Effects of Dietary Thiouracil on Thyroid Activity, Egg Production, and Eggshell Quality in Commercial Layers

Abstract

The effects of thyroid suppression induced during the rearing period by providing various dietary thiouracil (TU) regimens on plasma thyroxine (T4) concentrations, growth, and subsequent egg production (EP) and eggshell quality were determined in Single Comb White Leghorn chickens. Thiouracil was provided in the feed at levels of 0, .1, and .2% from 0 to 6 wk of age in Experiment 1, and at levels of 0, .05, and .1% from 6 to 16 wk of age in Experiment 2. In both experiments, T4 concentrations were reduced during TU treatment. However, T4 later became elevated at 12 and 20 wk in both dosage level groups in Experiment 1. Additionally, BW and egg weights were suppressed by both TU treatments, and EP was reduced up to Week 23 in the .1% TU-treated birds and through Week 25 in the .2% TU-treated birds. No effects on EP were noted in Experiment 2, but feed consumption (FC) was reduced during Week 6 in birds fed .05% TU and during Weeks 6, 10, and 19 in birds fed .1% TU. Both liver and thyroid weights were increased in .1% TU-treated birds relative to controls at Week 16. Eggshell quality was affected only in Experiment 2, in which birds given .05% TU had a higher relative conductance, or maximum rate of water loss, at Week 38 than 0 and .1% TU dosage levels, and .1% TU-treated birds had a higher breaking strength than 0 and .05% TU-treated birds at Week 22.(ABSTRACT TRUNCATED AT 250 WORDS)

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

“…Treatment of developing female chickens with thiouracil from 0-6 or 6-16 weeks of age decreased plasma T 4 , body weight and egg production. Some eggshell quality alterations were found in the experiment with thiouracil treatment from 6 to 16 weeks, but these alterations did not occur consistently (Peebles et al, 1994).…”

“…The 6-16 week thiouracil treatment did not have these effects. Likewise, neither experiment gave evidence of associations between plasma T 4 and altered eggshell quality (Peebles et al, 1994).…”

“…Temporary exposure of both female and male chicks to thyroid inhibitors for several weeks affects later reproductive development and performance, and manipulations of this type have been used in attempts to alter time of puberty, to attempt to improve reproductive performance in poultry, and in reinitiating egg laying following molting (e.g., Peebles et al, 1994;Siopes, 1997). It is generally accepted that thyroid hormones are involved in the onset of puberty in birds (Kirby et al, 1996).…”

Influence of supplemental dietary poultry fat on the performance of commercial layers inoculated before or at the onset of lay with F-strain Mycoplasma gallisepticum

“…Determined eggshell quality parameters included per-centage of eggshell weight (PSW) and eggshell weight per unit of surface area (SWUSA). Eggshell weight was obtained according to the procedure of Brake et al (1984), and the method of measurement of SWU-SA was as described by Peebles et al (1994). Eggshell weight was expressed as a percentage of total EW, and SWUSA was expressed as milligrams per square centimeter.…”

Differential effects of experimental hyperthyroidism on declined immunity of broiler chicken

“…The major type of circulating TH is thyroxine (T 4 ), which is then de‐iodinated into triiodothyronine (T 3 ) in the peripheral tissues (Whittow, ). A number of physiological actions in the birds including development of the central nervous system, musculoskeletal growth and reproductive function control are attributed to THs (Peebles, Miller, Boyle, Brake, & Latour, ). In last few decades, the endocrine system is recognized to have influence in the development and regulation of immune system.…”