|Wu, Z - UNIVERSITY OF WISCONSIN|
|Rius, A - UNIVERSITY OF WISCONSIN|
Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: July 28, 2001
Publication Date: N/A
Technical Abstract: The effect of dietary Ca concentration on P excretion in feces of lactating cows was determined by feeding diets containing 0.36% P and either 0.70 or 1.10% Ca, varied by calcium carbonate. The two diets were fed to 17 late-lactation Holsteins (DIM 233, SD 49) in a crossover design involving 3-wk periods. Fecal samples were collected at 3-h intervals on the last day and lactation performance was measured during the last 2 wk of each period. Increasing dietary Ca concentration from 0.70 to 1.10% increased fecal Ca concentration (P < 0.01), but did not affect fecal P concentration (P=0.19). Milk yield (29.4 and 28.8 kg/d, SEM 0.3) were not affected (P> 0.10) by treatment. The lack of treatment effect on performance is consistent with other studies using lactating cows and growing steers that suggest a tolerance of wide Ca:P ratios by ruminants. Many dairy diets are formulated to contain Ca in excess of NRC (2001) recommendations. Reducing gdietary P from the current high levels normally fed, as suggested by recen research, does not require a concomitant decrease in dietary Ca to maintain a Ca to P ratio of 2:1 for normal P absorption. This conclusion applies when normal to moderately high amounts of Ca (0.70 to 1.10%) are fed.