Using Eastern Gamagrass to Limit Weight Gains by Replacement Dairy Heifers: 2. Measuring Excreta and Digestibility On a Whole-Pen Basis.

Previously, research efforts that attempted to make whole-pen measurements of excreta output were complicated by organic bedding materials. New research pens equipped with sand-bedded freestalls offered potential for refinement of whole-pen collection methods, largely because sand-bedded freestall systems contain no organic bedding. Our research objective was to evaluate novel procedures for quantifying excreta produced from whole pens of dairy heifers. This study was conducted on a subset of heifers used in a larger production-scale study evaluating eastern gamagrass [Tripsacum dactyloides (L.) L.] haylage that was incorporated into a corn silage/alfalfa haylage based total mixed ration at rates of 0, 9.2, 18.4, or 27.6% of total dietary DM. The diet without eastern gamagrass also was offered on a limit-fed basis. Eighty Holstein dairy heifers were blocked by weight (heavy, 424 ± 15.9 kg; light, 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 collections were conducted twice for each pen. Under the conditions framed by our experimental design, pooled SEM for the excreta output of DM, OM, and NDF were 113, 85, and 81 g/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 DM, OM, and NDF digestibilities indicate that the whole-pen evaluation system detected linear (P ≤ 0.027) trends associated with the inclusion rate of EGG in the diet for DM and OM. This research technique facilitated excreta collection and estimation of diet digestibility coefficients on multiple animals simultaneously, thereby mitigating the need for individual animal measurements. The approach is viable, but requires collections of multiple pens for statistical analysis, as well as thorough homogenization of large volumes of manure.