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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #142942
Title: AVAILABILITY OF PHOSPHORUS IN DAIRY FEEDS

Author
item AGUERRE, M - UW-MADISON
item MARCOT, S - UW-MADISON
item HENSELMEYER, H - UW-MADISON
item Satter, Larry

Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/25/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Three trials were conducted to measure phosphorus availability in feed ingredietns. In trial 1 and 2, 10 and 9 cows in mid to late lactation were fed for 3 wks a low P basal diet (BD) containing 0.17-0.19% P (dry basis). During the last 3-d of the third wk 12 fecal samples (dispersed through the 24-hr day) were collected. Ytterbium was used as an external marker for estimating DM digestibility. Following this three wk period, all cows were assigned to a trt diet where the test feed (soybean meal and corn gluten feed for trials 1 and 2) was inserted to provide a source of P. The test feed replaced P-free starch in the BD and increased P content of the test diets to approximately 0.3%. Fecal samples were again obtained during the last 3 days of the two-wk test period. This cycle was repeated in trial 1 and 2, this time with cottonseed and corn distillers grain. Dry matter digestibility estimates from the two BD periods were averaged for calculating P availability of the two test feeds for trial 1. Marker problems prevented DM digestibility estimates in trial 2, so values of 67 and 65 % were assumed for BD and test diets. The incremental increase in fecal P excretion due to feeding of the test feed was considered as unavailable P. Trial 3, utilizing 10 cows, was conducted in the same way, except there was only one BD period sandwiched between two test feed periods (porcine meat and bone meal and dicalcium P). The availability of P in test feeds ranged between 64 to 85%. These values are slightly higher than availability values used by NRC (2001), suggesting that the NRC estimates of P requirement provide a moderate margin of safety.