Determination of optimal collection time of fecal grab samples in a chromium sesquioxide indicator digestion trail

A determination of time to collect fecal samples from animals in a Cr₂O₃ indicator digestion trial was made for mature beef cows. Five cows, differing In age, weight, dry matter consumption, stage of gestation, and stage of lactation were chosen as experimental animals. The cows were fed a ration of 10 percent alfalfa (Medicago sativa) pellets (91.5 percent DM) and 90 percent silage (20.0 percent DM). The silage consisted of Timothy (Phleum pratense) and Red Clover (Trifolium pratense). Each cow received 10 grams of chromium sesquioxide powder per day for 9 days before fecal sample collection was started. Fecal samples were collected at 2—hour Intervals for 24 hours after the ninth dosing with Cr₂O₃. Fecal samples were analyzed for percent fecal Cr₂O₃. From the 12 observed values for each cow, an average percent fecal Cr₂O₃ line and a multiple regression equation was determined which expressed the varying fecal Cr₂O₃ percentages by time for that cow as a hyperbolic curve. Also, the individual cow values at each sampling time were averaged and these twelve values were used to calculate an overall mean excretion line and an overall multiple regression equation expression of percent fecal Cr₂O₃ excretion at various times. Various characteristics of the excretion curves of the individual cows were compared, such as difference between lowest and mean percent fecal Cr₂O₃ (Amplitude), hours elapsed between the two times that the regression equation intersects with the mean excretion, and variation among animals of Cr₂O₃ excretion at specific sampling times. The coefficient of variation for curve amplitude was 12.44 percent. The intersection points of the overall mean excretion line with the overall predicted excretion curve were 11:12 a.m. and 1:24 a.m., which represent the optimal times for the collection of fecal samples. Coefficients of variation in Cr₂O₃ excretion among animals at or near these intersection times was higher (11-20 percent) than those at or near the minimum percent Cr₂O₃ excretion (4-14 percent).