ABSTRACTThree studies were carried out to investigate the response of broiler chickens fed betaine hydrochloride supplemented diets under dexamethasone induced stress conditions. The first experiment was conducted using 240 day-old Arbor acre broiler chickens. There were four treatments with three replicates (n = 20 birds/rep) to which concentrations of dexamethasone at 0, 1, 2 and 3 mg/L of water were administered daily. Results indicated a decrease (P > 0.05) in rectal temperature and increase (P > 0.05) in respiratory rate with increasing dose of dexamethasone. Birds receiving 0 mg dexamethasone had higher (P < 0.05) final body weight, daily weight gain, daily feed intake and feed conversion ratio. Corticosterone and thyroxine levels were significantly (P < 0.05) increased with an increase in dose of dexamethasone. Carcass cut weight of thigh and drumstick were significant (P < 0.05) with increasing dose of dexamethasone. Liver weights were higher (P < 0.05) in the dexamethasone groups. Dexamethasone increased tibia weight, length, and weight/length index and robusticity index significantly (P < 0.05). Villus height was higher (P < 0.05) in the groups containing dexamethasone compared with the control. Feed intake, rectal temperature and respiratory rate were good predictors of final weight. The second experiment was conducted using 240 day-old Arbor acre broiler chickens. There were four treatments with three replicates (n= 20 birds/rep) to which concentrations of dexamethasone at 0, 1, 2 and 3 mg/L of water were administered daily. All dexamethasone treated birds were fed 0.15% betaine HCl in their diets. Results indicated a decrease (P > 0.05) in rectal temperature with increasing dose of dexamethasone. Birds receiving 0 mg dexamethasone had the highest (P < 0.05) final body weight, average daily weight gain, average daily feed intake and feed conversion ratio. Thigh and drumstick weights rose significantly (P < 0.05) with increasing dose of dexamethasone. Betaine HCl effect on tibia weight, length, and weight/length index were significant (P < 0.05) with the control group performing better than the betaine treated groups. Feed intake, rectal temperature and respiratory rate were good predictors of final weight. The third experiment was conducted using 300 day-old Arbor acre broiler chickens. There were five treatments with three replicates (n= 20 birds/rep) made up of a treatment containing no dexamethasone and no betaine serving as the control. Another treatment was fed 0.30% betaine only supplemented diets, with the other three treatments given daily dexamethasone concentrations at 1, 2 and 3 mg/L of water, respectively. All dexamethasone treated birds were fed 0.30% betaine HCl in their diets. Results indicated a decrease (P > 0.05) in rectal temperature and respiratory rate with increasing dose of dexamethasone, especially with the betaine only group. Birds in the control and betaine only diets had significantly (P < 0.05) higher final body weight, daily weight gain and feed conversion ratio. Haematological indices were significantly (P < 0.05) increased for packed cell volume, heterophil, lymphocyte counts and hetrophil-lymphocyte ratio. Heart weight was significantly (P < 0.05) higher and the betaine only group had the least weight. Betaine increased tibia weight, length and weight/length index and ash was significantly (P < 0.05). Bursa weight was significantly (P < 0.05) higher with the 3 mg treated group having the least weight. Crypt depth was significant (P < 0.05) with the betaine-containing groups having higher crypth depth. The results showed that feed intake, rectal temperature and respiratory rate were good predictors of final weight. It was concluded that dexamethasone-induced stress had negative effects on broiler performance, organs, and tibia and blood compositions. Betaine HCl had positive effects on broiler performance, serum parameters, carcass cuts, viscera and immune organs. Thermoregulatory parameters with growth performance indices were good predictors of final weight of broiler chickens
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