The study was conducted to determine the effects of feeding a 16% CP diet, a 12% CP diet, or a 12% CP diet supplemented with crystalline Lys, Trp, and Thr (12% CP + AA diet) in a thermal-neutral (23 degrees C) or heat-stressed (33 degrees C) environment on various body and physiological measurements in growing pigs. Heat-stressed pigs were given a 15% lower daily feed allowance than thermal-neutral pigs to remove the confounding effect of feed intake caused by high temperature. No diet x temperature interaction was observed for any variables (P > 0.09) except for pig activity and pancreas weight. At 33 degrees C, pig activity and pancreas weight did not differ among dietary treatments (P > 0.05). In contrast, at 23 degrees C, pigs fed the 12% CP diet had greater activity than those fed the 16% CP diet or the 12% CP + AA diet (P < 0.05). Pancreas weight was greater for pigs fed the 12% CP + AA diet than those fed the 12% CP diet (P < 0.05) when maintained at 23 degrees C. Compared with 23 degrees C, the 33 degrees C temperature decreased pig activity, heat production, daily gain, feed efficiency, and affected the concentration and accretion of empty body protein and ash, as well as weights of heart, pancreas, stomach, and large intestine (P < 0.05). Pigs fed the 12% CP + AA diet attained similar levels of performance and rates of empty body water, protein, lipid, and ash deposition as pigs fed the 16% CP diet (P > 0.10). Pigs fed the 12% CP + AA diet had lower serum urea plus ammonia nitrogen concentrations (P < 0.01) and total heat production (P < 0.05) compared with those fed the 16% CP diet or the 12% CP diet. These results confirm that, with crystalline AA supplementation, growing pigs fed a 12% CP diet will perform similar to pigs fed a 16% CP diet. The data further indicate that lowering dietary CP and supplementing crystalline AA will decrease total heat production in growing pigs whether they are housed in a thermal-neutral or heat-stressed environment.

Dietary fiber may contribute up to 30% of the maintenance energy needs of growing pigs. Higher energy contributions may be obtained from dietary fiber fed to sows, along with some improvements in reproduction, health, and well-being. As long as cereal grain supplies and high-quality protein supplements are abundant, the use of fibrous feeds for swine most likely will be limited. However, as the human demand for cereal grains increases, swine producers, especially those with reproductive animals, may be economically forced to incorporate alternative feedstuffs. These feedstuffs might include lignified plant cell wall material such as grasses and legumes, and feed-milling and distillery by-products that contain a high level of fiber residues. The microflora in swine large intestine will be able to adapt to these lignified forages and by-product feeds much better than the microflora in humans. Swine microflora contain highly active ruminal cellulolytic and hemicellulolytic bacterial species, which include Fibrobacter succinogenes (intestinalis), Ruminococcus albus, Ruminococcus flavefaciens, Butyrivibrio spp., and Prevotella ruminicola. Additionally, a new highly active cellulolytic bacterium, Clostridium herbivorans, has been recently isolated from pig large intestine. The populations of these microorganisms are known to increase in response to the ingestion of diets high in plant cell wall material. The numbers of cellulolytic bacteria from adult animals are approximately 6.7 times greater than those found in growing pigs. None of these highly active cellulolytic bacterial species are found in the human large intestine. Thus, the pig large intestinal fermentation of fiber seems to more closely resemble that of ruminants than that of humans.

Twenty-seven 12-week-old barrows with average initial weight of 27 kg were randomly assigned to three treatments. The first group (HL) was fed to gain 19 kg body weight during the first 35 days (period 1) and to lose 5 kg during the second 35 days (period 2). The second group (MM) was fed to gain 7 kg during both periods 1 and 2. The third group (LH) was fed to lose 5 kg during period 1 and to gain 19 kg during period 2. At the end of the 70-day period, 7 pigs from each treatment were fasted for 30 hours and fasting heat production (FHP) was measured by indirect calorimetry. The animals were slaughtered and weights of stomach, small and large intestine, liver, pancreas, spleen, kidneys and heart were measured. Although all animals had the same final body weight, animals on the higher plane of nutrition during period 2 had significantly higher FHP and higher weights for stomach, small and large intestine, pancreas, liver and kidneys. FHP and the weights of small intestine, pancreas and liver from animals receiving the higher plane of nutrition during period 2 (LH) were 50% heavier than that from animals on low plane (HL). Positive correlations exist between FHP and weights of stomach, small intestine, large intestine, pancreas, liver and kidneys. These results indicate that prior nutritional history significantly influences FHP, which is highly correlated to weights of metabolically active organs.

Two experiments were conducted to evaluate the effect of excess protein on growth performance, carcass characteristics, organ weights, plasma urea concentration, and liver arginase activity of finishing barrows and gilts. In Exp. 1, 35 barrows and 35 gilts with an initial BW of 51 kg were used. Five pigs of each sex were slaughtered at the start of the study to determine initial body composition. The remaining 60 pigs were allotted to a randomized complete block (RCB) experiment with a 2x5 factorial arrangement of treatments (two sexes x five protein levels: 13, 16, 19, 22, and 25% CP). The experiment continued until the average BW was 115 kg, at which time three blocks of pigs (30 total) were selected randomly and slaughtered. Feed intake decreased with increasing protein concentration (linear, P<.05), and the reduction was greater in gilts than in barrows (P<.05). There was a trend toward a linear negative effect of dietary protein on ADG (P<.10) and also a quadratic effect of protein on protein accretion (P<.10). Fat accretion decreased linearly as protein level increased (P<.05). Increased protein concentrations increased liver, kidney, and pancreas weights (linear, P<.05). Plasma urea concentration increased with each protein concentration, with the exception of the 25 vs. 22% CP treatment in gilts. In Exp. 2, 18 barrows and 18 gilts (BW 63 kg) were allotted to an RCB design consisting of a 2x2 factorial arrangement of treatments with two sexes and two dietary protein concentrations (16 and 25% CP). The experiment was terminated when the average BW of pigs reached 105 kg. Average daily feed intake was greater (P<.10) in barrows than in gilts. Average daily gain was reduced by 18% in gilts when dietary protein was increased from 16 to 25% but was only reduced 3% in barrows (sex x protein, P<.10). Barrows had lighter livers (P<.005), greater arginase activities (P<.05), and greater plasma urea concentrations (P<.005) than did gilts. Increasing dietary protein concentration from 16 to 25% increased liver weight, arginase activity, and plasma urea concentration (P<.005). These data suggest that gilts are more sensitive than barrows to excessive intakes of protein. The more negative effects in gilts may be related to liver metabolic capacity and activity of urea cycle enzymes.

Surgical procedures are described for chronic cannulation of portal vein, ileal vein, abdominal aorta, and carotid artery in pigs. Silastic or Micro-Renathane tubing was used for cannulating portal vein and ileal vein, while carotid artery was cannulated with Micro-Renathane tubing. The lumen of Micro-Renathane tubing was coated with tri-dodecylmethyl ammonium chloride (TDMAC)-heparin complex. The abdominal aorta was cannulated via saphenous artery with vinyl tubing. This allows simultaneous collection of blood samples from hepatic portal vein and systemic artery (carotid or abdominal aorta) and continuous infusion of p-aminohippuric acid (PAH) into ileal vein. The constant PAH infusion provided an indicator-dilution method for estimating the blood flow rate in portal vein. In 13 pigs weighing 54 +/- 2.8 kg, the mean portal vein blood flow rate during the 8-h postprandial period was estimated to be 1,979 ml X min-1 X pig-1 or 37.8 ml X min-1 X kg-1 body weight. By simultaneously measuring the concentration of nutrients and metabolites in the portal and systemic arterial blood and multiplying porto-arterial differences by the estimated portal vein blood flow rate, the net absorption of nutrients (except long-chain fatty acids) and metabolites into hepatic portal system in conscious swine can be quantified.