Nutrient needs

The profitability of a piggery is very sensitive to the price of feeds used, the efficiency of the piggery's pig genotype to convert feed into meat and the price for market pigs at any particular time. To maximise profits, a delicate compromise must be reached between minimising feed costs and maximising pig meat returns.

Feed costs can vary between 55 and 70 per cent of a piggery's total operating costs. Reducing feed costs by using poor-quality diets may not be very economical, as feed usage would be higher and pig meat returns lower because of poor carcase grading. Using very high-quality diets or severely restricting feed intake does not improve carcase quality and returns.

To achieve a profitable compromise, pigs must be fed diets that satisfy their needs to reach their potential for lean meat growth, in the case of growers. This requires an understanding of the various nutrients and their importance. The feeding strategy used to maximise growth, consistent with producing carcases of acceptable market grading, is also important.

For optimum feed utilisation, nutrients must be provided in balanced amounts and at levels that satisfy the pig's needs for maintenance, growth and reproduction.

Energy

This is the most basic of all nutrients. Every activity of the body, whether physical or metabolic, requires energy. If energy supply (or food) is limited, the priority of its use within the body goes to essential maintenance functions to the detriment of the processes involved in reproduction and growth. Conversely, when there is an abundant supply of energy, growth accelerates to the rates permitted by the availability of other nutrients and the animal's genetic make-up (genotype). Any energy consumed above these needs are stored in the body as fat.

With pig feeding and nutrition, energy requirements are usually described in terms of digestible energy (DE) intake - the total amount of energy consumed in the food, less the amount that is not digested and, consequently, excreted in faeces. In Australia, the mega joule (MJ) is the unit that describes feed energy. (The conversion between calories and mega joules is 1000 calories = 4.1868 MJ.)

Amino acids

Amino acids are the chemical building blocks of protein (meat) and at least 20 different types occur in nature. A pig needs only eight or nine of these in its diet - the 'essential' amino acids. The pig's body can synthesise the remaining 'non-essential' amino acids . When pigs are fed grain-based diets, several essential amino acids are likely to be deficient: lysine, threonine, methionine, tryptophan and isoleucine. As all amino acides must be present in their correct balance for protein synthesis to occur, the essential amino acid is in least supply - the most limiting amino acid - determines the rate at which protein synthesis occurs.

Table 1 shows the ideal balance of amino acids needed in a diet to provide for maintenance (adult sows and boars) and protein deposition (growing pigs).

Table 1. The ideal amino acid pattern of dietary protein for growers and breeders
Amino acids Weaners
5-20 kg
Growers
20-50 kg
Finishers
50-100 kg
Lactating sows Pregnant sows
Lysine 100 100 100 100 100
Isoleucine 57 57 57 57 57
Methionine 30 30 30 30 30
Methionine + cystine 55 60 65 55 55
Threonine 63 67 70 60 60
Tryptophan 18 18 18 18 18

Vitamins

These essential substances play important roles in regulating many biochemical processes in the body. Feedstuffs typically used in pig diets contain various amounts of most vitamins; however, the relative availability of these can vary substantially. Therefore, it is difficult to accurately allow for any contribution from feed. To overcome this, adding a supplement to the diet that contains most of the vitamins is useful. This is a relatively inexpensive form of insurance against vitamin deficiencies, and may help reduce the effects of disease and environmental stresses on pig performance. If deficiency problems do occur, you may need to add more of the deficient vitamin.

Minerals

Minerals are essential compounds that provide the elements used to maintain the animal's bone structure and regulate many biochemical processes. The main mineral elements in diet formulation, considered individually, are sodium, calcium and phosphorus. Iron, zinc, copper and manganese are also required but only in trace amounts. Usually, these trace elements are added to the diet as a mineral premix.

Other nutrients and diet components

Pigs need certain essential fats that feedstuffs used in normal diets usually provide sufficiently. Fibre is another diet component that must be considered occasionally. Breeder diets must contain sufficient fibre (about 4 per cent) to satisfy appetite through a bulking effect and reduce constipation in these older animals. Weaners must be given diets that contain no more than 2 per cent fibre because young pigs cannot easily digest it (they may scour) and the high fibre restricts the intake of required nutrients due to their small stomach capacity. In summer months, pigs need diets that are low in fibre because their body generates more heat during fibre digestion. If low feed intakes are a problem, higher amounts of fat can be used in diets because fat is easily digested.

Good-quality water with a low dissolved-salt content and low bacteriological levels should always be freely available to all pigs.

Nutrient balance

The importance of providing essential amino acids in their correct levels and proportions to maximise protein synthesis has already been mentioned. Similarly, pigs use feed most efficiently if all the nutrients are in proportions that match those needed at the time. As energy is the fuel that drives all biochemical processes, most nutrients are needed to provide, in some proportion, the energy that is available for any given level of production. This applies to all nutrients, though most attention has been given to the balance between amino acids and energy.

Nutrient availability

When formulating a diet, it is important to consider only the amount of each nutrient available to the pig rather than the total amount of nutrient present in the ingredients in the diet. The animal will be able to use these available nutrients in maintenance, reproduction and growth processes.

This availability of nutrients is particularly important for amino acids in feed ingredients, where amino acid availability can be reduced in some feedstuffs by a high-fibre content that lowers amino acid digestibility. In the case of other feeds, high temperatures used during manufacture (such as meat and bone meal) may cause some amino acids to bind up in non-available forms, particularly lysine. Combinations of ingredients may be one way of balancing available nutrient requirements, as well as using synthetic amino acids to meet amino acid shortfalls.

The availability of phosphorus should also be considered because of both the additional cost of inorganic supplements and its importance in environmental pollution. Much of the phosphorus in vegetable matter is in a bound form called phytate, which is poorly available to the pig. Phytase enzymes are now commercially available as dietary supplements, which assist in releasing this bound phosphorus and lowering the amount of additional inorganic phosphorus required in diet formulation.

Effect of season

Like a human, a pig must maintain its deep body temperature at about 38°C. This becomes a problem when the ambient (environmental) temperature changes. There is a narrow range of environmental temperatures called the thermoneutral zone within which the pig can maintain all body functions without becoming stressed. The thermoneutral zone varies according to the pig's weight and housing conditions. If the environmental temperature falls below this zone, the pig will attempt to eat more feed and use this 'extra' feed to maintain body temperature. Conversely, if environmental temperatures increase above this thermoneutral zone, the pig will eat less to reduce the heat load that occurs during the digestion process.

Two options are available to optimise lean growth:

  • control the piggery's environmental conditions to maintain the thermoneutral zone as closely as possibly
  • adjust the dietary concentration of all nutrients according to the pig's feed intake. In summer, when high temperatures reduce feed intake, you need to increase the dietary specification of all nutrients, especially the critical essential amino acids (in reverse proportion to the reduction in feed intake). The opposite will apply in very cold conditions where the pig will attempt to eat more.

Finetuning feeding programs

It is difficult to prescribe any one feeding strategy that will ensure a maximum return in every piggery (see Table 2 for some guidelines and Table 3 for a guide to a larger number of diets that will better suit pigs as they grow). Therefore, managers must finetune their feeding programs. The objective of finetuning is to match feed allowances and dietary specifications so the pig receives nutrients in sufficient daily amounts to support the production level and carcase quality parameters being targeted. The amount of feed to be given to growers will vary according to the pig's genetic potential and the carcase grading scheme's severity. If a harsh grading scheme operates and over-fat pigs are severely penalised, feed allowance may need to be reduced to achieve a high percentage of prime grades. However, unless there is a proportional increase in the diet's dietary specification, nutrients such as amino acids will be undersupplied, the pig will grow slowly and grades will be poor. The pig will be lean only if it receives an adequate amount of balanced amino acids.

Your feed manufacturer or nutrition consultant can further advise on finetuning dietary specifications. Also, a consultant who uses a computer simulation program, such as AUSPIG, can make a detailed assessment of your pig production enterprise so you can more precisely finetune to maximise profitability.

Diet formulation and feeding:

Dry sows

  • Pregnant sows should be fed according to condition but not to over-fatness. (If intake is too high during pregnancy, intake is reduced when lactating.) The amount fed will depend on the sow's size and body condition, type of housing, environment, method of feeding and health.
  • Feeding levels of 2-2.5 kg of grain-based feed is suitable for most dry sows.
  • The heavier the sow, the greater the maintenance and amount of feed required.

Lactating sows

  • A sow needs approximately 85 MJ per day and 55 g available lysine to support a litter of 10 pigs. This can be achieved with 6 kg of a diet with 14.0 MJ DE and an available lysine DE of 0.55 g/MJ.
  • Separate lactating (wet sow) and dry sow diets should be used where storage facilities permit.
  • First-litter lactating sows may need a separate diet or supplement to allow for their lower appetite compared with older sows.

Creep

  • Suckling pigs need fresh diets from about 10 days of age. This diet should contain palatable and readily digestible ingredients.
  • This diet should be fed for the first week after weaning.

Weaner

  • Diets should be fed to established weaners without restriction until 20-25 kg live weight (about 8-10 weeks of age).
  • The diet's energy level should be at least 14.5 MJ because their stomach capacity is limited.
  • The feed must be kept fresh and troughs regularly checked for soiling.

Grower

  • Diets should be offered without restriction from about 20 kg until 45-60 kg live weight (about 14-16 weeks of age).
  • Use a high-energy diet (14-15 MJ DE/kg) during this growth phase to exploit the pig's high capacity for lean meat production.

Finisher

  • Diets should be fed from 45-60 kg at a feeding scale that optimises growth rate, feed efficiency and carcase quality. The scale is determined by market requirements, price differential between fat classes, the genetic potential of the pigs, sex (as entire males can tolerate higher levels of energy intake) and environmental temperatures (as the requirement for energy is higher in the cooler months).
  • Many commercial pigs can be fed without restriction. As a guide, if feed restriction is required, a maximum of 28-34 MJ of energy per day should be fed. That is, if a diet contains 13.5 MJ DE/kg, then 2.1-2.5 kg of feed must be offered daily to meet these needs.
Table 2. Suggested guidelines for nutrient content in conventional grain-based pig diets
Diet Creep <8 kg Weaner 8-25 kg Grower 25-60 kg Grower finisher >30 kg M/F
finisher >60 kg
Male finisher >60 kg Female finisher >60 kg Lactating
sow
Dry sow and boar Gilt developer
Voluntary feed intake (kg/day)# 0.3 1.1 2.3 3 3 3 3 5-6 >2.5 3.0
DE intake target (MJ/day)* 4.5 16 30-32 30-32 32-34 28-30 28-30 55-85 25 40
Energy
DE content (MJ/kg) 16.0 15.0 14 <14 13.2 13.2 13.2 14.0 13.0 13.2
Available amino acids
Lysine/DE (g/MJ) 0.80 0.75 0.65 0.60 0.53 0.55 0.50 0.55 0.40 0.55
Available amino acid : available lysine (ratio)
Methionine 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30
Methionine + cys 0.55 0.55 0.55 0.60 0.60 0.65 0.65 0.55 0.55 0.65
Tryptophan 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18
Threonine 0.60 0.62 0.65 0.67 0.70 0.70 0.70 0.60 0.70 0.70
Isoleucine 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57
Macro minerals
Calcium - min (g/kg) 8.0 7.0 6.5 5.5 5.5 5.5 5.5 8.0 6.0 8.0
Calcium - max (g/kg) 16 16 16 16 16 16 16 16 16 16
Avail phosphorous - min (g/kg) 6.0 4.0 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5
Max Ca : avail. phos - ratio 1.75 1.75 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0
Salt (g/kg) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5-5.0 2.5-5.0 2.5-5.0
Trace minerals ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
Vitamins ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

# Check actual intake to ensure that pigs can consume the nutrients required for production. The intake of conventional grain-based diet that dry sows require is about 2.5 kg per day. Older pigs, especially adults (though dry sows and boars more than sows in milk production, which require 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. It depends on the pig breed/strain, environment (including extent of feed wastage) and expected carcase quality. Pigs may need higher or lower DE allowances.

^ Natural feedstuffs usually provide vitamins and trace elements in variable amounts. A vitamin-mineral premix is usually added to diets as an insurance measure and any additional specific vitamin or mineral supplement is warranted only where a deficiency is demonstrated.

Table 3. A guide to dietary lysine requirements for growing pigs of average to above-average genotype
Feeding phase Age (weeks) Weight (kg) DE (MJ//kg) Av. lys/DE (g/MJ)
Early weaner 2-4 4-8 15.5 0.95
Weaner 1 4-7 8-16 15.0 0.85
Weaner 2 7-10 16-30 14.5 0.75
Grower 1 10-14 30-54 14.0 0.70
Grower 2 14-18 54-80 14.0 0.62
Finisher 18-20 80-95 13.2 0.52
Presale 20-22 95-108 13.0 0.49