The Comparative Physiological Development of the Reproductive and Adrenal Axis of the Gilt From Weaning to Puberty

The objective of this study was to examine the development of the reproductive axis of the gilt with respect to development of the adrenal glands. Groups of five gilts each were slaughtered at 4-wk intervals from 4 to 20 wk of age. Organ weights as well as activity of the adrenal glands were determined by histometry to determine nuclear to cellular volume ratios and thickness of zones of the cortex. Weights of the heart, lungs, spleen, kidneys, pineal, thyroid and adrenals were found to increase with age while relative weight of these organs was constant or decreasing. In contrast, weight and relative weight of the whole reproductive tract, oviducts and uterus showed growth spurts, first at 16 wk and later at 28 wk of age. The ovaries had one growth spurt at 16 wk of age. An increase at 12–16 wk was also evident in profiles of estradiol and LH determined from blood samples collected from another group of gilts sampled at weekly intervals until first estrus (207.8 ± 3.3 d, mean ± SEM). Measurement of relative nuclear volume and thickness of the adrenal cortex zonation during development failed to provide any evidence to support the hypothesis that an increase in activity or growth of the adrenal gland is responsible for the growth spurts in the reproductive axis during development.