Apparent digestibility of nitrogen and nitrogen retention of forages fed to steers in metabolism stalls.

Holstein steers in metabolism stalls were utilized to determine apparent digestibility of N (DN), N retention (NR) expressed as a percentage of total N consumed, and Mcal/kg digestible energy (DE) when diets of seven different classes of forages were fed. The best predictive equation for digestibility of N in the 153 forages studied was DN(%) = -98.1065 + 11.4724 (%CP) + 41.4475 (DE) - .1498 (%CP)2 - 1.2541 (DE)2 - 1.9309 (CP) (DE), with R2 = .74 and Sy.x = 8.63, where %CP is the percent crude protein of the forage. The best predictive equation for DN of sorghum silages, corn silages, legume hays and temperate grass hays contained both %CP and DE as predictor variables. The best predictive equations for DN of sorghum-sudan and bermudagrass hays contained only %CP and (%CP)2 as predictor variables. The predictive equation for DN of 14 alfalfa hays involved only the linear relationship to %CP. The best scheme for predicting NR as a percentage of N consumed in 116 forages was a combination of three equations as follows: 1) NR(%) = -47.0797 + 6.4733 (%CP) - .1542 (%CP)2 for forages, where DE = less than 2.42 Mcal/kg; 2) NR(%) = -67.6306 + 10.1354 (%CP) - .2726 (%CP)2, where DE = 2.42 - 2.87 Mcal/kg; and 3) NR(%) = 28.3458 + 4.4722 (%CP) - .1263 (%CP)2, where DE = greater than 2.87 Mcal/kg; R2 = .42 and Sy.x = 14.86.(ABSTRACT TRUNCATED AT 250 WORDS)