title: Hot topic: Successful fixed-time insemination within 21 d after first insemination by combining chemical pregnancy diagnosis on d 18 with a rapid resynchronization program.
abstract: Cattle that are not pregnant to first fixed-time artificial insemination (TAI) may be resynchronized for a second TAI if they are found nonpregnant at pregnancy diagnosis. The specific interval between first and second TAI ranges from 4 to 8 wk. The selected interval depends on the available method of pregnancy diagnosis and the efficiency of the resynchronization program. The objective of this experiment was to evaluate a pregnancy diagnosis and resynchronization system that achieved a 21-d interval between TAI. This 21-d interval approximates the natural return-to-service interval. It also enables resynchronization to be implemented within the same estrous cycle in which cattle are first inseminated. Holstein heifers were randomly assigned to a 21-d resynchronization program (21d_resynch; n = 40) or a control group in which estrus was observed for the purpose of re-insemination (control; n = 29). The 21d_resynch heifers were diagnosed for pregnancy on d 18 after a TAI (d 0) by using predetermined cut-off values for 2'-5' oligoadenylate synthetase 1 (Oas1) gene expression in leukocytes and plasma progesterone concentration. Heifers that were not pregnant to first TAI had greater expression of Oas1 at the time of PGF(2α) (d -3) than pregnant heifers, but this relationship was reversed on d 18 after TAI: the heifers that were pregnant to first TAI had almost 5-fold greater expression of Oas1 compared with nonpregnant heifers. Nonpregnant heifers in the 21d_resynch group were injected with a luteolytic dose of PGF(2α) on d 19 and were injected with GnRH on d 21 and submitted to TAI. The pregnancy per AI after first insemination was similar for 21d_resynch (50.0%; pregnancy diagnosis on d 18) and control (51.7%; pregnancy diagnosis on d 27). Likewise, no difference was detected in second insemination pregnancy per AI for 21d_resynch (36.8%; nonpregnant heifers TAI on d 21) and control (35.7%; nonpregnant heifers inseminated at return to estrus or after nonpregnant diagnosis on d 27). The interval between first and second insemination was shorter for 21d_resynch compared with control (21.0 ± 0 and 27.5 ± 2.1 d). The conclusion is that a TAI resynchronization can be programmed within 21 d of previous TAI when a d 18 pregnancy test and a rapid resynchronization are used.
authors.affiliation: Division of Animal Science, University of Missouri, Columbia 65211, USA. kevin_anderson@ncsu.edu
authors.forename: J C
authors.initials: JC
authors.lastname: Green
authors.forename: C S
authors.initials: CS
authors.lastname: Okamura
authors.forename: D J
authors.initials: DJ
authors.lastname: Mathew
authors.forename: E M
authors.initials: EM
authors.lastname: Newsom
authors.forename: M C
authors.initials: MC
authors.lastname: Lucy
mesh_terms: D015088:2',5'-Oligoadenylate Synthetase / Q000378:metabolism; D000818:Animals; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D011258:Pregnancy Tests / Q000662:veterinary*; D011374:Progesterone / Q000097:blood; D013997:Time Factors
chemical_list: D011374:Progesterone; D015088:2',5'-Oligoadenylate Synthetase