الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
The present study was carried out at Poultry Research Station belonging to El-Azzab, El-Fayoum Governorate, Animal Production Research Institute, Agricultural Research Center, Cairo.
It was aimed to point out the relationship between the level of thyroid activity and productive performance. This may aid to improve the productivity by means of optimizing the thyroid activity.
A total number of 800 one day old Fayoumi chicks (form two strains and two crosses), (PP and GG strains and PG and GP crosses). The chicks within each group (200 chicks) were subdivided at the second month of age into two subgroups. Chicks of the first subgroup were of a heavy body weight at the second month of age, while those of the second subgroup were of a light body weight. After sexual maturity (at six month age), chicks of each subgroup within groups (heavy and light) were classified according to the age at sexual maturity into early and late sexually matured (each 50 chicks each).
All birds were kept under a similar and standard conditions of management, environment, hygein and nutrition.
Experiment included two period. Detective survey of thyroid activity was carried out during the first experimental period lasted from 2 to 5 months of age which considered as growth stage. The growth parameters (live body weight and growth rate %), as well as blood indices [glucose, total protein, total lipids, (GOT), (GPT), (T3) and (T4)] were estimated and correlated with the different thyroid hormonal levels detected. The second experimental period(egg production period) started from the 3rd month after sexual maturity up to moult (19 months).
All egg productive parameters, egg number, egg weight and egg mass of the first ninety days, as well as blood indices correlated with the level of thyroid activity [glucose, total protein, total lipids, (GOT), (GPT), (T3) and (T4)] were estimated monthly along the experimental period.
Results obtained could be summarized as follows: During growth period (from 2-5 months age):
1.Significant variation was found in live body weight at different estimation intervals along the growth periods due to bird’s cross and strain and initial body weight. On the other hand, variation in live body weight was found to be of significant magnitude at the 4th month of bird’s strain and initial body weight. No significant variation was found due to bird’s strain or cross on live body weight when estimated all over the whole growth period. The heavy GP birds showed the highest body weight, while the light GP birds had the lowest body weight during the whole growth period (2-5 months of age).
2.birds strain had significant effect on the rate of growth estimated at the 3rd, 5th and during the whole growth period (2-5 months). However, no significant effect was found in the growth rate along the variation intervals of the growth period due to the initial body weight of the birds. The bird’s strain x initial body weight showed significant effect in growth rate at the 4th month of bird’s age. The light PG andheavy GG showed the highest growth rate, while the light and heavy GP recorded the lowest growth rate.
3.insignificant variations were found during the whole growth period (2-5 months) due to bird’s strain or cross on some studied blood parameters (total proteins, glucose, GOT, GPT and T3). However, bird’s strain and cross showed significant effect at estimation intervals differed according to the parameter estimated. Bird’s strain showed significant effect on plasma glucose, GOT and T3 at the 2” month, on plasma GPT, T3 and T4 at the 4th month and on plasma total lipids, T3 and T4 at the 5th month of age.
Variation in plasma total lipids and T4 only was found during the period from 2-5 months age.
4.The highest plasma T3 value was found in the light birds of the GG strain, while the light birds of the GP cross showed the lowest plasma T3 value. On the other hand, both heavy and light birds of GG strain showed the highest plasma T4 content while birds of the heavy PP strain showed the lowest plasma T4 average during the whole growth period (2-5 months).
5.Plasma T3 level was significantly correlated with plasma T4 content in PP strain, while it was significantly correlated with plasma GOT and GPT in GP cross. Live body weight showed a significant correlation coefficient with plasma T4 level in GP cross.
During egg production period:
1. Significant variations in egg number and mass were found at 6, 7 and 19 months of age and during the period from 6-8 months of age due to bird’s strain and cross, while egg weight was affected by bird’ strain when estimated at the 8th month of age and at moult only.
2.Bird’s initial body weight had significant effect on egg mass when estimated at the 6th month of age only, while it showed insignificant effect on both egg number and weight at any estimation intervals.
3.Age at sexual maturity had insignificant effect on average egg number but it significantly affected average egg weight at the 6th month and during the period from 6-8 months of age and average egg mass at the 7th month and during 6-8 month of age.
4.The late sexually matured heavy and light birds of PP strain showed the higher average egg weight at the first ninety days of egg production, while the early heavy birds of PP strain and PG cross attained the lowest egg weight average.
5.Significant variation in some plasma blood parameters (total proteins, total lipids, GOT, GPT and T3) was found due to bird’s cross or strain during the period from 6-8 months of age. However, insignificant variation was found in plasma glucose and T3 content due to bird’s strain during the same period.
6.The late matured light GP cross had the highest plasma T3 average, but the early matured heavy birds of GG strain and the early and late matured and light birds of PG cross had the lowest plasma T3 average. On the other hand, the highest plasma T4 level was found in late matured and heavy birds of PP strain, while the lowest level was found in birds of GG strain of late sexual maturity heavy and light body weight during the period from 6-8 months of age.
7. Plasma T3 level significantly correlated with T4 and live body weight in PP strain, and with egg weight in GG strain, and with growth rate in PG cross. Plasma T4 level, on the other hand, recorded a significant correlation coefficient value with average egg weight in all strains and crosses, while average egg number showed a negative and significant correlation with T4 in PP strain and PG cross. Same fmding was appeared between average egg mass and plasma T4 in PG cross. A significant correlation was found between T4 and Live body weight in all strains and crosses. Significant correlation had been recorded between T4 and growth rate in PP strain, while T4 showed the same significance level with GOT and plasma total protein in GP cross.