Herd Health

Extensive research in a number of livestock industries around the world has identified the impact of the interactions between stockpeople (animal handlers) and farm animals on farm animal behavior, welfare and productivity. Specifically, relationships between the animal’s fear of humans and productivity of animals have been found in the dairy industry and also in the egg, meat chicken and pig industries.

Because of costs associated with the construction and maintenance of freestall barns, dairy farmers may limit the number of feeding and resting places available for cows in order to maximize utilization of facilities. Facility design, such as whether there are two or three rows of stalls per feedline, may also influence the number of cows that have to share a particular resource. However, the impact of overcrowding on cow behavior, welfare and productivity should be considered.

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).

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).

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.

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.