If you've been breeding dairy cows for very long, you're probably familiar with what Voluntary Waiting Period (VWP) is and likely have some sort of VWP target that has been identified on your farm. Your VWP is simply the designated number of days that must pass after calving before a cow becomes eligible for breeding. Many herd managers can quickly tell you what their VWP is, but you'll probably notice that it varies from farm to farm. In your herd, you might tend to stick to a certain VWP, but you're sometimes tempted to push the VWP later on some cows. All of that is okay! A magic, perfect number for VWP doesn't exist.
There are a number of factors in the early postpartum period that affect when you might choose to begin breeding. First of all, the uterus needs a period of time to recover (involute) from pregnancy, which takes about a month. There is also the negative energy balance struggle, when early lactation cows are usually expending more energy than they can take in, and reproduction falls low on their body's priority list.
If you wait too long after calving before cows are eligible to breed, you'll likely begin to struggle with cows that are over-conditioned and producing less on an annual basis (both milk and calves). After about three months postpartum, maximum herd fertility is achieved and their is no further benefit of waiting. It's even possible that first-service conception rates start to decline after 120 days in milk.
If you start breeding too early, you'll be throwing money into cows that haven't even started cycling yet. You'll likely become frustrated with poor conception rates, and it's possible that you'll end up needing to dry off cows when they're still producing a significant volume of milk.
In your own herd (which is unique) you'll want to find the happy medium in order to achieve good, economical results. And it might take a little research to determine where the best spot is. If you've had the same VWP for a long time, you might consider thinking through what reproductive management dynamics have changed on your farm over those years. If a lot has changed, you might be due to reevaluate.
In general, you should probably be working with a VWP that falls somewhere between 45 and 90 days. Don't breed any cows before 45 days, and make sure that if you're going to wait until 90 days before breeding any cows that you're ready to manage accordingly, so that you don't lose prime opportunities for getting cows bred and maximizing production.
If you have a smaller herd and are keenly a each individual animal, there may be room for a more flexible VWP. Lets say you've established a VWP of 65 days. If there is a low-producing, healthy cow who has shown a good heat at 49 days, it might be worth breaking your VWP rule and breeding her with some inexpensive semen. Or maybe there are a few high-producing cows that have had a tough start to their lactation. It OK to say, "Hey, I'm not going to even start breeding these ladies until at least 80 DIM."
If you have a larger herd or simply don't have the ability to spend time altering management protocols for individual cows all the time, you'll probably want to choose a specific VWP which can be applied across the board. If you're using a timed breeding protocol, you may want to aim for somewhere around 70-75 DIM to maximize first-service conception rates and offset the costs of the injections.
Here are three examples to show how different VWPs might work for different herds:
Scenario #1: VWP = 50 days
- Good heat detection practices
- Not a high-producing herd
- Few postpartum disorders
- Low costs for semen / injections
- Wait to breed cows with "issues"
- Average production & health
- Mixture of timed breeding and breeding based on observed estrus
- Use expensive semen on good cows
- Large herd
- Weekly timed breeding protocol
- Aggressive resynchronization / pregnancy check protocol
If you've found a system that works well for you, there is no reason you should feel pressured to change it. There may be some slight economic benefits if you're willing to consider tweaks to the system, but there's no shame in finding out what works best for your individual herd and sticking with it. Every dairy herd is unique, and there's no "magic bullet" VWP number that everyone must use to succeed.
Lastly, remember that VWP is not, in any way, an indicator of herd performance!
For more information about VWP, feel free to peruse the following articles:
What is the ideal waiting period? - Jeff Stevenson, Hoard's Dairyman
Reproduction Practices on U.S. Dairy Operations - USDA, APHIS
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