Table 2.
Effects of embryonic thermal manipulation (ETM) and in ovo feeding (IOF) of r-aminobutyric acid (GABA) (G10) on rectal temperature (RT) of broilers exposed to heat stress (HS).
| Days of HS | CON | Treatments | Total | ||||
|---|---|---|---|---|---|---|---|
| CON | CON | – | – | – | |||
| G10 | – | – | G10 | – | G10 | ||
| TM | – | – | – | TM | + TM | ||
| HS | – | + HS | + HS | + HS | + HS | ||
| Day 1 | 41.4 ± 0.2 | 43.0 ± 0.4 | 43.5 ± 0.2 | 43.6 ± 0.4 | 43.7 ± 0.4 | 43.0 ± 0.2A | |
| Day 3 | 41.5 ± 0.1 | 42.5 ± 0.1 | 42.5 ± 0.1 | 42.7 ± 0.0 | 42.8 ± 0.1 | 42.4 ± 0.1B | |
| Day 5 | 41.4 ± 0.2 | 43.1 ± 0.2 | 42.7 ± 0.2 | 42.8 ± 0.1 | 43.2 ± 0.2 | 42.6 ± 0.1B | |
| Day 7 | 41.3 ± 0.1 | 43.1 ± 0.2 | 42.9 ± 0.1 | 43.0 ± 0.2 | 43.3 ± 0.4 | 42.7 ± 0.2AB | |
| Total | 41.4 ± 0.1a | 42.9 ± 0.1b | 42.9 ± 0.1b | 43.0 ± 0.1b | 43.3 ± 0.2b | NA | |
| P-value | |||||||
| Treatment (T) | < 0.001 | ||||||
| Day (D) | < 0.001 | ||||||
| T × D | 0.281 | ||||||
| Contrast | CON + HS vs G10 + HS and G10 + TM + HS | CON + HS vs TM + HS and G10 + TM + HS | |||||
| Day 1 | 0.143 | 0.121 | |||||
| Day 3 | 0.109 | 0.015 | |||||
| Day 5 | 0.445 | 0.609 | |||||
| Day 7 | 0.862 | 0.755 | |||||
The treatments are described as follows: CON chicks hatched from control eggs without in ovo injection and incubated at standard temperature, CON + HS chicks hatched from control eggs without in ovo injection, incubated at standard temperature but exposed to HS, G10 + HS chicks hatched from eggs injected at 17.5 days of incubation with 0.6 mL of 10% GABA dissolved in distilled water and exposed to HS, TM + HS chicks hatched from thermally manipulated eggs exposed to 39.6 °C for 6 h daily from embryonic day (ED) 10 to 18 and exposed to HS, G10 + TM + HS chicks hatched from eggs that received both previous treatments during incubation and exposed to HS. Data show mean ± SEM (n = 5). Means bearing different superscripts indicate significant differences by day (A.B) and treatment (a,b) effect (P < 0.05).