David K. Combs

Learn More
Increased liver blood flow (LBF) resulting from elevated feed intake in lactating dairy cows may increase steroid metabolism. Continuous infusion of bromosulphthalein (BSP; specifically metabolized in liver) was used to measure LBF. Similarly, progesterone (P4) and estradiol-17beta (E2) were administered by continuous infusion. Circulating concentrations at(More)
Our study investigated the effects of, and interactions between, forage particle size, level of dietary ruminally fermentable carbohydrate (RFC), and level of dietary starch on performance, chewing activity, and ruminal pH for dairy cows fed one level of dietary NDF. Twelve cows (48 DIM) were assigned to six treatments in a replicated 6 x 6 Latin square.(More)
Our study investigated the effects of, and interactions between, level of dietary ruminally fermentable carbohydrate (RFC) and forage particle size on milk production, nutrient digestibility, and microbial protein yield for dairy cows fed one level of dietary NDF. Eight cows (61 days in milk) were assigned to four treatments in a double 4 x 4 Latin square.(More)
Eight forages (alfalfa, birdsfoot trefoil, red clover, bromegrass, orchardgrass, perennial ryegrass, quackgrass, and timothy) at three maturities were evaluated for ruminal DM, CP, and NDF degradation kinetics. Duplicate dacron bags were incubated for 0, 3, 6, 10, 13, 25, 48, and 72 h in two late lactation Holstein cows fitted with ruminal cannulas over(More)
Our study investigated the effects of, and interactions between, level of dietary ruminally fermentable carbohydrate (RFC) and forage particle size on rumen pH and chewing activity for dairy cows fed one level of dietary NDF. Also, correlations between intake, production, chewing, and ruminal pH parameters were investigated. Eight cows (61 days in milk)(More)
Forty-six multiparous Holstein cows were assigned at 5 d postpartum to a completely randomized design employing a 2 x 3 factorial arrangement of treatments. Factors were 0 and 5% added prilled long-chain fatty acids (DM basis) and three forage to concentrate ratios (45:55, 64:36, 84:16). Diets consisted of immature alfalfa silage and a concentrate of(More)
The nutrient contents of perennial ryegrass (Lolium perenne L.) and alfalfa (Medicago sativa L.) are reasonably similar. Despite similarities, the lactation performance of dairy cows fed perennial ryegrass has not been compared with the lactation performance of dairy cows fed alfalfa. The present study was implemented to compare the performance of lactating(More)
We conducted two experiments to evaluate the effects of corn supplementation, source of corn, and corn particle size on performance and nutrient utilization of lactating dairy cows. In experiment 1, treatments were 1) direct-cut grass-legume forage without supplement, 2) direct-cut forage plus 10 kg DM of ground dry shelled corn-based concentrate, and 3)(More)
Despite several inherent characteristics that would appear to make hair a useful biopsy tissue, many problems make interpretation of data derived from hair analysis difficult. Endogenous minerals are incorporated into hair by several routes. Most attention on hair mineral incorporation has focused on element uptake within the hair follicle. Minerals(More)
Weekly reproductive health examinations were performed on 46 multiparous Holstein cows from 14 to 100 d post partum. Sixteen cows developed 19 nonsimultaneous ovarian cysts, with a mean day of first detection at 34.3 +/- 4.5 d post partum and a mean duration of 31.0 +/- 4.3 d after first detection. Coccygeal blood was collected three times weekly, and(More)