Influence of ruminal degradable intake protein restriction on characteristics of digestion and growth performance of feedlot cattle during the late finishing phase.
Two trials were conducted to evaluate the influence of supplemental urea withdrawal on characteristics of digestion (Trial 1) and growth performance (Trial 2) of feedlot cattle during the last 40 days on feed. Treatments consisted of a steam-flaked corn-based finishing diet supplemented with urea to provide urea fermentation potential (UFP) of 0, 0.6, and 1.2%. In Trial 1, six Holstein steers (160 ± 10 kg) with cannulas in the rumen and proximal duodenum were used in a replicated 3 × 3 Latin square experiment. Decreasing supplemental urea decreased (linear effect, P ≤ 0.05) ruminal OM digestion. This effect was mediated by decreases (linear effect, P ≤ 0.05) in ruminal digestibility of NDF and N. Passage of non-ammonia and microbial N (MN) to the small intestine decreased (linear effect, P = 0.04) with decreasing dietary urea level. Total tract digestion of OM (linear effect, P = 0.06), NDF (linear effect, P = 0.07), N (linear effect, P = 0.04) and dietary DE (linear effect, P = 0.05) decreased with decreasing urea level. Treatment effects on total tract starch digestion, although numerically small, likewise tended (linear effect, P = 0.11) to decrease with decreasing urea level. Decreased fiber digestion accounted for 51% of the variation in OM digestion. Ruminal pH was not affected by treatments averaging 5.82. Decreasing urea level decreased (linear effect, P ≤ 0.05) ruminal N-NH and blood urea nitrogen. In Trial 2, 90 crossbred steers (468 kg ± 8), were used in a 40 d feeding trial (5 steers/pen, 6 pens/ treatment) to evaluate treatment effects on final-phase growth performance. Decreasing urea level did not affect DMI, but decreased (linear effect, P ≤ 0.03) ADG, gain efficiency, and dietary NE. It is concluded that in addition to effects on metabolizable amino acid flow to the small intestine, depriving cattle of otherwise ruminally degradable N (RDP) during the late finishing phase may negatively impact site and extent of digestion of OM, depressing ADG, gain efficiency, and dietary NE.
Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, Baja California 21100 México.
Dixie
D
May
Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, Baja California 21100 México.
Jose F
JF
Calderon
Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, Baja California 21100 México.
Victor M
VM
Gonzalez
Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, Baja California 21100 México.
Martin
M
Montano
Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, Baja California 21100 México.
Alejandro
A
Plascencia
Facultad de Medicina Veterinaria y Zootecnia, UAT, Cd. Victoria, Tamaulipas, 87000 México.
Jaime
J
Salinas-Chavira
Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, Baja California 21100 México.
Noemi
N
Torrentera
Department of Animal Science, University of California, Davis E. Holton Rd, El Centro, CA 92242 USA.
Richard A
RA
Zinn
Cattle; Degradable protein; Digestion; Growth performance