|Hall, Mary Beth|
Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/5/2005
Publication Date: 7/26/2005
Citation: Hall, M. B., Larson, C. C. 2004. Effects of nonfiber carbohydrate source and protein degradability on ruminal protein fractions and NDF disappearance [abstract]. Journal of Dairy Science 87 Suppl. (1):463.
Technical Abstract: Effects of nonfiber carbohydrate source (NFC) and protein degradability (RUP) on concentrations (mM) of ammonia (NH3), amino acid (AA), and branch chain VFA (BCVFA) in ruminal fluid, and on in situ disappearance of NDF from sorghum silage were evaluated using 6 ruminally cannulated Holstein cows in a three period (21 d) partially balanced incomplete latin square design with a 3x2 factorial arrangement of treatments. Dietary treatments included three NFC sources (ground corn=starch=ST; molasses+sucrose=sugar=SU; and citrus pulp=soluble fiber+sugar=SF) and two concentrations of ruminally degradable protein (+or-RUP) achieved by addition or omission of expeller soybean meal. Total mixed rations were formulated to be isonitrogenous and offered ad libitum. Sorghum silage (2 mm Wiley mill grind) was incubated in situ in polyester bags (53 ± 10 µm pore size) inserted via the rumen cannula on days 16, 17, and 18 at intervals to allow incubation times of 0, 6, 12, 18, 24, 30, and 48 h; residual NDF was measured. Ruminal fluid samples were collected on day 20 just prior to feeding and hourly for 12 h. Protocols were applied in each period. Significance was declared at P#88040.05; values presented are least squares means. NH3 differed only for RUP x hr in hours 1 through 3 post-feeding, with -RUP greater than +RUP. AA differed by NFC in hr 1 through 3, with ST less than SU + SF, and for interactions of NFC x hr and RUP x hr for all hours. BCVFA differed by NFC source with ST greater than SU+SF, and SF tended to be greater than SU (P=0.07). BCVFA tended to differ by RUP x hr (P=0.10). In situ disappearance of NDF differed for NFC and NFC x RUP in hours 6, 18, 24, and 30, and tended to differ for NFC x RUP at 48 h (P=0.054). Differences did not appear to be solely due to ruminal pH. Differences in ruminal AA and BCVFA suggest that ruminal protein digestion or use differs by NFC source. Differences in in situ disappearance of NDF suggest that in situ results are not likely to be uniform across diets and may be best suited for relative evaluation of NDF digestibility.