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Licentiate thesis, 2013

Phosphorus to horses and cows

Ögren, Gunilla


It is important from a nutritional perspective to meet the phosphorus (P) requirements of animals. From an environmental perspective however, it is important not to feed more P than necessary, because excessive P will mainly be excreted with feces, and the soluble P fraction is vulnerable to runoff losses and may contribute to eutrophication. The recommended dietary P levels to dairy cows have successively decreased over the years but recently, an increase in the requirements to growing horses was suggested because fecal endogenous P losses might be higher than previously estimated. The main aim of this thesis was to assess fecal P losses in growing horses, and in brood mares and dairy cows kept on pasture in Sweden. In paper I, P balance and fecal P losses in growing horses in training fed a forage-only diet ad lib with (HP) or without (LP) P supplementation was studied. In addition, the proportion of the extractable (in dilute HCl solution) inorganic P fraction (Pi) of total P (TP) in feces was assessed. Fourteen Standardbred horses (aged 20 months) were used in a cross-over experiment. Feed intake was measured and spot samples of urine and feces were collected. Acid insoluble ash was used as indigestible marker to assess daily fecal output. Estimated P retention was low (<1.7 g/day) and only that for diet HP was significantly higher than 0 g/d. The fecal endogenous P losses were estimated to be less than 10 mg/kg body weight, which do not support the suggested increase in P requirements. The proportion of Pi of TP was > 85% and Pi increased linearly with P intake. In paper II, TP and Pi in feces from lactating and non-lactating dairy cows (n=167) and brood mares (n=74) kept on pasture was investigated and also the use of P supplements. Samples of feces, forages and pastures biomass were collected. The proportion of Pi of TP was greater for lactating horses than lactating cows (63±4 vs 49±5 %). Supplementation of lactating animals with P generally matched their estimated requirements and was therefore justified, while supplementation of non-lactating animals could not be justified. In conclusion, an increase in P requirement to growing horses seems not to be justified, and the high proportion of Pi in feces from horses indicates that P overfeeding of horses might be potentially more harmful to the environment than P overfeeding of dairy cows.


fosfor; träckprov; nutrition; hästar; kor

Published in

Rapport / Sveriges lantbruksuniversitet, Institutionen för husdjurens utfodring och vård
2013, number: 283
ISBN: 978-91-576-9116-3
Publisher: Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences

Authors' information

Ögren, Gunilla
Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management

UKÄ Subject classification

Animal and Dairy Science

URI (permanent link to this page)