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Pregnancy rate in beef heifers after synchrony to random or programmed estrous cycles
(36%). Pregnancy rate was higher (P <.05) for heifers with
(day 0), a greater (P <.05) percentage of PGF (74%) than CON
(Santa Cruz; n=195) were allotted into one of two
0). Following implant removal (day 9), heifers were
a Syncro-Mate-B (SMB) regimen will have higher pregnancy
administered a conventional SNM treatment. Heifers (n=97) in
administration of prostaglandin F2. (PGF2.) I I d prior to a
after implant removal. At the beginning of the SMB regimen
among heifers classified to be in diestrus (DI; 54%; n--69)
and 20. Estrous response rate was 95.5%. Pregnancy rate
and 9. All heifers were artificially inseminated 48 to 50 h
artificially inseminated 12 h after the onset of estrus.
before a SMB regimen. Progesterone concentration was
Blood samples were collected for P4 analysis on days 0, 9,
concentration was not affected by treatment or day x
determined from blood samples collected on day -I 1, -2, 0,
experiment 1, heifers (n=150) were categorized by the stage
heifers (59%) were in diestrus (P4 > I ng/ml). Mean P4
heifers was not different than heifers in MET or DI. Mean
hypothesis that fertility is enhanced when a progestin
n=48). Pregnancy rate among proestrus (PRO; 44%; n=l 8)
ng/ml plasma (52%; n=120) than heifers with P4 < I ng/ml
ng/n-d plasma (I 5%) on day 0. These results support the
of cycling heifers was similar for PGF (36%) and CON heifers
of the estrous cycle at the beginning of a SMB regimen (day
P4 > I ng/n-d plasma (3 8%) than for heifers with P4 < I
plasma ( 25%; n=30) on day 0. In experiment 2, beef heifers
plasma P4 concentration was affected by treatment and day.
Pregnancy rate was higher (P <.05) for heifers with P4 > I
rates to AI than heifers not in diestrus and that
SMB regimen will increase pregnancy rates to Al. In
synchrony regimen is initiated during diestrus, but methods
the PGF group were injected with PGF2. I I d (day -I 1)
to program estrous cycles to increase fertility warrant
treatment, but differed (P < .05) wrong days. Pregnancy rate
treatments. Heifers (n=98) in the control (CON) group were
was higher (P <.05) than heifers in metestrus (MET; 44%;
We hypothesized that heifers in diestrus at the beginning of
"Major subject: Physiology of Reproduction".
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