An important skill in dairy herdsmanship is the ability to detect when a cow is 'bulling'. In other words, when the cow is most fertile and therefore the correct time to artificially inseminate the cow, or serve her with a mature bull.
Bulling is sometimes known as 'estrus', 'heat'... and 'randy' in some establishments I have worked in! Bulling is part of the oestrous cycle, which lasts 21 days in cows and is a continuous cycle. If you would like to look at this cycle in-depth, please follow this link to my specific article on this topic... LINK
If you already have a prior knowledge of the cycle you will probably know that bulling is the result of a surge of oestrogen in the cow's bloodstream. This surge produces certain typical behaviour that is recognisable to stockmen who are round their cows most of the day but also behaviours that will be recognisable to most non-farming folk!
When I started working in dairy I had little idea how to spot bulling cows; through getting to know the herd I work with and taking a few minutes per day to allow for behaviour observation, I have learnt how to spot a bulling female fairly well.
So what do you look out for?
1) The first and most telling sign to look out for is mounting/riding and the reaction of the cow being mounted.
When a cow is bulling she is undergoing a period of sexual receptivity and excitement. Some cows mimic the role of a bull, by mounting another cow - the cow being mounted, unless bulling, will detest this behaviour and run off/struggle away. However, a bulling cow will allow this to happen and simply stand still.
It is important to note that the cow that is doing the mounting is not always bulling - once the cow has mounted, observe her behaviour afterwards to get more of an insight. Is she staying close to the same cow? Is she resting her chin on the cows' pin bones?
2) Which brings me to my next point... cows that are bulling at the same time usually stay together!
When herding the cows in for milking or simply just observing them in the yard you will often find that cows that are bulling will stick together in a small tight group - following one another wherever they go and you will find it harder than usual to separate them.
3) Chin resting!
This behaviour requires a fairly keen eye to spot. Essentially a cow is bulling and about to ride or has just ridden another, she will rest her chin on the pin bones (just about the tailhead) of another cow. Every time I have seen this behaviour the cow has almost certainly been bulling.
4) Rub marks!
When cows mount each other excessively throughout the day they can leave small rubbing marks on each other's hind quarters. Usually just infront of the pin bones or below the hook bones.
Remember that if the marks are fresh they are usually a little bit bloody - old scabs are not a sign of recent bulling behaviour!
Often I have been completing a task in the yard and have heard the same cow absolutely roaring her mouth off down the field for a good hour. This can be a good sign that she is bulling; it may be because she had a bulling mate who has somehow escaped her clutches and she is roaring to relocate her - or sometimes, they just have the urge to roar when they are at this point on their cycle!
Do not confuse this with cows that have just calved roaring - this will be because they have lost their calf and they are trying to find out where it is by roaring and waiting for a response.
6) Anything strange!
Once you get to know your cows' normal behaviour this factor will become easier to spot. Essentially when some cows are bulling they will just act very differently; standing alone, running off, calling out at a bull etc etc.
I had a cow chase me down 3 fields only to turn round and run off again when I discovered her - she was bulling mad! Generally any abnormal behaviour shown by one cow without a motive for food, suspect bulling.
7) Bulling string!
This is my least favourite detection tool because frankly I never seem to see it; if we relied on this as the only tool of detection, we would never AI a cow!
A thick clear mucus hangs from the vulva of the cow, indicating that she is on heat.
Whatever you do, don't get this confused with the first stages of labour of a pregnant cow - you would have a bit of a shock when you come to AI her!