Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2006
Publication Date: 9/1/2006
Citation: Reynal, S.M., Broderick, G.A., Larget, B. 2006. Short Communication: Effectiveness of sample duplication to control error in ruminant digestion studies. Journal of Dairy Science. 89:3501-3504. Interpretive Summary: When studying animal responses to treatments of interest, our measurements are affected not only by those treatments, but also by variation among the animals under the same treatment (i.e., inherent variation within the population) and by errors associated with the physical conduct of the experiment (e.g., experimental design, sampling, laboratory analyses, etc.). Although the most effective allocation of resources is to increase the number of animals assigned to each treatment, this may not be achievable in ruminant digestion studies due to the high cost of cannulating and maintaining those animals. Alternatively, multiple measurements from each animal will improve accuracy of estimates if day-to-day variation within animals and sampling and analytical errors contribute a substantial proportion of the total variation. Because of the complexity of the digesta sampling process, usually only one measurement of digesta flow is made and therefore information on variance due to sampling and analyses is lacking. In the present study, eight ruminally-cannulated lactating dairy cows were used to assess using sample duplication to control day-to-day variation within animals and errors associated with sampling and laboratory analyses. Sample duplication improved precision of measurements by reducing error variance by an average 29% among variables studied. Sample duplication can substantially reduce experimental error originating from day-to-day variation within cows, sample collection, and laboratory analyses, thus improving statistical power in ruminant digestion studies.
Technical Abstract: Eight ruminally-cannulated lactating dairy cows from a study on the effect of dietary rumen-degraded protein on production and digestion of nutrients were used to assess using sample duplication to control day-to-day variation within animals and errors associated with sampling and laboratory analyses. Two consecutive pooled omasal samples, each representing a feeding cycle, were obtained from each cow in each period. The effectiveness of sample duplication in error control was tested by comparing the variance of the difference in treatment means when taking two samples from each cow in each period to the variance when taking only one sample. Compared with no duplication, sample duplication improved precision by reducing variance by 50, 40, 31, 23, 23, and 9% for, respectively, rumen undegraded protein flows, ruminal neutral detergent fiber digestibility, microbial nonammonia N flow, microbial efficiency, organic matter flow, and organic matter truly digested in the rumen. For these same variables, reductions in the standard errors of the difference between treatment means due to sample duplication represented 100, 87, 73, 59, 58, and 27% of the predicted reductions resulting from doubling the number of experimental units without sample duplication. Sample duplication can substantially reduce experimental error originating from day-to-day variation within cows, sample collection, and laboratory analyses, thus improving statistical power in ruminant digestion studies.