The aims of the current study were to determine if the pattern of ovar
ian follicular growth and development in Bos indicus heifers is differ
ent to that reported in Bos taurus breeds, and to examine the factors
that determine which dominant follicle will ovulate. In addition, the
extent to which variation in follicular dynamics is attributable to va
riation between animals and over time was evaluated. The ovaries of 17
Brahman heifers were examined daily by transrectal ultrasonography us
ing a 7.5 MHz transducer for a total of 117 interovulatory intervals o
ver a period of 10 months. Size and position of individual follicles g
reater than or equal to 5 mm in diameter, and size of corpora lutea (C
L) were recorded. Circulating progesterone concentrations were determi
ned from plasma samples obtained twice weekly. Although size of domina
nt follicles and CL within the ovaries of Bos indicus heifers were sma
ller than reported for Bos taurus breeds, the overall patterns of domi
nant follicle growth were similar. There were significant correlations
between number of dominant follicles occurring prior to ovulation and
time of appearance of the second dominant follicle, duration of detec
tion of CL and size of the ovulatory follicle in the preceding oestrou
s cycle (P<0.05). There were significant animal effects on a number of
ovarian characteristics including number of dominant follicles per oe
strous cycle (P<0.001), with one heifer having four dominant follicles
in more than a third of oestrous cycles observed. In addition, change
s in daylength over the 10 month period were related to changes in dur
ation of the interovulatory interval, persistence and maximum diameter
of CL and size of ovulatory follicles. Liveweight change over the sam
e period was related to changes in maximum diameter of the first domin
ant follicle.