Summer disease

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Ahhh…. I love summer. The heat, flies, sweat, insatiable urges to drink massive quantities of Gatorade or to cool off in the nearest water trough.

Summer is the ultimate scapegoat for all of the world’s problems, including those on a dairy farm. Calves got scours? “‘Cause of the heat.” Milk production is dropping? “Dang heat.”

Got more cystic ovaries? “Gotta be the heat.”

Or is it? Let’s explore this one a bit further. An ovarian cyst is defined as an anovulatory fluid-filled structure that is more than 25 mm in size that persists on the ovaries for more than 10 days. They are a major cause of economic loss and reproductive dysfunction in dairies.

Cystic ovaries are not caused by cows being exposed to high environmental temperatures.

Most reproductive experts agree with this statement: the precise mechanism responsible for the malfunction of the endocrine cascade is unknown. So, the cause of cystic ovaries is unknown.

However, there is much known about the risk factors. These include heredity, increased milk production, estrogen content in forages, uterine infections, excessive body condition at dry-off, elevated milk ketone concentrations, calving difficulty, increase in lactation number, and metabolic disturbances due to negative energy balance.

Heritability estimates are low, and selection against cysts is probably not a profitable management plan. But, in Sweden, the incidence of cysts decreased from 11 percent to 3 percent over 20 years when AI bulls were culled if their daughters had an above-average occurrence of cysts. It has recently been shown that cystic cows produce equal or greater amounts of milk than cows without cysts, and the milk production level in the previous lactation prior to the onset of the cystic condition was not different than herd mates without cysts.

Dairy cattle that experience twinning, dystocia, retained placenta and uterine infection are most likely candidates to experience ovarian dysfunction. Cows over-conditioned at dry off were shown to be 2.5 times more likely to develop cystic ovaries. However, metabolic disturbances due to severe negative energy balance or ketosis is related to the development of cystic ovaries. Cystic cows are generally in their second or greater lactation — perhaps because periparturient problems are more common in older cows.

Ovsynch is a common treatment for cystic ovaries because it should be effective for all types of ovarian cysts, as it utilizes GnRH and PGF2a. Another protocol utilized is a CIDR/ PGF2a. It is a good idea to discuss the pros and cons, as well as cost-effectiveness, with your veterinarian.

Although progress has been made to unveil more information about the diagnosis, cause, and treatment of ovarian cysts, they are still a major challenge. Culling chronically cystic cows, avoiding under- and over-conditioning of dry cows, and minimizing periparturient problems appear to be important strategies for controlling cystic ovaries.

Now, is summer just about over yet?

Angela M. Daniels is a veterinarian with Circle H Headquarters LLC, a dairy and swine veterinary practice, food safety laboratory and DHIA milk-testing and contract research organization in Dalhart, Texas.



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