Buller steer syndrome (BSS) is an undesirable behavior characterized by one steer, the buller, being mounted and persistently ridden by other steers, called riders. Although bullers may also participate in mounting other cattle, the bullers are the animal being persistently mounted and ridden. BSS is a stressful and exhausting condition that can lead to reduced body weight gain, injury, secondary illness and possible death.
A Kansas feedlot survey published in 1976 estimated that bullers represented a $23 loss per case. According to the 2011 National Animal Health Monitoring System feedlot report, nearly 70% of feedlots with 1,000 or more cattle experienced BSS, with it affecting an average of 2.8% of the cattle in these feedlots, with an average treatment cost of $6.90 per case. The occurrence of BSS can be significantly greater for some feedlots, as Holstein steers have been reported to exhibit BSS more frequently than beef-breed steers, with some reporting an incidence rate of 10-20%.
Calculating the cost of BSS per case is difficult, as there are many things to account for, such as reduced body weight gain and feed efficiency of bullers and riders, additional labor to process bullers, additional facilities to separate bullers, associated morbidity treatments, animal and feed costs for mortalities and carcass bruising of rider steers. With the increased purchasing cost for animals, feed, medication, facilities and labor, one can expect the estimated cost of BSS to be significantly greater today compared to the past.
Mounting behavior in cattle is complex, as it can be social, sexual or abnormal. Along with other aggressive behaviors, such as head-butting, mounting other cattle is a behavior used to exert dominance over other cattle within the pen. Upon commingling cattle or adding new cattle in a pen, cattle may demonstrate aggressive behaviors toward each other to determine the dominance hierarchy within the pen. Not surprisingly, a Canadian feedlot study observed that BSS most often occurred during the first 30 days cattle were on feed.
Mounting behavior is commonly recognized as a sexual behavior that is performed by cattle to identify female cattle in estrus and possibly attract a bull for breeding. The detection of buller steers by rider steers appears to be more likely due to changes in posture and behavior rather than pheromones. The male sex hormone, testosterone, and female sex hormone, estrogen, have considerable effects on cattle behavior. Research demonstrated that administering estrogen (estradiol benzoate) increased the dominance and social rank of cattle.
They also demonstrated that androgens, such as testosterone, can increase dominance as well, presumably by the conversion of testosterone to estrogen via the aromatase enzyme. Other research with freemartin heifers demonstrated that testosterone administration increased vulvar interest, head-to-head fighting and the flehmen (upper lip curl) response, while estradiol administration increased vulvar interest, head-to-head fighting and mounting behavior.
In steers, researchers demonstrated that estradiol injections resulted in the greatest frequency of steers receiving sniffs, giving sniffs, mounting successfully, giving chin rests, receiving chin rests, standing when mounted and refusing to stand when mounted. Testosterone injections to steers also increased successful mounts, chin rests given and chin rests received compared with untreated control steers. Attempted mounts and flehmen responses were greatest for steers that were administered testosterone.
Researchers demonstrated that steers and heifers administered estradiol benzoate were much quicker to detect heifers in estrus and mounted heifers in estrus more frequently than steers or heifers administered testosterone or untreated controls. Progesterone is known to inhibit the behavior associated with estrus. In cows that had their ovaries removed, standing estrus behavior that was initiated by estradiol injection was reduced with increasing concentrations of progesterone injections, according to research.
Mounting and riding behavior can also be abnormal, as it is speculated cattle might perform this behavior out of boredom. Cattle housed in concentrated areas need to spend less time eating to reach satiety compared with cattle housed in pasture. In addition, this could be a learned or copycat behavior or a form of play in young cattle.
BSS has long been implicated with the use of ear implants, which commonly contain synthetic forms of estrogen, progesterone or testosterone to promote body weight gain. In a University of Nebraska-Lincoln study with mixed pens of steers and heifers, implanted heifers were mounted and mounted others more frequently compared with nonimplanted heifers. Heifers were preferentially mounted by both steers and heifers, while steers chose not to mount other steers. However, heifers would mount steers as well.
Estradiol has long been speculated as the cause of BSS in feedlot cattle due to reports of greater concentrations of estrogen in the serum and urine of bullers. Some research studies have reported differences in BSS incidence due to implant type, which may be due to the hormone concentration in the ear implant or the timing of implant administration or readministration. In addition to the first 30 days of feedlot entry, BSS incidence has also been reported to be greater approximately 60 days after reimplanting, according to research conducted at Texas A&M University. Hormone concentrations of bullers, riders and nonparticipant animals have shown mixed results.
Research from the mid 1970s reported lesser serum concentrations of estrogen and testosterone for buller steers compared with unaffected steers. However, other research from Kansas State University reported lesser progesterone and greater testosterone concentrations for buller steers compared with non-buller control steers. Estrogen concentration did not increase from feedlot entry to the time of bulling, and unfortunately, no direct comparison was made with non-buller controls at the time of bulling.
Interestingly, while off-label use is not permitted, some researchers tested feeding melengestrol acetate (MGA) to nonimplanted steers, which showed a numerical decrease in the incidence of bullers (1.11% versus 0.44%). However, the incidence of BSS was low in general and did not allow them to robustly test the hypothesis that MGA reduced the incidence of BSS.
A summary of these results on hormone concentrations for steers with BSS may indicate that the causative nature of BSS could be linked to estrogen and progesterone metabolism. Future research is needed to test if synthetic progesterone, like MGA, can reduce BSS, which is thought to be brought about by greater concentrations of estrogen.
Though this behavior has been studied for decades, there still aren’t great solutions to treat or prevent BSS. The most common practice is to remove bullers from their home pen to be placed in a buller or hospital pen for a few days before being returned to their home pen. Unfortunately, some bullers relapse and are subject to mounting once again and may need to be permanently removed from their home pen.
Another helpful action would be to check the implant in the ear to see if pellets are damaged or crushed. Feed availability may play a factor, as some research documented empty bunks at the time bulling took place. Other environmental enrichment, such as toys and brushes, could possibly help reduce the occurrence of boredom. Bulling rails, which are an extension of the fence, may be an option to provide bullers a place to escape from riders.
As mentioned previously, this is an issue in the feedlot industry that could use more research to help solve this problem. — Michigan State University Extension
