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Journal of Animal Science Abstract - Animal Nutrition

Phosphorus balance and fecal losses in growing Standardbred horses in training fed forage-only diets1


This article in JAS

  1. Vol. 91 No. 6, p. 2749-2755
    Received: Oct 31, 2012
    Accepted: Feb 17, 2013
    Published: November 25, 2014

    2 Corresponding author(s):

  1. G. Ögren,
  2. K. Holtenius and
  3. A. Jansson 2
  1. Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden


This study examined the P balance and fecal P losses in growing Standardbred horses in training fed a forage-only diet with or without P supplementation and assessed the magnitude and proportion of the soluble, inorganic P (Pi) fraction in feces. Fourteen Standardbred horses (aged 20.0 ± 0.3 mo) adapted to ad libitum intake of grass forage containing 0.25% P were used in a crossover experiment investigating 2 dietary treatments with (high-P) and without (low-P) mineral supplementation for 6 d. Daily feed intake and refusals were weighed. Spot samples of feces were collected twice daily on d 4 to 6 and analyzed for total P and Pi. Acid-insoluble ash was used as a marker for total fecal output. Spot samples of urine were collected once on d 4 to 6 and analyzed for P and creatinine. Daily P intake was greater (P < 0.001) for the high-P diet (32.0 ± 0.6 g) than the low-P diet (17.5 ± 0.6 g), and the individual intake ranged from 13.3 to 38.4 g/d. Total fecal excretion of P was also greater (P < 0.001) for the high-P diet (30.3 ± 0.8 g/d) than the low-P diet (17.0 ± 0.8 g/d) whereas excretion in urine was less than 0.2 g/d on both diets. Using simple regression analysis, fecal endogenous P losses were estimated to be less than 10 mg/kg BW. Phosphorus retention was 1.6 ± 0.6 and 0.3 ± 0.6 g/d on the high- and low-P diets, respectively, but only that for the high-P diet was greater (P < 0.05) than 0 g/d. The proportion of Pi of total fecal P excretion was 100 ± 3% for the high-P diet and 87 ± 3% for the low-P diet (P = 0.005) and Pi increased linearly with P intake (y = 1.10x – 4.44; r2 = 0.91; CV = 9.9%; P < 0.001). In conclusion, on this forage-only diet significant retention of P occurred at a daily P intake of 7.1 g/100 kg BW. Phosphorus was mainly excreted in feces and both total fecal P and Pi excretion had a strong relationship to P intake. More than 80% of total P appeared to be soluble. Fecal endogenous P losses were similar to those described previously in growing horses.

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