The normal oestrus cycle of a dairy cow will vary from 17 to 24 days, and should begin within 30-40 days of calving. Cows presented as “not seen bulling” will be for one of two reasons. They are either not detected bulling or they genuinely are not cycling. The underlying reason will determine how best to solve the problem.
Non-detection of bulling is usually a far greater problem than non-cycling cows. The minimum recommended time for oestrus detection is at least 20 minutes three times a day, with one of these periods at night. There are various heat detection aids available ranging from low-tech tail paint to high tech pedometers and collars.
There is also the problem of cows not showing oestrus behaviour, even when they are bulling. Modern dairy cows are approaching the limit of what their body can cope with in terms of milk production. Consequently, they don’t have much “spare” energy with which to show oestrus behaviour. This means attention needs to be paid to feeding – both the quality of the diet and the way in which it is fed – to maximise intakes.
Another common problem on farm is the presence of lame cows – these cows often don’t show oestrus behaviour because they are having enough trouble walking. This coupled with lower food intakes, adds to the problem.
Assuming heat detection is perfect, there is still the problem with cows that genuinely do not cycle – anoestrus cows. These fall into four types of cows. Firstly, and still quite common on farm, is the pregnant cow. These appear at routines semi-regularly as anoestrus and serve as a reminder to check farm records and keep them up-to-date. It is worth mentioning at this point that 5-10% of pregnant cows will show bulling behaviour while in calf – but it always pays to recheck them.
Secondly are the cows in true anoestrus. These have ovaries with no organised activity when scanned and are often, thin, high-yielding or lame ie, short on energy. These would start cycling in time but more commonly require vet treatment to start ovarian activity.
The third group of cows are cystic cows, which fall into two categories – follicular cysts and luteal cysts. These cows often have cycled well initially and then got “stuck”. Cows with follicular cysts have come up to the point of bulling and then stopped. The follicle should burst to release the egg. These cows are bulling permanently and should constantly show oestrus. This only happens rarely in modern cows and serves as a reminder as to how difficult oestrus detection can be.
Cows with luteal cysts have “stuck” mid-cycle. The cow is pre-programmed to come into oestrus every three weeks or so unless she gets pregnant. However, with luteal cysts this pre-set mechanism fails, so the cow carries on as if she is pregnant.
Both types of cyst require vet treatment in order to return the cow to normal cycling activity.
The fourth reason for anoestrus is cows with endometritis “whites”. Often these will have vaginal discharge but this is not true of all cases. The most effective treatment for this is to bring the cow into oestrus allowing her to clean herself up.
It is important to get non-cycling cows checked regularly. Some problems, especially whites only get worse when they are left. A vet will be able to advise on fixed time AI, although this should only be considered once all other factors are under control.