The Demand Day A Unit for Adaptive Stocking Rate Management Austin Sewell Agren Inc., Carroll, IA

Definition:  The Demand Day (DD) is a standard unit of measure of forage demand for large wild or domestic herbivores.  1 DD equals 12 Megacalories (Mcal) per day intake of net energy for maintenance and gain. What is a Demand Day?

Meets criteria for a standard unit of measure (Hinnant 1994) 1.The standard should be readily and widely accessible. 2.The standard should be easy to use. 3.The standard should be invariable. Legitimacy

Formula NEm (Mcal) + NEg (Mcal) 12 Demand Unit Equivalent* = = *Where NEm is net energy for maintenance, NEg is net energy for gain or loss, W is average animal bodyweight in pounds, and ADG is average daily gain or loss of animal bodyweight in pounds. Demand Days = Demand unit equivalent multiplied by No. of days

Example  1150 lb. cow with calf, 2 months old, gaining 1.1 lbs. per day  Average cow weight = 1150 lbs.  Calf born at 80 lbs, 160 lbs at 2 months, ADG = 1.1

 Cow demand equivalent: = = Example (cont.)

 Calf demand equivalent: = = Example (cont.)

 Cow-calf pair demand equivalent: = 1.1 Example (cont.)

Example  Computer applications (TGM)

Animal Unit  Ambiguous past  Should be defined as 26 lbs Dry Matter intake per day (Scarnecchia 1985)  Meets Hinnant’s criteria as a standard unit of measure

DD vs. AUD  Similarities  Both model forage intake.  Both standard units of measure for forage demand.  Differences  DD directly tied to animal production, AUD not.  DD considers forage quantity AND quality, AUD only considers quantity. (IES an example).

SR Mgmt PracticeDemand SideSupply Side Setting Initial SR Historical grazing records Vegetation inventory (composition, biomass) Monitoring SR Forage demand, use ratings Vegetation monitoring Adjusting SR Relies on actual forage demand and pasture use ratings Relies on vegetation monitoring Simulating forage balance Nutrient supply Spp. composition, biomass production, harvest efficiency Demand Side vs. Supply Side

Class Subclass [1] [1] PDR [2] Range (%) [2] Representative PDR Value [3] (%) [3] Description None0-105 Vegetation appears practically undisturbed when viewed from an angle or from a distance. Light − Preferred areas and high-choice [4] forage show moderate use. [4] Light use of primary [5] or low-choice [6] forage. [5] [6] Moderate − Most accessible forage shows use. High-choice forage heavily used. Primary forage is moderately grazed and supplying most of the demand. Light use of low-choice forage Heavy − High-choice forage completely used. Primary forage is closely grazed over most of the area. Moderate use of low-choice forage Severe Pasture appears stripped of forage. Primary forage almost completely used. Low-choice forage shows considerable use and is carrying the grazing load. Pasture Use

LightModerateHeavy PDR (Cum. DD used/Cum. DD produced) Pasture Use Rating (%PDR) NoneSev Curve based on Hart (1986) Pasture Use

System of Use

Adaptive SR Management  Stocking rate needs to be managed more adaptively – more responsively and proactively  For this, we need quicker turnover of management phases.  Demand side methods have faster turnover

Why the Demand Day?  Advantages over AUD  Accounts for forage quality  Directly related to animal production  Better suited for demand side approach to stocking rate management  Better suited to Productivity-Stocking Rate theoretical model  Demand side better suited to forage balance simulation (Rittenhouse and Bailey 1996)  Demand side stocking rate management better suited to adaptive management

References  Hart, R. H How important are stocking rates in grazing management? In. P.E. Reece and J.T. Nichols (Eds.). Proceedings, The Ranch Management Symposium, November 5-7, 1986, North Platte, Nebraska. Univ. Neb. Ext. Serv., Lincoln, Neb., pp  Hinnant, R. T What is an animal-unit? A time to conform. Rangelands: 16(1) pp  Rittenhouse, L. R. and D. W. Bailey Spatial and Temporal Distribution of Nutrients: Adaptive Significance to Free-Grazing Herbivores. Proc. Grazing Livestock Nutrition Conf. 3:31-61.