A total of 80 specific-pathogen-free (SPF) Sprague–Dawley rats weighing (180 ±10) g were maintained in a standard animal house with an ambient temperature of (25 ±1) C and relative humidity of (50 ± 5)% under a 12 h/12 h light/dark cycle. Animals were observed for 7 days before mating (female:male = 1:1). Occurrence of copulatory plug was used to indicate successful mating and day 0 of pregnancy. Pregnant rats were individually housed during gestation and provided standardized pellet food and water ad libitum.