actually be detrimental to growth and feed efficiency. As lysine is an expensive part of the diet it is unwise to include excess.
Generally, the lysine/energy ratio required is related to weight and age. As pigs get older, their need for lysine falls. This is because heavier pigs cannot grow as high a proportion of muscle tissue as lighter pigs and a greater proportion of the food energy is required for maintenance rather than growth. The ratio required also depends on the sex, genotype (i.e. their genetic make-up) and their shed environment. Ideally, diets should be formulated to match these conditions.
Diets can be formulated manually however special feed formulation programs or better a simulation model such as AUSPIG is the best way to match diet specifications to your pigs’ needs. It is an amino acid and energy model which simulates the nutrient needs of a pig of any age while taking into account genotype, sex, environment, feeding methods and market requirements. Recommendations are tailor-made for a herd and, when acted on, enhance production efficiency and lower feed costs.
The table below gives a guide to some dietary specifications for pigs of different ages, showing how their needs change as they grow. Dietary specifications for narrower weight ranges and other classes (such as lactating sow) are provided in the Nutrient Needs article. More information about how much to feed different classes of pigs is in the Feeding Guidelines article.
# Check actual intake to ensure pigs can consume the nutrients required for production. Intake of conventional grain-based diet required by dry sows is about 2-2.5 kg per day. Older pigs, especially adults (and more suitable for dry sows and boars than sows in milk production which requires high nutrient intake), can consume more of a bulkier feed, i.e. with more roughage and lower concentration of nutrients.
* This is the suggested daily DE intake for the heaviest pig in the weight class for which the diet is intended to be fed. Depends on the pig breed/strain, environment (including extent of feed wastage) and expected carcase quality. Pigs may need to be fed higher or lower DE allowances.
Larissa Dann, Sara Willis, Alison Spencer