|Hall, John - VIRGINIA TECH|
|Staigmiller, Robert - RETIRED ARS|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 14, 1998
Publication Date: N/A
Interpretive Summary: Progestin treatment can aid in inducing heifers to reach puberty which may decrease age at first breeding. However, subsequent estrus synchronization with progestins may not be advisable in heifers implanted with progesterone to induce puberty. Heifers can be placed on regrowth in irrigated pastures during the fall and still make acceptable gains for attainment of puberty and breeding the following spring. Trace mineral supplementation before breeding did not affect reproduction in these heifers, although plasma copper levels were quite low in one treatment. Over supplementation of mineral may have decreased first service conception rates. Provision of a trace mineralized salt mix for one month before and during the breeding season was adequate for reproductive performance.
Technical Abstract: A study was conducted to evaluate the influences of nutritional management, trace mineral supplementation, and exogenous progesterone on attainment of puberty in beef heifers. One hundred eighty heifers were assigned at weaning to blocks and treatments. Treatments included two dietary regimens (corn silage vs pasture + oatlage), trace mineral supplementation, and puberty induction strategy (with or without progestin implant). Heifers receiving pasture + oatlage were managed on grass-legume pastures from October 14 until December 14, and then placed in pens and fed an oatlage-based diet through May 1994. Heifers on the corn-silage based diet were housed in pens throughout the study. Norgestomet was implanted in half of the heifers on April 11 for 10 d. Progestin implant increased (P < .05) the number of heifers puberal by the end of the study compared to nonimplanted heifers (88% vs 70%). Fewer implanted heifers tended (P < .10) to be pregnant at fall palpation than nonimplanted heifers (83.5 vs 92.1%). Trace mineral supplementation decreased (P < .05) first service conception rates but did not affect total AI pregnancy rates. Plasma copper levels were below recommended levels in heifers fed oatlage-based diets without trace minerals. We conclude that heifers can be placed on regrowth in irrigated pastures during the fall and still make acceptable gains for attainment of puberty the following spring and that progesterone treatment can aid in inducing heifers to reach puberty.