ABSTRACT: We studied the effects of supplementing
N as distillers dried grains with solubles (DDGS)
or urea to steers consuming corn-based diets. Six ruminally
and duodenally cannulated steers (244 kg) were
used in 2 concurrent 3 × 3 Latin squares and fed 1 of
3 corn-based diets: control (10.2% CP), urea (13.3%
CP), or DDGS (14.9% CP). Periods were 14 d, with
9 d for adaptation and 5 d for collection of urine and
feces. Urinary 15N15N-urea enrichments, resulting from
venous infusions of 15N15N-urea, were used to measure
urea kinetics. Dry matter intake (6.0 kg/d) was not affected
by treatment, but N intake differed (99, 151, and
123 g/d for the control, DDGS, and urea treatments,
respectively). Urea-N synthesis tended to be greater (P
= 0.09) for DDGS (118 g/d) than for the control treatment
(52 g/d), with the urea treatment (86 g/d) being
intermediate. Urea-N excreted in the urine was greater
(P < 0.03) for the DDGS (35 g/d) and urea treatments
(29 g/d) than for the control treatment (13 g/d). Gastrointestinal
entry of urea-N was not statistically different
among treatments (P = 0.25), but was numerically
greatest for DDGS (83 g/d), intermediate for urea (57
g/d), and least for the control (39 g/d). The amount
of urea-N returned to the ornithine cycle tended to be
greater (P = 0.09) for the DDGS treatment (47 g/d)
than for the urea (27 g/d) or control treatment (16
g/d). The fraction of recycled urea-N that was apparently
used for anabolism tended (P = 0.14) to be greater
for the control treatment (0.56) than for the DDGS
treatment (0.31), with the urea treatment (0.45) being
intermediate, but no differences were observed among
treatments in the amount of urea-N used for anabolism
(P = 0.66). Urea kinetics in cattle fed grain-based diets
were largely related to the amount of N consumed. The
percentage of urea production that was captured by
ruminal bacteria was greater (P < 0.03) for the control
treatment (42%) than for the DDGS (25%) or urea
treatment (22%), but the percentage of duodenal microbial
N flow that was derived from recycled urea-N
tended (P = 0.10) to be greater for the DDGS treatment
(35%) than for the urea (22%) or control treatment
(17%). Thus, ruminal microbes were more dependent
on N recycling when the protein supplement was
largely resistant to ruminal degradation.
ABSTRACT: We studied the effects of supplementingN as distillers dried grains with solubles (DDGS)or urea to steers consuming corn-based diets. Six ruminallyand duodenally cannulated steers (244 kg) wereused in 2 concurrent 3 × 3 Latin squares and fed 1 of3 corn-based diets: control (10.2% CP), urea (13.3%CP), or DDGS (14.9% CP). Periods were 14 d, with9 d for adaptation and 5 d for collection of urine andfeces. Urinary 15N15N-urea enrichments, resulting fromvenous infusions of 15N15N-urea, were used to measureurea kinetics. Dry matter intake (6.0 kg/d) was not affectedby treatment, but N intake differed (99, 151, and123 g/d for the control, DDGS, and urea treatments,respectively). Urea-N synthesis tended to be greater (P= 0.09) for DDGS (118 g/d) than for the control treatment(52 g/d), with the urea treatment (86 g/d) beingintermediate. Urea-N excreted in the urine was greater(P < 0.03) for the DDGS (35 g/d) and urea treatments(29 g/d) than for the control treatment (13 g/d). Gastrointestinalentry of urea-N was not statistically differentamong treatments (P = 0.25), but was numericallygreatest for DDGS (83 g/d), intermediate for urea (57g/d), and least for the control (39 g/d). The amountof urea-N returned to the ornithine cycle tended to begreater (P = 0.09) for the DDGS treatment (47 g/d)than for the urea (27 g/d) or control treatment (16g/d). The fraction of recycled urea-N that was apparentlyused for anabolism tended (P = 0.14) to be greaterfor the control treatment (0.56) than for the DDGStreatment (0.31), with the urea treatment (0.45) beingintermediate, but no differences were observed amongtreatments in the amount of urea-N used for anabolism(P = 0.66). Urea kinetics in cattle fed grain-based dietswere largely related to the amount of N consumed. Thepercentage of urea production that was captured byruminal bacteria was greater (P < 0.03) for the controltreatment (42%) than for the DDGS (25%) or ureatreatment (22%), but the percentage of duodenal microbialN flow that was derived from recycled urea-Ntended (P = 0.10) to be greater for the DDGS treatment(35%) than for the urea (22%) or control treatment(17%). Thus, ruminal microbes were more dependenton N recycling when the protein supplement waslargely resistant to ruminal degradation.
การแปล กรุณารอสักครู่..
