The Relationship between Age and Genotype and Circulating Concentrations of Triiodothyronine (T3), Thyroxine (T4), and Growth Hormone in Commercial Meat Strain Chickens

Abstract

The presence of the sex-linked dwarf gene (dw) in homozygous male (dwldw) and female (dw/-) meat strain chickens is associated with a significant reduction in circulating levels of triiodothyronine (T3). Heterozygous (Dw/dw) male broiler strain chickens have T3 concentrations similar to those in homozygous (Dw/Dw) male broilers. Genetically normal (Dw/Dw) but significantly slower growing roaster strain male meat chickens had consistently higher T3 than the faster growing broilers at all ages in one experiment but only at 8 weeks in a second experiment. Age and not growth rate appears to have a greater influence on serum T3 concentrations in the slow-and fast-growing normal strains. Growth hormone levels were significantly higher in the dwarf chickens at all ages and in all three experiments. The heterozygous and homozygous broilers had similar GH levels and the slow-growing, genetically normal roasters had intermediate concentrations between the broiler and dwarf lines. GH was influenced to a greater extent by the rate of body weight gain than by increasing age in the genetically normal fast and slow growing Strains. 0 1986 Society for Experimental Biology and Medicine. 36

Relationships Among Mineral Balance in the Diet, Early Growth Manipulation, and Incidence of Tibial Dyschondroplasia in Different Strains of Meat Type Chickens

“…Across all four treatments, chicks that gained the most weight from 21 to 28 days had significantly lower GH concentrations, and this was independent of differences in feed consumed during this time. These data support the hypothesis of Lilburn et al (1986a) that measured differences in GH are effected by rates of gain during some arbitrary time period, and that genetic potential and diet influence GH through their influence of growth rather than having direct effects per se. Fox et al (1972;1974) reported similar findings with beef steers.…”

“…Any dietary or genetic factors that decrease BW gain generally will result in increased circulating growth hormone (GH) (Marks, 1979;Burke and Marks, 1982;Lilburn et al, 1986a;Lauterio and Scanes, 1987). The data herein suggest that during a period of nutritional rehabilitation, GH concentrations may be influenced more by absolute weight gain during the repletion period rather than by starting BW or feed intake during the period.…”

“…The original report by Leach and Nesheim (1965) showed that the macrominerals Ca and P were precluded from having a significant effect on the incidence of the anomaly. In the 20 yr since the original report, however, the incidence of TD in commercial broiler flocks has increased greatly together with a major 'The vitamin premix provides per kilogram of diet: vitamin A, 7,570 IU; vitamin D, 2,200 ICU; menadione sodium bisulfite, 4.4 mg; vitamin E, 6.6 IU; thiamine, 3.5 mg; riboflavin, 11 mg; niacin, 62 mg; pantothenic acid, 21.5 mg; folacin, 1.2 mg; biotin, 150 |j.g; vitamin B12, 11 (ig; ethoxyquin, 125 mg. ^he trace mineral premix provides per kilogram of diet: manganese, 60 mg; iodine, 1.2 mg; iron, 20 mg; copper, 2.0 mg; zinc, 20 mg; cobalt, .20 mg. increase in the growth rate of the modern broiler chicken and associated changes in growth physiology (Marks, 1979;Burke and Marks, 1982;May and Marks, 1983;Lilburn et al, 1986a). Concomitant with changing growth rates, recent evidence suggests that Ca and P can play a role in the development of a TD lesion (Edwards and Veltmann, 1983;Edwards, 1984;Hulan et al, 1985;Kling, 1985) independent of any effects on bone mineralization.…”

Posthatch Ontogeny and Sex-Related Differences in Somatotroph Numbers in the Chicken Adenohypophysis

“…It has been reported that plasma concentrations of GH decline with age earlier in broiler than layer breeds (Scanes and Harvey, 1982). The observed progressive sexual dimorphism in somatotroph numbers may contribute to higher circulating GH concentrations in male vs. female broiler or meat-strain chickens, as reported in other studies (Burke and Marks, 1982;Stewart and Washburn, 1983;Lilburn et al, 1986).…”

Concentrations of hormones, glucose, triglycerides and free fatty acids in the plasma of broiler chickens selected for weight gain or food conversion

“…genotype X environment interactions) and to improve selection methods. Although it is clear that pituitary and thyroid hormones can play an important role in these processes (Scanes et al, 1984(Scanes et al, , 1986Lilburn et al, 1986;Decuypere and Kiihn, 1988) no complete picture of the relationships between these hormones and protein gain and efficiency is available.…”