For those pigs that succeed in surviving the initial few days of life (e.g., 85 to 95%), their body weight approximately doubles during each subsequent week of life to at least three weeks of age. This demonstrates that there is a large quantity of nutrients supplied through the milk to the litter.
The neonatal pig contains less than 2% body fat and almost no subcutaneous fat. Consequently, the young pig must be provided a large amount of energy from fat or carbohydrate in the colostrum in order to survive. Because of the low body-fat covering, the newborn pig must have supplemental heat to prevent chilling and to maintain a normal body temperature. If the floor and room temperatures are below the pig's comfort zone, heat pads and/or heat lamps provide an effective source of supplemental heat.
Colostrum consumption is critical for the survival of the neonatal pig for several reasons, namely that of supplying nutrients and antibodies. Antibodies are not transferred across the placenta to the developing fetus, but can be transferred through mammary tissue into the milk. Because maternal antibodies do not reach the pig during fetal development, the consumption of colostrum antibodies are essential for the pig's health and survival postnatally. Antibodies are produced by the sow in response to vaccinations or subclinical disease exposure. These antibodies are transferred to colostrum and absorbed by the young pig during the initial 24 to 36 hours of birth but not thereafter. Colostrum gradually changes to a mature milk within three days of farrowing.
Because of the rapid growth-rate of the pig and the low concentration of iron in sow milk, the pig's requirement for this nutrient is not supplied in an adequate quantity. Iron is a component of hemoglobin that carries oxygen to the rapidly growing tissues. A supplemental source of iron must be administered to the pig within a few days of birth to prevent anemia. An intramuscular injection of 100 to 200 mg iron is the most common method of administration. Feeding iron salts to sows has been shown to prevent anemia in the nursing pig, but it is due to the resulting high iron content in the sow's feces, not to an increase in the iron content in the sow's milk. Because the young pig normally consumes some sow feces, the pig will ingest iron through this avenue. However, when pigs are farrowed in crates and the sow's excrement is passed directly into a pit, the pigs may not receive an adequate supply of iron from this source. After the pig is weaned, the scientific research evidence indicates that an iron injection is not necessary.
Sow milk (i.e., 3 to 21 days) is relatively constant in its protein, lactose, calcium, and phosphorus concentrations. Milk contains an excellent source of nutrients that are highly digestible (> 95%) by the pig. Certain milk constituents (e.g., selenium, vitamin E, fat) may, however, decline with increasing parity depending on the nutritional and body- condition status of the sow. Milk does not provide an adequate quantity of water for the young, rapidly growing nursing pig, and a waterer should be provided for the litter.
In this region of the United States, older sows are more prone to a deficiency in vitamin E and selenium than younger sows. Sow milks have lower selenium and vitamin E concentrations at the end of lactation, and these concentrations are lower in the milks of older sows. Consequently, the progeny of older sows are more likely to exhibit a deficiency of these nutrients at birth or within a week or two postweaning. The sow diet should be adequately fortified with these nutrients to prevent this deficiency.
Fat is not effectively used by the fetus, but becomes the major source of energy for the nursing pig. Fat is at a relatively high concentration in colostrum and in mature milk, ranging from 5 to 9%. The nursing pig is capable of effectively using the fat in sow milk. This is because sow-milk fat is emulsified when it is released by the milk gland, and the pig secretes a large amount of the enzyme lipase, both of which are responsible for breaking the fat down to its constituent fatty acids. The amount of fat in sow milk is largely influenced by genetics and the sow's body fat content, but it is also dependent upon the sow's lactation feed intake and the amount of fat in the lactation diet. Sows with a low body-fat content transfer less fat to the mammary glands. Adding fat to the sow's diet during the last phase of gestation has been shown to improve the survivability of lightweight pigs mainly by increasing the fat content of colostrum and milk. This allows the lightweight nursing pig to consume more energy. The addition of 5% fat to the diet has not shown any detrimental effect on lactation feed intake, but does increase the sow's energy intake, increases milk fat content, increases pig weaning weight, reduces sow weight loss during lactation, and may shorten the weaning to rebreeding interval.
Sow milk does not contain an adequate quantity of nutrients to sustain the rapid growth of a young pig beyond 21 days of age. Under conditions of low milk production, creep feed should be provided to the litter. Normally, the young pig will "become interested" in a creep feed around 10 days of age, but the consumption of creep feed is quite variable among litters. If creep feed is fed, the Early-Wean die-tary nutrient recommendation (Table 3) can be provided, but care should be taken to only add a small quantity per day to maintain freshness and prevent wastage. When sow milk production is low, the provision of commercial milk replacers and electrolytes to the pigs may be necessary if the sow is producing an inadequate quantity of milk, or if diarrhea is present in the young pigs.