1. Breeding activity of a mixed age group of bulls on extensive pasture J.L. Clavelle, L. Fritz, J.M. Stookey and C. Waltz Saskatoon, Saskatchewan, CANADA Jean L. Clavelle University of Saskatchewan Large Animal Clinical Sciences Western College of Veterinary Medicine 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 1. Determine breeding activity of bulls of various ages and 2. Compare and correlate dominance rank and breeding activity. 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. Animals 7 Charolais bulls (aged 4 (n=1), 3 (n=4) and 2 (n=2) years) and 202 cow-calf pairs. Observations were made from May 28 to July 15, 1999. There were 2, 7- hour 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. 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. Results 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). Fig. 1 Observer with a horse was able to be close to cattle without causing agitation or distress 5. Several breeding strategies were observed: 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. 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. 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). Fig. 4a-f Bull herding an estrus cow and her calf away from another bull. Conclusion 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. Acknowledgements 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. 3. Low ranking bulls tended to perform more estrus checks than high ranking bulls in both periods (Fig. 2). 4. There was no significant difference in the frequency of copulation between high and low ranking bulls in both periods (Fig. 3). 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). Fig. 3 Frequency of copulations in high- and low-ranking males in the first and second observation period. Fig. 2 Frequency with which males check females for estrus in both the first and second observation period. abc e d f abc