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Effect of Elevated Ambient Temperatures on Puberty in Gilts¹

University of Missouri³, Columbia 65211

Abstract

Effects of elevated ambient temperature on puberty and related physiological responses were studied in 40 gilts. Group 1 (n = 20) gilts were born in September and Group 2 (n = 20) gilts were born in March. Gilts were placed in environmentally controlled chambers at 140 d of age. After a 10-d acclimation period at 20°C, 35% relative humidity (RH), and 12 h light (L)/12 h dark (D), gilts within each group were randomly assigned to one of two treatments: control (C; 15.6°C, 35% RH, 12 h L/12 h D) or heat stress (HS; 33.3°C, 35% RH, 12 h L/12 h D). Daily detection of estrus with a boar began at 180 d of age and continued for 50 d. All gilts not reaching puberty by 230 d of age received 1,000 IU pregnant mare serum gonadotropin (PMSG) and 7 d later were examined by laparotomy. Rectal temperatures (REC) and respiration rates (RESP) were taken twice daily. Food intake (FI) and water usage (WC) were recorded daily. Blood samples were collected weekly and BW recorded at 150, 190, and 230 d of age. No differences (P > .05) were observed due to season of birth. Heat-stressed gilts had greater (P < .001) REC and RESP and consumed more (P < .01) water than C gilts. Food intake and ADG were not different between treatments (P > .05). More gilts (P < .01) reached puberty by 230 d of age under C conditions (18/20) than under HS conditions (4/20). Average age at puberty for C gilts was 204.5 ± 5 d and 213.3 ± 9 d for HS gilts. Mean progesterone concentrations over the entire experimental period for C and HS gilts not reaching puberty by 230 d of age were .7 ± .3 and 1.4 ± .5 ng/ml, respectively. Gilts that were HS had a greater (P < .08) incidence of cystic follicles than C gilts (50% vs 0%) following PMSG injection. These results indicate that chronic exposure to elevated ambient temperatures delays puberty in gilts.

¹ Contribution from the Missouri Agric. Exp. Sta. Journal Series No. 10536.

² Present address: Dept. of Anim. Sci., North Carolina State Univ., Raleigh 27607.

³ Dept. of Anim. Sci.