Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2000
Publication Date: N/A
Interpretive Summary: Enhancing growth, performance and production of domestic animals is of great economic concern to the producer. To this end, producers are seeking ways to enhance an animal's performance by modulating natural hormone production and secretion. Of particular importance is a hormone produced by the pituitary gland, growth hormone (GH), which stimulates growth, milk production, etc. One of the many known factors that affect GH production is estrogen, a natural female reproductive hormone. The effect of estrogen on GH has been extensively investigated in rodents, but not in livestock. In this study we found that the estrogenic compound, zeranol, can stimulate GH production in sheep. The knowledge acquired regarding the action of estrogen on GH production will be of interest to scientists in academia and industry who are investigating ways to enhance growth and performance in sheep. This study provides additional support for the use of hormonal supplements by producers to enhance growth and performance in domestic ruminants.
Technical Abstract: This experiment evaluated relationships between pituitary messenger RNA levels of the transcription factor Pit-1, the growth hormone releasing-hormone receptor (GHRHR), and synthesis and secretion GH in growing wethers. The experiment also evaluated the influence of the estrogenic compound, zeranol, on these relationships. Newborn wethers (n=70) were randomly assigned to a control group or to one of three zerano treatment groups that were implanted (12 mg, Ralgro) at 0, 45, and(or) 90 d of age. Twenty-eight days after implantation (i.e. d 28, 73, 118) and on d 135, sera were collected serially from wethers (n=5) from each group and then their pituitary was collected. As wethers gained weight with age, the pituitary increased in size and so did the relative message levels of Pit-1 and GH (effect of time, P<.01). However, as wethers reached 135 d of age, serum concentrations of GH had declined while concentrations of IGF-I had increased (linear contrast, P<.01). Additionally, zeranol increased serum concentrations of GH and IGF-I and this effect on GH appeared to be a consequence of increased pulse amplitude, particularly at 73 and 118 d of age (treatment x time, P<.074). This result could have been due to increased pituitary expression of GH (treatment, P<.08). Zeranol appeared to modulate pituitary expression of transcripts containing exon 3 of Pit-1 (treatment, P<.01) and GHRHR (treatment x time, P=.056), however, pituitary message levels of Pit-1 and GHRHR were not positively correlated to pituitary expression of GH mRNA or serum concentrations of GH.