Estrus has been traditionally described as an “all or none” response (Allrich, 1994). This means that once blood estradiol reaches a critical threshold then the cow expresses estrus. Additional estradiol in the system will not necessarily change or amplify the behavior. Although the “all or none response” is stated clearly in the literature, it perhaps should be reexamined with modern-day high producing dairy cows (see below).

The threshold level of estradiol is different for individual cows. Behavior of individual cows in estrus is highly variable with mounts received ranging from 1 to >100 and time in estrus ranging from 30 minutes to >30 hours. The highly variable nature of the behavior makes estrus difficult to study scientifically because the high coefficient of variation for estrous traits (number of mounts, etc.) makes it difficult to detect statistical differences when treatments are imposed.

Estrus involves a variety of behaviors that are expressed by the individual cow either alone or when interacting with other cows in the herd (Hurnik, 1987). Cows that are approaching estrus (pre-receptive phase), in estrus (receptive phase, standing to be mounted), and going out of estrus (post-receptive phase) cluster together and form sexually active groups (SAG).

The classical and definitive behavior of the cow in estrus is standing still when mounted from behind by another cow. A variety of other behaviors precede this behavior, including mounting other cows, licking and being licked, chin pressing and having chin pressed upon, and sniffing and being sniffed in the urogenital area. A scoring scale for estrous behaviors had been developed and published (van Eerdenburg et al., 1996 (see below).

The expression of such behaviors during the pre-receptive and post-receptive phases may be slightly different for primiparous and multiparous cows (Hurnik, 1987). Cows are most active at the beginning of estrus. Mounting and standing activity decreases in a near-linear fashion thereafter (Hurnik, 1987). Cows in estrus are more active because they are restless (walking more) and interact physically with other cows.

Scoring system

Scoring systemfor behavioral estrus as proposed by van Eerdenburg et al., 1996:

  • Mucous vaginal discharge: Score 3
  • Cajoling: Score  3
  • Restlessness: Score 5
  • Sniffing vagina of another cow: Score 10
  • Chin rest: Score 15
  • Mounted but not standing: Score 10
  • Mounting (or attempt) other cows: Score 35
  • Mounting head side of other cow: Score 45
  • •Standing heat: Score 100

Factors that affect estrous behavior

There are a large number of housing and environmental factors that can affect the expression of estrus. Most notable among these include housing. The classic studies of Vailes and Britt (1990) demonstrated that cows prefer a dirt surface over a concrete floor for the expression of estrus. Sore feet and legs diminish activity and estrous expression. The number of mounts received by lame cows was decreased by 70% in one study (Sood and Nanda, 2006). Other important factors include stress-induced hormone release (inhibitory to estrous expression) and environmental temperature (high environmental temperatures are inhibitory to estrous expression).

The size of the SAG can determine the overall activity of the individual cow at estrus. Hurnik (1987) reported that the number of mounts received by an individual cow increased five-fold from one to three cows in estrus at the same time. Because of this, estrus synchronization may improve estrous detection rates because more cows are in estrus at the same time. A variety of other inhibitory factors have been suggested including rain and snow storms, dominant cows, poor conditions (deep mud and low ceilings), crowding, and feeding (Allrich, 1994). Conditions that distract or frighten cattle or that inhibit normal social interactions will decrease estrous expression.

It goes without saying that a cow must be standing up to show the standing behavior. This may explain why estrus is sometimes detected when cows are moved to the milking parlor (a time when cows lying in free-stalls are forced to stand up and interact with other cows).


Implementation of the Iowa Veterinary Rapid Response Team (IVRRT) is an example of how individual states have been preparing for foreign animal disease outbreaks.

The Iowa program consists of a nearly all-volunteer force, says Mark Shearer, the veterinary response coordinator for the Iowa Center for Agriculture Security.

IVRRT has members from nearly every one of Iowa’s 99 counties. Further, there are team members from Iowa’s bordering states of Illinois, Minnesota, Missouri, Nebraska and Wisconsin, according to Shearer.

He says the team’s 310 members are among the state’s most vital first responders. Nearly 300 of the members are practicing veterinarians. Sixty percent of these 300 are food animal veterinarians. In addition to veterinarians, other members include farmers, animal health technicians, slaughter plant workers, scientists and veterinary medical students.

“The animal industry and the veterinarians who serve the animal industry have a great stake in identifying and controlling animal disease,” Shearer says. “They realize more than anyone else the economic impact it has on Iowa.”

IVRRT members are responsible for animal disease surveillance and diagnosis, as well as for control and eradication of diseases. In the event of a disease outbreak, they may become involved in quarantining animals, prohibiting animal movement, disinfecting farms, euthanizing animals and planning for carcass disposal, according to Shearer.

When there is a confirmed positive of any highly infectious disease, IVRRT will be called out to be part of the control and mitigation of the disease, he adds.

IVRRT works with the Iowa Department of Public Health, the U.S. Department of Agriculture and other state and federal partners, including the U.S. Department of Homeland Security. The state veterinarian and Iowa Secretary of Agriculture oversee the program. Some 20 to 30 other states also have developed similar response teams.

Contact your state veterinarian’s office or department of agriculture for Rapid Response Teams in your state.



Clostridium difficile in calves and the similarity between bovine and human C. difficile PCR ribotypes was investigated by conducting a case-control study of calves from 102 dairy farms in Canada.

Fecal samples from 144 calves with diarrhea and 134 control calves were cultured forC. difficile and tested with an ELISA for C. difficile toxins A and B. C. difficile was isolated from 31 of 278 calves: 11 (7.6%) of 144 with diarrhea and 20 (14.9%) of 134 controls (p = 0.009). Toxins were detected in calf feces from 58 (56.8%) of 102 farms, 57 (39.6%) of 144 calves with diarrhea, and 28 (20.9%) of 134 controls (p = 0.0002).

PCR ribotyping of 31 isolates showed eight distinct patterns, Seven have been identified in humans, two of which have been associated with outbreaks of severe disease (PCR types 017 and 027). C. difficile may be associated with calf diarrhea, and cattle may be reservoirs of C. difficile for humans.


Rodriguez-Palacios A, Stämpfli HR, Duffield T, Peregrine AS, Trotz-Williams LA,
Arroyo LG, et al. Clostridium difficile PCR ribotypes in calves, Canada. Emerg Infect Dis, ISSN: 1080-6059. 2006 Nov. Available from