OPINION: Mastitis, lameness can impact cow fertility

Successfully getting heifers bred and getting cows bred back is an ongoing challenge on dairy farms no matter where you are nor what season it is. Reproductive success requires so many things to go right — you need to breed cows to conceive and when they conceive, they need to stay pregnant. The answers to many reproductive problems lies in developing good action plans through research, ideally, but not necessarily research done on actual working dairy farms.

Like other health situations in dairy cows (ketosis, subclinical milk fever, DA’s, lameness, etc.) it turns out major problems on dairies are interrelated. A disease may affect a cow on its own but it can also make the cow more susceptible to another disease or even make that disease more serious than it would be if it occurred alone.

In the past few years, a number of studies have investigated how mastitis affects the cow beyond just its impact on the cow’s immediate health and milk quality. The studies have been quite consistent in finding that getting even mild mastitis reduces the chances that the cow will get pregnant on her next heat and then retain that pregnancy. These research studies have been performed in different parts of the world where dairy production systems are quite different from each other and found pretty much the same thing. That implies that the impact on fertility is not related to any particular management system or production level — it seems to be how mastitis can affect the cow herself.

Now, of course, people want to find out if you can prevent how mastitis impacts fertility. It does turn out that some of the impact on fertility can be prevented; we just don’t know how those preventive treatments actually work.

Lameness impacts fertility too. Lame cows may not show the usual estrus behaviour so they can be more difficult to get bred. Cows that were sound when they were bred but become lame in the month after breeding are were more likely to come up open. We don’t really know yet how to lessen the impact becoming lame has on the fertility of dairy cows.

Even if we could reverse the impact of lameness on bred cows, it is not really clear that that is the best way to invest our time. There is no dispute that individual cows that become lame (or get clinical mastitis), will be less fertile. For most herds, though, the impact on overall herd fertility is likely very small. That is what a recent study from the U.K. showed. That study was one of the few where enough herds participated so that it was possible to look at the impact not only on the individual cow but on the herd too.
It turned out that although the situation was serious for those individual cows that got mastitis or became lame, it was difficult to detect much impact on the dairy herd itself.

The value of knowing that? Well, we already know many of the things we can do to reduce the chances that a cow will become lame or get clinical mastitis. We also know that lameness and mastitis have other impacts that are more serious than their impact on fertility even to the individual cow. Focusing on those preventive steps is more likely to benefit the herd overall than focusing on reversing the impact of mastitis or lameness after it happens.