BEEF SPECIES SYMPOSIUM: Nutrient requirements of the beef female in extensive grazing systems— Considerations for revising the Beef NRC1 J. C. Whittier*2 *Department of Animal Sciences, Colorado State University, Fort Collins 80523
© 2014 American Society o f Animal Science. All rights reserved.
The B eef Species Symposium titled “Nutrient Requirements o f the B eef Female in Extensive Grazing Systems— Considerations for Revising the B eef N R C ” was held at the Joint Annual Meeting o f the American Dairy Science Association and Am erican Society o f Anim al Science in Indianapolis, IN, July 8 to 11, 2013. The committee for this symposium was composed o f a subset o f m embers o f the W 1012 Improving ruminant use o f forages in sustainable production systems for the western U.S. multistate project. They included Allison M. M eyer (University o f Wyoming), Dan B. Faulkner (University o f Arizona), Eric J. Scholljegerdes (New M exico State University), Jim E. Sprinkle (University o f Arizona), Sergio A. Soto-Navarro (New M exico State University), Richard C. Waterman (USDA-ARS Fort Keogh Livestock and Range Research Laboratory), Joel S. Caton (North Dakota State University), Mark K. Petersen (USDA-ARS Fort Keogh Livestock and Range Research Laboratory), Chad J. M ueller (Oregon State University), Kenneth C. Olson (South Dakota State University), and Jack C. W hittier (Colorado State University). The purpose o f the symposium was to pres ent current information on the specific characteristics o f grazing environments in the western United States as they relate to the nutrient requirement predictions o f the b eef female. These grazing environments are dynamic, with changes occurring within season, from year to year, and across soil types, topography, and elevation. Such grazing circumstances are also highly variable with di verse plant communities and level and timing o f precipi tation patterns. B eef cows on western ranges have dem onstrated their ability to adapt to such variation through
'A symposium held at the Joint Annual Meeting, July 8-11, 2013, Indianapolis, IN, with publication sponsored by th z Journal o f Animal Science and the American Society of Animal Science. Corresponding author: [email protected] Received May 9, 2014. Accepted May 13, 2014.
J. A n im . Sci. 2 0 1 4 .9 2 :2 7 7 3 -2 7 7 4 d o i:1 0 .2 5 2 7 /ja s 2 0 14-8043
efficiency o f nutrient utilization. Therefore, this sym posium was presented to provide the Eighth Revised Edition Committee for the Nutrient Requirements o f B eef Cattle with pertinent information on beef females grazing in extensive environments, particularly the semiarid regions o f the western United States. The overview and rational for the sym posium were given by J. C. W hittier. The first presentation was a dual presentation by 2 USDA-ARS scientists, S. W. C olem an (El Reno, OK) and S. A. G unter (W oodward, OK), whose presentation was titled “ Difficulties as sociated w ith predicting forage intake by grazing b eef cow s” (Colem an et al., 2014). The basis o f this presen tation was that the current N RC m odel (NRC, 2000) is based on a single equation that related DM1 to m eta bolic size and net energy density o f the diet. Although this m odel was a significant im provem ent over previ ous m odels, it does not include a function that includes anim al demand, largely determ ined by m etabolic or linear size, physiological state, genetics, or any com bination thereof. Forage DM I is really modified by its nutritive value and balance, herbage m ass and struc ture, locom otion, clim ate, profitability o f bites, the in teraction w ith genetics, and level and type o f supple m entation. The presenters suggested that the revision to the NRC m odel needs to be more robust in its ability to account for the wide variation in the environm ent, dietary characteristics, and m etabolic demands. The symposium continued with the next speaker, R. C. Waterman, who presented “An assessm ent o f the 1996 B eef NRC: M etabolizable protein supply and de mand and effectiveness o f m odel perform ance predic tion o f b eef females within extensive grazing systems” (W aterman et al., 2014). Dr. Waterman noted that nutri tionists have questioned the adequacy o f the MP system (NRC, 2000) for predicting protein supply and demand o f b eef cows grazing arid and semiarid rangelands. A better understanding o f nutrient supply and demand o f
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beef cows grazing arid and semiarid rangelands would improve predictive models, which could aid in designing least cost supplements that compliment rangeland forage nutrient composition. A primary objective of the assess ment of the current NRC model for predicting MP was to demonstrate strengths and weaknesses of the model in terms of predicting extensive range beef cow performance within arid and semiarid environments in the western United States. The presenter concluded that the current MP portion of the 1996 beef NRC model functions as a calculator with no direct feedback influencing animal per formance predictions. There is, however, one exception with young growing animals (e.g., heifer development), where MP allowable gain is predicted; however, this pre diction does not carryover once a cow enters gestation or lactation. Dr. Waterman suggested that there is a great opportunity to account for MP supply and/or absorption and partitioning of N as either going toward energy use or protein accretion. Second, for heifers being developed on native range in late winter to early spring, the current Beef NRC model does not accurately adjust for compen satory gain, and consequently, the accuracy of the model prediction is poor. Third, there is a need for more exten sive regionally based nutrient composition data for grazed forage. Finally, there is overall poor predictive agreement from the existing beef NRC model with actual perfor mance data for range beef cows produced in extensive arid and semiarid rangelands in the western United States, which is likely driven by the aforementioned factors. The third presentation, by M. K. Petersen, was titled “Potential limitations of NRC in predicting energetic re quirements of beef females within western U.S. grazing systems" (Petersen et al., 2014). Dr. Petersen pointed out that the current NRC model is based on an assessment of cow energy balance and efficiency in extensive grazing settings that have occurred on a nominal basis over short time intervals and have not been used to model lifetime energy utilization (output Mcal/intake Meal = lifetime energetic efficiency). Predictions of energetic require ments of pen-fed cows have been shown to be consid erably different than cows grazing in extensive envi ronments. ft was suggested that a model for predicting the energetic requirements of beef females in extensive grazing environments must account for energy costs for maintenance, tissue accretion, and mobilization and that these costs are lower in some beef breeds. The most ef ficient models should reflect the potential for cattle that fit semiarid grazing environments with low input man
agement. Successful range cattle are likely the result of natural selection for efficiency. Animals exposed to a variety of stressors may continually adapt so that energy expenditure is reduced. Critical factors comprising cow lifetime achievement, including reproductive success, disease resistance, and calf weaning weight, may be driven by cow caloric utilization in energy-limiting envi ronments. Therefore, ME adjustments for adapted cattle within these landscapes with seasonal BW changes can alter seasonal NEm requirements, ft was suggested that a more complete understanding of greater productivity in the field than the current model proposes will help direct future research and inform models to simulate energetic accountability and subsequent female performance. The symposium concluded with a summary presen tation by K. C. Olson, who offered the following recom mendations to the NRC revision committee: 1) embrace interaction between protein and energy metabolism in the ruminant and, in turn, consider how this drives in take, 2) consider interactions between rumen metabo lism and animal metabolism, 3) embrace variability, do not overly focus on “tight” relationships based on highly controlled experimental situations, and 4) do not be afraid of moderate r2 values and recognize that ex plaining 40% of the variation in intake for beef females grazing in extensive environments with high diversity is a lot. Dr. Olson also challenged researchers operat ing in extensive environments to improve the collection and reporting of baseline data such as weather, herbage availability and quality, and diet quality. He further en couraged enhancing reported data on the extent and rate of digestibility of beef females when grazing extensively managed forages. LITERATURE CITED Coleman, S. W., S. A. Gunter, J. E. Sprinkle, and J. P. S. Neel. 2014. Difficulties associated with predicting forage intake by grazing beef cows. J. Anim. Sci. 92:2775-2784. NRC. 2000. Nutrient requirements o f b eef cattle. 7th rev. ed. Update 2000. Natl. Acad. Press, Washington, DC. Petersen, M. K., C. Mueller, J. T. M ulliniks, A. J. Roberts, T. DelCurto, and R. C. Waterman. 2014. Potential limitations o f NRC in pre dicting energetic requirements o f beef females within western U.S. grazing systems. J. Anim. Sci. 92:2800-2808. Waterman, R. C., J. S. Caton, C. A. Loest, M. K. Petersen, and A. J. Roberts. 2014. An assessment o f the 1996 Beef NRC: Metabolizable protein supply and demand and effectiveness o f model performance pre diction of beef females within extensive grazing systems. J. Anim. Sci. 92:2785-2799.
Copyright of Journal of Animal Science is the property of American Society of Animal Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
© 2014 American Society o f Animal Science. All rights reserved.
The B eef Species Symposium titled “Nutrient Requirements o f the B eef Female in Extensive Grazing Systems— Considerations for Revising the B eef N R C ” was held at the Joint Annual Meeting o f the American Dairy Science Association and Am erican Society o f Anim al Science in Indianapolis, IN, July 8 to 11, 2013. The committee for this symposium was composed o f a subset o f m embers o f the W 1012 Improving ruminant use o f forages in sustainable production systems for the western U.S. multistate project. They included Allison M. M eyer (University o f Wyoming), Dan B. Faulkner (University o f Arizona), Eric J. Scholljegerdes (New M exico State University), Jim E. Sprinkle (University o f Arizona), Sergio A. Soto-Navarro (New M exico State University), Richard C. Waterman (USDA-ARS Fort Keogh Livestock and Range Research Laboratory), Joel S. Caton (North Dakota State University), Mark K. Petersen (USDA-ARS Fort Keogh Livestock and Range Research Laboratory), Chad J. M ueller (Oregon State University), Kenneth C. Olson (South Dakota State University), and Jack C. W hittier (Colorado State University). The purpose o f the symposium was to pres ent current information on the specific characteristics o f grazing environments in the western United States as they relate to the nutrient requirement predictions o f the b eef female. These grazing environments are dynamic, with changes occurring within season, from year to year, and across soil types, topography, and elevation. Such grazing circumstances are also highly variable with di verse plant communities and level and timing o f precipi tation patterns. B eef cows on western ranges have dem onstrated their ability to adapt to such variation through
'A symposium held at the Joint Annual Meeting, July 8-11, 2013, Indianapolis, IN, with publication sponsored by th z Journal o f Animal Science and the American Society of Animal Science. Corresponding author: [email protected] Received May 9, 2014. Accepted May 13, 2014.
J. A n im . Sci. 2 0 1 4 .9 2 :2 7 7 3 -2 7 7 4 d o i:1 0 .2 5 2 7 /ja s 2 0 14-8043
efficiency o f nutrient utilization. Therefore, this sym posium was presented to provide the Eighth Revised Edition Committee for the Nutrient Requirements o f B eef Cattle with pertinent information on beef females grazing in extensive environments, particularly the semiarid regions o f the western United States. The overview and rational for the sym posium were given by J. C. W hittier. The first presentation was a dual presentation by 2 USDA-ARS scientists, S. W. C olem an (El Reno, OK) and S. A. G unter (W oodward, OK), whose presentation was titled “ Difficulties as sociated w ith predicting forage intake by grazing b eef cow s” (Colem an et al., 2014). The basis o f this presen tation was that the current N RC m odel (NRC, 2000) is based on a single equation that related DM1 to m eta bolic size and net energy density o f the diet. Although this m odel was a significant im provem ent over previ ous m odels, it does not include a function that includes anim al demand, largely determ ined by m etabolic or linear size, physiological state, genetics, or any com bination thereof. Forage DM I is really modified by its nutritive value and balance, herbage m ass and struc ture, locom otion, clim ate, profitability o f bites, the in teraction w ith genetics, and level and type o f supple m entation. The presenters suggested that the revision to the NRC m odel needs to be more robust in its ability to account for the wide variation in the environm ent, dietary characteristics, and m etabolic demands. The symposium continued with the next speaker, R. C. Waterman, who presented “An assessm ent o f the 1996 B eef NRC: M etabolizable protein supply and de mand and effectiveness o f m odel perform ance predic tion o f b eef females within extensive grazing systems” (W aterman et al., 2014). Dr. Waterman noted that nutri tionists have questioned the adequacy o f the MP system (NRC, 2000) for predicting protein supply and demand o f b eef cows grazing arid and semiarid rangelands. A better understanding o f nutrient supply and demand o f
2773
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beef cows grazing arid and semiarid rangelands would improve predictive models, which could aid in designing least cost supplements that compliment rangeland forage nutrient composition. A primary objective of the assess ment of the current NRC model for predicting MP was to demonstrate strengths and weaknesses of the model in terms of predicting extensive range beef cow performance within arid and semiarid environments in the western United States. The presenter concluded that the current MP portion of the 1996 beef NRC model functions as a calculator with no direct feedback influencing animal per formance predictions. There is, however, one exception with young growing animals (e.g., heifer development), where MP allowable gain is predicted; however, this pre diction does not carryover once a cow enters gestation or lactation. Dr. Waterman suggested that there is a great opportunity to account for MP supply and/or absorption and partitioning of N as either going toward energy use or protein accretion. Second, for heifers being developed on native range in late winter to early spring, the current Beef NRC model does not accurately adjust for compen satory gain, and consequently, the accuracy of the model prediction is poor. Third, there is a need for more exten sive regionally based nutrient composition data for grazed forage. Finally, there is overall poor predictive agreement from the existing beef NRC model with actual perfor mance data for range beef cows produced in extensive arid and semiarid rangelands in the western United States, which is likely driven by the aforementioned factors. The third presentation, by M. K. Petersen, was titled “Potential limitations of NRC in predicting energetic re quirements of beef females within western U.S. grazing systems" (Petersen et al., 2014). Dr. Petersen pointed out that the current NRC model is based on an assessment of cow energy balance and efficiency in extensive grazing settings that have occurred on a nominal basis over short time intervals and have not been used to model lifetime energy utilization (output Mcal/intake Meal = lifetime energetic efficiency). Predictions of energetic require ments of pen-fed cows have been shown to be consid erably different than cows grazing in extensive envi ronments. ft was suggested that a model for predicting the energetic requirements of beef females in extensive grazing environments must account for energy costs for maintenance, tissue accretion, and mobilization and that these costs are lower in some beef breeds. The most ef ficient models should reflect the potential for cattle that fit semiarid grazing environments with low input man
agement. Successful range cattle are likely the result of natural selection for efficiency. Animals exposed to a variety of stressors may continually adapt so that energy expenditure is reduced. Critical factors comprising cow lifetime achievement, including reproductive success, disease resistance, and calf weaning weight, may be driven by cow caloric utilization in energy-limiting envi ronments. Therefore, ME adjustments for adapted cattle within these landscapes with seasonal BW changes can alter seasonal NEm requirements, ft was suggested that a more complete understanding of greater productivity in the field than the current model proposes will help direct future research and inform models to simulate energetic accountability and subsequent female performance. The symposium concluded with a summary presen tation by K. C. Olson, who offered the following recom mendations to the NRC revision committee: 1) embrace interaction between protein and energy metabolism in the ruminant and, in turn, consider how this drives in take, 2) consider interactions between rumen metabo lism and animal metabolism, 3) embrace variability, do not overly focus on “tight” relationships based on highly controlled experimental situations, and 4) do not be afraid of moderate r2 values and recognize that ex plaining 40% of the variation in intake for beef females grazing in extensive environments with high diversity is a lot. Dr. Olson also challenged researchers operat ing in extensive environments to improve the collection and reporting of baseline data such as weather, herbage availability and quality, and diet quality. He further en couraged enhancing reported data on the extent and rate of digestibility of beef females when grazing extensively managed forages. LITERATURE CITED Coleman, S. W., S. A. Gunter, J. E. Sprinkle, and J. P. S. Neel. 2014. Difficulties associated with predicting forage intake by grazing beef cows. J. Anim. Sci. 92:2775-2784. NRC. 2000. Nutrient requirements o f b eef cattle. 7th rev. ed. Update 2000. Natl. Acad. Press, Washington, DC. Petersen, M. K., C. Mueller, J. T. M ulliniks, A. J. Roberts, T. DelCurto, and R. C. Waterman. 2014. Potential limitations o f NRC in pre dicting energetic requirements o f beef females within western U.S. grazing systems. J. Anim. Sci. 92:2800-2808. Waterman, R. C., J. S. Caton, C. A. Loest, M. K. Petersen, and A. J. Roberts. 2014. An assessment o f the 1996 Beef NRC: Metabolizable protein supply and demand and effectiveness o f model performance pre diction of beef females within extensive grazing systems. J. Anim. Sci. 92:2785-2799.
Copyright of Journal of Animal Science is the property of American Society of Animal Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
