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The study objectives were to test the hypothesis that heat stress (HS) during gestational development alters postnatal growth, body composition, and biological response to HS conditions in pigs. To investigate this, 14 first parity crossbred gilts were exposed to one of four environmental treatments (TNTN, TNHS, HSTN, or HSHS) during gestation. TNTN and HSHS dams were exposed to thermal neutral (TN, cyclical 18–22°C) or HS conditions (cyclical 28–34°C) during the entire gestation, respectively. Dams assigned to HSTN and TNHS treatments were heat-stressed for the first or second half of gestation, respectively. Postnatal offspring were exposed to one of two thermal environments for an acute (24 h) or chronic (five weeks) duration in either constant TN (21°C) or HS (35°C) environment. Exposure to chronic HS during their growth phase resulted in decreased longissimus dorsi cross-sectional area (LDA) in offspring from HSHS and HSTN treated dams whereas LDA was larger in offspring from dams in TNTN and TNHS conditions. Irrespective of HS during prepubertal postnatal growth, pigs from dams that experienced HS during the first half of gestation (HSHS and HSTN) had increased (13.9%) subcutaneous fat thickness compared to pigs from dams exposed to TN conditions during the first half of gestation. This metabolic repartitioning towards increased fat deposition in pigs from dams heat-stressed during the first half of gestation was accompanied by elevated blood insulin concentrations (33%; P = 0.01). Together, these results demonstrate HS during the first half of gestation altered metabolic and body composition parameters during future development and in biological responses to a subsequent HS challenge.

Ewes of three genotypes (Hampshire, n = 59; Rambouillet, n = 36; crossbred, n = 57) were used to determine the efficiency of melengestrol acetate (MGA) and(or) PG-600 (a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin) in inducing fertile estrus in seasonally anestrus ewes. Ewes were assigned randomly, within genotype, to treatments in a 2 x 2 factorial arrangement. Treatments were control, .125 mg of MGA given twice per day for 9 d (MGA), a single 5-mL injection of PG-600 (PG-600), and the combination of treatments MGA and PG-600 (MGA/PG-600). Feeding of MGA began on May 14, 1990, and ended on May 23. Injections of PG-600 were given immediately after the last feeding of MGA or vehicle on May 23. All ewes were exposed to fertile, brisket-painted rams on May 24 (d 0) for 40 d. Ewes were checked for estrus twice daily for 9 d. Laparoscopy was performed, to assess ovulation rate (OR), on d 6 for ewes that were not detected in estrus and on d 12 for ewes that exhibited estrus. Percentage of ewes mated was increased by MGA (P less than .001). Ovulation rate of ewes exposed to rams was increased by PG-600 (P less than .01) and this effect was enhanced by MGA (P less than .05), whereas MGA alone tended to decrease OR (P less than .10). Melengestrol acetate decreased the interval to lambing by 6.5 d (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Correlations among ages and weights at vaginal opening (AVO, WVO), positive vaginal smear (AVE, WVE), and copulatory plug (AVP, WVP) were determined using 623 mice. Two additional experiments were conducted to determine association of each with serum concentrations of estradiol and incidence of ovulation. Female mice were weaned at 21 days and 24 days of age were assigned randomly to mate with males. Mice were checked daily to determine AVO, AVE, and AVP. Mice were weighted weekly and WVO, WVE, and WVP were obtained by interpolation. Genetic correlations among ages and weights were small and mainly negative. Phenotypic correlations were small to moderate and mainly positive. Genetic correlations among the three measures of age and among the three measures of weight were moderate to high and positive; respective phenotypic correlations were somewhat smaller. In experiment 2, mice were checked daily for the three reproductive measures and bled at vaginal opening (n = 23), positive smear (n = 18), or copulatory plug (n = 19). Serum was assayed for estradiol via radioimmunoassay. No differences were found among the three indicators (p = 0.34). In experiment 3, mice were randomly assigned to be killed after detection of vaginal opening, positive smear, or copulatory plug. Oviducts were removed and flushed with saline to determine presence of ova. A greater (p < 0.05) proportion of mice had ovulated when killed after detection of copulatory plug (20/22) than after positive smear (4/27), and the proportion was greater after positive smear than after vaginal opening (0/14).(ABSTRACT TRUNCATED AT 250 WORDS)