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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #206940
Title: Influence of seasonal forage quality on glucose kinetics of young beef cows

Author
item Waterman, Richard
item Grings, Elaine
item Geary, Thomas
item Roberts, Andrew
item Alexander, Leeson
item Macneil, Michael

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2007
Publication Date: 7/3/2007
Citation: Waterman, R.C., Grings, E.E., Geary, T.W., Roberts, A.J., Alexander, L.J., MacNeil, M.D. 2007. Influence of seasonal forage quality on glucose kinetics of young beef cows. Journal of Animal Science 85:2582-2595. doi 10:2527/jas.2007-0023.

Interpretive Summary: Extensive western range livestock production systems rely heavily on rangeland forages to meet nutritional needs for grazing livestock throughout the year. Interannual variation in both quantity and quality of rangeland forage in the Northern Great Plains, as well as throughout much of the western United States, may play a pivotal role in how well grazing ruminants sequester nutrients into their tissues. This variation in forage quality may influence grazing range beef cows’ ability to utilize dietary nutrients via changes in tissue responsiveness to insulin. Identifying specific periods and(or) production states where this phenomenon manifests will provide insight into the development and implementation of strategic and targeted supplementation practices that improve nutrient utilization during times of nutritional imbalances and may improve lifetime productivity for grazing range beef cows. Therefore, a 2 year study was conducted to monitor blood metabolites, glucose activity via glucose tolerance tests (GTT), and forage chemical composition every 90 d on young range cows (2 to 4 years of age). Cows were managed on four pastures in both years of the study, varying in size from 36 to 76 ha in year 1 and 49 to 78 ha in year 2. Regardless of year, cow age, or cow physiological status, season of the year influenced glucose half-life. Effects of season on glucose half-life closely followed forage quality assessments. These results demonstrated that mature or senescent forages (late fall through early spring) create nutritional imbalances that make it more difficult for cows to incorporate glucose into body tissues. Seasonal changes in serum metabolites were also observed and corresponded with changes observed in forage quality. Results of this study support our hypothesis that as season progresses and forage quality declines, maternal tissues become less responsive to actions of insulin, such that targeted supplementation with biologically potent glucogenic precursors during these seasons of nutritional stress may improve cow performance.

Technical Abstract: Extensive western range livestock production systems rely heavily on rangeland forages to meet nutritional needs for grazing livestock throughout the year. Interannual variation in both quantity and quality of rangeland forage in the Northern Great Plains, as well as throughout much of the western United States, may play a pivotal role in how well grazing ruminants sequester nutrients into their tissues. This variation in forage quality may influence grazing range beef cows’ ability to utilize dietary nutrients via changes in tissue responsiveness to insulin. Identifying specific periods and(or) production states where this phenomenon manifests will provide insight into the development and implementation of strategic and targeted supplementation practices that improve nutrient utilization during times of nutritional imbalances and may improve lifetime productivity for grazing range beef cows. Therefore, a 2-yr study was conducted to monitor serum metabolites, glucose kinetics via glucose tolerance tests (GTT), and forage chemical composition every 90 d on young range cows (2 to 4 yr of age; n = 28). Cows were managed on 4 pastures in yr 1 and 2, varying in size from 36 to 76 ha in yr 1 and 49 to 78 ha in yr 2. Regardless of year, cow age, or cow physiological status, season of the year (P = 0.02) influenced glucose half-life. Effects of season on glucose half-life closely followed assessments describing forage quality with glucose half-lives of 46, 39, 43, and 51 ± 3.9 min for May, August, December, and March, respectively. Elevated glucose half-life during seasons when forage quality is of lower nutritive value indicates that tissue responsiveness to the actions of insulin follow seasonal changes in forage quality. Glucose half-life tended (P = 0.09) to decrease between May and August, and increase (P = 0.04) between December and March, and show a tendency (P = 0.10) for faster half-life in seasons of higher nutrient density (May and August) when compared to seasons of lower nutrient density (December and March). Seasonal changes in serum metabolites were also observed and corresponded with changes in forage quality. Results of these data support our hypothesis that as season progresses and forage quality declines, maternal tissues become less responsive to actions of insulin, such that targeted supplementation with biologically potent glucogenic precursors during these seasons of nutritional stress may improve cow performance.