12 Factors affecting Jersey in vitro embryo pregnancy rates
M. Oliveira A , C. Demetrio B , T. Baumgartner C , R. Santos D and D. Demetrio AA RuAnn Genetics, Riverdale, CA, USA
B Universidade de São Paulo, Piracicaba, SP, Brazil
C Jer-Z-Boyz, Pixley, CA, USA
D Universidade de Uberlândia, Uberlândia, MG, Brazil
Reproduction, Fertility and Development 34(2) 240-240 https://doi.org/10.1071/RDv34n2Ab12
Published: 7 December 2021
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Several factors need to be coordinated to obtain a live calf from an in vitro-produced embryo (IVPE). The objective of this study was to determine whether embryo and recipient selection before fresh embryo transfer (ET) could affect pregnancy rates (PR) of Jersey IVPE transferred to Jersey recipients at Jer-Z-Boyz Ranch, located in Pixley, California, that milks 4500 cows with a 305-day mature-equivalent milk production of 9341 kg, and have been using ET to increase the number of high-genetic-merit animals in their herd. Data from 994 IVPE transfers performed between December 2019 and April 2021 were collected and analysed. Jersey embryos from high-genetic-merit donors, were produced at the RuAnn Genetics laboratory (Riverdale, CA) as described by Demetrio et al. (2020 Anim. Reprod. 17, e20200053). Grade 1 or 2 embryos from morula (4) to hatched blastocyst (8) stage were removed from culture on Day 7 after IVF, loaded into straws with synthetic oviductal fluid (SOF)-HEPES-based holding medium and kept in a straw incubator at 35°C until the time of ET (up to 7 h). Heifer recipients (11 months) or lactating cows (56 to 192 days in milk (DIM), first to fourth lactation) received an embryo 7 or 8 days after natural oestrus (first service). Only recipients that had a corpus luteum (CL) on the day of ET received an embryo (ipsilateral uterine horn). Pregnancy diagnosis was performed by rectal palpation 37 to 44 days after oestrus, and the pregnancy rate (PR) was calculated as the number of pregnant recipients divided by the total ET. The Bernoulli model was fitted to the data. Recipient category (heifer vs. cow), stage (4 and 5 vs. 6 to 8), grade (1 vs. 2), DIM (≤65 days vs. >65 days), season (cold (November through May) vs. hot (June through October)), lactation number (first and second vs. third and fourth), donor, and sire were included in the models. This embryo program has been in constant adjustment since 2017, with the objective to obtain the highest PR possible. Preference to first and second lactation recipients, over 65 DIM, transferred 7 and 8 days after oestrus, at first service is given based on previous observations, which is why these data are unbalanced. There were no statistical differences among heifers (n = 173) and lactating cows (n = 821), despite the numerical differences (46.8% vs. 52.9%). Embryos that reach the blastocyst stage or older had higher PR than younger embryos (56.7 vs. 45.3; P < 0.05). Cows that received an embryo after 65 DIM (n = 639) had higher PR (54.8% vs. 46.7%; P < 0.05). First- and second-lactation recipients (n = 537) had higher PR than third- and fourth-lactation recipients (56.6% vs. 46.1%; P < 0.05). Higher PR can be achieved with good quality embryos (grade 1) selected at an optimal stage of development (blastocyst or older at Day 7 of in vitro culture) transferred to Jersey heifers or lactating cows (first and second lactation over 65 DIM) recipients. Grade 2 embryos should be used with caution during summer.
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