Supplemental Thyroid Hormones and Hatchability of Turkey Eggs

Abstract

Fertile turkey eggs were injected with thyroid hormones to test the effects of exogenous hormones on hatchability. Physiological doses of thyroxine (T4) and triiodothyronine (T3) of 50 and 25 ng, respectively, injected at setting, depressed hatchability. Conversely, injections of T4 and T3 at 25 days of incubation significantly (P less than .05) improved hatchability. Injections with thyroid-stimulating hormone (TSH) or tyrosine had no significant effect on hatchability when injected at setting or at 25 days of incubation. Injections of thyroid-releasing hormone (TRH) had no effect on hatchability when injected at setting but significantly (P less than .05) improved hatchability when injected at 25 days of incubation. Because T4 and T3 significantly (P less than .05) depressed hatchability when injected whereas TSH and TRH had no effect on hatchability when injected at setting, these data suggest classic negative feedback mechanisms function very early in the embryonic turkey. The improvement in hatchability observed when thyroid hormones were injected at 25 days of incubation offers further evidence that hypothyroidism may be a cause of poor hatchability among turkey eggs.

Improved Hatchability of Turkey Eggs at High Altitudes Due to Added Oxygen and Increased Incubation Temperature

“…The observations of this study support previous hypotheses (Christensen and Biellier, 1982;Christensen, 1985) that aberrant metabolism of turkey embryos during pipping and hatching results in a high embryonic death rate late in the incubation period. Most embryonic mortality occurs during the paranatal period (24 to 25 days for turkey embryos) at both sea level (Cherms, 1981) and high altitude (Bagley, 1987).…”

Quantification of Prolactin Messenger Ribonucleic Acid, Pituitary Content and Plasma Levels of Prolactin, and Detection of Immunoreactive Isoforms of Prolactin in Pituitaries from Turkey Embryos During Ontogeny1

“…As PRL is thought to modulate a multiplicity of actions in vertebrates [2,40], changes in PRL mRNA, pituitary content, and plasma concentrations in PRL observed before and after hatching might have an effect on at least one if not all of the physiological parameters mentioned above. Thyroid hormones are involved and are important for the survival of the embryo during hatching [10,39]. Since PRL was reported to act on thyroid hormone metabolism in chicken embryo via specific receptors in the liver [11][12][13], and PRLR mRNA is present in the thyroid and the liver of adult turkey hens [41], the variations in PRL observed in our study about the time of hatching may therefore act on thyroid hormones by modulating their concentrations and/or activation.…”

“…A stimulatory role upon T-cell maturation [8] and possibly on thymus development [9] was reported in the chicken. In addition, thyroid hormones, which appear to be important for the survival of the embryo during hatching [10], can be influenced by PRL [11][12][13]. Furthermore, PRL also seems to be involved in the control of osmoregulation by stimulating the reabsorption of NaCl from the fetal urine by the metanephric kidneys [14,15].…”

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

“…Early hatching is associated with increased plasma T 3 (review: Decuypere and Kühn, 1988). Small amounts of exogenous T 4 introduced into turkey eggs prior to incubation can improve hatchability (Christensen, 1985), and differences in 5 D II activity and plasma T 4 concentrations (substrate availability) leading to T 3 production appear to play a role in different hatching times in weight-selected lines of chickens .…”