It is widely assumed that Pregnancy Rate (PR) is the best indicator to assess your herd reproductive performance. Defined as the proportion of eligible cows that become pregnant in a 21-day period, it tells you how fast cows are getting in calf after the voluntary waiting period. Fertility is one of Raquel’s special interest areas and she has carried out a lot of farm training on her Spanish dairy farms. Here she gives us a deep dive into pregnancy rate and what is actually affecting it on farm.
Generally, the higher the PR, the higher the productivity of the herd as we maximise the time that cows are in the most productive time of lactation, in addition to reducing days open and culling rate.
So, it looks easy – you just need to serve cows when they are bulling and they will get pregnant if they are healthy enough… Unfortunately, it’s not this simple. Achieving pregnancy at the right time and doing this cost-effectively is a real challenge and a common cause of frustration for both farmers and advisors.
Pregnancy rate values above 20% are considered good, although above 25% is even better and 30% or over is very good. But let’s have a deeper look where these values come from.
Pregnancy rate is a combination of submission rate (SR) and conception rate (CR) and can be illustrated by the following equation:
PR= SR x CR
This means pregnancy rate is influenced by both how good heat detection is and how fertile your cows are. Farms which have identical PR values could be due to factors affecting either submission rate or factors affecting conception rate – no two farms are the same! Same problems, don’t necessarily mean the same solutions!
So, if your Pregnancy Rate is a problem, what is the bottleneck? Is it heat detection? Or fertility? Or maybe both?
The first step is to look at your data and try to find out specific problem areas and develop strategies for improvement. For this, accurate records are paramount. Lack of data can be a frustrating situation for both advisor and farmer. No data, no analysis, no action! On-farm software is an excellent investment (as long as there is a commitment to enter the data) but a simple spreadsheet could do the work perfectly well and is fairly cheap!
Ideally, the submission rate should be more than 70%, although 50-60% is relatively common. Lower values than this likely require intervention. Some farms can achieve 80-90% especially if they use strategies such as fixed-time AI. If submission rate is very high, it is always worth checking if cows are being served at the correct time. Sometimes submission rates can be artificially high where any cow ‘suspected’ to be in heat is served, even if this is not a true heat. This strategy only leads to poorer fertility results.
Poor heat detection might not only be caused by lack of observation but also due to cows not showing signs of heat due to slippery surfaces or lameness or even, not cycling at all (anoestrus cows).
Visual observation is the best method of heat detection but there are many additional aids to improve submission rate:
- Tail chalk or paint
- Stickers
- Kamar detectors
- Pedometers and collars
- Eartags
- Electronic pressure sensors
- Vasectomised bulls
- Hormone synchronisation protocols
Heat detection is probably the easiest variable to influence in order to improve pregnancy rate and one or more of these aids can be used alongside visual observation.
The other variable in the equation is the Conception Rate or the ability of the cow to get pregnant after being served. The first step in investigating conception rate is to check whether the AI technique is performed correctly!
An external AI technician service should reduce the risk of this happening but if you are doing DIY AI, please make sure you do a ‘refresher’ at least every five years to avoid developing ‘bad habits’ over time. Obviously we can provide this service for you(!)
AI timing can also influence fertility. Serving cows before 40 days in milk (typical VWP) usually gets poor results as most of the cows are still in negative energy balance. In contrast, some farmers opt for delaying the first service in very high yielding cows arguing more profitability in milk production. Without entering into this technical discussion, truth is that this management decision could distort the value of the PR at first service which will look worse by decreasing the SR as these cows fall out of the window period, although the CR could be perfectly fine.
It is beyond the scope of this article to discuss the innumerable health, nutritional, environmental or genetic factors that may impact cow conception. But it goes without saying that any health issues such as mastitis, lameness or ketosis or adverse environmental conditions such as heat stress, poor cow comfort and overstocking will negatively influence reproductive performance in a herd.
Regular fertility routines play a crucial role in any reproductive strategy. Early diagnosis and treatment of postpartum disease including metritis, ovarian cysts etc., will help reduce timing to first heat after calving in order to serve the cows as soon as possible after the Voluntary Waiting Period. Another key point is the re synchronisation of empty cows or pregnancy losses (the sooner, the better!) in order to get cows re-served as soon as possible.
Make sure your fertility visits are at an appropriate frequency: ideally weekly. Vet fertility visits shouldn’t be considered an expense but an investment as they could make a huge difference in terms of reproductive success and therefore, herd efficiency.
In summary, reproductive evaluation of the herd is not just about one value and although pregnancy rate is a useful indicator, a deeper examination of the data will help to determine problem areas and design improvement strategies in order to maximise productivity. As always, if you have any questions about your fertility or anything specific in this article, please speak to your vet.
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