title: Effect of dietary phosphorus content on milk production and phosphorus excretion in dairy cows.
abstract: BACKGROUND
  Phosphorus (P) supplementation is costly and can result in excess P excretion. This study investigated the effects of reducing dietary P on milk production and P excretion in dairy cows over a full lactation.
  
  
  METHODS
  Forty-five multiparous Holstein dairy cows were divided into 15 blocks according to expected calving date and previous milk yield, and assigned randomly to one of the three dietary treatments: 0.37, 0.47, and 0.57% P (DM basis); these P levels represent the NRC recommendations, Chinese recommendations, and the amount of dietary P commonly fed by Chinese dairy farmers, respectively. Average daily feed intake was calculated from monthly data on feed offered and refused. Milk yields of individual cows were recorded weekly, and milk samples were taken for analysis of protein, fat, solids-not-fat, lactose, and somatic cell count. Blood samples were collected on days -6, -3, 0, 3, 6 relative to calving, and then monthly throughout lactation, and analyzed for P and Ca concentrations. Spot samples of feces and urine were collected for 3 consecutive d during weeks 12, 24, and 36, and P concentrations were analyzed. Reproduction and health data were recorded.
  
  
  RESULTS
  Dietary P did not affect dry matter intake or milk yield (P > 0.10). Milk fat content was slightly higher in cows fed 0.37% P than in cows fed 0.47% P (P = 0.05). Serum concentrations of P and Ca did not reflect dietary P content (P > 0.10). Fecal and urinary P both declined linearly (P < 0.05) as dietary P decreased from 0.57 to 0.37%. Fecal P content was 25% less when dietary P was 0.37% compared to 0.57%. Health events and reproductive performance were not associated with dietary P content (P > 0.05).
  
  
  CONCLUSIONS
  Lowering dietary P from 0.57 to 0.37% did not negatively affect milk production, but did significantly reduce P excretion into environment.
authors.affiliation: Institute of Dairy Science, Zhejiang University, Hangzhou, P. R. China ; College of Animal Science and Technology, Zhejiang Agriculture and Forestry University, Lin'an, Hangzhou, P. R. China.
authors.forename: Chong
authors.initials: C
authors.lastname: Wang
authors.affiliation: Institute of Dairy Science, Zhejiang University, Hangzhou, P. R. China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Institute of Dairy Science, Zhejiang University, Hangzhou, P. R. China.
authors.forename: Diming
authors.initials: D
authors.lastname: Wang
authors.affiliation: Institute of Dairy Science, Zhejiang University, Hangzhou, P. R. China.
authors.forename: Jianxin
authors.initials: J
authors.lastname: Liu
authors.affiliation: Institute of Dairy Science, Zhejiang University, Hangzhou, P. R. China.
authors.forename: Hongyun
authors.initials: H
authors.lastname: Liu
authors.affiliation: School of Veterinary Medicine, University of Pennsylvania, 382 West Street Road, 19348 Kennett Square, USA.
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wu
keywords: Dairy cows; Milk production; Phosphorus excretion; Phosphorus requirement