Embryo and cow factors affecting pregnancy rate after embryo transfer to multiple-service dairy cows
Estrada-Cortes E1, Ortiz WG1, Chebel RC1,2, Jannaman EA, Moss JI1, de Castro FC3, Zolini AM1, Staples CR1, and Hansen PJ1
Department of Animal Sciences1 and Large Animal Clinical Sciences2, University of Florida, Gainesville, Florida, USA; Departamento de Medicina Veterinária3, Universidade de São Paulo (USP), Pirassununga, São Paulo, Brazil.
Embryo transfer (ET) is as a method to improve fertility in repeat-breeder cows. The supplementation with rumen-protected choline has improved reproductive performance in dairy cows. Here we evaluated whether pregnancy success after embryo transfer in cows inseminated > 2 times without becoming pregnant depends upon characteristics of the embryo or recipient. Embryos were 1) produced in vitro using conventional Holstein semen and oocytes of undetermined breed collected at an abattoir and transferred fresh (abattoir; n=16); 2) produced in vitro using X-sorted Holstein sperm and Holstein oocytes collected at an abattoir, cultured with either vehicle (n=56) or 1.8 mM choline chloride (n=48) and transferred fresh; or 3) produced in vitro using X-sorted Holstein sperm and Holstein oocytes collected at an abattoir and transferred after freezing with ethylene glycol (n=43). Recipients were lactating Holsteins on a commercial dairy in north Florida and had been inseminated 2-7 times. The embryo transfers, conducted during summer and early fall, were performed 8 d after the last GnRH injection of an ovulation synchronization program. Pregnancy diagnosis was at day 33 after last GnRH. Characteristics of recipients examined were disease diagnosis in the current lactation (metritis, retained placenta, mastitis and other diseases), parity, milk production, days in milk and number of previous inseminations. Pregnancy rate (PR) was analyzed by the GLIMMIX procedure of SAS. PR was lower (P=0.007) for cows receiving frozen embryos (7.0%; 3/43) than for cows receiving fresh abattoir embryos (43.8%; 7/16), fresh embryos cultured with vehicle (19.6%; 11/56), and fresh embryos cultured with choline (29.2%; 14/48), but there were not significant differences between fresh embryo types. The only significant recipient factor affecting PR was diagnosis of metritis (P=0.059). For all embryo types, PR was lower for cows with metritis (7.1%; 2/28) than for cows without metritis (24.4%; 33/135). In conclusion, PR of multiple-service dairy cows after ET was reduced when using frozen embryos or when recipients experienced metritis in the current lactation. Further work to evaluate effects of choline supplementation of culture medium is warranted. Keywords: Embryo transfer, lactating cows, metritis.
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