Tri-State Swine Nutrition Guide

Bulletin 869-98

Digestive Tract Changes

The consumption of milk by the nursing pig results in the growth or proliferation of a group of bacteria (Lactobacillus spp.) in the stomach and intestinal tract. These bacteria use some of the lactose in milk to produce lactic acid, which lowers the pH in the stomach. This acidic condition aids the digestion process and prevents the growth of other microorganisms, some of which may be detrimental to pig performance. After the pig is weaned or when milk products are eliminated from the starter diet, these bacteria are quickly reduced in number, whereupon other bacteria become established in the intestinal tract. If pathogenic bacteria are allowed to predominate during this transition period, diarrhea, disease, and weight losses can occur. The health status of weaned pigs, particularly those transported long distances, should be closely monitored during the initial weeks postweaning.

Sow colostrum contains antibodies that are directly absorbed through the pig's intestinal tract during the first 24 to 36 hours of life, but another group of antibodies (IgA) is also present in the mature milk of the lactating sow. These latter antibodies are not absorbed, but remain in the intestinal tract, attach to the villi, and protect the intestinal lining against pathogenic bacteria. After the pig is weaned, these milk antibodies (IgA) no longer are supplied. Until the pig develops its own immune system, the intestinal tract of the pig is susceptible to disease conditions.

Nutrients are absorbed in the small intestine through microscopically elongated villi. Although digestive enzymes are produced by the pancreas, the tips of the villi in the small intestine also contain digestive enzymes. Upon weaning, the villi become shorter in length, and the digestive enzymes from the villi are temporarily lost. Consequently, when the villi length becomes shortened, the absorptive area and the overall digestive capacity of the weaned pig is reduced. The inclusion of plasma protein, zinc oxide, and lactose from dried whey in the initial starter diet has been shown to prevent or reduce the severity of the postweaning lag which is frequently encountered by young weanling pigs.

The secretion of digestive enzymes and the types of enzymes secreted by the young pig are dependent upon the age, weight, and diet fed to the pig. Although the nursing pig can effectively secrete enzymes for the digestion of colostrum and milk products, the enzymes necessary to digest the more complex components of plant and other animal products are inadequately secreted by the young pig. As the pig matures, its ability to secrete the enzymes necessary for digesting the complex protein and starch components of plant and animal products increases (Figure 6). When the pig is weaned at a younger age or is lighter in body weight, its ability to produce these digestive enzymes is lower than older pigs or pigs weaned at heavier weights. Consequently, the digestion of the complex dietary components is poorer with lighter-weight pigs. Feeds used in the diets of younger and lighter-weight pigs during the early weeks postweaning should closely match the pig's enzyme production profile. As the pig becomes older and heavier, the pig can effectively digest higher dietary concentrations of complex plant and animal products. The transition to less costly diets at appropriate pig weights and time postweaning will allow optimum performance during the entire nursery period.

Because of the digestive enzyme transition that the pig goes through from birth to eight weeks of age, the changing morphology of the intestinal villi, and the necessity of initially using specialized feed sources during the early phases postweaning, a phase-feeding program is highly recommended during the entire starter period. The use of specialized feed components (e.g., plasma protein, milk products, soy protein concentrate, etc.) has increased the cost of early weaning diets, but appears to be essential during the period that the gut is maturing. The production phases and nutrient recommendations for these periods are presented in Table 3. Although this nursery feeding program is now popular, phase feeding has always been used with grower-finisher pigs, but diets in the nursery period are changed more frequently. Pigs that are weaned at heavier weights will also bene-fit from at least a short-time feeding of the initial starter diet. The premature changing to a less costly diet may be economically appealing but can cause unthriftiness and poor pig uniformity. It is therefore suggested that the change of diets to the latter phases be based largely on pig weight, not pig age. All weaned pigs should receive the initial starter diet for at least a short time (seven to 14 days) postweaning. It is recommended that an early weaning diet be fed to pigs lighter than 8 lb. (regardless of pig age), with the Starter-1 nutrient levels fed from 12 to 15 lbs., the Starter-2 dietary requirements to 25 lbs., and the Starter-3 recommendations provided until the pig reaches 50 lbs. body weight.