Recent data from National Milk Records (NMR) shows that the mean calving interval of UK dairy herds has slipped to around 427 days. In most cases this is not because of extended lactation management practices but delayed rebreeding. It was with this in mind that DairyCo Extension Officer Judith Stafford arranged for a group of Derbyshire dairy farmers to get together with Veterinary Surgeon Jonathan Statham, of Bishopton Veterinary Group in Ripon, (a member of the XL Vets group of practices) to look at recent thinking on heat expression and the role of automated heat detection systems.
"Calving interval slippage can sometimes be seen as a symptom of the modern dairy producer simply not having enough time to spend on heat detection," says Mr Statham, "but in fact the problem is more complex than that.
"In many cases the cow may be expressing some secondary signs of heat but not actually standing to be mounted by other cows. And it is standing heat that is so crucial when it comes to the timing of insemination.
"Standing heat is the only really reliable indication of ovulation and therefore when to serve the cow but there is evidence that this period is getting shorter and of less intensity in modern herds. The average period of standing heat lasts for a maximum of eight to 10 hours and may be considerably less in some cows.
"A cow may well be showing secondary signs of heat, such as restlessness, milk drop, chin rubbing, or mounting other cows but these can be expressed for a variable length of time before or after she has been on standing heat," explains Mr Statham. "If you are missing genuine standing heat you are likely to be much less accurate with your insemination time.
"More important than wasting semen by inseminating early, is the risk you might also inseminate too late missing a cycle and having to wait a further 21 days," he continues.
"Another often underestimated consequence of inaccurate insemination timing can mean either or both semen and egg are of poor quality. With a window of often only six to eight hours when the egg is of the best quality you need to have inseminated at the right time to make sure good quality semen meets it at the optimum time. A poor quality egg or semen might mean that you get a conception but the embryo will be of poor quality and may well not survive the first few days.
"Studies suggest that more than 40% of fertilised eggs are lost as 'early embryonic death' between fertilisation and day 30 in Holstein dairy cows compared to only 28% in British Friesians (Diskin & Morris, 2008). Leroy et al (2008) indicated that egg quality was already reduced in high yielding dairy cows, with no margin for further challenge to embryo survival," he says.
Standing heat can be a tricky thing to spot. Approximately 70% of standing heat is expressed between 6pm and 6am and the Holstein as a breed tends to show standing heat for a shorter time period. There are other factors such as nutrition, disease, lameness, slippery floors, low buildings and stress that can all work against the cow expressing heat by standing to be mounted. As a cow approaches standing heat her motor activity increases, Mr Statham explains. Activity tends to be a build up over a few days and it is this sign that automated heat detection systems are so good at spotting.
"They are able to identify the signs of standing heat by comparing the movements of a cow with the previous 24 hours activity," he says. "The system can then alert you to the right time to inseminate to ensure optimum egg and semen quality. Automated heat detection systems can also alert you to cows that should have come on heat but haven't, those who are expressing signs of heat too frequently and could be cystic and those cows that show reduced movement, potentially due to impending sickness. As with all automated systems, good stockmanship and interpretation are still indispensable.
"It's important to note that activity meter systems can be affected by changes such as turning the cows out to grass, or moving cows between groups," Mr Statham says. "Systems that use neck collars as well as pedometers are really useful as combining movement from walking with chin rubbing and head bobbing may give a more accurate prediction of ovulation.
"Spending more time observing cows is always beneficial, and other heat detection aids such as tail paint or heat mount detectors such as 'Kamars' are helpful but do rely on cows expressing full standing heat for accurate timing. You might get the cow in calf but could still be faced with early embryonic loss with poor semen or oocyte quailty," he concludes.