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Title: USING A RANGE-LIVESTOCK MODEL TO ESTIMATE MAXIMUM COW-CALF STOCKING RATES ON A MIXED-GRASS PRAIRIE

Author
item Andales, Allan
item Ahuja, Lajpat

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 5/11/2006
Publication Date: 7/9/2006
Citation: Andales, A.A., Ahuja, L.R. 2006. Using a range-livestock model to estimate maximum cow-calf stocking rates on a mixed-grass prairie. ASABE Annual International Meeting. Portland, OR. July 9-12, 2006.

Interpretive Summary: Matching stocking rate with the availability of green forage is a way of reducing production costs and maintaining sustainability of a cow-calf operation. Savings can be achieved by appropriately stocking cow-calf herds on native rangelands. Mechanistic simulation models of the rangeland-livestock production system that incorporate interactions between soil, plants, animals, and the atmosphere can help ranchers determine the appropriate stocking rates. This preliminary study explored the possibility of using the USDA-ARS GPFARM decision support system to estimate the maximum cow-calf stocking rate that does not diminish animal weights under normal and low rainfall conditions on a semiarid native mixed-grass prairie in southeast Wyoming, U.S.A. This paper gives an initial assessment of simulated responses of animal weights to varying stocking rates.

Technical Abstract: Matching cattle stocking rate with the availability of green forage is a way of reducing production costs and maintaining sustainability of a cow-calf operation. The objective of this study was to estimate the maximum cow-calf stocking rate that does not diminish animal weights under normal and low rainfall conditions on a native mixed-grass prairie in southeast Wyoming, U.S.A. using the USDA-ARS GPFARM Range-Livestock model. Forage production and Hereford cow-calf weights were simulated over a range of stocking rates [6.1, 5.0, 4.0, 3.5, 3.0, and 2.0 ha (cow-calf pair)-1] for 2 rainfall scenarios (dry = 255 mm yr -1 and normal = 395 mm yr -1). Calving was simulated in March and weaning at 180 days old. Cattle were stocked on 88 ha of native northern mixed-grass prairie (warm season grasses, cool season grasses, and forbs) from June to September. Daily allowable forage depletion was set at 50% of available forage. Simulated cow/calf weights (at a sale date of 30 September) and total forage intake for the 6 stocking rates were compared to estimate the maximum stocking rate for each rainfall scenario. The GPFARM simulations showed that animal weights and forage intake did not diminish even at a very high stocking rate of 2.0 ha (cow-calf pair)-1 pair under normal rainfall conditions. However, they diminished under extremely dry conditions at stocking rates more intensive than 4.0 ha (cow-calf pair)-1. The stocking rate should not be more than 4.0 ha (cow-calf pair)-1 at this mixed-grass prairie site when a dry year is expected (e.g. precipitation = 255 mm yr –1; 3% probability). The model gave reasonable responses of cattle weight gain to variable stocking. It can potentially be used to estimate appropriate stocking rates to maintain the sustainability of a cow-calf operation on northern mixed-grass prairie. However, further verifications of model results with experimental data are needed.