Effects of concentration of dietary phosphorus on amount and route of excretion.
Objectives were to determine the effect of dietary concentration of P in DM on routes of excretion of P and to evaluate direct and indirect measures of calculating DM digestibility and P excretion. Twelve lactating Holstein cows were fed 20 kg of DM containing .41% P daily for 4 wk and then were assigned randomly to one of three diets: low (.30%), medium (.41%), or high (.56%) in P for 9 wk. Total collections of excreta (feces and urine) and milk were made during wk 4, 7, 10, and 13. At wk 4, cows excreted 88.2% of P consumed daily: 68.6% of excreted P in feces, 1.0% in urine, and 30.3% secreted in milk. Cows assigned to the low P diet decreased intake by 26.8% and excretion of P in feces by 22.7% in wk 13 compared with wk 4, whereas cows fed the high P diet increased intake by 36.5% and excretion of P in feces by 48.6%. Digestibility of DM was 62.6% when calculated from total collection of feces but only 55.7 or 56.5% when estimated indirectly using Cr or acid detergent lignin as indigestible markers. Apparent excretion of P was less than that estimated using either of the marker techniques (49.7 vs. 59.1 and 58.1 +/- .7 g/d of P) because digestibility of DM was underestimated. A prediction equation was developed for P excretion based on P intake and milk production.
Morse
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D
Dairy Science Department, University of Florida, Gainesville 32611-0920.
Head
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HH
Wilcox
C J
CJ
van Horn
H H
HH
Hissem
C D
CD
Harris
B
B
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004063:Digestion; D005243:Feces / Q000737:chemistry; D005260:Female; D007774:Lactation; D008892:Milk / Q000737:chemistry; D016226:Phosphorus, Dietary / Q000008:administration & dosage* / Q000493:pharmacokinetics* / Q000652:urine
D016226:Phosphorus, Dietary