Three duodenally cannulated, lactating Holstein cows were dosed with rare earth-labeled grain to evaluate effects of passage model, sampling site, and marker dosing time on digesta passage parameters. Cows were given ad libitum access to feed twice daily. Rare earth-labeled grain (applied by the 24-h immersion technique) was fed immediately before (Dy) or 2 h after (Yb) the morning feeding, and duodenal digesta and feces were sampled. Marker excretion curves were fit to a two-compartment, biexponential model, using curve peeling or to a series of two-compartment models, with one to six orders of gamma time-dependency in the fast compartment, using nonlinear regression. Passage estimates from the curve-peeled, biexponential model were similar to those from the best fit of the nonlinear models, which had three orders of gamma time-dependency. Ruminal passage rate of grain, averaged across models, sampling site, and dosing time, was .077/h. Estimates of time to first appearance of marker at the sampling site and mean retention times were longer (8 vs 1 h and 25 vs 17 h, respectively), but passage rates were similar, when determined from fecal compared with duodenal samples (P < .05). Marker dosing time did not influence any of the parameters. It is concluded that both curve-peeling (linear regression) and nonlinear regression methods can be equally useful for evaluating passage kinetics of grain in dairy cows and that sampling site and time of marker dosing have little effect on passage parameter estimates.
Temporal changes in soil composition are of interest in determining nutrient transport in the soil. This study was conducted to determine whether electromagnetic (EM) soil conductivity differences can be linked to feedlot manure application and then be used to trace these differences over a growing season. A series of soil conductivity maps of a research cornfield have been generated using GPS and EM induction methods. The site used in this study was treated over a six-year period with manure and compost applied at rates matching either the phosphorus or the nitrogen requirements of the corn. The plot was split with sub-treatments of a cover crop and no cover crop. Image processing techniques were used to establish treatment means for each of the growing season surveys. This method differentiated (P<0.05) the cover crop region and no-cover crop region with the exception of the period of rapid growth of the corn crop. This approach also distinguished (P<0.05) the nitrogen check treatment (commercial application rate) versus manure or compost treatment for both the cover crop and no-cover areas at strategic times in the growing season. The EM methods also provide insights into the dynamics of nutrient transformations and are supported with soil analysis. This paper will present the details of the methods used and the results of the study for one growing season.
