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Effects of Restriction of Dietary Energy Intake during the Prepubertal Period on Secretion of Luteinizing Hormone and Responsiveness of the Pituitary to Luteinizing Hormone-Releasing Hormone in Heifers¹

University of Nebraska^,4, Lincoln 68583

Abstract

The working hypothesis that a low plane of nutrition during the prepubertal period delays puberty in heifers by retarding the prepubertal increase in secretion of luteinizing hormone (LH) was investigated. Secretion of LH and the responsiveness of the pituitary to LH-releasing hormone (LHRH) were compared in heifers fed a growing diet (which allowed spontaneous occurrence of puberty; n = 12; control) or an energy deficient diet (which delayed puberty, n = 11; delayed) during the prepubertal period. The dietary treatments were initiated when the heifers were 299 ± 14 ( ± SD) d of age (d 0 of the experiment) and continued until d 175 of the experiment (474 ± 14 d of age). Weight gains were .79 ± .05 ( ± SE) and .21 ± .03 kg·head^-1 · d^-1 for control and delayed heifers, respectively. Puberty occurred on d 120 ± 14 of the experiment (428 ± 13 d of age) in control heifers, whereas none of the delayed heifers attained puberty during the feeding period. Serum concentration of LH and the frequency of LH pulses increased rapidly during the 175-d feeding period in control heifers. In delayed heifers, serum LH concentration increased less rapidly and no increase in pulse frequency was detected during the experimental period. Amplitude of LH pulses tended to be higher in control than delayed heifers. Responsiveness of LH secretion to LHRH was lower in delayed than control heifers. It is speculated that failure of secretion of LH to increase is the causative factor for delayed puberty when dietary energy is limited during the prepubertal period in heifers.

¹ Published as Paper No. 7899, Journal Series, Nebraska Agr. Res. Div. Appreciation is expressed to Mrs. Cheryl Rieck and Mrs. Jane Ossenkop for assistance in preparation of this manuscript and Mr. Kenneth Pearson for technical assistance in the laboratory. We also thank Dr. Jerry Reeves, Washington State Univ., Pullman, WA for the LH antisera, Dr. Leo Reichert, Albany Med. College, Albany, NY for the purified LH used for iodination and Dr. R. H. Rippel, Abbott Lab., North Chicago, IL for the LHRH preparation.

² Present address: Dept. of Anim. Sci., The Ohio State Univ., Columbus, OH.

³ Reprint requests: Dr. James E. Kinder, 218 Marvel Baker Hall.

⁴ Dept. of Anim. Sci.

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