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Relationship between Endogenous Estradiol-17ß and Estrous Behavior in Heifers^1,2,

Purdue University⁴, West Lafayette, IN 47907

Abstract

Thirty-five Holstein heifers were used to examine the relationship between endogenous estradiol-17ß and estrous traits. During a non-superovulation period (NSP), estrous cycles were synchronized and during the periovulatory stage blood samples were collected every 6 h for 120 h for subsequent determination of estradiol-17ß and progesterone. In addition, continuous observation for estrous behavior was performed for 98 h. A gonadotropin-induced superovulation period (SP) was begun 12 d after estrus was detected during NSP. Heifers were injected with FSH twice daily for 4 d and single injections of prostaglandin were given on d 14 and IS. Beginning at d 14, blood samples were collected every 6 h for 120 h for subsequent determination of estradiol-17ß and progesterone. Continuous observation for estrous behavior was performed for 98 h. Peak estradiol-17ß was greater during SP than during NSP (49.0 ± 3.1 vs 12.9 ± 3.0 pg/ml serum). Thirty-three and 31 of the 35 heifers were in estrus during NSP and SP, respectively; duration of estrus was 2.3 h longer during SP than during NSP. However, number of behavioral interactions during estrus did not differ between NSP and SP. In conclusion, estrous traits were similar, whereas peak estradiol-17ß concentrations were markedly different between NSP and SP.

¹ Journal Paper No. 11,719, Purdue Univ., Agric. Exp. Sta.

² The authors would like to thank Tammy Miller and Diana Seevers for their invaluable technical expertise and Max Lowe, Miles Laboratories, Inc., for the gift of prostaglandin.

³ Reprint requests.

⁴ Dept. of Anim. Sci.