Abstract
The objective of this study was to determine the effects of dietary betaine supplementation on growth performance, carcass characteristics, rectal temperature, respiration rate and immune response of growing rabbits under high ambient temperature. A total of 120 weaned New Zealand White male rabbits, 6
weeks old, were randomly divided into five experimental treatments (24 each). Animals were fed
ad libitum the basal diet supplemented with 0 (control), 250, 500, 750 and 1000
mg betaine/kg diet from 6 to 12
weeks of age. Animals were provided with water freely. The average daily temperature and relative humidity inside the rabbitry were 30.3
±
0.9
°C and 76.2
±
2.5%, respectively. Under heat stress conditions, diet significantly increased the body weight and hot carcass weight and significantly reduced the feed conversion. Dietary 1000 and 750
mg betaine/kg increased (
P
<
0.05) final body weights (2529.1 and 2418.5
g, respectively) compared with the control (2110.3
g). Betaine supplementation ameliorated some of the adverse effects of heat stress on immune responsiveness, rectal temperature and respiration rate. Dietary 250, 500, 750 and 1000
mg betaine/kg led to a decrease in rectal temperature (40.03, 39.85, 39.63 and 39.53
°C, respectively) compared with the control (40.20
°C). The inclusion of 1000
mg betaine/kg in the growing rabbits' diets nearly doubled the humoral and immune responses compared to the controls (
P
<
0.05) and significantly reduced rectal temperature and respiration rate. Serum T3, T4, total protein, globulin and total lipids were significantly increased while serum glucose concentration was significantly decreased due to dietary betaine. In conclusion, supplemental dietary betaine enhanced growth performance and humoral and cell-mediated immunity as well as reduced rectal temperature and respiration rate in growing rabbits subjected to heat stress. From an economic point of view, high levels of betaine are not recommended because betaine is reasonably effective at lower, less expensive, doses.