The most distinctive behaviour of the adult bull is determined by the rut. The rut lasts six months on average and with the majority of bulls occurs between April and September. In the research paddock 15 adult bulls were observed. Below shows summarised seasonal distribution of rutting behaviour.
Externally the rut can more or less be seen by the secretion of the occipital glands, often by a swelling of the testicles, but always by the typical behaviour. Rutting behaviour is only shown when cows are present. Usually it occurs at the age of 4-5 years. In individual cases it can take place from the age of three up.
The rutting periods of the adult bulls last between a few weeks up to 7 months and occur in irregular intervals of 3-17 months.
The duration of the rut depends on internal and external factors. The constitution and the hormonal condition of the bull are apparently decisive but also his self assertion towards competitors. At the beginning of the main breeding season in winter more or less all adult bulls are in rut. The strongest ones then take over a cow group and defend it against rivals. The remaining bulls try to compete for the cows but in 94.5% of all cases are being chased away by the group-holder and either migrate or stay at the periphery of the group.
Depending on his constitution the group-holder herds the cows for 3-5 months, but he can be replaced by a competitor before that.
Some bulls that do not have a chance to take over a cow group during the main breeding season come into a second rut in spring or in summer. Because of the lack of competitors they then succeed in herding a cow group. In some cases these bulls even succeed in reproduction. Mostly the bulls stay in bachelor groups or solitarily in summer, even though there are contacts or even short-term associations with cows.
- Bull groups occur throughout the year and consist of a changing number of adult and/or subadult bulls.
- Older buIls live more solitarily.
- Outside the main reproduction time, in summer, the cows live in cow groups without an adult bull. These groups consist of adult cows with their young, other adult cows, and male and female subadults.
- At the beginning of the breeding season in winter (April to May) almost all adult bulls are in rut. The cow groups are taken over by a bull who then herds them for three to five months.
- After taking over a group, the herding bull chases away all subadult bulls who then join bachelor groups. However, he tolerates the young cows who remain in their mothers' group.
- Before parturition the pregnant cow leaves the group and gives birth in a remote area. She then lives alone with the calf for up to three weeks.
- Mothers with young calves join together, forming the basis of a new cow group (core group).
- Toward the end of winter the herding bull loses interest in the cows and leaves them voluntarily. He then lives solitarily or joins other bachelors.
- Weaker adult and above all young bulls who did not have the chance to take over a cow group during the main breeding season come into rut a second time in summer or in autumn. They then also herd cow groups but are driven away by dominant bulls at the beginning of the winter at the latest.
1. bull group
1a. older bulls may live solitarily
2. cow group
3. bull joins cow group
4. bull herds cow group
5. dominant bull expels subad. males, these join bachelor groups
6. pregnant cow segregates before parturition
7. cows with young calves form new core group
8. bulls leave cow group voluntarily
9. younger or weaker bulls herd cow group temporarily
Size of symbols corresponds to respective age class.