bull

A cow bulls when she enters estrus, the physiological state in which she is fertile and receptive to mating. This is a natural cycle occurring roughly every 17 to 24 days in cattle, though the exact interval varies by breed, age, and environmental conditions. During this window, which typically lasts 12 to 18 hours, the cow's hormonal changes trigger behavioral and physical signs that alert a stockman or a bull to her breeding readiness.

The signs of bulling are observable enough to guide breeding decisions on farm. A cow in heat may show restlessness, reduced feed intake, swollen and reddened vulva, clear mucus discharge, and most characteristically, she will stand passively when mounted or when pressure is applied to her hindquarters. Some cows also bellow more frequently or attempt to mount other cattle. These indicators allow a trained observer to identify the optimal moment for natural service or artificial insemination.

Detecting and Recording Bulling

Successful beef and dairy operations depend on reliable detection of bulling. On smaller farms, visual observation twice daily catches most cycles. On larger operations, tail chalk or paint applied to the tailhead transfers when a cow is mounted, leaving a visible mark. More recently, electronic detection systems using accelerometers worn as leg bands record changes in activity and lying behavior that correlate with estrus, feeding data into herd management software.

The term bull as a verb carries an old meaning rooted in the animal itself: the cow's behavior is fundamentally a readiness for the bull. Stockmen speak of "a cow coming into bull" or "bulling hard," the latter describing obvious, easy-to-spot signs. Failure to recognize bulling windows extends calving intervals, reduces conception rates, and increases the cost of production because the productive lifespan of the animal is stretched across fewer offspring.

Timing matters in both dairy and beef herds. In dairy, synchronizing bulling across a group of cows using hormonal protocols (prostaglandin injections, progesterone devices) allows timed artificial insemination without waiting for natural heat detection. In beef herds relying on natural service, a bull is typically kept with cows during the breeding season so that bulling cows are mated promptly. Missed or misidentified bulling cycles directly reduce weaning weights and breed-back percentages, metrics that drive herd profitability.