ASPEN INTAKE AND PREFERENCE BY SHEEP: IMPLICATIONS FOR HERBIVORY

AND ASPEN DECLINE

Beth Burritt and Juan Villalba

Objectives• To determine the effect of phenolic glycosides

on intake of aspen leaves by sheep• To determine sheep preference for aspen and

two understory species (Utah pea and smooth bromegrass)

Methods – Intake Trial

• Group 1 – Low PG; Group 2 – High PG• N = 10• Collected fresh leaves each morning• Leaves fed to lambs for 2 hours each morning

after overnight fast• Alfalfa pellets fed 1 to 5 PM each afternoon

8/12 8/13 8/14 8/15 8/160

2

4

6

9/16 9/17 9/18 9/19 9/200

2

4

6

8

7/9 7/10 7/11 7/120

2

4

Low PGPeriod 2

Period 3

Period 1 Low PG

Low PG

High PG

High PG

High PG

Inta

ke (

g/kg

0.75

BW

)Intake of Aspen with High and Low Levels of

Phenolic Glycosides

Methods – Preference Trial

• Omitted lambs with low preference for aspen• N=12 • Collected fresh forage each morning• Forage fed to lambs for one hour each

morning after overnight fast• Alfalfa pellets fed 1 to 5 PM each afternoon

Intake of Smooth Bromegrass, Utah Pea and Aspen by Period

July August September0

1

2

3

4

5

6Brome

Pea

Aspen

Inta

ke (g

/kg0

.75)

a

b

a

bb

a

a

b

a

July August September0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1 AspenPeaBrome

Pro

port

ion

of F

orag

es

Proportion of Forages Eaten by Sheep Offered Aspen, Utah Pea, and Smooth Bromegrass

Percent Crude Protein and Neutral Detergent Fiber of Forages Fed to Sheep

Aspen Utah Pea SBG0

2

4

6

8

10

12

14

16

18

20

July August September

% C

rude

Pro

tein

Aspen Utah Pea SBG0

10

20

30

40

50

60

% N

eutr

al D

eter

gent

Fib

er

Things I Learned(Not in Objectives)

Aspen Leaves Don’t Weigh Much

0 2 4 6 8 10 120

5

10

15

20

25

30

35

40

Aspen Sucker Weight (g)

Aspe

n Su

cker

Hei

ght

(inch

es)

Height-Weight Relationship of 13 Aspen Suckers

454 g = 1 lb28 g = 1 oz

Tree #17/23/13

59 g DM

59 g = .13 lb or 2.1 oz

Tree #27/23/13

49 g DM

49 g = .12 lb or 1.8 oz

Tree #37/23/13

57 g DM57 g = .13 lb or 2 oz

Tree #47/23/13

74 g DM

74 g = .16 lb or 2.6 oz

Tree #57/23/13

29 g DM

29 g = .06 lb or 1 oz

1) If a 500 lb cow elk ate 3% of body weight each day: 500 lb * 3% = 15 lb/day

2) assume 20% of her intake was aspen:15 lb * 20% = 3 lb of aspen leaves/day

3) and suckers weighed 30 g (Tree 5):3 lb/day = 46 suckers/day0.066 lb/sucker

She would strip 46 suckers/day

Some Sheep Don’t Like

Aspen

Inta

ke (

g/kg

0.75

BW

)Aspen Intake Last Day of Trial

(Periods 1-3)

Omitted from preference trial

1 2 4 6 10 15 16 21 20 26 3 5 7 9 12 13 18 23 28 300

5

10

15

20

25

30

SeptemberAugustJuly

Animal Number

Low PG High PG

Huge Variation in Intake

May be I should cut back on the aspen

Average Preference for Aspen Leaves

2 4 6 10 15 16 26 5 7 9 23 280

10

20

30

40

50

60

70

80July August September

Animal Number

Pref

eren

ce fo

r Asp

en (%

of d

iet)

Conclusions

• The effect of phenolic glycosides was inconclusive.

• Preference for aspen increased as the season progressed.

• Browsing herbivores may prevent aspen regeneration.

• Selectively culling herbivores or providing supplements may improve aspen regeneration.

Think outside the box to identify problem animals

QUESTIONS?