It can be a challenge to keep cows healthy on a dairy with common diseases such as mastitis, lameness, metritis and others negatively impacting herd profitability. A review of existing research shows that per-incident cost of some health events can approach $500, and that nearly one out of every three cows that experience a significant health issue may be culled.

Because of this negative impact on profitability, dairy producers have worked with their nutritionists and veterinarians to establish well-formulated rations, protocols and procedures designed to prevent these health events from happening. But despite best efforts, some cows are still affected and require treatment.

But why do some cows get sick and others in the same environment that eat the same feed and go through the same routines seem to avoid these adverse health events?

Ask most producers, and they will tell you that their best cows are the ones that seemingly don’t exist. These cows are the ones that never get sick, breed back on first service, calve without incident and don’t get mastitis.

Except for routine procedures such as dry-off, reproduction protocols or vaccination, they rarely end up on a sick cow or vet check list, and their production is high enough to go unnoticed.

These cows with moderate to high production and little time in the sick pen likely will not end up on the cull list – which means they stay in the herd longer. Cows that stay in the herd past their first or second lactation have a significant impact on profitability.

“Third-, fourth-, fifth-lactation and higher cows in our herd have already paid their rearing costs,” says Simon Vander Woude of Vander Woude Dairy in Merced, California, “So they are just making money.”

Long-lasting cows do make money. Recent data from Larson Acres, a 3,000-cow dairy in southern Wisconsin, showed that while 70 percent of the cows in the herd are in the first or second lactation, 30 percent of cows in their third lactation or greater are giving around 3,600 pounds more than those younger cows.

Mike Larson, general manager of Larson Acres, says, “It’s very important for us to continue to improve our daily milk production to increase the proportion of older cows in our herd.” Larson admits that most cows leave the herd due to mastitis and lameness and targets reduction of both of those health events to maintain longevity.

Having more multiple-lactation cows in the herd also has an impact on cull rate and reduces the number of replacements needed to maintain herd numbers.

One of the objectives on Vander Woude Dairy is to be efficient with the number of heifers on feed. In order to do that and still have enough replacement heifers, there has to be a low cull rate in the milking herd, and part of that low cull rate is due to healthy cows. He says, “Mastitis, lameness, metabolic issues and DAs, those are all reasons cows get culled in first, second or third lactation. We do a good job of managing those risks, but we’re always looking to get better.”

Vander Woude shares that there are times when he comes across a cow card of a cow with multiple lactations and realizes she’s only had one case of mastitis in her lifetime. The absence of any documented health events makes those cows go blissfully unnoticed. Greater insight is telling us that the genetics these cows carry may put them at lower risk for being affected by certain health events.

Kent Weigel, professor and chair of the University of Wisconsin – Madison’s Department of Dairy Science, says that he’s certain that long-lasting cows have a genetic predisposition to stay in the herd longer. “We’ve done the research to look at the heritability of some of these health disorders – 5, 10, 15 percent depending on the event – so we know there is a genetic component."

"We also know these health traits are correlated. For example, cows that don’t get milk fever or ketosis also tend to breed back faster, maintain body condition and so forth, and therefore stay in the herd longer.”

Knowing that there is a genetic component to health events (even with low heritabilities), can producers actually make progress if they choose to select for healthier cows? One only needs to look at the progress made in improving fertility traits such as daughter pregnancy rate (DPR) to know that genetic progress can be made in lower heritability traits.

Remember that heritability is the proportion of the total variation that can be measured due to genetics. With DPR, we know that management and environment accounts for about 96 percent of the variation, so the heritability for DPR is approximately 4 percent for average-managed herds.

We’ve known for some time that our intense selection on milk production over the decades has had a negative impact on fertility.

Yet even at this low heritability, Figure 1 (AIPL presentations, accessed Dec. 1, 2015) shows that we’ve made genetic progress and actually shown positive improvement in cow fertility.

Much of this upturn can be attributed to genetic selection.

If progress can be made in fertility traits, then progress can be made in health traits as well. And if we can identify the genetics that tell us which cows are at a lower risk for being affected by certain health events, then we should be able to better identify what makes those trouble-free cows so special.

Like other genomic indicators, we should be able to do this at a very young age, creating a potentially powerful selection tool that will help producers build a healthier herd.

Producers who want to be efficient with heifer production place a significant emphasis on the genetics of those animals. Knowing which heifers will be longer-lasting, more trouble-free cows would be an important part of the selection process.

Weigel says the power of genomic selection of replacement heifers is making more accurate decisions early in an animal’s life regarding future performance. “If I play the stock market and I know I’m going to be right more than half the time, I’m going to be really rich."

"That’s what genomic selection is about – increasing the odds of making a good decision – and over the long term, it will make a significant difference.”

Producers who select for health traits could realize the profitability advantages that come from a healthier herd – fewer vet bills, lower treatment costs and more salable milk. Weigel says that just adds to the benefit of longer-lasting cows. “Those cows that can stay in the herd a long time and do so in a quiet and profitable way really make an enormous difference.”  PD

References omitted due to space but are available upon request. Click here to email an editor.

Cheryl Marti is an associate director, genetics and reproduction manager and dairy franchise lead with Zoetis. Email Cheryl Marti.