Breeding activity of a mixed age group of bulls on extensive pasture
J.L. Clavelle, L. Fritz, J.M. Stookey and C. Waltz
University of Saskatchewan
Large Animal Clinical Sciences
Western College of Veterinary
Medicine
Jean L. Clavelle
Saskatoon, Saskatchewan, CANADA
Introduction
A common management strategy during the breeding season is to turn bulls
out as a mixed age group, a strategy that is thought to be an inefficient use
of bull power (Blockey, M.A., 1979. Observations on group mating of bulls
at pasture. Appl. Anim. Ethol., 5:15-34). Blockey (1979) found that younger
bulls in a mixed age group were at a significant disadvantage because they
were more frequently interrupted during mating compared to older (and
typically more dominant) bulls and had a higher rate of culling due to injuries
and lameness.
Objectives
4. There was no significant difference
in the frequency of copulation
between high and low ranking bulls in
both periods (Fig. 3).
Copulations per 10 hours
of observation
High-Ranking
6
Low-Ranking
NS
5
4
3
2
NS
1
0
First
Second
Observation period
Fig. 3 Frequency of copulations in high- and low-ranking males in the first
and second observation period.
5. Several breeding strategies were observed:
1. Determine breeding activity of bulls of various ages and
2. Compare and correlate dominance rank and breeding activity.
I. High ranking bulls were observed to displace low ranking bulls from
estrus females. This may suggest that high ranking bulls use low
ranking bulls as ‘heat detectors’ and may explain why low ranking bulls
tended to perform more estrus checks.
Materials and Methods
Pasture location Rudy-Rosedale PFRA pasture, 60 km south of
Saskatoon, Saskatchewan, Canada. The pasture was divided into two
paddocks (384 and 768 hectares) of primarily native prairie and crested
wheat grass.
II. Bulls in the lower half of the social hierarchy (bulls ranked 4, 6 and 7)
were observed to perform ‘herding’ behaviour (Fig. 4a-f). Bulls would
attempt to drive one or several females away from the presence of
higher ranking bull.
Animals 7 Charolais bulls (aged 4 (n=1), 3 (n=4) and 2 (n=2) years) and
202 cow-calf pairs.
III. Cows that stood to be mated by higher ranking bulls were observed
to fervently avoid the lowest ranking bull who would however, breed the
cows while running (Fig. 5a-d).
Observations were made from May 28 to July 15, 1999. There were 2, 7hour observation sessions: a morning (from 6 am till 1 pm) and afternoon
(from 1 pm to 8 pm) period. All focal bulls were observed for both a morning
and afternoon period each week for a total of 14 hours of observation.
a
Observations were made from horseback or while leading the horse as this
allowed observers to be near cattle without causing agitation or disruption of
their normal activity (Fig. 1). General activity was recorded using 5-min
interval sampling. Interactions and breeding activity of the focal bulls were
recorded with continuous sampling.
b
d
c
e
f
Fig. 4a-f Bull herding an estrus cow and her calf away from another bull.
Fig. 1 Observer with a horse was
able to be close to cattle without
causing agitation or distress
Results
a
1. Events were defined in terms of the first 3 weeks (first period) and
remaining 4 weeks (second period). A total of 226 and 323 hrs of
observation were completed in the first and second periods respectively.
2. Dominance rank tended to be correlated with age (ie. the oldest bulls
were most dominant).
3. Low ranking bulls tended to
perform more estrus checks than
high ranking bulls in both periods
(Fig. 2).
Frequency per hour of
observation
High-Ranking
Low-Ranking
b
c
Fig. 3a-c Female who had originally stood for high ranking bull ran away
from a low ranking bull (a); high ranking bulls follow the low ranking bull as
he chases female (b); female mounted by low ranking bull while running (c).
Conclusion
5
p=0.08
4
3
p=0.051
The bulls in this study did not approach breeding activity in the same
manner. Individual bulls utilized several breeding strategies that were in part
dependent on their dominance ranking.
2
1
Acknowledgements
0
First
Second
Observation period
Fig. 2 Frequency with which males check females for estrus in both the
first and second observation period.
This research received financial support from the Agricultural Development
Fund. We would like to thank Steve Beck and Peter Gonnett for their
assistance in organizing this project.