Title page for ETD etd-06062008-170400
|Type of Document
||Garrett, Jennifer L.
||Varying rumen available carbohydrate and rumen available protein in diets of lactating cattle
|Polan, Carl E.
|Herbein, Joseph H. Jr.
|James, Robert E.
|Thye, Forrest W.
|Vinson, William E.
|Webb, Kenneth E. Jr.
- duodenal nutrient flow
- lactating cows
|Date of Defense
Two studies were conducted to evaluate the effects of
varying dietary sources of rumen available carbohydrate
(RAC) and rumen available protein (RAP) on milk yield and
milk composition, nutrient flow to the duodenum, ruminal and
total tract nutrient digestibilities, and ruminal pH,
ammonia-N, and VFA concentrations in lactating cows. The
first study was a response surface design utilizing nine
dietary combinations of RAC and RAP. The response surfaces
of all milk variables were saddle-shaped. Because of the
saddle-shaped surfaces, an optimum combination of RAP and
RAC for milk production variables was not obvious from the
limited range of RAC and RAP used in this study. Ridge
analysis of the saddle surfaces predicted maximum milk yield
when dietary RAC was below 69 % of the DM and RAP below 60%
of CP in alfalfa-corn silage based diets. In the second
study, four cannulated (ruminal and duodenal) cows were
utilized in a 4x4 Latin square design. Four of the nine
original diets were selected to provide the largest range of
RAC and RAP. Nutrient flow, digestiblities and ruminal
parameters were evaluated. Although the in situ incubations
indicated that rates of DM, CP, and NDF degradabilities
differed among diets, no effects on overall ruminal pH and
total VFA concentrations were detected. Additionally, DM,
OM, NDF, ADF, and N flows to the duodenum were not affected
by dietary treatment. Nonmicrobial N flow was greater for
the barley-based diet, yet microbial flow was not different.
The differences in rates of availability determined by in
situ methods were not large enough to illicit a measurable
difference in nutrient digestion and utilization.
Additionally, the data implied that none of the diets were
limiting in RAC and RAP for vigorous microbial activity.
Fat-corrected (3.5%) milk production was greatest (P<.05)
when alfalfa-corn silage based diets contained supplements
providing intermediate (69 % RAe) carbohydrate availability
(corn and barley) and low (60 % RAP) ruminal protein
availability (BM and SBM). The increase in fat-corrected
milk was consistent with the predicted milk production
response in the previous study when RAP exceeded 62% of CP.
However, the ruminal parameters, nutrient flow, and nutrient
digestibility measurements did not adequately explain the
increased milk production when diets contained increased
|| Approximate Download Time
| 28.8 Modem
|| 56K Modem
|| ISDN (64 Kb)
|| ISDN (128 Kb)
|| Higher-speed Access
next to an author's name indicates that all
files or directories associated with their ETD
are accessible from the Virginia Tech campus network only.
If you have questions or technical
problems, please Contact DLA.