Physical aspects of non-ruminant nutrition
Nutritionally adequate diets fed to pigs can be expected to yield varied responses due to physical attribute differences, feeding and processing methods, ingredient selection and other factors. Independent and interrelated effects of such dietary characteristics are of special interest where feed intake control in self-fed pigs is of prime economic importance. Evidence is provided in this thesis that rate of gain, feed conversion and carcass quality can be influenced by nature and texture of fibrous ration ingredients, pelleting, antibiotic supplementation and pig sex. A 3 x 25 factorially arranged swine feeding experiment was conducted with finishing rations to assess the effects of: three fibrous diluents (cellulose, wheat bran, oat hulls), two or three daily feedings, two fiber moduli, pelleting, antibiotic supplementation and sex (gilt vs. barrow) comparisons. Response criteria included weight, gains, feed intake and conversion, energy and protein digestibility coefficients, carcass traits, gastrointestinal weights, and chemical and physical measurements upon the ingesta from selected gastrointestinal segments. Ingesta assessment included specific gravity, Klasson lignin, proximate principle components, and ingestal fluid physical characteristics. Treatments increasing daily feed intake included oat hulls, three daily feedings, fine moduli, pelleting or barrows. Growth rate increased only in barrows or pellet-fed groups. Cellulose or antibiotic supplementation improved feed conversion, whereas oat hulls impaired it. Oat hulls depressed digestible energy coefficients but increased protein digestibility. Both energy and protein digestibility coefficients were improved by antibiotic supplementation; however, both bulk type and moduli exerted an influence on this response. Module effects were many and varied; the finer module generally increased feed intakes and conversion. It was noteworthy that fine wheat bran failed to exhibit many characteristic responses of wheat bran. This effect was attributed to destruction of the physical form in bran, namely "flakiness". Carcass quality paralleled nutrient digestibility and feed intake alterations. The degree of finish, as influenced by fibrous diluent type, feeding frequency or sex, was associated with carcass yield. It was postulated that fluid retention differences in the gut, primarily between fibrous diluent sources, influenced the relative degree of tissue hydration and thereby affected carcass yield. Changes in carcass yield were associated with visceral weight differences observed on fibrous diluent or antibiotic comparisons. Gastric density characteristics reflected attributes of dry feed. Pelleted, fine module or antibiotic-fortified feed increased, gastric density but this effect became dissipated in the intestinal regions. It is possible that appetite inducing effects of these treatments were manifested in terms of stomach filling capacity. Ingesta differences attributable to fibrous diluent sources were maintained throughout the tract. The most voluminous ingesta source was wheat bran and the least, oat hulls. In terms of dry matter percentage, oat hull ingesta was the highest and wheat bran the lowest. Larger quantities of ingesta occurred in the rectal segment of oat hull fed animals. It was postulated that this affect reflected ingesta volume differences upon lumen distention and defecation initiation. Although dry matter and ingestal fluid physical measurement differences prevailed, these were difficult to correlate with animal performance and ration utilization. Increased fat levels were present in rectal samples from animals fed wheat bran. Antibiotic supplementation increased ingestal fluid pH and viscosity, but tended to reduce surface tension. The large number of significant high order interactions rendered specific interpretation difficult, but such findings emphasize the important role that physical characteristics of the diet play in determining growth and development of animals fed nutritionally balanced rations.