Molt induced by gonadotropin-releasing hormone agonist as a model for studying endocrine mechanisms of molting in laying hens.
Molt induced by infusion of a gonadotropin-releasing hormone agonist (GnRH-A, ([D-Leu6,Pro9]-GnRH N-ethylamide]) has been used as a model for studying the endocrine mechanisms of molting. Molt induced by GnRH-A was also compared with that induced by feed withdrawal (FW). Thirty-three laying hens were divided into three groups: 1) sham infused (controls), 2) molted by GnRH-A infusion (GnRH-A), or 3) molted by FW. All groups had reduced day length. Birds were weighed and blood was sampled twice per week. Plasma was assayed for thyroxine (T4), triiodothyronine (T3), and progesterone (P4); egg production was recorded. A separate group of GnRH-A molted (n = 8) and control (n = 4) hens were killed during the molt and liver, ovary, and oviduct were weighed. Plasma T4 concentrations were elevated (P less than .01), whereas plasma T3 did not change and plasma P4 decreased (P less than .05) in the GnRH-A group compared with the control group. Plasma T4 was higher (P less than .05) in the GnRH-A group than in the FW group, whereas plasma T3 was higher (P less than .05) in the FW group than in the GnRH-A group. Plasma P4 concentrations declined to similar low levels in the GnRH-A and FW groups. The GnRH-A caused weight loss (P less than .05) from the ovary, oviduct, and liver. The GnRH-A-molted hens lost less BW (P less than .001) and were out of lay for 12 days less than FW-molted hens. Postmolt rates of lay were not significantly different for the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Dickerman
R W
RW
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
Bahr
J M
JM
D000818:Animals; D001835:Body Weight; D002645:Chickens / Q000097:blood / Q000502:physiology*; D005260:Female; D005508:Food Deprivation / Q000502:physiology; D008099:Liver / Q000254:growth & development; D009929:Organ Size; D010053:Ovary / Q000254:growth & development; D010057:Oviducts / Q000254:growth & development; D010058:Oviposition; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D010906:Pituitary Hormone-Releasing Hormones; D014284:Triiodothyronine; D011374:Progesterone; D013974:Thyroxine