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In recent years, substantial progress has been made in understanding the sources of biological variation and genetic components of feed efficiency in growing animals consuming energy-dense mixed diets during the post-weaning phase. Much less is known about within-animal variation of feed efficiency for beef cows consuming moderate to low-quality forage diets common to most cow/calf production systems. Considerable evidence indicates the existence of a genetic by environment interaction for feed efficiency. Phenotype for feed intake and feed efficiency are most practically and cost effectively determined during the post-weaning growing stage. However, due to the additional nutrient sinks associated with gestation and lactation, and the cost, labor and technology required to measure economically relevant traits in mature cows, little is known about forage utilization efficiency in beef cows. The beef cow/calf segment of the industry represents, by far, the greatest opportunity to reduce beef production input costs and reduce the industry's carbon footprint. We reason that selection tools for feed intake and feed efficiency developed over the last 20 years are effective for the post-weaning growing and finishing phases, although only marginally effective for beef cows consuming unprocessed, moderate to low-quality forage. In this session, we will discuss challenges, opportunities, and experiences associated with measuring forage intake and recovered energy in beef cows. [ABSTRACT FROM AUTHOR]

Our objectives were to 1) determine diet selection of goats and cattle grazing woody plant-encroached tallgrass prairie, and, 2) determine the effect of the presence of goats on cattle diet selection. In 2019, pastures (n = 6) were allocated to 1 of 2 experimental grazing treatments. Pastures (n = 3) grazed by cattle only (crossbred Angus yearling heifers) were moderately grazed year-round at 4.2 ha per heifer. Pastures (n = 3) grazed by cattle (similar heifers) and goats (Boer x Spanish crossbred mature does) were moderately grazed year-round at 4.7 ha per heifer and 2.3 ha per goat simultaneously. Each pasture was burned in 6 patches (2 patches per year) to facilitate range management objectives. Every 35 d from May 2022 until June 2023, fecal samples were collected from all animals and stored frozen and later composited into 2 composites per animal species per pasture. Composites were then analyzed by a commercial lab with DNA barcoding and high-throughput sequencing. For statistical analysis, the top 50 Exact Sequence Variants (ESVs), representing species of forage, across all treatments were used for analysis. Each ESV was georeferenced to eliminate plants that did not grow in the study area, and assigned to a representative functional group: graminoid, forb, legume, and woody plant. Analysis of variance and Tukey's post-hoc separation of estimated marginal means were performed to assess the effects of season, grazer species, and the interaction. The interaction of season and grazer species was significant (P < 0.01) for the percentage of diet selected from each functional group of plants. As expected, goats selected a greater percentage of their diet as woody plants in summer (57%) and winter (74%) compared with cattle (27%). Cattle selected more grass in winter (34%) than goats (11%). Goats selected more forbs in spring (33%) than cattle (10%). However, goats selected a lesser percentage of their diet as legumes in summer (16%) than cattle (58%), which was unexpected. Overall, these results indicate that both species of grazers select a diverse diet from these diverse pastures, and selection is dynamic over time. Goat presence in a pasture does not seem to drastically alter cattle selection, actually complementing cattle in these pastures where goats can be used to target species cattle do not prefer. [ABSTRACT FROM AUTHOR]