Last week we bred eight cows and six heifers. This is a pretty high number for our herd, but we’re breeding all heats in an effort to get ahead before the heat of summer takes its usual toll on our conception rate. We’re also providing some extra encouragement to cows getting later into their lactation for that same reason. Six of the eight cows came into heat as a result of our “synch program”. I use quotes because this isn’t something that we do very often, but it is still an important part of our reproduction management, which is a huge part of dairy farm management.
A synch program is basically a sequence of hormone injections that can be given to a cow to influence her reproductive (estrous) cycle and help her come into heat (estrus) and conceive. ABS Global, a genetics company we do business with, lists a variety of different protocols on their website that can be used depending on a farm’s needs. It’s important to note that these hormones have no impact on milk production, nor are they transferred to the milk. Instead, they are simply a tool used, in various ways, to encourage and assist cows’ estrous cycles.
In the past our farm tried a Presynch – Ovsynch protocol that required 5 shots and took over a month start to finish. We didn’t like that it took so much time, required so many shots, and resulted in timed-AI (where the animal is bred regardless of whether she has showed signs of heat). We didn’t have great success getting cows bred with this protocol, and therefore, it didn’t last long on our farm. We’ve noted a much higher conception rate breeding on natural heats, so we generally try to give our cows the opportunity to cycle on their own before we intervene.
Before I go into deeper discussion, I’d like to touch on a few things that will hopefully enhance the significance of this to those not involved in dairy reproductive management. A cow must have a calf to continue to produce milk, so getting a cow “bred back” is a crucial step toward keeping her in the herd. We keep track of our cows’ lactations using “days in milk” (DIM), which is simply the number of days since the cow delivered her calf. This unit is used for most aspects of management, including reproduction.
A lot of our cows start cycling early in their lactations, and will show their first heat at 30-40 DIM. We don’t breed on these early heats. We think that’s too soon to expect her body to actually be ready to start carrying another calf, so we employ a voluntary waiting period (VWP) of 60 DIM (a common choice). On a few high-producing cows, we will extend the VWP to 90 DIM due to the challenge of drying off a cow that is still producing at a high level, but that’s a different issue. For any cow, once the VWP has passed, we breed her any time she shows a natural heat.
Since giving up on Ovsynch, at the end of the VWP we don’t take any specific action to bring the cow into heat. We wait for her body to start cycling (if she hasn’t already) and for her to show a natural heat so that we can see she’s ready. A cow’s estrous cycle is 21 days, so if she came in heat at 40 DIM, we expect to see her again at 61 DIM. While this “wait and see” method works for the large majority of our herd, it unfortunately doesn’t work on everything. At some point, we have to do something to help a cow along if she hasn’t shown a heat and we want to keep her around.
So what if we wait, but we don’t see? At about 100 DIM (or more in some of last week’s cases), if a cow has not shown a natural heat, we will employ a very simple synch protocol by giving her a prostaglandin (PG) injection. The PG basically resets her estrous cycle, and most of the time she’ll come in heat within a few days. If she does, we breed her. After 7 days if she hasn’t shown a heat, we give a second PG shot. We’ve had nearly 100% success with the second shot. If this protocol doesn’t work, there is probably something else wrong with the cow causing her not to properly cycle.
Last week we gave PG shots to eight cows during Sunday evening milking. By Friday, six of those eight cows had come into heat and been bred. Yesterday during evening milking (Sunday, 7 days after the first shots) we gave a second shot to the two unbred cows. Now we will wait to see if those two come into heat this week. If they do, they were just at a point in their cycle when the reset button (PG) doesn’t work. If they don’t, we will check them out more closely to see if we can determine what else might be going on. With several natural heats also occurring last week, if our conception rate was very high, we will have an extremely busy week of calving next January!