Abstract
<h2>ABSTRACT</h2> Two experiments were conducted to evaluate breed [Angus (AN), Brahman (BR), and varying percentages of BR × AN breeding] and prostaglandin F<sub>2α</sub> (PGF) type [dinoprost tromethamine (dinoprost) vs. cloprostenol sodium (cloprostenol)] in suckled cows (Exp. 1; n=504) and 2-yr-old virgin heifers (Exp. 2; n=309) synchronized with a Select Synch + controlled intravaginal drug-releasing insert and timed-AI protocol (SSCT). On d −7, cows and heifers received gonadotropin-releasing hormone and controlled intravaginal drug-releasing inserts. At controlled intravaginal drug-releasing insert removal (d 0), cows were stratified by BCS, days postpartum, parity, and breed; heifers were stratified by BCS and breed. In both experiments cattle were randomly allotted to receive either dinoprost (25 mg) or cloprostenol (500 μg). Estrus was detected 3 times per day for 72 h after PGF, and AI was conducted by the am/pm rule. At 72 h after PGF, nonresponders were timed artificially inseminated and received gonadotropin-releasing hormone. The AI pregnancy rates were similar (<i>P</i> > 0.05) between PGF treatments in Exp. 1 (51%) and Exp. 2 (46%). In Exp. 1, AN (52%), 1/4 to 3/8 BR (42%), and 1/2 BR (59%) cows had similar AI pregnancy rates, whereas 1/2 BR (59%) had a greater (<i>P</i> < 0.05) AI pregnancy rates compared with cows with ≥3/4 BR (41%). In Exp. 2, heifer breed had no effect on AI pregnancy rates. In conclusion, dinoprost and cloprostenol in a SSCT protocol yielded similar AI pregnancy rates in cows and 2-yr-old virgin heifers across all breed types; however, AI pregnancy rates were influenced by breed type in cows but not 2-yr-old virgin heifers.
Accepted Version
Published Version
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