Minimizing Interservice Intervals
- [Narrator] Minimizing interservice intervals is key for maximizing reproductive efficiency in dairy cattle.
It plays a key role in the profitability of a dairy operation because of its impact on management expenses and long term milk production.
An interservice interval is simply the number of days between services.
The time from one artificial insemination event to the next artificial insemination event.
An interservice interval can be measured on an individual cow, but is most useful as a calculated average for the entire herd.
The interservice interval might also be referred to as the interbreeding interval, reinsemination interval, or interval between services.
The economic impact of interservice intervals becomes evident when evaluating a herd's pregnancy rate.
Pregnancy rate is often considered the best single measurement of reproductive performance in a dairy herd, and is simply defined as the percentage of eligible cows that become pregnant in a given time frame.
It can be calculated by multiplying AI submission rate, SR, by conception rate, CR.
Improving the pregnancy rate in a dairy herd has been clearly shown to increase profitability.
According to an economic chart developed at the University of Wisconsin, each percentage point gain in pregnancy rate has an associated gain of 10 to 32 dollars per cow, per year.
Interservice intervals become an important component of the pregnancy rate calculation after first insemination, impacting submission rates, specifically.
Let's look at an example.
The pregnancy rate for a dairy herd with a 50% submission rate and a 30% conception rate is 15%.
A number that certainly could be better.
Looking specifically at the submission rate portion of the equation, there are two likely factors limiting the pregnancy rate for this herd.
One is heat detection, and the other is a weak strategy for timely reinsemination of cows, not caught in estrus right away.
Maybe a few cows are being inseminated three weeks after first insemination, but others are going for a greater length of time before being diagnosed as not pregnant and reinseminated.
Now let's look at this example herd a year later.
Maybe they've made some improvements to the facilities to accommodate better estrus detection, or they've installed an activity monitoring system, or they're using more timed AI for some of the repeat breeders.
Submission rate is now at 60%, a 10% improvement with the same conception rate, the result is a three percent jump in pregnancy rate, which is estimated to be a gain of $66 per cow, per year.
Now if they were able to bump these numbers up a bit further, a submission rate of 70% and conception rate of 40%, both of which are achievable, would make for a pregnancy rate of 28%, a 13% increase worth $215 per cow, per year.
Again these numbers are achievable, but only if serious attention is given to the interservice intervals.
Interservice intervals commonly average more than 40 days, but getting that number down, ideally below 40 days, will not only increase a herd pregnancy rate, but will decrease average days open and decrease calving intervals, something most herd managers are trying to accomplish.
Regardless of what strategies are used for pregnancy diagnosis and reinsemination, there is an opportunity to catch open cows by heat detection during the three weeks following insemination.
Every estrus detected that is followed with timely reinsemination will have a positive impact on lowering the average interservice interval for the herd.
There is value, even if heat detection isn't the primary reproductive strategy for the herd.
So what can be done to boost heat detection?
One option is to focus on training.
For most operations, there are multiple people working around the cows, especially during the day.
Each of them probably has a different level of understanding and responsibility when it comes to reproductive management.
With at least a basic level of training for how estrus is displayed in cows, and how observation of estrus can be recorded, they can contribute to the reproductive management success.
Maintain good animal identification.
Have you ever heard someone say, hey, that black cow over there is in heat?
That may be helpful if it's a Jersey herd, but in a herd with Holstein cows, more information is needed.
An easy to read ear tag is probably a good place to start.
Keep good records.
It isn't fun to have to worry about keeping records, but they sure can help increase efficiency, and they don't have to be complicated.
Someone can keep a pen and paper in their pocket and write down heats, or they can use a nifty app on their phone.
Either way if the information is kept in an organized fashion, there will be benefits of timely insemination and more information to diagnose problems when they arise.
Lastly, activity monitoring systems have grown in popularity and can be great for catching heats.
They can help catch a higher percentage of cows in heat, and they lessen the need for personnel to catch and record every heat.
They do still require time and attention to work well.
There's a decent chance that cows which haven't shown a heat by 24 days post AI, may be pregnant.
What's most important to know at that stage is which ones are open.
Various pregnancy diagnosis options can provide that information.
Traditional pregnancy diagnosis by rectal palpation is commonly done in the 35 to 45 day window.
There are now options to test earlier by other methods, but this is a sound method that has a place in efficient management.
Using ultrasound for pregnancy diagnosis can shave a week or so off of the time, which may also help with our goal to minimize interservice intervals.
Ultrasound is often done in the 28 to 35 day window.
The third option includes a number of variations.
Pregnancy Associated Glycoproteins, abbreviated PAG, can be tested for in either milk, or blood around 28 to 32 days.
One advantage to this approach is that it may allow for more frequent diagnosis.
Maybe testing a group of cows every week, rather than waiting for a veterinarian, which might be less frequent.
One disadvantage of early pregnancy diagnosis is that some cows may correctly test positive for pregnancy, but later lose that pregnancy.
A significant percentage of pregnancies are lost between 28 and 45 days.
Negative pregnancy results mean the cow is open and progress can be made towards timely reinsemination of those cows.
Looking at the bigger rebreeding strategy, there are many possibilities.
Hopefully if practices are in place for good conception rates on the previous service, and some of the open cows are caught in estrus, 17 to 24 days later and inseminated, there won't be a large percentage of cows to deal with later.
If day 32 is the target for pregnancy diagnosis, or setting up open cows for timed AI, it is possible to get a jump start by giving GnRH on day 25.
GnRH doesn't have any negative effects on pregnancy, but it is the first treatment for a standard off sync timed AI protocol.
A week's time can be gained with this strategy.
On day 28, it is possible to start diagnosing for pregnancy.
If a PAG test is used, that allows four days to get results before day 32, which is a common target for pregnancy diagnosis and initiating timed AI protocols for open cows.
On day 39, any of the common pregnancy diagnosis options can be used, but the number of days open is adding up quickly.
These strategies are often best visualized working them out on a calendar.
For this example, cows could either be checked for pregnancy by a PAG test on day 28, or by ultrasound on day 32.
The off-sync timed AI protocol can be initiated on day 32, for open cows, which is GnRH on day 32, a Prostaglandin F2 alpha treatment a week later, then GnRH again approximately 56 hours after Prostaglandin, then AI on day 42.
In summary, interservice intervals are an important part of reproductive efficiency and the associated economics of any dairy operation.
They impact the herd's pregnancy rate, and they can be improved by taking a close look at heat detection methods, being strategically efficient with pregnancy diagnosis and using some sort of synchronization strategy for cows that would otherwise go too long before reinsemination.
Frequently Asked Questions