Feed intake -- Feed intake is used synonymously with feed disappearance from feeders or storage bins. Feed disappearance includes feed that is eaten and feed that is wasted or spilled and probably overestimates actual feed consumed. Certain processing methods (e.g., pelleting), feeder design and management practices reduce feed disappearance because feed wastage is reduced, but they may have little effect on feed intake. Other practices, such as liquid or paste feeding, may produce a real increase in feed consumption.
Why is feed intake important?
Growing pigs and lactating sows generally are given free or ad libitum access to feed, whereas boars and non-lactating gilts or sows are limit-fed. It is assumed that when swine are not limit-fed, they will consume feed in quantities sufficient for maximum production.
A number of factors may alter feed consumption, resulting in greater or lesser amounts of feed consumed than expected. As feed consumption varies, so does the daily supply of nutrients. Nutrient intake can be standardized by adjusting nutrient levels in a diet inversely with changes in feed intake.
However, altering nutrient density is not advisable when energy is the limiting factor.
What factors affect feed intake?
Pigs consume feed in meals. As pigs advance from weaning to slaughter weight, meal frequency decreases from about 12 to five meals per day. Factors that alter daily feed consumption do so by either reducing or prolonging the duration of individual meals as opposed to affecting meal frequency.
• Energy density
The amount of energy consumed depends on the amount of feed eaten and the amount of energy per pound of feed. Pigs typically eat until their energy requirements are satisfied. Adding fat to a diet reduces feed intake because energy density increases. Fibrous feeds (e.g., barley, alfalfa and oats) dilute energy density and increase bulk when added to a diet.
As dietary fiber increases, feed intake increases until gastrointestinal capacity is reached, causing intake to reach a plateau. This plateau may occur before energy needs are satisfied. Energy dilution is of particular concern for pigs weighing less than 80 lb and for most lactating sows. This is because energy intake tends to be limiting for maximum performance in these classes of swine, even when they are fed low-fiber diets.
Consistent exposure to environmental temperatures above or below the pig’s thermoneutral zone affects feed consumption. As environmental temperature increases from comfortable to moderately stressful, feed consumption declines proportionally. However, extreme heat stress drastically reduces feed consumption. Susceptibility to heat stress increases as body weight increases. Conversely, feed consumption increases as environmental temperature is reduced within a moderate range.
Finishing pigs in a cold environment eat more because their maintenance energy requirement is increased to maintain body temperature. Growth rate may not be affected, but poorer feed efficiency results. However, severely coldstressed pigs may not grow because they can not consume sufficient amounts of energy above their maintenance requirement.
The effects of cold weather are less detrimental as body weight increases. Limit-fed swine are an exception because they can not voluntarily adjust energy intake. The manager must make these adjustments and increase feeding level according to severity of the cold stress.
A summary of eight studies below shows that feed consumption is affected by gender. Although differences in feed intake between barrows and gilts may occur at lighter weights, they probably are not of practical importance until pigs weigh about 80 lb or more. After 80 lb, barrows will consume more feed than gilts. It appears boars consume less feed than gilts during the grower phase, but they have similar feed intakes in the finisher phase.
Relative effect of sex on feed intake (boar = 100)
Grower (45 to 130 lb)---100---108---105
Finisher (130 to 250 lb)---100---114---101
Genetics play an important role in determining feed intake levels in swine. Genetic lines selected primarily for improved feed efficiency or for leanness may also be indirectly selected for low feed consumption. Thus, pigs from different genetic lines may consume different amounts when given free access to feed. However, it is not possible to make general statements about differences in feed intake among genetic lines. For example, some high lean gain genotypes were thought to have reduced feed intake.
This might seem logical because carcass leanness is increased by restricting feed intake. However, there is evidence that pigs with high lean growth potential and those with medium or low lean growth eat similar amounts of feed. Therefore, feed intake patterns of genetic lines should be determined from previous records and daily consumption should not be used to classify pigs according to lean growth type.
Severely restricted consumption at weaning is a common occurrence and the principal cause of postweaning lag. This problem has been addressed in our nutrient recommendations (Table 11), and further adjustments in nutrient density are not needed. The starter 1 (or transition) diet should contain highly palatable and digestible ingredients (see example diets in Table 19) to encourage pigs to begin eating as quickly as possible.
• Amino acids
Pigs fed diets that are not correctly balanced for amino acids may exhibit reduced feed intake. The severity varies depending on the levels and characteristics of the amino acids involved. Formulation errors that allow some alternative feed ingredients or crystalline amino acids to be used incorrectly cause these problems.
Such errors can be avoided by using our lysine, tryptophan, threonine and methionine recommendations when formulating diets.
• Gestation feeding
Sows that are overfed during gestation exhibit reduced feed consumption during lactation. The excess energy consumed during gestation is stored as fat and used during lactation, resulting in greater lactation weight loss. Sows fed our recommended amounts during gestation (adjusted for environment as necessary) gain less weight during gestation and lose less weight during lactation. They obtain the additional energy needed during lactation by eating more feed.
The total amount of feed eaten for the combined gestation and lactation periods may be similar whether sows are overfed or fed correctly during gestation. However, sows that are too fat at farrowing may cause management difficulties and are more likely to crush their pigs.
• Feed acceptability
Pigs may reduce consumption or refuse to eat when the diet contains unpalatable or objectionable ingredients. This may be noticed first among limit-fed swine, because they eat well defined meals. The effects on pigs given free access to feed are less obvious and may not be noticed until performance losses occur.
Certain odors, textures, flavors and tastes (especially bitter) may contribute to reduced feed intake. Some ingredients may reduce palatability when large quantities are used in the diet. Small quantities of mold and(or) mycotoxin contaminated feeds may dramatically reduce feed intake.
To avoid these problems, do not use poor quality ingredients in swine diets. Stale feed may be considered unacceptable to swine that are hesitant to eat because of stress. Lactating sows, newly weaned pigs and pigs recovering from disease can be encouraged to eat by providing fresh feed several times per day.
Spilled or wasted feed left on the ground or floor of a pig pen for more than 30 minutes probably will not be eaten.
• Other factors
Crowding, limited feeder space and disease often reduce feed consumption. These problems should be identified and treated by making the appropriate changes in management or facilities, rather than by making diet changes.
Further, altering nutrient density will not overcome performance reductions resulting from crowding. Feeder design and management affect feed consumption somewhat, but play a greater role in managing feed wastage.
Assuming adequate feed access is provided, feeder design usually is of less importance than adjustments to reduce or minimize feed wastage. One exception may be sows during lactation, if the feeder design limits a sow’s access to feed.