Fernandez Novo, AitorSantos López, SergioPesantez Pacheco, Jose LuisPérez Villalobos, NatividadDe las Heras Molina, AnaGonzález Martín, Juan VicenteAstiz, Susana2025-01-232025-01-232021Fernandez-Novo, A., Santos-Lopez, S., Pesantez-Pacheco, J. L., Pérez-Villalobos, N., Heras-Molina, A., Gonzalez-Martin, J. V., & Astiz, S. (2021). Effects on synchronization and reproductive efficiency of delaying the removal of the intravaginal progesterone device by 24 h in the 5d co-synch protocol in heifers. Animals, 11(3), 1-13. https://doi.org/10.3390/ANI1103084910.3390/ani11030849https://hdl.handle.net/20.500.14352/115889Author Contributions Conceptualization: S.A. methodology, all authors; software, A.F.-N., S.S.-L., J.L.P.-P., N.P.-V., J.V.G.-M. and S.A.; validation, A.F.-N., N.P.-V. and S.A.; formal analysis, A.F.-N., S.S.-L., J.L.P.-P., N.P.-V., A.H.-M. and S.A.; investigation, A.F.-N. and S.A.; resources, A.F.-N., S.S.-L., N.P.-V. and S.A.; data curation, A.F.-N., S.S.-L., N.P.-V., A.H.-M., J.V.G.-M. and S.A.; writing—original draft preparation, A.F.-N., N.P.-V. and S.A.; writing—review and editing, all authors; visualization, A.F.-N. and S.A.; supervision, A.F.-N., N.P.-V. and S.A.; project administration, S.A.; funding acquisition, A.F.-N., S.S.-L. All authors have read and agreed to the published version of the manuscriptIn beef herds, increasing animal welfare, improving reproductive performance and easing animal management are key goals in farm economics. We explored whether delaying the removal of the intravaginal progesterone device by 24 h in heifers synchronized with a 5d Co-synch 72-h protocol could improve reproductive efficiency of fixed-time artificial insemination (FTAI). In experiment 1, we examined the total synchronization rate (TSR) in cycling Holstein heifers. Heifers (13.4 ± 0.69 mo.) were randomly assigned to the standard 5d Co-synch 56-h protocol (5dCo56; n = 10), 5d Co-synch 72-h (5dCo72; n = 17), or the modified 5d Co-synch 72-h protocol, in which removal of the progesterone device was delayed by 24 h (6dCo48; n = 19). In experiment 2, 309 cycling beef heifers on 18 commercial farms were subjected to the 5d Co-synch 72-h or 6-d Co-synch 48-h protocol and conception rate (CR) studied. In experiment 1, the three protocols led no differences on TSRs of 80.0% (5dCo56), 88.2% (5dCo72), and 89.5% (6dCo48). In experiment 2, the CR from the beef heifers, observed during two consecutive reproductive seasons did not differ: 59.7% for 5dCo72 and 62.0% for 6dCo48 (p = 0.907). Therefore, delaying removal by 24 h provides satisfactory results without reducing reproductive efficiency of heifers.engAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/journal article2076-2615https://doi.org/10.3390/ani1103084933802721https://www.mdpi.com/journal/animalsopen access636.09:617636.09:611.013Conception rateOvarian physiologyFTAICo-synchHolstein heifersObstetricia veterinariaPatología veterinaria3109.10 Cirugía