The study examined the effects of phenolic glycosides on aspen leaf intake by sheep in three trials. In the intake trial, sheep were fed aspen leaves with either low or high levels of phenolic glycosides. Intake varied but was generally lower for leaves with high phenolic glycosides. In the preference trial, sheep preferred smooth bromegrass and Utah pea over aspen in July and August, but preferred aspen in September. There was large variation between individual sheep in their aspen intake. The study suggests browsing herbivores can prevent aspen regeneration through leaf consumption and selectively culling problem animals or providing supplements could help improve aspen regeneration.

1. ASPEN INTAKE AND PREFERENCE BY
SHEEP: IMPLICATIONS FOR HERBIVORY
AND ASPEN DECLINE
Beth Burritt and Juan Villalba

2. 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)

3. 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

4. 4
2
6
4
2
0
Period 1 Low PG
High PG
8/12 8/13 8/14 8/15 8/16
8
6
4
2
0
9/16 9/17 9/18 9/19 9/20
0
7/9 7/10 7/11 7/12
Period 2 Low PG
Period 3
Low PG
High PG
High PG
Intake (g/kg0.75 BW)
Intake of Aspen with High and Low Levels of
Phenolic Glycosides

5. 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

6. Intake of Smooth Bromegrass, Utah
Pea and Aspen by Period
6
5
4
3
2
1
0
July August September
Intake (g/kg0.75)
Brome
Pea
Aspen
a
b
a
b
b
a
a
b
a

7. Proportion of Forages Eaten by Sheep Offered
Aspen, Utah Pea, and Smooth Bromegrass
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
July August September
Aspen
Pea
Brome
Proportion of Forages

8. Percent Crude Protein and Neutral Detergent Fiber
of Forages Fed to Sheep
20
18
16
14
12
10
8
6
4
2
0
Aspen Utah Pea SBG
% Crude Protein
July August September
60
50
40
30
20
10
0
Aspen Utah Pea SBG
% Neutral Detergent Fiber

9. Things I Learned
(Not in Objectives)

10. Aspen
Leaves Don’t
Weigh Much

11. Height-Weight Relationship of 13 Aspen Suckers
40
35
30
25
20
15
10
5
0
0 2 4 6 8 10 12
Aspen Sucker Height (inches)
Aspen Sucker Weight (g)
454 g = 1 lb
28 g = 1 oz

12. Tree #1
7/23/13
59 g DM
59 g = .13 lb or 2.1 oz

13. Tree #2
7/23/13
49 g DM
49 g = .12 lb or 1.8 oz

14. Tree #3
7/23/13
57 g DM
57 g = .13 lb or 2 oz

15. Tree #4
7/23/13
74 g DM
74 g = .16 lb or 2.6 oz

16. Tree #5
7/23/13
29 g DM
29 g = .06 lb or 1 oz

17. 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/day
0.066 lb/sucker
She would strip 46 suckers/day

18. Some Sheep
Don’t Like
Aspen

19. Intake (g/kg0.75 BW)
Aspen Intake Last Day of Trial
(Periods 1-3)
30
25
20
15
10
5
0
Low PG High PG
1 2 4 6 10 15 16 21 20 26 3 5 7 9 12 13 18 23 28 30
Omitted from preference trial
Animal Number
September
August
July

20. Huge Variation in Intake
May be I should
cut back on the
aspen

21. Average Preference for
Aspen Leaves
80
70
60
50
40
30
20
10
0
July August September
2 4 6 10 15 16 26 5 7 9 23 28
Preference for Aspen
(% of diet)
Animal Number

22. 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.

23. Think outside the box to identify
problem animals

24. QUESTIONS?