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    The concept of the high fertility cycle has been proposed by Middleton, Fricke and others. The idea is that timely pregnancies in one lactation may lead to less body condition loss, fewer health issues, greater fertility and reduced pregnancy loss in the next lactation. To some degree, the same concept applies to udder health. Maintaining excellent udder health in one lactation makes it easier to maintain excellent udder health in the next. While the concept of a high udder health cycle has not been proposed in the veterinary literature, there are similarities between it and the high fertility cycle that are worth exploring.
    One of the main drivers for continued poor udder health is recurrence of clinical mastitis. A high proportion of cows experiencing a clinical mastitis event in a lactation will experience additional cases during the same lactation. Many of these cows will also experience more clinical mastitis in subsequent lactations. There are several reasons why mastitis may recur. One, some organisms are more likely to cause recurrent clinical mastitis. High recurrence rates have been observed for both E. coli and Strep uberis infections, for example. Staph aureus is notorious for causing recurrent clinical mastitis; however, this is because of persistency of infection rather than actual new infections. Indeed, there is some question whether cows that experience clinical mastitis, and subsequently actually clear the infection, are really more likely to suffer another clinical case, or that recurrence occurs more commonly because of persistent infections. In either case though, it is fair to say that once a cow has experienced a case of clinical mastitis, she is more likely to suffer from additional cases in her current or subsequent lactations, meaning she is not in the high udder health cycle.
    Another driver for poor udder health is chronic, subclinical infections. Most mastitis infections on most dairies are subclinical. Just because a cow never shows clinical mastitis does not mean that she has good udder health. It is common to find cows on most farms with persistent, high somatic cell counts, and many of these cows may never have shown clinical signs of mastitis. These cows are not in the HUHC.
    Chronically infected cows can serve as reservoirs of organisms to infect others. This most commonly occurs with contagious pathogens such as Strep ag, Staph aureus, Mycoplasma and Prototheca, but can happen with almost any pathogen if the reservoir is of sufficient magnitude. Thus, chronically infected cows can keep other, previously clean cows, out of the HUHC.
    Finally, mastitis leads to increased culling. Increased culling leads to a narrowing of choices on whom to cull, and may eventually lead to producers keeping cows that they would rather cull because of increased involuntary culls. On many farms, some of these potential culls that are kept too long may be chronic mastitis cows, whom are not in the HUHC.
    Cows that experience the HUHC often never get clinical mastitis. They have persistently low SCCs. This makes them significantly less likely to get mastitis again or to be culled. By staying in the herd, they contribute to overall herd udder health positively. As the proportion of cows with persistently low SCCs increases in a herd, the clinical mastitis rate goes down, the percentage of cows with chronic infections goes down and culling due to mastitis goes down.
    Over time, it becomes easier to maintain low SCCs and clinical mastitis rates. The HUHC also makes it easier for us humans to manage herds. Fewer cases of mastitis makes milking easier and faster. Fewer cases means a smaller hospital pen and fewer treated cows to deal with on a daily basis. Fewer cases mean fewer treatments to administer, lower drug costs and reduced death rates. In HUHC herds, life on the dairy is better for cows and for people. This points out an important concept: While the high fertility cycle is described as referring to a single cow, in reality having many cows in the high fertility cycle makes reproductive management easier for other cows too. The result is a herd with a high fertility cycle. The same is true for HUHC herds. Some of this is due to direct effects and some to indirect effects. In any system, maintaining great results may require less overall effort, and certainly less disruption, than constantly trying to fix problems and improve results. One might think of it as the effort required to keeps cows locked in their pens versus getting them back in and locked in their pens, especially if they are running down the middle of that county highway in front of your farm. Keeping your cows and your herd in the HUHC makes future success easier; this is the most powerful concept of the HUHC.
    How do you get your herd into the HUHC? Understand the importance of new infection risk/rate. Simply put, it means knowing how many clean cows are getting infected each month and knowing how to stop that process. Remember, a cow cannot become chronic if she never got infected in the first place. Also understand the impact of chronically infected cows in your herd and how to eventually reduce that population. All the tools you need to get your herd into the HUHC are available. Rely on your veterinarian for recommendations, information and to help you steer the course.
    Yes, the HUHC is a real thing, and just like with the high fertility cycle, once your herd is in it, future success is easier to achieve. More and more herds are achieving the HUHC today. Is it time for your herd to be one of them?
    Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at [email protected] with comments or questions.

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