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Bovine Embryo Transfer Pregnancies. II. Lengths of Gestation¹

Colorado State University², Fort Collins 80523

Abstract

Lengths of gestation were determined from 1,484 pregnancies resulting from embryo transfer procedures. Least-square means of lengths of gestation by breed of embryos (P<.005) were: Holstein, 278.7; Angus, 281.0; Hereford, 285.7; Simmental, 287.6 and Limousin, 289.7 d. Recipient breed had a small effect on length of gestation (P<.005). The length of gestation for recipients less than 4 yr old was 2.7 d shorter (P<.005) than for older recipients. As asynchrony of recipient and donor estrus changed by 1 d, length of gestation changed linearly by .78 d (P<.005). Male calves were carried 1.4 d longer than females (P<.005). Embryo age at time of transfer, embryo quality, length of embryo storage between collection and transfer, and donor age did not affect length of gestation significantly. Lengths of gestation of 185 embryo transfer pregnancies were 1.5 d longer (P>.1) than those of 305 matched control pregnancies from the same farms. We conclude that length of gestation of embryo transfer calves and length of gestation of non-embryo transfer calves are influenced by similar factors.

¹ This research was supported by NIH grant HD-13487. We wish to acknowledge the efforts of the clients and personnel of the Embryo Transfer Laboratory, Colorado State University.

² Anim. Reprod. Lab.