title: Methods for assessing phosphorus overfeeding on organic and conventional dairy farms.
abstract: Phosphorus (P) losses from dairy farms can severely damage aquatic ecosystems, so it is important to have tools to assess overfeeding of P. This study screened P intake and faecal excretion of different P fractions in dairy cows on conventional and organic farms, compared the P feeding level of the herds against the recommendations and analysed different sampling and analysis methods for assessing the general status of P feeding on the farms. The organic (n=14) and conventional farms (n=15) were of comparable size and were located in southern Sweden. On each farm, feed intake was registered for 10 cows representing four different lactation stages and their P intake was calculated and related to current recommendations. Faecal samples taken from the same cows were analysed for total P (TP) and soluble P. Milk production data for the cows were obtained from the Swedish official milk recording scheme. TP was determined in one slurry sample per farm. More than 70% of the cows studied, representing both conventional and organic herds, consumed P in excess of the recommendations. Conventional herds had higher P content in the ration than organic herds, and lactating cows in conventional herds had higher faecal concentrations of total and soluble P than those in organic herds. However in dry cows, the P content of the ration and soluble P and TP in faeces did not differ between the two management systems. Soluble P was well correlated to TP in faeces, and both were good indicators of P overfeeding.
authors.affiliation: 1 Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, SE-753 23 Uppsala, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Nordqvist
authors.affiliation: 1 Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, SE-753 23 Uppsala, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Holtenius
authors.affiliation: 1 Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, SE-753 23 Uppsala, Sweden.
authors.forename: R
authors.initials: R
authors.lastname: Spörndly
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle; D004787:Environmental Pollution / Q000517:prevention & control*; D005243:Feces / Q000737:chemistry; D005260:Female; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000187:drug effects / Q000706:statistics & numerical data*; D015233:Models, Statistical; D058871:Organic Agriculture; D016226:Phosphorus, Dietary / Q000009:adverse effects* / Q000378:metabolism*; D013548:Sweden
chemical_list: D016226:Phosphorus, Dietary