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Comparison of three different reproductive management strategies for lactating dairy cows emphasizing detection of oestrus or synchronization of ovulation and Timed Artificial Insemination (TAI)
Vazquez, R.; Denholm, K.; Pinho, P...
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Objectives: The aim of this study was to compare three reproductive management strategies for first insemination of lactating dairy cows: Ovsynch; PRID-synch, both using oestrus detection and subsequent timed artificial insemination (TAI); and Double-Ovsynch at TAI.
Materials and methods: A total of 1681 Holstein cows from two commercial Scottish dairy farms were randomised by parity to three different reproductive strategies for first AI. For the first two protocols, cows were eligible to be inseminated by detected oestrus between 50 and 70 days in milk (DIM) and were subsequently enrolled in either one of the following two protocols:
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Ovsynch (n=541), GnRH (G1) at 70±3 DIM, PGF2α (PG1) 7 d later, PGF2α (PG2) 24h later and GnRH (G2) 32h later, followed by FTAI 16 h after;
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PRID-synch (n=562), GnRH (G1) + PRID at 70±3 DIM, PGF2α (PG1) 7 d later, PGF2α (PG2) + PRID removal 24h later and GnRH (G2) 32h later, followed by FTAI 16 h after.
For the third protocol, Double-Ovsynch (n=578), 53±3 days after parturition, cows received an injection of GnRH, PGF2α 7 d later and GnRH 3 d after, as presynchronization. Then at 70±3DIM, the breeding Ovsynch including an injection of GnRH (G1), PGF2α (PG1) 7 d later, PGF2α (PG2) 24h later and GnRH (G2) 32h later, followed by FTAI 16 hours later.
Ovarian monitoring was performed by transrectal ultrasonography at 43±3 and 50±3 DIM in all animals, and 70±3 (G1) and 77±3 (PG1) DIM only for the cows that were synchronized. Pregnancy was diagnosed by transrectal ultrasonography between 28 and 35 days after AI.
Results: Twenty-eight-day pregnancy rates for first AI was similar among treatment groups: Ovsynch (44%; 162/365), PRID-synch (41%; 158/383) and Double-Ovsynch (45%; 160/353). Cows with a corpus luteum (CL) at 77±3 DIM (PGF1) were 3.23 times more likely to be pregnant regardless of the treatment group (p<0.001). Primiparous cows were more likely to be pregnant at 28 days than multiparous cows in all treatment groups (Ovsynch 59% vs 35%; PRID-synch 47% vs 38%; and Double-Ovsynch 55% vs 39%) (p<0.001).
Conclusions: There was no significant difference in pregnancy rate at 28 days among treatment groups, which is consistent with previous comparable studies (Fricke et al., 2014, Robichaud et al., 2016). This may have been due to cows in the first two protocols being mated to observed oestrus on commercial farms where heat detection efficiency and P/AI on standing oestrus were good (57% and 46% respectively); which may have over-inflated the 28 days pregnancy rate in these two groups; however, these results are reflective of the expected performance of the protocols in a commercial setting. Primiparous cows submitted to Double-Ovsynch did not have higher pregnancy rate compared with the other two strategies in contrast to other published reports (Souza et al., 2008; Borchardt et al., 2016).
Keywords: Dairy, reproduction, oestrus, synchronization, TAI.
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Affiliation of the authors at the time of publication
University of Glasgow, Glasgow, United Kingdom; 2CEVA Sante Animale, Loudeac, France.
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