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Comparison of the effects of two shortened timed-AI protocols on pregnancy per AI in beef cattle
مقایسه اثرات دو پروتکل کوتاه شده با هوش مصنوعی به هنگام روی بارداری در هوش مصنوعی در گاوهای گوشتی-2020 The objective was to compare pregnancy per AI (P/AI) between two shortened timed-AI (TAI) protocols in
beef cattle. This study also determined whether administration of eCG in heifers and timing of AI in cows
would affect P/AI. Cattle were submitted at random to either a modified 5-d Co-synch protocol (Day
0 ¼ progesterone releasing device (CIDR); Day 5 ¼ CIDR removal and 500 mg of cloprostenol (PGF); Day
8 ¼ 100 mg GnRH concurrent with AI) or J-synch protocol (Day 0 ¼ CIDR insertion and 2mg of estradiol
benzoate i.m.; Day 6 ¼ CIDR removal and 500 mg PGF; Day 9 ¼100 mg GnRH concurrent with AI). In
Experiment 1, 1135 heifers (13e15 mo of age) received an estrus detection patch (Estrotect™) on Day 5
and 579 were selected at random to receive 300 IU of equine chorionic gonadotropin (eCG) at the time of
CIDR removal. Patches were scored from 0 to 3 based on color change between initial application and AI;
0 ¼ unchanged, 1¼ 50% change, 2 ¼ > 50% change, 3 ¼ missing. Estrus was defined to have occurred
when the patch was scored 2 or 3. In Experiment 2, 399 cyclic, non-lactating beef cows from 1 location
were submitted to either the modified 5-d Co-synch or J-synch protocol and within each protocol cows
were TAI at either 66 ±1 (n¼ 199) or 72 ±1 h (n ¼ 200) following CIDR removal. Transrectal ultrasonography
was used in both experiments to determine presence of a corpus luteum (CL) on Day 0, and to
diagnose pregnancy 35 d after TAI. In Experiment 1, eCG increased estrus rate only in heifers without a CL
on day 0 that were submitted to the modified 5-d Co-synch protocol (41.9 vs. 69.6%). Heifers submitted to
the J-synch protocol had greater (P ¼ 0.03) P/AI compared with those in the modified 5-d Co-synch (48.7
vs. 41.1%) and heifers that expressed estrus before AI had increased (P < 0.0001) P/AI compared to those
that did not (53.6 vs. 36.5%). Administration of eCG and presence of a CL tended to affect P/AI (P ¼ 0.13).
In Experiment 2, cows submitted to the J-synch protocol tended (P ¼ 0.07) to have greater P/AI compared
to those in the modified 5-d Co-synch (74.1 vs. 66.5%). There was no association between P/AI and timing
of AI. In summary, the J-synch protocol resulted in greater P/AI than the modified 5-day Co-synch
protocol in heifers and cows. Administration of eCG increased estrus rate in heifers without a CL at
the start of the protocol and tended to improve P/AI in all heifers. Timing of AI (66 vs. 72 h) had no effect
on P/AI in cows subjected to either TAI protocol. Keywords: 5-d Co-Synch | J-synch | Pregnancy per AI | Cyclicity | Estrus detection | eCG |
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