The invisible cow is one that you see three times a year: at calving, breeding, and then again at dry off. This is a cow that comes in, performs, and generates profit. This invisible cow is the research goal of Kirby Krogstad of The Ohio State University, and with each project, he gets a little closer to understanding what creates this cow.

Krogstad and his research partner worked with a set of approximately 900 cows to quantify associations of body condition score (BCS), BCS change, and hyperketonemia (HYK) with mastitis, reproduction, and milk yield — three important levers for success in the modern dairy herd. Hyperketonemia is associated with fat being mobilized to support lactation but can also lead to a host of other concerns. How can we get in front of the issue to prevent HYK and therefore improve success?

The transition cow has long been studied, recognizing that a successful transition typically translates into a successful lactation. The cow-side blood beta hydroxybutyrate (BHB) test is affordable and easy to use, quickly identifying ketotic cows struggling through the first week of lactation. Many producers have implemented fresh cow monitoring to quantify the severity and guide treatment choices. With all that effort to test, treat, and hope, does it work? Even if you find that struggling cow — and you treat her with the common dose of propylene glycol — how likely is she to fail anyway?

All cows in the dataset were tested for BHB between three to seven days in milk, considered to have HYK if BHB was at least 1.2 millimoles per liter (mmol/L) and drenched with propylene glycol if they were positive. The data is not analyzing a treatment effect, but rather it is assessing the associations of disease, milk production, and fertility with HYK incidence and BCS dynamics.

The BHB effects

The saying, “She’ll milk it off,” refers to how readily the dairy cow will turn fat into energy when intake is limiting. As fat mobilizes, it either fully oxidizes and goes straight to energy for lactation or partially oxidizes, resulting in the formation of ketones, which accumulate in the blood and create hyperketonemia. The national dairy herd experiences anywhere from 10% to 30% prevalence of HYK. However, on the January edition of “Dairy Science Digest” podcast, Krosgstad recommended herd HYK benchmarks for the first week in milk of:

• 10% or less of cows in their second lactation
• 20% or less of cows in their third lactation and beyond

Pregnancy loss, defined as confirmed pregnant at Day 30 then open at a 60-day recheck, is associated with elevated BHB and BCS change.

“There is a linear increase in pregnancy loss with body condition decrease. Cows who lost more than 0.375 BCS in early lactation were five times more likely to lose their fetus,” Krogstad said.

“This was a big magnitude effect we captured in the data,” described Krosgstad. “It’s very compelling biology. During a negative energy balance event, we see damage in the development of the egg and blastocyst, making it less viable to carry to term. She’s simply not ready yet.”

Interestingly, there was not a BCS association with mastitis, but there was a significant association of mastitis with HYK. Cows with hyperketonemia had 35% higher odds for mastitis. That doesn’t mean that every fat cow will get mastitis, but it demonstrates greater risk. There is a clear biological explanation for this observation. BHB binds to a very specific receptor on the cell, and that receptor can alter immune function. So, when flooded with BHB, the immune cell may be less able to fight off disease, such as mastitis.

The mature cow with three or more lactations testing above 1.2mmol/L of BHB was associated with a reduced milk yield of 11.8 pounds per cow per day when compared to non-HYK counterparts. This is especially important to recognize as our nation’s dairy herd is aging.

The most critical time to monitor BHB levels is the first week in milk. Lipolysis will happen, but the timing matters – it is nuanced. Healthy lipolysis supports a cow through her most productive time. By week two, typically milk has come in and high BHB can be associated with elevated milk yields. However, when BHB is elevated during the first week, before milk yield is high, that suggests she’s off feed and heading into trouble.

Thin cows (under 2.75 BCS) during early lactation were 80% more likely to be culled. Cows that lost 0.75 units in BCS or more were 1.8 times more likely to be culled. This aligned nicely with the HYK results showing that for every 1 mmol/L increase in BHB, there was a 70% higher culling risk.

Perhaps the old adage of “An ounce of prevention is worth a pound of cure” might apply. We’re reminded by Krogstad to find the ideal BCS and keep it steady. Keep your herd within the range of 3 to 3.5, striving to not lose more than 0.25 at a time. Over time, you’ll find this management practice will generate more “invisible cows” in your herd.

These findings were summarized in a peer-reviewed open access Journal of Dairy Science article found at www.journalofdairyscience.org. To learn more, listen in to the monthly podcast, “Dairy Science Digest” on your favorite podcast platform.