Effects of Cysteamine on Serum Levels of Cortisol,T3,T4 and IL-2 in Pre- and Post-Weaning Piglets

Eighteen litters of newborn piglets were divided randomly to control and treatment groups. From 12 days of age,piglets in treatment group were fed starter diet supplemented with 120 mg/kg cysteamine (CS),while the control group were fed basal diet. Piglets were weaned at 35 days of age (D35) in both groups. 6 piglets from each group were slaughtered on D28 (7 d before weaning),D35 (weaning day),D36.5,D38,D42 and D45 (36 h,72 h,7 d and 10 d after weaning),respectively. Radioimmunoassay was applied to determine the serum levels of cortisol,T3,T4 and IL-2. The results indicated that: (1) Cortisol level was stable before weaning in control group,followed by an abrupt increase on D36.5,and was restored to the level of weaning on D42. In treatment group,cortisol level exhibited a tendency of increase from D35 to D36.5,and was restored and stabilized at the level of weaning from D38 onwards. T3 level in control group was higher on D36.5 than that on D28,but there were not significant differences among other age groups. In treatment group,T3 level kept stable throughout the period of investigation. For control,T4 level increased on D36.5 and returned to the weaning day level on D38. T4 level was stable from weaning day to 45 days in treatment group. IL-2 level was kept stable in both groups until D45 when a significant increase was observed. (2) Cortisol level in treatment group decreased markedly by 30% compared with control group on D36.5. CS treatment increased both T3 and T4 levels by 49.2% and 31% on D35, and 38.6% and 45.8% on day 45 (P<0.05),respectively. No significant differences were observed on other ages for T3 and T4,although a tendency of increase was shown in treatment group. IL-2 concentration in treatment group increased by 22.1% (P<0.05),12.6% (P<0.05) and 17.8% (P<0.05) on D36.5,D38 and D45,respectively. The results suggested that cysteamine might help to enhance the resistance of the piglets to weaning stress through increased serum levels of T3,T4 and IL-2,and decreased cortisol secretion during pre- and post-weaning period.