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The effects of relative humidity (RH) and high ambient temperature (T) on physiological responses and animal performance were studied using 12 groups (10 gilts per group) in pens inside respiration chambers. The microclimate in the chamber was programmed so that T remained constant within a day. Each day, the T was increased by 2 degrees C from low (16 degrees C) to high (32 degrees C). Relative humidity was kept constant at 50, 65, or 80%. The pigs' average initial BW was 61.7 kg (58.0 to 65.5 kg), and their average ending BW was 70.2 kg (65.9 to 74.7 kg). Respiration rate (RR), evaporative water (EW), rectal temperature (RT), skin temperature (ST), voluntary feed intake (VFI), water-to-feed ratio (rW:F), heat production (HP), and ADG were analyzed. The animals had free access to feed and water. We determined the T above which certain animal variables started to change: the so-called inflection point temperature (IPt) or "upper critical temperature." The first indicator of reaction, RR, was in the range from 21.3 to 23.4 degrees C. Rectal temperature was a delayed indicator of heat stress tolerance, with IPt values ranging from 24.6 to 27.1 degrees C. For both these indicators the IPt was least at 80% RH (P < 0.05). Heat production and VFI were decreased above IPt of 22.9 and 25.5 degrees C, respectively (P < 0.001). For each degree Celsius above IPt, the VFI was decreased by 81, 99, and 106 g/(pig.d) in treatments 50, 65, and 80% RH, respectively. The ADG was greatest at 50% RH (P < 0.05). Ambient temperature strongly affects the pigs' physiological changes and performance, whereas RH has a relatively minor effect on heat stress in growing pigs; however, the combination of high T and high RH lowered the ADG in pigs. The upper critical temperature can be considered to be the IPt above which VFI decreased and RT then increased. Temperatures of the magnitude of both these IPt are regularly measured in commercial pig houses. We conclude that the upper critical temperatures for 60-kg, group-housed pigs fed ad libitum are between 21.3 and 22.4 degrees C for RR, between 22.9 and 25.5 degrees C for HP and VFI, and between 24.6 and 27.1 degrees C for RT. It is clear that different physiological and productive measurements of group-housed, growing-finishing pigs have different critical temperatures.

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An experiment was conducted to investigate the influence of dietary factors on the partitioning of nitrogen excretion and on the pH and composition of urine and feces of fattening pigs. Sixteen male hybrid pigs of 80 to 90 kg BW were allotted to one of four diets: based on grains, by-products, grains plus tapioca, or grains plus sugar beet pulp. Diets were formulated to have similar contents of NE and CP and a similar lysine:NE ratio. Diets differed in nonstarch polysaccharide content (NSP) and dietary electrolyte balance (dEB). During an 8-d period, urine and feces were quantitatively collected daily in metabolism cages and mixed to a slurry. There was no effect of the diet on total nitrogen excretion (P > .05). However, the nitrogen excretion pattern differed between diets (P < .001). Pigs fed the by-product- and the sugar beet pulp-based diets excreted less nitrogen via urine and more nitrogen via feces than pigs fed the grain- and tapioca-based diets. The type of diet significantly affected the pH of urine, feces, and slurry. The pH of slurry from pigs fed the sugar beet pulp-based diet was .44 to 1.13 units lower than that of slurry from pigs fed the other three diets. An increased dietary NSP content reduced the pH of feces and slurry. A decreased dEB reduced the pH of urine and slurry. We conclude that dietary NSP influences the partitioning of excretory nitrogen between urine and feces. Dietary NSP and dEB can influence the pH of urine, feces, and slurry.

Recent public concern about air pollution from pork production units has prompted more research to develop methods to reduce and control odors. Masking agents, enzymes and bacterial preparations, feed additives, chemicals, oxidation processes, air scrubbers, biofilters, and new ventilation systems have been studied. Research relating the effects of the swine diet on manure odors has been scarce. Introducing feed additives to bind ammonia, change digesta pH, affect specific enzyme activity, and mask odors has been either costly or not consistently successful. Recent research emphasis has focused on manipulating the diet 1) to increase the nutrient utilization of the diet to reduce excretion products, 2) to enhance microbial metabolism in the lower digestive tract to reduce excretion of odor-causing compounds, and 3) to change the physical characteristics of urine and feces to reduce odor emissions. Primary odor-causing compounds evolve from excess degradable proteins and lack of specific fermentable carbohydrates during microbial fermentation. Reductions in ammonia emissions by 28 to 79% through diet modifications have been reported. Limited research on reduction of other odorous volatile organic compounds through diet modifications is promising. Use of synthetic amino acids with reduced intact protein levels in diets significantly reduces nitrogen excretions and odor production. Addition of nonstarch polysaccharides and specific oligosaccharides further alters the pathway of nitrogen excretion and reduces odor emission. Continued nutritional and microbial research to incorporate protein degradation products, especially sulfur-containing organics, with fermentable carbohydrates in the lower gastrointestinal tract of pigs will further control odors from manure.

We investigated the effects of dietary carbohydrates on the composition and pH of fecal material and on the ammonia emission from the slurry of growing pigs. Thirty-four barrows (BW approximately 40 kg) were randomly allotted to 1 of 10 diets. A basal diet was formulated to meet all requirements for protein, amino acids, minerals, and vitamins. The control diet was composed of the basal diet plus heat-treated cornstarch. In the other diets, the cornstarch in the control diet was replaced with three levels of either coconut expeller, soybean hulls, or dried sugar beet pulp. Feces were collected separately from urine in a balance experiment. Feces were mixed with a standardized urine (ratio of 1:2.5, wt/wt) to form a slurry. A sample of this slurry was placed in an in vitro system to determine the pH and the ammonia emission for 16 d at 20 degrees C. The fecal and slurry DM contents decreased (P < .001) and the total VFA concentrations increased (P < .001) when the level of dietary carbohydrates increased. The pH and the ammonia emission decreased as the level of carbohydrates increased (P < .001). The addition of soybean hulls to the diet had the greatest effect on reducing the pH and ammonia emission (P < .001), and the effects of sugar beet pulp and coconut expeller were approximately the same. A linear relationship was found between the intake of dietary nonstarch polysaccharides (NSP) and the ammonia emission (P < .001). For each 100-g increase in the intake of dietary NSP, the slurry pH decreased by approximately .12 unit and the ammonia emission from slurry decreased by 5.4%. We conclude that replacing cornstarch in the diet with components that have a high concentration of fermentable carbohydrates increases the VFA concentration of feces and slurry and reduces the pH and ammonia emission from the slurry of growing pigs.

We investigated the effects of dietary factors on the pH and the ammonia emission from slurry of growing-finishing pigs. Sixteen male hybrid pigs (80 to 90 kg BW) were allotted to one of four diets based on barley-wheat, tapioca, barley-tapioca, and sugar beet pulp. Diets were formulated to have similar NE and CP contents and a similar lysine:NE ratio. Diets differed in nonstarch polysaccharide content (NSP) and dietary electrolyte balance (dEB). Urine and feces were daily collected quantitatively in metabolism cages and mixed as a slurry at the end of the collection period. After mixing, the pH and the ammonia emission from the slurry were measured daily in a laboratory setup for 7 d at 20 degrees C. The type of diet affected the pH of the slurry and the ammonia emission (P < .001). The pH of the slurry from pigs fed the sugar beet pulp-based diet was .8 unit lower and ammonia emission was 52 to 53% lower than that of the other three diets. The low dEB and high NPS sugar beet pulp-based diet increased the VFA concentration and reduced the pH and ammonia emission from the slurry. We conclude that dietary NSP and dEB influence the pH and ammonia emission from slurry of growing-finishing pigs.

A 2 x 3 factorial experiment was conducted with 24 finishing pigs (Yorkshire x [Finnish Landrace x Dutch Landrace]) to determine the effects of dietary buffering capacity (BC) and carbohydrate sources on apparent total tract digestibility (TD), N retention, and manure characteristics. Twelve of these pigs were fitted with steered ileo-cecal value cannulas to measure the apparent ileal digestibility (ID) of N. Experimental variables were two levels of BC (High = 600 mEq/kg and Low = 530 mEq/kg) and three dietary carbohydrates (tapioca [28%], soybean hulls [25%], and sugar beet pulp [25%]). The two levels of BC were achieved by adjusting the amounts of alkalogenic limestone and acidogenic Ca sulfate in the diet. Pigs were fed twice daily at 2.4 x maintenance requirement for metabolizable energy (418 kJ ME/BW(0.75)). Chromic oxide was used as an indigestible marker. Feces and urine were collected over 5 d for nutrient balance and in vitro measurements of pH and ammonia emission over 7 d. No significant interactions between BC and dietary carbohydrates on the ID, TD, N retention, or manure characteristics were observed. Lowering BC with Ca sulfate did not affect digestibility of most nutrients, except for a negative impact on the TD of Ca (P = 0.015) and Mg (P = 0.003). Although all pigs receiving Ca sulfate had more acidic urine (by 0.49 pH units; P = 0.001), ammonia emission from manure was not lowered, irrespective of the carbohydrate source. Carbohydrates affected significantly the ID and TD of most nutrients, whereas N retention remained similar (P > 0.10). Urinary N:fecal N ratios in manure of pigs fed diets with tapioca, soybean hulls, and beet pulp were 2.09, 1.35, and 1.67, respectively. These ratios corresponded with in vitro ammonia emission (169, 125, and 148 mmol/7 d; P = 0.023). In conclusion, these results indicate that the acidification of urine in pigs fed Ca sulfate in the presence of NSP-rich carbohydrates was achieved. However, acidity of manure and ammonia emission were not affected. The addition of NSP from soybean hulls and(or) sugar beet pulp reduced ratios of urinary:fecal N, and thereby ammonia emission.