Milk production is largely under genetic control, but can be influenced by environmental and management factors. The selection for high-producing genotypes has resulted in sow lines that produce large quantities of milk. This results in heavier litter and pig weaning weights, with the sows having a high nutrient requirement for lactation. Upon farrowing, the sow largely uses dietary nutrients for the synthesis of milk. If the dietary nutrients are not provided, the body will use tissue reserves in an attempt to meet milk production demands. When this occurs, the breakdown of sow tissue to provide these nutrients will result in a loss of body weight and possibly body function. If excessive, this may result in the premature culling of high- producing sows because of anestrus problems or their subsequent failure to conceive upon weaning.
Sows that are too fat or over-conditioned when they enter the farrowing house (body-condition score 4.5-5) will have a lower feed intake during lactation compared with sows that have lower body-condition scores. Feed intake during lactation is therefore of utmost importance in maintaining high sow-milk production and for successful rebreeding after weaning. Although sows with a low body-fat content will frequently have a longer weaning-to-breeding interval, a low lactation feed intake is perhaps more responsible for poor breeding performance after weaning than is low body-fat content. It is essential that feeding practices and farrowing-house conditions allow the sow to consume a high quantity of feed. A high lactation feed intake is needed to maintain high milk production and a minimum loss of body fat. Sows should be brought up to full-feed as quickly as possible after they farrow, but some producers have observed a higher incidence of constipation and mastitis, metritis, and agalactia (MMA) if this is done too rapidly.
It has been demonstrated that sows vary in their desire to consume feed, during the initial week postpartum. Sows that lactate for 14 days or less will have a lower feed intake than those that have a longer lactation period. Consequently, with shorter lactation lengths, the diet needs to be fortified to a higher nutrient content to ensure that milk production demands are met and that the weaning to rebreeding interval is not prolonged. Feed intake will increase each week during a four-week lactation period.
First-parity animals normally consume less feed during lactation than older sows. Because of this, the diet of parity-one sows should be formulated to contain a higher concentration of nutrients.
Most sows will consume from eight to 10 gallons of water per day during lactation. Water flow in the waterer should supply a minimum of 1,500 ml/minute (1.5 quart/min). A separate waterer should be available for the nursing pigs.
The feeding practice for lactating sows that many producers find most helpful is to feed a minimum amount of feed the first day (3 to 5 lbs.) and then to increase that amount by 2 to 3 lb. per day, so that the sow is on full feed by day five of lactation. From this time until weaning, the sow should be fed all she will consume. This assumes that the sow is nursing a litter of nine to 12 pigs.
It is a common practice to feed lactating sows twice a day, but most sows cannot consume enough feed with this feeding practice. The method of feeding lactating sows is critical during the summer months when feed intake is particularly low. The cooler times of the day are generally during the early morning hours. Under these conditions it is important to have an ample quantity of feed in the sow feeder in the evening so that some remains by morning. Therefore, it is wiser to provide feed on a full-feed basis, or to feed a minimum of three times a day. Do not allow the feed to spoil and become moldy in the sow feeder.
Perhaps the limiting factor that restricts feed consumption is the type of feeder used, particularly for mature sows. Because we are now retaining older sows in the herd, their heads are larger and there is a greater difficulty for them to obtain feed from the older-type feeder. New types of sow feeders are now available that allow a full day's feed allotment to be added and have a larger feeding space.
There are several nutritional and management reasons why many sows do not consume an adequate quantity of feed during lactation. These reasons and possible solutions are:
The inclusion of fat in the sow's lactation diet has been shown to increase milk-fat content. During the summer months, or when the farrowing house becomes overheated, the addition of fat to the sow's diet may also be of benefit in reducing the body-heat stress and in improving the sow's subsequent rebreeding performance. The inclusion of fat (5 to 10%) in the lactation diet results in a lower amount of heat being released during the digestion process, resulting in lower heat stress on the sow.
The synthesis of milk proteins by the mammary gland is influenced largely by genetics and the dietary amino acid supply. Under conditions when the diet does not provide an adequate quantity of amino acids for milk production, body tissue proteins are selectively broken down, and the released amino acids are used for milk protein synthesis. However, the feeding of a diet low in protein will clearly result in decreased milk production and lower litter weaning weights.
The dietary protein (amino acids) concentration provided to the sow during lactation is of extreme importance in meeting the needs for milk production. The dietary concentration of protein (amino acids) should be adjusted to reflect both the sow's feed intake and milk-production capability. The nutritional requirements of sows of differing productivities for both first and later parities are presented in Table 12. These recommendations reflect normal sow feed intakes during lactation. When other factors lower the sow's feed intake, then the dietary amino acid concentrations need to be adjusted to meet the sow's daily requirements.
In contrast to the gestation period, the lactating sow can more effectively use synthetic lysine if the sow has access to feed continually. Because there is a higher feed intake during lactation, there is a continual absorption of nutrients. This allows for full utilization of absorbed synthetic lysine. When synthetic lysine is used in the lactation diet, care should be taken to ensure that methionine, valine, and threonine are not limiting. If a corn- soybean meal mixture is used and formulated to meet the lysine requirement, there is generally no need to provide additional amino-acid supplementation. If the sow is fed only two times per day, the use of synthetic lysine in the lactation diet is not recommended.
When constipation is a problem, the addition of a fiber source (wheat bran, beef pulp, alfalfa meal) at a 5% level may be helpful. Fiber inclusion in the lactation diet will, however, lower the energy value of the diet. Within a few days of farrowing, the fiber should therefore be withdrawn from the diet and replaced with corn as the sow needs additional energy to sustain high milk production.
Sow milk contains both macro- and micro-minerals. Calcium and phosphorus are maintained at a relatively constant concentration in sow milk even when the diet provides an inadequate amount. As during late gestation, if an adequate quantity of calcium and phosphorous is not provided in the lactation diet, the sow will demineralize skeletal tissue to meet her needs for milk production. Consequently, high-producing sows and those lactating for a long time are more prone to leg fractures and/or paralysis of the hind quarter (Downer Sow Syndrome). This situation may be worsened upon weaning or when sows are grouped together or mated to a large boar.
Selenium and vitamin E concentrations are lower in the milks of older sows. This situation presents a common problem in the tri-state area. Pigs nursing older sows are therefore more prone to the deficiency at birth and after weaning. Because sow body fat contains a large storage of vitamin E, the loss of body fat results in the depletion of vitamin E body stores. Part of the Vitamin E in milk is derived from the body fat as well as from the diet. This condition would have as great an effect on her progeny during the postweaning period as on her own future reproductive performance.
Swine producers should work with their nutritionists (university or feed company) to ensure that the diets for their reproducing animals are adequately fortified to meet the lactation performance of their sow herd.