Dairy cattle must calve on a regular basis to maximise profitability.
This is a reflection of higher milk yield in the earlier stages of lactation, as well as the greater number of calves that are produced over the lifetime of a cow with shorter calving intervals.
The standard target interval is 365 days, though few producers manage to achieve this.The calving interval can in turn be thought of as a reflection of two main parameters, the heat detection rate and the conception rate; that is seeing the cows bulling and then getting them pregnant to that service.
While conception rate can arguably be a harder nut to crack, as so many different factors affect it, there really is no excuse for not maximising the effectiveness of your heat detection. To give some idea of the impact it can have, consider the difference between accurately detecting 50% of your cows in oestrus and 60% of them. Dairy Co quote an average improvement of 4 days from your calving to conception interval, 6% from your cull rate and an increased profitability of 1p/litre for that relatively modest change. Not to be sniffed at!
The strict definition of heat detection rate is “the percentage of cows eligible for service in a 21-day period that were actually served”. This can be calculated by many computerised management systems. If not, one of the easiest ways to assess your heat detection is to assess the time between successive services for repeat breeder cows, the “inter-service interval” – this is easily brought up in graph form on management systems such as Interherd and a good level of heat detection would result in 70% of returns falling in the 18-24 day interval.
So how to maximise heat detection? Firstly and most importantly, remember that while mounting other cows is highly suggestive of heat, the only definitive sign of oestrus is a cow standing to be mounted. All the other signs are less conclusive. Standing heat is the crucial point in terms of timing of service – ovulation occurs very roughly 8 hours after the end of standing heat, which is the origin of the well-known and generally useful am-pm service rule.
Secondly, it is important to remember that expression of heat is extremely variable in terms of duration – while the average may be 10-12 hours, perfectly normal cows may only show standing heat for an hour or two. For higher producers there is some evidence that Holsteins as a breed tend to show standing heat for a shorter time and less intensely. Another vital point to consider is that 70% of cows will express standing heat between 6pm and 6am. So if we combine the fact that many cows will show shorter than average heats and that the majority will show that activity overnight, it is easy to see how they can be missed.
With all the advances in technology and all the equipment available at every trade gathering these days, it may be a surprise that the most effective method of detecting cows in heat still remains human observation, through which detection rates of 70% are possible. But to be effective it has to be well managed and a structured part of the daily routine. From the discussion above we can see that optimum levels of heat detection require repeat observations – ideally four times a day for half an hour, with particular emphasis on the night time observations.
The road to excellent heat detection rates is paved with good intentions, but if this sort of regime is not going to be possible then relying on observation alone will be inadequate. In such cases producers need to recognise that they require assistance! This can take several forms, all of which have their advantages and potential pitfalls, from monitoring by outside professionals to tailhead marking and activity monitors.