Technical note: Whole-pen assessments of nutrient excretion and digestibility from dairy replacement heifers housed in sand-bedded freestalls

Authors: Coblentz, Wayne; HOFFMAN, PATRICK - University Of Wisconsin; ESSER, NANCY - University Of Wisconsin; BERTRAM, MICHAEL - University Of Wisconsin

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2013
Publication Date: 9/27/2013
Citation: Coblentz, W.K., Hoffman, P.C., Esser, N.M., Bertram, M.G. 2013. Whole-pen assessments of nutrient excretion and digestibility from dairy replacement heifers housed in sand-bedded freestalls. Journal of Animal Science. 91:4841-4848.

Interpretive Summary: Researchers attempting to improve the nutrient utilization in livestock need to measure what is excreted by the animal (feces and urine) in order to know the impact of the diets being studied. Collecting excreta on an individual animal basis is the most common method, but this approach is very labor intensive and costly, and many animal nutrition research facilities are not equipped to do this. Thus, while conducting animal feeding trials, we also have been looking for ways to measure excreta output on a whole-pen basis with multiple animals. Previous research efforts have been complicated by the use of organic bedding materials (such as wood shavings) which requires cumbersome analytical techniques to quantify excreta apart from the bedding. In this feeding trial, we tested the use of sand bedding based on the concept that it is entirely inorganic; therefore, ash can be used as an internal marker to separate quantities of sand from excreta. When using these refined methods, calculations of experimental error were much smaller than those determined previously from whole-pen collections with organic bedding materials. Potentially, statistical power could be improved further through a variety of options, and adding additional collections over a typical production trial lasting from 90 to 150 days would not be prohibitive on the basis of labor requirements or analytical costs. Generally, the whole-pen excreta collection system defined in this technical note is viable and would permit quantification of excreta output, as well as diet digestibility, on a whole-pen rather than an individual animal basis. While these results are encouraging, further refinements for homogenizing large volumes of pen manure are worthy of future evaluation.

Technical Abstract: Our objectives were to describe and test refined procedures for quantifying excreta produced from whole pens of dairy heifers. Previous research efforts attempting to make whole-pen measurements of excreta output have been complicated by the use of organic bedding, which requires cumbersome analytical techniques to quantify excreta apart from the bedding. Research pens equipped with sand-bedded freestalls offered a unique opportunity for refinement of whole-pen fecal collection methods, primarily because sand-bedded freestall systems contain no organic bedding; therefore, concentrations of ash within the manure, sand, and feces can be used to correct for contamination of manure by sand bedding. This study was conducted on a subset of heifers from a larger production-scale feeding trial evaluating ensiled eastern gamagrass [Tripsacum dactyloides (L.) L.] haylage (EGG) that was incorporated into a corn silage/alfalfa haylage-based blended diet at rates of 0, 9.1, 18.3, or 27.4% of total DM. The diet without EGG also was offered on a limit-fed basis. Eighty Holstein dairy heifers were blocked (heavy-weight, 424 ± 15.9 kg; light-weight, 324 ± 22.4 kg), and then assigned to 10 individual pens containing 8 heifers/pen. One pen per block was assigned to each of the 5 research diets, and whole-pen fecal collections were conducted twice for each pen. Grab fecal samples also were gathered from individual heifers within each pen, and subsequent analysis of these whole-pen composites allowed reasonable estimates of OM and NDF excreta output. Under the conditions of our experimental design, pooled SEM for the excreta DM, OM, NDF, and NDF (ash corrected) output were 0.113, 0.085, 0.093, and 0.075 kg/heifer/d, respectively. For DM excretion, this represented about one-third of the SEM reported for previous whole-pen collections from bedded-pack housing systems. Subsequent calculations of apparent DM and OM digestibilities indicated that the technique was sensitive, and linear trends (P = 0.027) associated with the inclusion rates of EGG within the diet were detected. This technique allows estimation of apparent diet digestibilities on multiple animals simultaneously, thereby mitigating the need for isolating individual animals to obtain digestibility coefficients. The approach appears viable, but requires hand labor for collections of multiple pens, thorough mixing of large volumes of manure, as well as analytical corrections for sand ingested by lounging heifers.