The effect of dietary pH and phosphorus source on performance, gastrointestinal digesta, bone characteristics and body composition in weanling pigs

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Virginia Tech


Crossbred pigs (n=144, avg age and weight - 28 ± 3 d, 7.5 kg) were used in two 6 wk trials to assess the effects of dietary pH and phosphorus source on performance, gastrointestinal digesta pH and chloride ion concentration (Cl⁻), bone characteristics and body composition. Pigs were blocked according to weight within sex and litters were balanced across groups. Treatments were randomly allotted within blocks to a 3 x 2 factorial arrangement with three dietary pH levels (5.4, 6.0 and 6.7) and two phosphorus sources: dicalcium phosphate (DCP) and defluorinated phosphate (DFP). Pigs fed the pH 6.7 diet had reduced average daily gain (ADG, P < .01) and average daily feed intake (ADFI, P < .001) during wk 1-3 and overall compared with pigs fed the pH 6.0 diet, but ADG and ADFI were not effected when the pH 5.4 diet was fed. There was a dietary pH by phosphorus source interaction (P < .05) for ADFI. DCP fed pigs had increased ADFI as dietary pH was reduced from 6.7 to 5.4, but DFP fed pigs had similar ADFI as dietary pH decreased from 6.0 to 5.4, and decreased ADFI as dietary pH increased from 6.0 to 6.7. Dietary pH had little influence on F:G, and phosphorus source had little effect on either ADG, ADFI or F:G.

Dietary pH did not influence the pH and Cl⁻ of the digesta for any gastro-intestinal section measured, except the Cl⁻ in the stomach; both pH 5.4 and 6.7 fed pigs had a higher (P < .01) Cl⁻ than the pH 6.0 fed pigs. Only shear force of the fourth metacarpal and specific gravity of the fourth metatarsal were increased (P < .01) for pigs fed the DCP compared with DFP diets. Neither dietary pH nor phosphorus source influenced backfat or loin muscle area.

These results suggest that maintaining the acidifity of the diet during the first 3 wk after weaning at 28 d of age is important with the primary response seen in ADFI. Varying dietary pH from 5.4 to 6.7 had little or no effect on gastrointestinal digesta characteristics, bone development and body composition.