The ascites syndrome, as a consequence of high oxygen demands of the fast-growing tissues in meat type chicken is accompanied by a marked increase in broiler mortality. Thyroid hormones concentration has been reported to be reduced in ascitic chickens prior to death and thyroxine (T4) administration was suggested to diminish the mortality rate from the ascites syndrome in broiler chickens. Therefore, the aim of the present study was to ascertain whether the long-term administration of T4 for 14 consecutive weeks might be associated with any changes in blood hematological and biochemical attributes in Cobb 500 broiler breeder hens to provide valuable recommendations for T4 administration in reducing the ascites incidence.
A total of seventy 47-wk-old Cobb 500 breeder hens were randomly allotted to control or extra-T4 treated (T4) groups. The hens in the T4 treatment group individually received an oral administration of pure T4 (0.3 mg/bird per day) dissolved in 1 mL of water for 14 successive weeks. The birds were reared under the same conditions and fed a corn-soybean based diet (155 g/d per bird; 2700 kcal metabolizable energy/kg, and 14.0, 2.99, and 0.36% crude protein, calcium, and phosphorus) with a free access to fresh drinking water. Body weight and egg production were recorded on a weekly basis. Blood samples (5 mL) were obtained from the brachial vein at weeks 47, 50, 53, 55, 57, 59, and 61 of age to determine the percentages of lymphocytes, monocytes, heterophils, eosinophils, basophils, and heterophil to lymphocyte (H:L) ratio. Plasma/serum samples were analyzed for T3 and T4. The concentrations of total protein, albumin, globulin, total cholesterol, high-(HDL), low-(LDL), very low-(VLDL) density lipoprotein, triglycerides, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) were quantified in the plasma samples. The concentration of glucose, calcium, phosphorus, and ALP were determined in serum samples.
The concentration of T4 was elevated in the T4 hens (27.08 ng/mL) as compared with that in the control birds (10.24 ng/mL; P = 0.003); whereas plasma T3 concentration was not influenced by the long-term administration of T4 (P > 0.05). A decrease in body weight was recorded in T4 birds (4,369 and 4,257 g for control and T4 birds, respectively; P = 0.040). No differences in egg production were found between the experimental groups. Thyroxine administration increased the total number of leukocytes (11.5 × 103/mL) compared to the control (10.7 × 103/mL) birds (P < 0.001). Likewise, a higher total erythrocyte number was found in hyperthyroid hens (2600 vs. 2400 × 103/mL for control and T4 birds, respectively; P < 0.001).
Overall, the long-term administration of T4 in broiler breeder hens had no adverse effects on blood hematological and biochemical characteristics, and apart from increases in the concentration of some attributes, the recorded values were within their reference ranges. According to unaffected H:L ratio, the birds orally administered by extra T4 did not experience stress during the trial. The present study, however, did not evaluate the progeny chicks in term of ascites incidence. Application at the farm level requires further substantiation of the present findings, with an eye to immune- and growth-associated effects in progeny broilers.
Published data on the beneficial effect of short-term administration of thyroxine (T4) in broiler breeder hens to reduce the ascites incidence in their progeny chicks raises the question as to what extent might the long-term maternal administration of T4 affect the blood hematological and biochemical attributes in breeder hens. A total of 70 broiler breeder hens (47-wk-old) were randomly allotted to control or thyroxine treated (T4) groups. Pure T4 (0.3 mg/bird per day) was orally administered to T4 birds for 14 successive weeks, whereas the control group received the drinking water only. Blood samples were obtained from the brachial vein prior to the initiation of the trial as well as weeks 50, 53, 55, 57, 59, and 61 of age. Body weight was decreased but egg production was not affected by T4 treatment. Plasma concentration of T4, but not triiodothyronine (T3), was increased in T4-treated hens (P < 0.05). The total number of leukocytes and erythrocytes were also higher in T4 birds. A significant effect of time was observed for erythrocyte number and plasma cholesterol concentration (P < 0.05). The long-term administration of T4 did not affect the concentrations of serum calcium and plasma total protein, albumin, globulin, cholesterol, triglyceride, high density lipoprotein, low density lipoprotein, very low density lipoprotein, alanine amino transferase, and aspartate amino transferase (P > 0.05). However, serum concentrations of phosphorus, glucose, and alkaline phosphatase were higher in T4 hens as compared to their control counterparts. In spite of differences in circulatory concentrations of a number of traits between the experimental groups, the recorded values were within their reference ranges. Therefore, the administration of T4 for an extended period of time had no apparent adverse effect on the clinical profile in subjected hens, which may practically support the implementation of this preventative treatment as an approach to decrease the ascites incidence; however, a lower incidence rate in the progeny chicks produced from hens receiving T4 for long-term periods of time remains to be elucidated.
