Abstract: 572

COMPARISON OF FSH AND LH RESPONSE TO FOLLICLE ASPIRATION IN CATTLE SELECTED (TWINNER) AND UNSELECTED (CONTROL) FOR TWIN BIRTHS.

S. E. Echternkamp^{1 *}, K. E. Gregory¹ , B. R. Lindsey² , M. Mussard² , J. E. Kinder^{2 *}
USDA, ARS, US Meat Animal Research Center, Clay Center, NE ¹
University of Nebraska, Lincoln, NE ²

Long-term genetic selection for dizygotic twins in cattle has resulted in a larger pool of ovarian small antral follicles (1-5 mm diameter), enhanced recruitment of growing follicles, and the subsequent selection of twin or multiple dominant/ovulatory follicles within a wave of follicular development. The endocrine role of FSH, LH and IGF-I in mediating the enhanced follicular development was evaluated using the follicle aspiration experimental model. All follicles >5 mm were aspirated transvaginally in 12 Twinner and 12 Control cyclic crossbred cows on d 7 or 8 (estrus=d 0). Jugular vein blood samples were collected at 12-h intervals for 48 h before aspiration and at 6-h intervals for 96 h after aspiration. FSH, LH and IGF-I were measured by RIA; IGF-I was acid-ethanol extracted. Follicular development was monitored daily by ultrasonography. Data were analyzed by repeated measures ANOVA for population, time and the interaction. Plasma FSH concentration was elevated (p<0.01) within 6 h after aspiration, was maximal (84.2±3.5 ng/ml) at 24 h, and returned to baseline (32.4±3.5 ng/ml) by 66 h; LH was unaffected (p>0.1) by aspiration. Plasma FSH (46.0±2.3 vs 40.5±2.3 ng/ml) and LH (1.42±.12 vs 1.35±.12 ng/ml) concentrations did not differ (p>0.1) between Twinner vs Control cows, whereas plasma IGF-I concentrations (74.5±8.0 vs 47.8±8.0 ng/ml; p<0.03) were greater in Twinners. Results suggest that the enhanced follicular recruitment in Twinner cows after aspiration was not related to the magnitude or timing of the endogenous FSH response but was associated with greater IGF-I concentrations.

    This abstract is being presented on Tuesday, August 3 at 5:00 PM at Todd 116.