Assessing different sampling regimes for estimating dietary characteristics using internal markers

Authors: Beck, Matthew - Matt; PROCTOR, JARRET - Texas A&M University; SMITH, JASON - Texas A&M Agrilife; GOUVÊA, VINICIUS - Texas A&M Agrilife; Kasuske, Zachery; FOOTE, ANDREW - Oklahoma State University; Gunter, Stacey; BECK, PAUL - Oklahoma State University

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2023
Publication Date: 12/1/2023
Citation: Beck, M.R., Proctor, J.A., Smith, J.K., Gouvêa, V.N., Kasuske, Z.A., Foote, A.P., Gunter, S.A., Beck, P.A. 2023. Assessing different sampling regimes for estimating dietary characteristics using internal markers. Applied Animal Science. 39(6):411-422. https://doi.org/10.15232/aas.2023-02452.
DOI: https://doi.org/10.15232/aas.2023-02452

Interpretive Summary: Beef cattle performance and environmental impacts are driven by dry matter digestibility (DMD), crude protein digestibility (CPD), and digestible energy content of the diet (DE). These factors influence losses such as enteric methane emissions and nutrients excreted. Internal markers can be used to estimate these factors. Using internal markers require fecal sampling through additional animal handling. However, animal handling can cause stress, which then can influence intake and subsequently DMD, CPD, and DE. Thus, optimizing fecal sampling protocols is necessary to minimize cattle stress. ARS scientists at Bushland, TX and Woodward, OK; as well as scientists from Oklahoma State University and Texas A&M AgriLife compared actual DMD, CPD and DE to estimated values using three internal markers and various sampling frequency protocols. They discovered that DMD, CPD and DE could all be adequately estimated with minimal additional animal handling requirements. These findings allow for optimized labor, time, and animal handling requirements in beef cattle feeding research.

Technical Abstract: The objectives of this experiment were to optimize fecal sample collection protocols for using internal markers [acid detergent insoluble ash (ADIA), indigestible neutral (INDF) and acid detergent fiber (IADF)] to estimate dry matter digestibility (DMD), crude protein digestibility (CPD), and digestible energy (DE). Steers (n = 6; 754 ± 20.5 kg body weight) used in this experiment were part of a larger study containing two experimental periods, where steers were fed a starter diet in the first period and then a finisher in the second period. Steers were housed in individual pens and dry matter intake was measured. Fecal collection bags were fitted to steers for 4-days during each dietary period. Once bags were placed, spot fecal samples were collected every 12-h for 2-days. The fecal sampling regimes evaluated were either: 1) one sample taken in the morning (AM-1d); 2) samples taken in the mornings of 2-days (AM-2d); 3) a morning and evening sample taken for 1-day (AM&PM-1d); or 4) a morning and evening sample taken for 2-days (AM&PM-2d). The ADIA marker was found to be inadequate under the current experimental conditions. When using INDF and IADF, the AM-1d fecal sampling protocol provided adequate agreement with actual measurements for DMD and DE, but did not meet the threshold set when assessing CPD. Agreement between estimated and observed DMD, CPD, and DE were improved when using INDF and IADF with the following trend in sampling protocols: AM-1d < AM-2d< AM&PM-1d < AM&PM-2d and this was largely driven by improvements in precision and not accuracy. However, researchers will need to determine if the improvements in method precision is worth the increased requirements in labor, time, and animal handling requirements. This decision will be driven by experimental design limitations.