Effects of supplemental ruminally degradable protein versus increasing amounts of supplemental ruminally undegradable protein on nitrogen retention, apparent digestibility, and nutrient flux across visceral tissues in lambs fed low-quality forage.
Two experiments were conducted to determine effects of supplemental ruminally degradable protein (RDP) vs. increasing amounts of supplemental ruminally undegradable protein (RUP) on intake, apparent digestibility, N retention, and nutrient flux across visceral tissues in lambs fed low-quality forage. Lambs were fed a basal diet of crested wheatgrass hay (4.2% CP) for ad libitum consumption, plus 1 of 4 protein supplements: isolated soy protein (RDP source) fed to meet estimated RDP requirements (CON), or corn gluten meal (RUP source) fed at 50, 100, or 150% of the supplemental N provided by CON (C50, C100, and C150, respectively). In Exp. 1, 12 lambs (29.9 +/- 2.7 kg) were used. Forage OM intake was not affected (P = 0.46) by protein degradability or by increasing RUP (P >/= 0.31). Apparent total tract OM digestibility was not affected (P = 0.10) by protein degradability, but increased (P </= 0.004) with increasing RUP. Urinary N excretion was not affected (P = 0.20) by protein degradability, but increased (P </= 0.006) with increasing RUP. Similarly, N retention (g/d) was not affected (P = 0.69) by protein degradability, but increased (P = 0.001) as RUP increased. However, N retention (% of digested N) was not affected (P >/= 0.40) by protein degradability or level of RUP. In Exp. 2, 16 catheterized lambs (32 +/- 5 kg) were used. Net release of ammonia-N from the portal-drained viscera (PDV) was greater (P = 0.02) for CON than for C100 and increased linearly (P = 0.002) as RUP increased. Net uptake of ammonia-N by liver was not affected (P = 0.23) by protein degradability, but increased linearly (P = 0.04) as RUP increased. Net urea-N release from liver was not affected (P >/= 0.49) by protein degradability or level of RUP. Net uptake of urea-N by PDV was greater (P = 0.02) for C100 compared with CON and increased (P = 0.04) with increasing RUP. Neither net release from PDV nor hepatic uptake of alpha-amino N were affected (P >/= 0.12) by protein degradability or level of RUP. Hepatic ammonia-N uptake accounted for 82, 38, 98, and 79% of net urea-N release from the liver for CON, C50, C100, and C150, respectively. Hepatic alpha-amino N uptake for all treatments greatly exceeded that required for the remaining urea-N release by the liver, suggesting that alpha-amino N may serve as a temporary means of storing excess N by liver between supplementation events. The pattern of net release or uptake of N metabolites between supplementation events requires further investigation.
Atkinson
R L
RL
Department of Animal Science, University of Wyoming, Laramie 82071, USA.
Toone
C D
CD
Robinson
T J
TJ
Harmon
D L
DL
Ludden
P A
PA
D000641:Ammonia / Q000378:metabolism; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D002408:Catheters, Indwelling / Q000662:veterinary; D004044:Dietary Proteins / Q000494:pharmacology*; D019587:Dietary Supplements; D004063:Digestion / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D008099:Liver / Q000378:metabolism*; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D009751:Nutritional Requirements; D011897:Random Allocation; D012756:Sheep / Q000254:growth & development / Q000378:metabolism*; D014781:Viscera / Q000378:metabolism*
D004044:Dietary Proteins; D000641:Ammonia; D009584:Nitrogen