Endocrine Mechanisms of Puberty in Heifers: Estradiol Negative Feedback Regulation of Luteinizing Hormone Secretion 1

Abstract

The hypothesis that luteinizing hormone (LH) secretion in prepubertal females is responsive to estradiol negative feedback and that decreased feedback occurs as puberty approaches was tested in heifers. In the first experiment, seven heifers were maintained prepubertal by dietary energy restriction until 508 days of age (Day 0). All heifers were placed on a high-energy diet on Day 0 at which time they received no additional treatment (CONT), were ovariectomized (OVX) or were ovariectomized and subcutaneously implanted with estradiol-17 beta (OVX-E2). This feeding regimen was used to synchronize reproductive state in all heifers. A second experiment was performed with 16 prepubertal heifers using the same treatments at 266 days (Day 0) of age (CONT, OVX and OVX-E2) but no dietary intake manipulation. In both experiments, LH secretion increased rapidly following ovariectomy in OVX heifers. In the initial experiment, LH secretion was maintained at a low level in OVX-E2 heifers until a synchronous rapid increase was noted coincidental with puberty in the CONT heifer. In the second experiment, LH secretion increased gradually in OVX-E2 heifers and attained castrate levels coincidental with puberty in CONT heifers. A gradual increase in LH secretion occurred as puberty approached in CONT heifers. These results indicate that: a) LH secretion in prepubertal heifers is responsive to estradiol negative feedback; and b) estradiol negative feedback decreases during the prepubertal period in beef heifers.

Creep-feeding to stimulate metabolic imprinting in nursing beef heifers: impacts on heifer growth, reproductive and physiological variables

“…In addition, blood samples were collected on 10-day intervals during the development phase to estimate onset of puberty by determining the first pubertal increase in plasma progesterone concentrations. Heifers were considered pubertal once plasma progesterone concentrations were ⩾1.0 ng/ml, followed by a cyclic pattern of plasma progesterone < and ⩾1.0 ng/ml suggestive of normal estrous cycles (Day et al, 1984). Puberty attainment was declared at the first sampling that resulted in plasma progesterone ⩾1.0 ng/ml.…”

Evaluation of pre-breeding reproductive tract scoring as a predictor of long term reproductive performance in beef heifers

“…The onset of puberty in heifers is initiated by a decrease in oestradiol receptors in the hypothalamus and pituitary, ending the prepubertal negative feed-back and resulting in the first LH surge and ovulation (Day et al, 1984, Day et al, 1987. This shift occurs at a specific critical BW (as a proportion of adult BW) and critical age which varies amongst animals (Pence et al, 2007).…”

Endocrine changes from birth to puberty in the heifer

“…Although it is generally accepted that this hypothesis may be applicable to farm species, appropri¬ ate experimental results are limited. Conflicting data have been recorded for the heifer; some workers have reported that episodic LH release increases gradually from birth to puberty (Schams et al, 1981;Day et al, 1984), while others have been unable to detect such changes (González-Padilla et al, 1975a;McLeod et al, 1984). The infrequent blood sampling regimen used in the study of Gonzalez-Padilla et al (1975a) was inadequate to identify changes in episodic patterns of gonadotrophin secretion, and the use of only limited periods of frequent sampling (Schams et 1981 ; Day étal, 1984) could lead to inaccurate estimations of LH episode frequency.…”