W. G. Pond

Yorkshire weanling barrows weighing an average of 17 kg were assigned in four groups of eight pigs in each of two replicates (64 pigs) to a completely randomized experiment in a 2 × 4 × 4 factorial arrangement (slaughtered at 48 or 89 kg; fed 0, 20, 40 or 60% alfalfa meal; slaughtered at 2, 4, 8 or 12 hr after the last feeding). A level of 20% alfalfa meal, resulting in a level of 26% cell wall in the diet, had no significant effect on daily gain and feed-to-gain ratio compared with a level of 0 alfalfa meal; 40 or 60% alfalfa meal significantly depressed daily gain and efficiency of feed utilization compared with 0 or 20%. Backfat thickness was inversely related to level of alfalfa meal in the diet; cross-sectional area of the longissimus muscle was not affected by diet. Weight of the empty gastrointestinal tract (all segments except stomach) was increased with increasing fiber in the diet. Apparent digestibility of dry matter, cellulose, hemicellulose and nitrogen was progressively decreased with increasing fiber. Percentage of dry matter in digesta of all sections of the gastrointestinal tract was negatively correlated with cell wall content of diet and digesta. The lower dry matter of digesta of pigs fed high fiber was associated with a faster rate of passage and is suggested as being responsible for the lower digestibility of dry matter, nitrogen and cell wall components in pigs fed high fiber diets. Pigs slaughtered at 48 kg body weight had significantly higher apparent digestibility of dry matter, nitrogen and cell wall constituents than pigs slaughtered at 89 kg, probably due to the higher rate of passage of digesta in the heavier pigs. It is concluded that the depressing effect of fiber on apparent digestibility is due to the greater rate of passage of digesta in pigs fed high fiber and that there is no significant adaptation to high fiber diets with age during the growing-finishing period.

The perinatal development of the brain is highlighted by a growth spurt whose timing varies among species. The growth of the porcine cerebrum was investigated from the third trimester of gestation (70 days postconception) through the first 3.5 weeks of postnatal life (140 days postconception). The shape of the growth curves for cerebrum weight, total protein mass, total cell number (estimated by DNA content), and myelination (estimated by cholesterol accretion) were described. The growth velocity of cerebrum weight had two peaks, one at 90 days and the other at 130 days postconception, whereas that of total protein was greatest from 90 to 130 days postconception, and that of total DNA was greatest between 90 and 110 days and again at 130 days postconception. The growth velocity for total cholesterol continued to increase during the entire period, suggesting that myelination continued after the growth spurts for cells (protein and DNA). The growth velocity patterns observed in these contemporary pigs suggest that this species may be an appropriate model for human brain development, not only in the perinatal pattern of increase in mass of the cerebrum, as established previously, but also with regard to the patterns of cellular development and myelination.

Production of volatile fatty acids (VFA) in the cecum and colon and their utilization as an energy source were studied in growing and finishing swine fed diets containing 0, 20, 40 or 60% alfalfa meal. The pH in the cecum and colon had an average value of 5.9, which supports fermentation of lumen contents. Increasing dietary fiber increased the concentration (mM/liter) of VFA in the large intestine; VFA ratio was changed in the cecum (increased acetic: propionic-butyric acids) but not in the colon. VFA disappearing from the lower gastrointestinal tract were equivalent to 79, 147, 227 and 155 kcal per day for pigs fed 0, 20, 40 and 60% alfalfa meal, respectively, at 48 kg body weight and 47, 231, 285 and 245 kcal per day, respectively, at 89 kg body weight. VFA produced in the large intestine can therefore provide up to 6.9, 11.3, 12.5 and 12.0% of the energy required for maintenance in the 48 kg pig and 4.8, 11.4, 14.0 and 12.0% in the 89 kg pig fed 0, 20, 40 and 60% alfalfa meal, respectively.

Twenty-one genetically lean, obese or contemporary barrows (6 mo old; seven of each genotype) were assigned to individual tether stalls and fed a control diet (low-fiber) or a diet containing 80% alfalfa meal (high-fiber) at 1.50% of initial body weight for 71 d (1.75% for d 1 to 4). Backfat thickness was recorded ultrasonically at 2-wk intervals, and body weight was recorded at the beginning and end of the 10-wk experiment. Pigs were slaughtered after a 24-h fast, and carcass weight, length and backfat thickness and cross-sectional area of the longissimus muscle were measured. Weights of cecum, heart, liver and kidney and of full and empty stomach and colon and empty small intestine were recorded. Volume and weight of colon and cecum contents were determined. Restriction of digestible energy reduced weight gain to zero or below in pigs fed alfalfa meal compared with 220 g daily in pigs fed the low-fiber diet. Restriction of energy reduced backfat in all three genotypes. Liver, kidney and empty segments of the gastrointestinal tract as a percentage of body weight were increased by high fiber. Obese pigs had smaller longissimus muscle area, more backfat and smaller liver, heart, empty stomach and colon than lean or contemporary pigs, but there were no diet X genotype interactions for any of these traits. Obese pigs consistently had smaller digesta volumes and dry matter weights than the other genotypes. The increased relative organ weights and the associated disproportionate contribution of these organs to body energy expenditure have important implications for effects on basal metabolic rate.(ABSTRACT TRUNCATED AT 250 WORDS)