The Demand DayThe 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

12

0.454ADG60.454W0.077 0.750.75

NEm (Mcal) + NEg (Mcal)

12

Demand UnitEquivalent*

=

=

*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

0.7

12

8.4

12

00.45411500.077 0.75

Cow demand equivalent:

12

0.454ADG60.454W0.077 0.750.75 =

=

Example (cont.)

0.4

12

3.61.5

12

0.4541.160.4541200.077 0.750.75

Calf demand equivalent:

=

=

12

0.454ADG60.454W0.077 0.750.75

Example (cont.)

Cow-calf pair demand equivalent:

0.7 + 0.4 = 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 Practice Demand Side Supply 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]

PDR[2] Range (%)

Representative PDR Value[3] (%)

Description

None 0-10 5Vegetation appears practically undisturbed when viewed from an angle or from a distance.

Light

− 10-16 13

Preferred areas and high-choice[4] forage show moderate use.

Light use of primary[5] or low-choice[6] forage.16-34 25

+ 34-40 37

Moderate

− 40-44 42 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.

46-56 50

+ 56-60 58

Heavy

− 60-66 63High-choice forage completely used.

Primary forage is closely grazed over most of the area.

Moderate use of low-choice forage.

66-84 75

+ 84-90 87

Severe 90-100 95

Pasture appears stripped of forage.

Primary forage almost completely used.

Low-choice forage shows considerable use and is carrying the grazing load.

Pasture Use

Light Moderate Heavy

10-40 40-60 60-90

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Ind

. A

nim

al

Pro

du

cti

on

PDR (Cum. DD used/Cum. DD produced)

Pasture Use Rating (%PDR)

None Sev.

0-10 90-100

Curve based on Hart (1986)

Pasture Use

System of Use

Re al World

M e asure me nts& Obse rv ations

Re cordKe e p ing &Plann ing

Pasture:Forage

Animals:K ind of animalC lass of animalPhy siologic al

status

Intake (ac tual)

Pas ture use rating(see guide)

Am ount of feeds (drym atter; w eight)

An ima l Numbers; Bodywe igh t; D a tes in & ou t

Observed PDR (DDused/DD produc tion)

Pasture Produc tion

Calc ulated ME intake

DD used from pasture

Dem and Day s

D iet Selec tion

Feeds

Forage BalanceS im ulation (T G M)

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. 1986. 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. 77-87.

Hinnant, R. T. 1994. What is an animal-unit? A time to conform. Rangelands: 16(1) pp 33-35.

Rittenhouse, L. R. and D. W. Bailey. 1996. Spatial and Temporal Distribution of Nutrients: Adaptive Significance to Free-Grazing Herbivores. Proc. Grazing Livestock Nutrition Conf. 3:31-61.