Estimation of annual phosphorus excretion from pigs in Korea

The objective was to estimate the annual phosphorus (P) excretion from pigs in Korea based on P and phytate-P concentrations in commercial swine diets. Fifty-eight samples from commercial diets for various growth stages of pigs were collected from 16 swine farms and analyzed for P and phytate-P concentrations. The P concentrations ranged from 0.54% to 0.66%. Phytate-P contents in the piglet phase 1 and 2 diets were less (0.19% and 0.22% vs. 0.28% to 0.31%; p < 0.05) than those in the growing pig or sow diets. Fecal P excretion was calculated based on total P, phytate-P, and phytase concentrations: fecal P excretion (g/day) = [total P in feed (g/kg) - apparent total tract digestible (ATTD) P in feed (g/kg)] × feed intake (kg/day). The Gompertz model was adapted to estimate feed intake from suckling to finishing pigs, from birth to 121.5 kg body weight (BW), on days 0 to 180. Feed intake for gestating and lactating sows was adapted from the NRC. The ATTD P in the feed was estimated using the following equation: ATTD P (g/kg) = 0.135 + 0.649 × total P (g/kg) - 0.445 × phytate-P (g/kg) + 0.470 × phytate-P × (1 - e^{-0.824 × phytase}). The phytase concentration in all diets was assumed to be 500 FTU/kg. Urinary P excretion for the market swine was estimated using the following equation: Urinary P excretion (g/day) = BW (kg) × 0.007 (g/kg BW/day). The urinary P excretion for reproductive sows was adapted from a previous study. The total annual P excretion for market pigs was estimated to be 1.94 kg/year, which is equivalent to a pig with a BW of 44.1 kg at 93 days of age. For gestating and lactating sows, the total annual P excretion was estimated to be 3.26 kg/year and 6.89 kg/year, respectively. Assuming a population ratio of 91:7:2 for market pigs, gestating sows, and lactating sows, the annual P excretion from all market and breeding swine in Korea was estimated to be 2.15 kg/year.