Galen E. Erickson

The 8th revised edition of the Nutrient Requirements of Beef Cattle was released in 2016, with the recommendations provided in the publication being used extensively in both research and production settings. In the context of research needs identified in that publication, our objective was to review research on beef cattle nutrient requirements published since 2016 and identify knowledge gaps that should be addressed. Relative to energy requirements, the effects of environmental temperature and grazing activity, along with stress and disease, on maintenance requirements are inadequately characterized or defined. In addition, relationships between retained energy and protein should be more fully elucidated, and additional guidance on body weight at a target compositional endpoint is needed. Areas of continuing concern include accurately and precisely predicting microbial protein supply, predicting N recycling, and the metabolizable protein requirements for maintenance. Mineral and vitamin requirements are often challenging because of a lack of consistency in models used to determine requirements and potential effects of unique production settings on requirements. Based on recent research with feedlot cattle, zinc and chromium requirements should be examined more closely. Because predictions of dry matter intake are critical to supplying nutrients, additional development of prediction equations is needed, especially for beef cows and grazing beef cattle in general. Given considerable research in prediction of greenhouse gases, reevaluation of 2016 recommendations is warranted, along with a need for the updating of equations to predict excretions of N and P. Composition of feeds, particularly byproducts from ethanol production or other industrial streams, represents a knowledge gap, with obtaining reliable energy values of these feeds being a notable challenge. Nutritional models provide the means to integrate nutrient requirement recommendations into practice, and moving towards mechanistic models that take advantage of artificial intelligence and precision livestock farming technologies will be critical to developing future modeling systems.

The objective was to evaluate the inclusion of three corn ethanol byproducts in finishing cattle diets: high protein distillers grain (HPDG) was used as a source of protein in the diet to entirely replace whole cottonseed and soybean meal, dry fiber plus solubles (DFS) and wet fiber plus solubles (WFS) were used as energy-protein sources in the diet to replace a portion of the corn and entirely replace whole cottonseed and soybean meal from the conventional diet. Diets were formulated to be isonitrogenous with all diets containing 15% corn silage, 12% soybean hulls, 0.55 to 0.85% urea, and 1.80% mineral and vitamin supplements on dry matter (DM) basis. The treatments were (% DM): 1) control (CON): 8% whole cottonseed, 5% soybean meal, and 57.6% ground corn; 2) HPDG: 10.3% HPDG and 60.35% ground corn; 3) DFS: 30% DFS and 40.35% ground corn; 4) WFS: 30% WFS and 40.35% ground corn. Pre-planned contrasts included CON diet vs. HPDG diet, CON diet vs. DFS diet, and CON diet vs. WFS diet. In Exp. 1, 258 Nellore bulls were blocked by initial shrunk body weight (BW; 423 kg ± 36.6 kg), allocated into 44 pens in a randomized complete block design, and fed for 102 d. The average daily gain was greater (P = 0.02) for DFS than CON. Final BW (P = 0.02), hot carcass weight (HCW; P < 0.01), and Longissimus muscle area (P = 0.03) were greater for DFS than CON. In Exp. 2, 4 ruminally cannulated Nellore steers (initial BW = 389 ± 37 kg) were used in a Latin square design. Steers fed the WFS diet had less (P = 0.01) DMI than CON steers. The ether extract intake was greater (P = 0.02) for DFS and tended (P = 0.09) to be greater for WFS than CON, but HPDG did not differ from CON (P = 0.22). Steers fed DFS diets had 39.9% greater neutral detergent fiber intake (P < 0.01) than CON. Digestibility of DM was less (P < 0.01) for DFS than CON. Feeding HPDG and DFS decreased (P < 0.01) the molar proportion of rumen acetate, increased (P < 0.01) rumen propionate, and decreased acetate:propionate ratio (P < 0.01) compared to CON. Ruminal pH was not affected (P ≥ 0.82) by treatments, while ruminal ammonia nitrogen was greater for CON (P ≤ 0.01) compared with HPDG, DFS, and WFS. Feeding HPDG was a viable protein supplement alternative to sources like whole cottonseed and soybean meal in finishing diets. Feeding WFS and DFS improved cattle performance by displacing a portion of the flint corn and entirely replacing whole cottonseed and soybean meal.

The primary reason livers are condemned is due to abscesses, which are visible lesions detected on the liver during routine harvest of the animal. Condemned livers are deemed not fit for human consumption, and result in over $15M in lost income to the U.S. beef industry each year. Liver scoring is a 4-level measurement of abscess severity: 0 (no abscesses), A− (mild: 1 to 2 small abscesses), A (moderate: 2 to 4 active abscesses), and A+ (severe: 1 or more large, active abscesses). We quantified the degree to which known sources of variation, including genomic differences among animals, contribute to the incidence of liver abscesses in 1,747 feedlot cattle fed a range of diets. Diets were grouped based on corn type (dry-rolled corn [DRC], high-moisture corn [HMC], DRC/HMC or steam-flaked corn [SFC]) and byproduct (none, modified distillers grains plus solubles [MDGS], and Sweet Bran fed at 20%, 35%, or 40%). A common set of SNP (n = 44,666) from the Illumina BovineSNP50 v2 and GGP Bovine 100K were used for genomic analyses. The posterior mean (posterior standard deviation) heritability estimate of liver score was 0.10 (0.05). Within-diet heritability estimates were not significantly different from zero but ranged from 0.02 (0.02) (MDGS) to 0.29 (0.32) (Sweet Bran fed at 35%). A BayesB Genome-Wide Association Study (GWAS) with showed that liver score is a very polygenic trait with no large effect quantitative trait loci (QTL) segregating in this population. The genetic and phenotypic correlations of liver score with hot carcass weight, 12th rib fat, longissimus muscle area, or marbling score were not significantly different from zero. Results from the current study show that genomic selection for reduced liver score could be a useful tool to reduce the occurrence of liver abscesses in feedlot cattle, alongside current mitigation strategies; however, more data are needed to gain a better understanding of the genetic basis of liver score, as well as the relationship between liver score and other economically relevant traits, and potential genetic × diet interactions.

The Long‐Term Agroecosystem Research (LTAR) network of the United States Department of Agriculture (USDA) consists presently of 18 sites within the contiguous United States that are managed by the Agricultural Research Service (ARS) and its partners. The LTAR network focuses on developing national strategies for more efficient, resilient, and profitable agricultural production systems, improved environmental quality, and enhanced rural prosperity. The Platte River High Plains Aquifer (PRHPA) LTAR site is managed jointly by the University of Nebraska‐Lincoln (UNL) and USDA‐ARS and is one of the LTAR sites that conduct research on both integrated cropping and grazing systems. The PRHPA region encompasses multiple land resource areas and diverse agricultural production systems. The PRHPA sites, predominantly located in eastern Nebraska, are designated as an integrated system focused specifically on the region's dominant production practices of row crop (corn and soybean), managed pastures, and beef cattle production. Here, we focus on C₃ cool‐season smooth bromegrass (Bromus inermis Leyss.) pasture grazing systems under prevailing and alternative management practices for the region. The sites evaluate continuous and rotational grazing with and without pasture fertilization (prevailing practices). In an additional treatment, cattle are supplemented with dry distillers grains plus solubles, while manure supplies fertilization (alternative practice). Main measurements at the site evaluate plant and animal productivity, forage quality, greenhouse gas fluxes, and soil physical, chemical, and biological properties. This paper describes the regional characteristics of the PRHPA site, ongoing LTAR research related to pasture and livestock production, stakeholder engagement, and future research plans.