Manipulation and regulation of post-weaning growth in the pig

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The objective of this dissertation was to investigate the manipulation and regulation of post-weaning growth in the pig. Specific objectives, as reflected in the individual chapters of this thesis, were to investigate the basis for differences in post-weaning growth rate and the modification of growth achieved through the use of two feed additives: tylosin phosphate (TP) and ractopamine hydrochloride (RAC). In the first experiment, 18 cannulated barrows (initial BW = 32.6 ± 1.2 kg) were utilized to evaluate the impact of TP on energy and nutrient digestibility
in growing pigs fed corn- soybean meal or corn-soybean meal-distillers dried grains with solubles (DDGS) based diets. Results of this study indicated that the ileal digestibility of all indispensible AA, except leucine, and the apparent total tract digestibility of energy and fiber was lower (P < 0.05) in corn- soybean meal -DDGS-based diets than in corn -soybean meal-based diets. Tylosin phosphate did not affect digestibility of AA or digestibility
and gastrointestinal tract flow of energy ( P> 0. 10). A second experiment was conducted to determine if a higher fiber diet alters the response of finishing pigs to TP and RAC in terms of N and water utilization and energy digestibility using 72 gilts (initial BW = 107.4 ± 4.2 kg) housed in individual metabolism pens. Ractopamine HCl improved ADG (P < 0.0001), feed efficiency ( P < 0.0001), and N retention ( P < 0.001) and tended to increase daily water intake ( P < 0.10) , and the response to RAC was similar in both corn – soybean meal based and corn – soybean meal – DDGS based diets. Tylosin phosphate tended to increase ADG in pigs fed corn – soybean meal based diets (
P < 0.10) , but not in diets containing 30% DDGS ( P > 0.10) , but this response was not accompanied by changes in N balance

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