If you’ve heard it once, you’ve heard it a thousand times. Mastitis is an insidious profit-robber that steals milk production, increases reproductive problems and challenges the overall productivity of your cows. However, new research shows it’s worse than you thought, especially when it comes to reproduction.

It’s not just clinical mastitis in early lactation that reduces reproductive performance. Subclinical cases during the first 90 days of lactation can cause the same damaging results. So, if your herd’s reproductive performance has been below par, it may be that subclinical mastitis has been derailing your efforts.

With these new facts in hand, the time has come to rethink your mastitis management program. Don’t let subclinical mastitis rob you of reproductive performance. As is the case with clinical mastitis, there are steps you can take to prevent it. Here’s why you need to do an even better job of mastitis control on your dairy, especially when it comes to subclinical infections.

Quantifiable results

Until now, clinical infections carried most of the blame for mastitis-related problems. 

As a result, treatment protocols have been developed and attached to action points based on clinical signs. These concepts and procedures are not wrong. But this new research has shed light on the fact that you must target mastitis at the subclinical stage, too.

Subclinical mastitis is much like subclinical hypocalcemia on your dairy — unless you look for it, you usually don’t know the problem exists.

What began as a study at the University of Tennessee about the effects of early lactation clinical mastitis on reproduction has revealed a deeper insight into the disease’s harmful nature and the wide-reaching effects it has on your dairy.

Researchers used 12 years of precise per-quarter mastitis infection data and reproductive records from 752 Jersey cows and made several intriguing discoveries. First of all, more than half of the cows were infected with mastitis during early lactation. Second, of those infections, more were subclinical in nature than clinical. These results reveal that it is definitely worth your time to focus your attention here.

“We went further into the data set and found that subclinical mastitis does have an impact on reproductive parameters,” explains Steve Oliver, University of Tennessee mastitis research specialist.

First published in the June 2001 Journal of Dairy Science and updated at the 2002 American Dairy Science Association meeting, scientists noted that cows that developed clinical or subclinical mastitis before their first service (during the first 90 days of lactation) had between seven to 10 increased days to first service when compared to uninfected herd mates.

While interesting, these results were compounded by the fact that services per conception increased from 1.6 for uninfected cows to 2.1 for infected cows.

This is significant in that services per conception affects conception rate — the percent of cows pregnant after one service — which is one of the major factors driving pregnancy rate. This explains why producers struggling with subclinical and clinical mastitis also struggle to maintain pregnancy rates.

The results only got worse for cows that began with subclinical infections that evolved into clinical cases. Those animals typically increased days to first service by about 26 days more than uninfected herd mates, and services per conception jumped to 4.3, or more than double than that for cows in the infection-free control group.

Additionally, it didn’t matter which organism caused the mastitis infections — whether it was gram-negative or a gram-positive agent had no bearing on the outcome. Researchers followed cases that involved Escherichia coli, Streptococcus dysgalactiae, coagulase-negative Staphylococci, Staphylococcus aureus and Streptococcus uberis infections. All of the infections impacted reproductive parameters similarly.

“Subclinical infections are the ones that trip people up, because we don’t know they are there,” admits Neal Schrick, University of Tennessee reproductive specialist.

More research coming

A study now under way at the University of California-Davis is searching for clues about the relationship between mastitis and early embryonic death. Researchers are currently analyzing the data for both clinical and subclinical infections and their impact on cow reproductive performance in this area.

And while it’s premature to draw any conclusions just yet, it is not unexpected that subclinical mastitis will have a similar negative effect on early embryonic death once scientists sort through the data. “Subclinical mastitis probably does have an effect because whatever initiated the infection and increased the somatic cell counts will likely be able to create the events that cause changes to reproductive cycles,” explains Dale Moore, University of California-Davis veterinarian in the Department of Population Health and Reproduction.

Prevention remains key

Meanwhile, mastitis isn’t going anywhere, and so you must do everything possible to minimize infection rate and severity. The results from this research emphasize the importance of mastitis control in the dry pen so that it doesn’t carry over into the transition period, asserts Oliver. And, he suggests that producers must understand that if a cow has an infection, whether it is clinical or subclinical, it will probably take extra effort to achieve a successful pregnancy.

“We’re not going to be able to prevent all infections,” Oliver concludes. “But, a good mastitis monitoring program, good records, and an awareness of the existence of clinical and subclinical cases would go a long way in minimizing some of the breeding problems in our industry.”

A new look at estrous effects

Why does mastitis impact reproductive function? And what are the physical responses to infections?

These are the big questions about mastitis’ impact on reproductive parameters. For years, researchers have theorized that the infection affects the endocrine system, but were not sure quite what was going on.

Results from soon-to-be-published research at the University of Tennessee show that cows experimentally infected with Streptococcus uberis showed significant reduction in follicular function. That is, if cows developed clinical mastitis before the onset of estrus, most did not show estrous behavior.

“Clinical mastitis infections delayed estrus by a full cycle,” explains Neal Schrick, University of Tennessee reproductive specialist. “Even though ovulatory follicles were the same size as for cows in the control group, mastitis-infected cows had reduced estrogen levels and did not have a surge of luteinizing hormone that is necessary for ovulation.”

Furthermore, the infected cows had significantly higher cortisol levels in their blood, indicating that animals experienced a stress load from the mastitis infection.

“For now, there is no cure-all to reverse this process,” says Schrick. “There is some work currently being done that may provide some answers, but it is still about two years away from completion. So, the emphasis remains on mastitis prevention and control.”

How time of mastitis infection impacts reproduction

This graph shows the effect that the time of mastitis infection has on several reproductive parameters. The blue bar indicates results for cows that developed clinical or subclinical mastitis infection before first insemination; red refers to cows infected between first insemination and pregnancy, and the green bar refers to cows that developed mastitis after pregnancy confirmation or were uninfected during the study period.

Source: University of Tennessee