The chute trip many cows take before going out to grass has traditionally been associated with vaccinating cows for diseases that can cause abortion. This makes sense, as most breeding occurs on pasture, and it’s a good idea to be protected before breeding starts. However, vaccinating cows whenever convenient may not result in the best conception rates.

The reason for this has to do with how the vaccine reacts inside the cow. As an effect of creating immunity to the diseases being vaccinated against, the animal’s body produces inflammation in the ovaries. While the animal recovers completely, the ovaries are not fully functioning for a period of time, and this leads to a temporary decrease in fertility.

How much fertility is impacted is due to several factors, primarily whether a modified live or a killed vaccine is used. Because a modified live vaccine involves using a replicating virus, these vaccines create significantly more inflammation than killed vaccines do. As a result, cows require a longer period of time to recover from a modified live injection than a killed.

Data says close to breeding will decrease fertility
This phenomenon was clearly documented in a study published by South Dakota State University in 2018. The study entitled “Influence of vaccination with a combined chemically altered/inactivated BHV-1/BVD vaccine or a modified live BHV-1/BVD vaccine on reproductive performance in beef cows and heifers” involved cows that had been previously vaccinated with two doses of modified live vaccine as heifers and subsequently a single dose of either killed or modified live vaccine between 27 and 89 days before AI. 60% of the killed vaccine recipients bred AI, versus 52% of those receiving modified live vaccines.

The second aspect of note in this study revealed that cattle vaccinated within 37 days of AI were 12% less likely to settle AI as compared to those vaccinated at least 46 days before breeding. This is an issue of great concern to us when we look at the timing of vaccinations given before cattle go to grass. It is not abnormal for cattle to get worked around Memorial Day weekend before going to pasture. If the bulls or AI are going to occur before July, we can expect to see a decrease in first service conception rates as a result. This may influence your decision on the best time to get the cattle worked.

Don’t try to save a chute trip
One thing that is undoubtedly a bad idea is to give pre breeding vaccinations when setting up cattle for AI. While it is tempting to try to save a chute trip by giving shots at this time, it will assuredly lead to inflammation in the ovaries when we’re trying to AI.  The same goes for Bang’s vaccination during this time period. While I sympathize with wanting to save a day working cattle, semen is usually pretty expensive, and you waste money by not getting those shots done earlier.

With the complications associated with timing pre breeding shots correctly, if you’re struggling to determine when to get the job done, it is best to work with your herd veterinarian to  develop a plan. These shots need to coordinate with other interventions, such as deworming or other vaccinations. To get the most benefit for your cows while in the chute, leverage your veterinarian’s knowledge about each of these products to find a time that will provide the most positives and fewest negatives for your herd.