Real-time polymerase chain reaction (PCR) was used to quantify 16 procaryotic taxa in the rumina of two lactating dairy cows following supply and subsequent withdrawal of the feed additive monensin (13.9 mg/kg of diet dry matter) in a high-starch, silage-based ration. PCR was conducted on DNA from rumen samples collected 6 h post feeding on two successive days before monensin supplementation, after 30 days of monensin supplementation, and at six weekly intervals after monensin withdrawal. Mean values of relative population size (RPS, the percent of bacterial 16S rRNA copy number) for genus Prevotella increased (P < 0.05) from 41.8% without monensin to 49.2% with monensin and declined to 42.5% after monensin withdrawal. Mean RPS values for two biohydrogenating species (Megasphaera elsdenii and Butyrivibrio fibrisolvens) were low (<0.4%) and declined several-fold in response to monensin. Mean RPS values for the biohydrogenating species Eubacterium ruminantium, four cellulolytic species, four starch- or dextrin-fermenting species, and Domain Archaea were not altered (P > 0.10) upon monensin feeding or withdrawal. The data suggest that monensin in high-starch diets does not suppress populations of classical ruminal Gram-positive bacteria or the availability of H2, though it may affect bacteria involved in biohydrogenation of lipids that regulate bovine mammary lipogenesis.
An experiment was conducted to test the accuracy of the metabolizable protein system in predicting the amount of urea that would be useful in a corn-based cattle diet. Treatment diets included a basal, low-protein (7.8% CP) negative control (NC) with no supplemental N and a positive control (PC) that contained soybean meal. Urea was added to the NC diet in quantities calculated to be either 25% deficient (LU), equal to (MU) or 25% in excess (HU) of the urea fermentation potential ( UFP ). In vitro rumen fermentation studies were used to determine sequential ammonia production and digestible dry matter content of the diets. In a growth trial, 12 individually-fed Angus, Hereford and Angus X Hereford steers weighing an average of 213 kg were assigned randomly to each treatment diet. At the conclusion of the 112-d trial, rumen ammonia and jugular blood urea N (BUN) concentrations were determined on two steers from each treatment before feeding and at 1, 2, 3, 4 and 5 h postfeeding. In vitro ammonia concentrations of the NC and PC treatments were lower (P less than .05) than that of urea containing diets. In vivo rumen ammonia concentrations at 1 h postfeeding and BUN levels at 3 h postfeeding were low for both the NC and PC diets compared with urea-containing diets. Both of these values increased with each successive increase of added urea to the NC diet. During the initial 70 d of the growth trial, daily gains were improved (P less than .05) by addition of urea up to the MU level, which fulfilled the calculated UFP .(ABSTRACT TRUNCATED AT 250 WORDS)
A two-stage in vitro ruminal fermentation experiment was conducted to determine the extent of marker migration and the effects of marker addition on digestibility. Fermentation studies were terminated either at the end of stage I, the fermentation phase, or stage II, the pepsin digestion phase. Treatment diets contained ytterbium-marked corn plus chopped Coastal bermudagrass hay and nonmarked corn plus chopped hay. After stage I of the in vitro ruminal fermentation, 90% of ytterbium was recovered. Of this, 8.8% of the ytterbium had migrated to the hay, 2% was recovered in the supernatant and 89.2% remained bound to the corn. After completion of both stages, 72% was recovered, of which 7.9% was bound to corn, 33.6% was bound to the hay, 1.1% was recovered in the stage I supernatant and 57.4% was associated with the acid pepsin supernatant. Dry matter digestion was not affected after stage I but after stage II, digestibility was decreased 7% due to marker addition. A ruminal-cannulated Holstein steer weighing approximately 680 kg was used to determine turnover rates from the rumen of liquid and five different particle sizes of corn. Corn from each of two processing methods was fractionated into five particle sizes by dry-sieving. The corn particles included steam-rolled corn (SRC) retained on a 4-mm sieve and marked with dysprosium, SRC retained on a 2-mm sieve and marked with erbium, cracked corn (CC) retained on a 4-mm sieve and marked with yttrium, CC retained on a 2-mm sieve and marked with ytterbium, and CC retained on a 1-mm sieve and marked with samarium.(ABSTRACT TRUNCATED AT 250 WORDS)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.