BASIC PROTEIN METABOLISM IN RUMINANTS

The concept of feeding rumen degradable protein with either urea, soybean meal (SBM) or a combination urea and blood meal (BM) was investigated. Daily gain of mid-gestation cows was not improved by supplementation of SBM or a combination of urea and dried delactosed whey (DDW) compared to an all urea supplement. When protein was limiting in a heifer growth trial, heifers supplemented with urea, BM and condensed liquid whey (CLW) gained slightly faster than heifers supplemented with urea and BM although differences were not significant. In a lamb growth trial, lambs fed (ad libitum) diets supplemented with a combination of urea and either DDW or casein had increased daily gains (P \u3c .01), feed intakes (P \u3c .005) and gain/feed ratios (P \u3c .05) compared to lambs fed a diet supplemented with urea alone. In a second lamb growth trial and a steer growth trial, animals supplemented with urea-DDW gained faster and more efficiently than animals fed urea alone. Animals fed SBM-urea or SBM-DDW gained faster and more efficiently than animals fed urea or urea-DDW. In a third lamb growth trial and a second steer growth trial, the relative value of BM compared to SBM was 251% to 348% depending on type of experimental design and method of data analysis used. In a steer abomasal trial, supplementation of urea-DDW to a 30% solka floc diet compared to urea supplementation alone, increased abomasol flows of nonammonia nitrogen (NAN), bacterial N and total amino acids. Supplementation of urea-DDW to a 30% corn starch diet compared to urea supplementation alone increased amino acid flow, but did not affect NAN flow or bacterial N flow. In a second steer abomasol trial, supplementation of urea-DDW compared to urea alone increased NAN flow, bacterial N flow (P \u3c .10) and total amino acid flow (P \u3c .06). Supplementation of BM-urea-DDW compared to BM-urea increased total amino acid flow. In a lamb rumen fermentation trial, supplementation of urea-DDW compared to urea alone, increased bacterial growth (P \u3c .05) and increased molar proportions of iso-butyrate (P \u3c .01), iso-valerate (P \u3c .01) and valerate (P \u3c .01)