Infants (<1 year of age):
- Body weight:
- At 1 month: 40-53 kg.
- At 4 months: 64-84 kg
- Body length is 121-150 cm (females) to 132-151 cm (males).
- Horns are straight and appear V-shaped when viewed frontally.
- Individual coloration is variable, as it is in adults, but a dark neonate often lightens a few months after birth; thereafter, it tends to darken with age.
- Calves are weaned at 4-6 months, but in some populations, suckling may last 18 months or until the next calf is born. They graze for brief periods at about 2 months of age.
Juveniles (1-2 years of age):
- Body weight is 259-323 kg (females) to 283 kg (males).
- Body length is 178-196 cm (females) to 194 cm (males).
- Horns are 30-46 cm long and curve slightly outwards.
- Deciduous dentition is complete: 0/3, incisors; 0/1, canines; 3/3, premolars; total, 20. It may be complete as early as 3 months of age.
Subadults (2-3 years of age):
- Body weight is 314-493 kg (females) to 282-483 kg (males).
- Body length is 191-219 cm (females) to 191-225 cm (males).
- Horns are 41-86 cm along the curvature, and the tips grow towards one another. In bulls, horns thicken at their bases, and the boss begins to take shape.
- Tooth replacement is at a maximum in the 3-5 year age groups.
- Males can reach sexual maturity at 2.5-3 years of age, but older herd bulls usually prevent them from breeding until they are at least 7-8 years of age. Age of puberty is determined by body weight.
Young adults (4-5 years of age):
- Body weight is 397-576 kg (females) to 378-617 kg (males). Females attain adult weight during fourth year, when they are also sexually mature and usually give birth to their first calf.
- Males maintain growth throughout their lives.
- Body length is 215-238 cm (females) to 211-255 (males).
- Tips of the horns begin to sweep backwards. Horns reach their adult shape in cows; the boss (i.e., the raised, rounded area at the base) continues to enlarge in bulls.
Adults (>5 years of age):
- Body weight is 312-637 kg (females) to 488-768 kg (males).
- Body length is 215-249 cm (females) to 225-267 cm (males).
- In older cows, tips of the horns are widely separated, and they wear and may break with age. In bulls, the backward sweep of the horns is completed, and the boss is well-shaped, though it continues to thicken with age. The widest span is reached in this age class (up to 104 cm), but the length of the horns along the curvature can be less than in younger age classes.
- Coloration may change to black or dark brown; old animals become nearly hairless in spots, and hairs may become white, particularly those on the face and neck.
- Permanent dentition is in place by 6 years of age.
