Abstract
Effects of removal of the ovary containing the largest follicle (via unilateral ovariectomy) on subsequent follicular activity and ovarian function were evaluated in estrous cycling Brahman cows (n = 9). A sterile bull equipped with a chin-ball marker and daily observations were used for detection of estrus. Ultrasonography to assess ovarian characteristics was performed daily from d 0 (estrus) of the first estrous cycle until the second estrus (time when the ovary with the largest follicle was removed). Before unilateral ovariectomy, 7 out of 9 cows had the CL and the largest follicle on the same ovary (i.e., the active ovary). Following the third observed estrus (i.e., the next estrus occurring after unilateral ovariectomy) the remaining ovary was scanned daily for a complete estrous cycle. Blood samples were collected daily during both scanning periods for analysis of serum concentrations of Progesterone (P-4) by RIA. Cows with one or two ovaries had similar (p>0.10) numbers of follicular waves, estrous cycle lengths, numbers of follicles during the first, second and ovulatory wave and d on which the P, peak occurred. However, cows with two ovaries had larger (p<0.003) large-sized follicles (13.5 +/- 0.5 mm) and higher (p<0.004) peak serum concentrations of P-4 (10.5 +/- 0.9 ng mL(-1)) than cows with one ovary (10.7 +/- 0.5 mm and 7.7 +/- 0.9 ng mL(-1), respectively). There was a positive correlation between size of the largest follicle and number of ovaries (r = 0.76; p<0.003) and a tendency for a positive correlation between size of the largest follicle and serum peak P-4 concentrations (r = 0.55; p<0.06). In conclusion, removal of the ovary containing the largest follicle did not affect follicular waves or estrous cycle length, but increased follicular populations on the remaining ovary; indicative of ovarian follicular compensatory hypertrophy. In addition, size of the largest follicles and concentrations of P-4 were lower after unilateral ovariectomy.