Angus and Angus x Hereford heifer
calves born in spring or fall seasons were allotted
by weight at weaning to be exposed to bulls for
calving at either 24 or 30 mo of age. Comparisons
were made llwithin birth season-heifers born in
the same season were first exposed to bulls at
either 14 to 16 or 19 to 22 mo of age and 2) within
breeding season-heifers born in different but
consecutive seasons (spring-fall or fall-spring) were
exposed to bulls during the same season but at
different ages. Spring-born heifers exposed for
30-mo calving were heavier (336 vs 302 kg) and
taller (P e .01) at breeding than those exposed for
24-mo calving. Also, more were observed in estrus
and became pregnant (P < .011 during a
21-d AI breeding period, but season-long (63 d)
pregnancy rates were not different (86%). Fall-born
heifers exposed for 24- or 30-mo calving were
similar for weight, hip height, and body condition