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Herd Health

Find information about mastitis, transition cows, vaccination protocols, working with your veterinarian, hoof care and hoof trimming.

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Milk fever is a disorder affecting about 6 percent of dairy cows each year in the United States. Subclinical milk fever, defined as blood calcium (Ca) concentration falling below 8 milligrams per deciliter (mg/dl), occurs in up to 50 percent of older cows during the days immediately following calving. The decline in blood calcium concentration near calving represents a breakdown in the calcium homeostatic mechanisms of the body. Blood Ca in the adult cow is maintained around 8.5 to 10 mg/dl. There are 3 grams Ca in the plasma pool and only 8 to 9 grams Ca in all the extracellular fluids (outside of bone) of a 1,300-pound cow. The fluid within the canaliculi of bone may contain another 6 to 15 grams Ca; the size of this Ca pool being dependent on the acid-base status of the animal (larger during acidosis and smaller during alkalosis).

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So often in veterinary medicine, as in other medical fields, we are looking for diagnostic tests to aid in treatment and to prognosticate for various diseases. Both infectious and noninfectious diseases may be diagnosed by detecting the causative agent, clinical signs, pathological changes, biochemical changes or surrogate evidence of past or present exposure to an agent (antibody).

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Severity of heat stress is quantified using a temperature humidity index (THI). Both ambient temperature and relative humidity are used to calculate a THI. Signs of heat stress become evident in dairy cows when the THI exceeds 72. The same THI can be produced by various combinations of temperature and humidity (see Figure 1). Dairy producers can purchase a thermometer or hygrometer and use Figure 1 to determine the level of heat stress at different locations on the dairy. Measurements should be taken at the level of the cows’ backs, along the feeding area, in the freestalls and in the holding pen.

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Metabolic diseases are those associated with the chemical processes necessary for maintenance of life. In cattle, metabolic diseases include errors in electrolyte/mineral metabolism, of which parturient hypocalcemia (milk fever) is most common, or errors associated with energy metabolism, including ketosis and displaced abomasum. Metabolic diseases are associated in that the occurrence of one increases the risk of another. These associations tend to leverage the impact of disease on the animal.

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Body condition scores (BCS) provide an indication of the energy status of dairy cattle. Condition scores can be used on both heifers and cows, although primarily they are used on the lactating dairy herd. Essentially, body condition scoring provides an objective indication of the amount of fat cover on a dairy cow. This evaluation is accomplished by assigning a score to the amount of fat observed on several skeletal parts of the cow. Various point systems are used to score the animal. The most commonly used system ranges from 1.0 to 5.0, in increments of 0.1 or 0.25. One point of body condition equals 100 to 140 pounds gain in bodyweight. Larger frame cows require additional bodyweight to increase one point, compared to smaller frame or narrow cows.

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