The effect of increasing photoperiod and food restriction in sexed, broiler-type birds. II. Plasma thyroxine, triiodothyronine, insulin-like growth factor-I and insulin.
1. Sexed broiler-type chicks were raised either under a continuous (CON) 23 h light (L) and 1 h dark (D) schedule or an increasing photoperiod (INC). From 5 to 11 d of age birds were fed either: ad libitum (AL), energy intake (kJ ME) restricted to 9.414 x gBW0.67 (R1) or energy intake (kJ ME) restricted to 6.276 x gBW0.67 (R2). 2. Blood samples were taken at 4, 7, 11, 14 d of age and weekly thereafter to 49 d of age. Plasma thyroxine (T4), triiodothyronine (T3), insulin-like growth factor-I (IGF-I) and insulin were determined. 3. CON birds had elevated plasma T3 concentrations to 21 d of age, and greater plasma T4 concentrations at 11 and 21 d of age concurrent with greater food intake. Elevated plasma T3 concentrations in INC birds at 28 d of age coincided with lower plasma IGF-I concentrations at a time when growth and food intake were greater than CON birds. 4. Food restriction elevated plasma insulin and T4 but depressed plasma T3 and IGF-I. Plasma T3 was greater for food-restricted birds at 21 d of age, but subsequently, was generally lower than ad libitum-fed birds which may account for a lack of complete 'catch-up' in growth. 5. Plasma T3 was higher in females at 11 d of age when growth was equivalent for both sexes. From 28 to 42 d, when sex differences in growth became most apparent, plasma T3 was greater in males.
Newcombe
M
M
US Department of Agriculture, Poultry Research Laboratory, Georgetown, DE 19947.
Cartwright
A L
AL
Harter-Dennis
J M
JM
McMurtry
J P
JP
D000818:Animals; D002645:Chickens / Q000097:blood*; D002940:Circadian Rhythm; D002149:Energy Intake / Q000502:physiology; D005260:Female; D005508:Food Deprivation / Q000502:physiology*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D011897:Random Allocation; D012727:Sex Characteristics; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D007328:Insulin; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D013974:Thyroxine