Effects of concentration of dietary phosphorus on amount and route of excretion

• Published in: Journal of dairy science 1992-11, Vol.75 (11), p.3039-3049
• Main Authors: Morse, D. (North Dakota State University, Fargo), Head, H.H, Wilcox, C.J, Van Horn, H.H, Hissem, C.D, Harris, B. Jr
• Format: Article
• Language: English
• Subjects: Animals; Cattle - metabolism; DIETA; DIGESTIBILIDAD; DIGESTIBILITE; Digestion; EXCRECION; EXCRETION; FECES; Feces - chemistry; Female; FOSFORO; HECES; Lactation; LAIT; LECHE; Milk - chemistry; MINERALES; MINERAUX; ORINA; PHOSPHORE; Phosphorus, Dietary - administration & dosage; Phosphorus, Dietary - pharmacokinetics; Phosphorus, Dietary - urine; REGIME ALIMENTAIRE; URINE; VACAS LECHERAS; VACHE LAITIERE
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.s0022-0302(92)78067-9

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 0.41% 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 +/- 0.7 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