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United States Department of Agriculture

Agricultural Research Service


Location: Forage and Livestock Production Research

2010 Annual Report

1a. Objectives (from AD-416)
The long-term objective of this project is to determine the feasibility of producing grass-fed beef in the Southern Great Plains and resolve the major constraints to finishing cattle on forages. If it is not possible to produce beef with 100% forage inputs, then we will develop systems that utilize more forage inputs to lessen our dependence on feed grains, increase revenues to local rural communities and small farmers, and produce more beef under free range conditions that appeal to the socially conscious consumer. In some cases, we will use sheep as a ruminant model to rank forages based on nutritional qualities, determine the impact of dietary supplementations on forage digestibility and protein metabolism, and the effect of genetics on forage intake and utilization. Over the next 5 years we will focus on the following specific objectives: Objective 1: Design, install, and evaluate, year-long forage-based livestock production systems that include multiple forage species to fill the forage deficit gaps in the spring and fall. Sub-objective 1.A. Develop year-long forage-based livestock production systems utilizing perennial cool-season forages and annual and perennial warm-season forages. Sub-objective 1.B. Determine the most efficient combination of beef cattle genotypes and forage-based production systems. Sub-objective 1.C. Determine the impact of maternal influence on postweaning performance of cross-bred calves from two-breed cross cows where calves are managed under two postweaning systems to enhance the efficiency of finishing cattle on pasture. Objective 2: Define and develop management strategies to mitigate nutrient imbalances that limit the production of grass-fed beef by year-round grazing systems developed for the southern Great Plains. Sub-objective 2.A. Compare the digestibility and N utilization of perennial cool-season grass species that may be used to fill-in the forage deficit gaps in a multiple forage species production system used to produce grass-fed beef. Sub-objective 2.B. Determine if energy or protein limits average daily gain (ADG) of calves grazing warm- and cool-season grasses under short-duration intensive-stocking management as part of a system to produce grass-fed beef. Sub-objective 2.C. Determine low-cost supplementation for stockers grazing cool-season and warm-season forages to approach genetic potential for postweaning stocker gains in purebred and crossbred stocker lambs. Sub-objective 2.D. Develop methodology to determine forage intake using forage canopy spectral reflectance and evaluate genetic effects for forage intake and efficiency of forage utilization.

1b. Approach (from AD-416)
Stocker calves of different breed types will be used to determine the interaction between breed type and intensity of livestock management on the rate and efficiency of body weight gain. Combinations of warm- and cool-season forage resources will be evaluated as components of a year-round grazing system. Nutrient imbalances that limit efficiency of beef production on pasture will be identified and management practices to mitigate these imbalances will be developed. New methodology to determine nutrient intake of grazing animals will be developed to give pasture managers a new tool to aid in their decision making process.

3. Progress Report
Ruminant animals are able to use forages for protein and energy sources for maintenance, growth and production. It is known that stocker gains on forages are made more economically than gains on mixed grain rations, but stocker gains are often below genetic potentials. Consequently, it would seem reasonable to provide supplemental feed to stockers to better approximate genetic potential, if such supplementation could be accomplished without substituting grain intake for forage intake. Research at the Grazinglands Research Laboratory was conducted to determine if low-level protein supplementation could improve gain on bermudagrass pastures. For two grazing seasons, Suffolk, Katahdin, and reciprocal-cross (Katahdin x Suffolk, Suffolk x Katahdin) lambs were grazed on bermudagrass pastures, either supplemented with a natural protein or unsupplemented. Animals were stratified by weight, breed, and gender and randomly assigned to: 1.2 hectares of common bermudagrass with (n = 2) or without (n = 2) access to a commercial 21% CP protein supplement. Katahdin-sired lambs had greater ADG, independent of protein supplementation. There was a trend for greater ADG in Katahdin lambs on protein vs. unsupplemented Katahdin, but little evidence to support an advantage for protein-supplemented lambs in any breed group. Heterosis in ADG was evident in the study in the unsupplemented lambs but not in the protein supplemented lambs.

4. Accomplishments
1. Protein supplementation not effective in enhancing growth of stocker lambs on bermudagrass. Forage quality declines throughout the growing season and grazing animal performance reflects the lower nutrition during the mid- to late-growing season. For grazing on warm-season forages, such as bermudagrass, animal performance is also negatively impacted by heat stress, and stocker performance on warm-season forages often does not approach the genetic potentials of the livestock. Katahdin (a tropically adapted hair breed of sheep) or Katahdin crosses were shown to be generally superior to purebred Suffolk lambs (a temperate climate breed) in gains on bermudagrass forages during summer grazing trials. Protein supplementation had little benefit on stocker gain in Katahdin, Suffolk, or reciprocal-cross lambs. There was an indication of hybrid vigor for average daily gain in lambs only when they were not supplemented with protein, suggesting that protein supplementation may narrow the performance gap between purebred and crossbred lambs. While it is evident that using tropically adapted breeds are beneficial for summer grazing, further research is needed to optimize supplementation strategies for summer grazing.

2. Multiple tropically adapted beef breeds suited for southern US cattle herds. To improve the overall value of calves from the southern USA cow herds, tropically adapted Bos indicus and Bos taurus breeds are being evaluated to determine the impact of tropical adapted breed type on dry matter intake and digestibility of low- and high-quality forage diets with and without protein supplementation. In one experiment, with Boran-, Brahman-, Tuli- , and Gelvieh-sired steers, breed of sire had no effect on diet digestibility. Boran-sired steers had lower dry matter intake of the low-quality diet than the other breed types used. In a second experiment, dry matter intake of the low-quality diet was increased when supplemental protein was fed. Steers with 25% Senpol or Tuli breeding had greater dry matter intake than steers with 25% Brahman breeding or purebred Romosinuano steers. We confirmed previously developed concepts describing the interaction of low quality forage diets and protein supplementation are applicable to these breed types. Alternative sources of tropical adaptation in beef cattle can be incorporated into cow herds that generate stocker calves. The resulting prodigy could enter existing production systems without changing management strategies.

Review Publications
Phillips, W.A., Holloway, J.W., Warrington, B., Venuto, B.C. 2009. Stocker and feedlot performance of beef heifers sired by Braunvieh and Wagyu bulls from Angus-, Brahman-, Senepol- and Tuli-sired dams. Professional Animal Scientist. 25:809-814.

Phillips, W.A., Northup, B.K., Venuto, B.C. 2009. Dry matter intake and digestion of perennial and annual cool-season grasses by sheep. Professional Animal Scientist. 25:610-618.

Peng, Y., Brown, M.A., Wu, J., Liu, Z. 2010. Different oilseed supplements alter fatty acid composition of different adipose tissues of adult ewes. Meat Science. 85(3):542-549.

Burke, J.M., Coleman, S.W., Chase, C.C., Riley, D.G., Looper, M.L., Brown, M.A. 2010. Interaction of breed-type and endophyte-infected tall fescue on milk production and quality in beef cattle. Journal of Animal Science. 88:2802-2811.

Looper, M.L., Black, S.G., Reiter, S.T., Okimoto, R., Johnson, Z.B., Brown, M.A., Rosenkrans, C.F. 2010. Identification of polymorphisms in the enhancer region of the bovine prolactin gene and association with fertility in beef cows. Professional Animal Scientist. 26:103-108.

Last Modified: 07/24/2017
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