Betaine and Antioxidants Improve Growth Performance, Breast Muscle Development and Ameliorate Thermoregulatory Responses to Cyclic Heat Exposure in Broiler Chickens

Abstract

Heat stress (HS) is an environmental stressor challenging poultry production and requires a strategy to cope with it. A total of 288-day-old male broiler chicks were fed with one of the following diets: basal diet, basal with betaine (BET), or with selenium and vitamin E (AOX), or with a combination of BET and AOX, under thermoneutral and cyclic HS. Results showed that HS reduced average daily feed intake (ADFI) (p = 0.01) and average daily gain (ADG) (p < 0.001), and impaired feed conversion ratio (FCR) (p = 0.03) during rearing period (0⁻42 day). BET increased ADG (p = 0.001) and decreased FCR (p = 0.02), whereas AOX had no effects. Breast muscle weight was decreased by HS (p < 0.001) and increased by BET (p < 0.001). Rectal temperature was increased by HS (p < 0.001) and improved by BET overall. Respiration rate was increased by HS (p < 0.001), but BET decreased it during HS (p = 0.04). Jejunum transepithelial resistance was reduced by HS and had no effect on permeability whereas BET increased jejunum permeability (p = 0.013). Overall, the reductions in ADG of broiler chickens during HS were ameliorated by supplementation with BET, with much of the increase in ADG being breast muscle.

Keywords: antioxidant; betaine; broiler; growth; heat stress.

Figure 1

Rectal temperature in chickens fed either a control diet (CON, filled square), the control diet plus betaine (BET, filled tringle), the control diet plus supplemental antioxidants (AOX, open square) or the control diet plus both BET and AOX (open tringle) under either thermoneutral (a,c) or cyclic heat stress (b,d). Panels (a,b) indicate the effect of time of day (TM) pooled across days of the experiment with the standard error of the difference for the interaction between TM, BET and AOX displayed on the data from the chicken receiving the control diet. Panels (c,d) indicate the effect of day of experiment pooled across time of day with the standard error of the difference for the interaction between day of experiment (DAY), BET and AOX displayed on the data from the chicken receiving the control diet. There were significant main effects of temperature (TEMP) (p < 0.001), DAY (p < 0.001) and TM (p < 0.001) and TEMP × AOX (p = 0.048), TM × DAY (p < 0.001), TEMP × TM (p < 0.001), DAY × TM (p < 0.001), TM × BET (p = 0.015), DAY × BET (p < 0.001), TM × DAY × BET (p = 0.040), DAY × TEMP × AOX (p < 0.001), DAY × BET × AOX (p < 0.001), and TM × DAY × TEMP × BET × AOX (p < 0.014) interactive effects. There were no other main or interactive effects (p < 0.05).

Figure 2

Respiration rate in chickens fed either a control diet (CON), CON plus betaine (BET), CON plus supplemental antioxidants (AOX) or CON plus both BET and AOX under either thermoneutral (TN) or cyclic heat stress (HS) at 12:00 h on day 41 of the experiment. Data are means with the standard error of the difference for the interaction between temperature (TEMP), BET and AOX. The p-values for the effects of TEMP, BET, AOX, TEMP × BET, TEMP × AOX, BET × AOX, and TEMP × BET × AOX were <0.001, 0.017, 0.16, 0.048, 0.24, 0.37, and 0.69, respectively.

Figure 3

Jejunum transepithelial electrical resistance (TER) in chickens under either thermoneutral (TN) or cyclic heat stress (HS) and fed either a control diet (CON), CON plus betaine (BET), CON plus supplemental antioxidants (AOX), or CON plus both BET and AOX.

Figure 4

Jejunum fluorescein isothiocyanate (FITC)-dextran (4 kDa) permeability in chickens under either thermoneutral (TN) or cyclic heat stress (HS) and fed either a control diet (CON), CON plus betaine (BET), CON plus supplemental antioxidants (AOX), or CON plus both BET and AOX.

Figure 5

Glutathione peroxidase activity (GPx) in chickens under either thermoneutral (TN) or cyclic heat stress (HS) and fed either a control diet (CON), CON plus betaine (BET), CON plus supplemental antioxidants (AOX), or CON plus both BET and AOX at day 21 and 42.