Hepatic corticosteroid-binding globulin (CBG) messenger RNA expression and plasma CBG concentrations in young pigs in response to heat and social stress1,2

Abstract

Plasma cortisol, porcine corticosteroid-binding globulin (pCBG), hepatic CBG expression, and other physiological and behavioral measures of stress were studied in pigs in response to elevated temperature in conjunction with establishing a social hierarchy. Twenty-four crossbred pigs were weaned at 25 d of age (three or six pigs from six sows) and housed in littermate groups at 23 +/- 2 degrees C. At 57 d of age (d 0), animals were weighed and placed under general anesthesia for collection of blood (10 mL) and liver (approximately 100 mg) samples. On d 1, three unacquainted pigs of similar BW (23 +/- 1 kg) from different litters were allotted to each of eight nursery pens within two environmentally controlled rooms (12 pigs per room). From d 1 to 7, one room was maintained at 23 +/- 2 degrees C (CON) and the other at 33 +/- 2 degrees C (HEAT). Both rooms were kept at 23 +/- 2 degrees C from d 8 to 14. Animals were videotaped for 72 h beginning on d 1 and 8 to document behavioral changes in response to room temperature. The social hierarchy of pigs within each pen was based on fight activity recorded on d 1 to 3. Blood and liver tissue were collected again on d 7 and 14. The ADG for HEAT pigs increased (P < 0.05) over d 8 to 14 compared with d 1 to 7. In contrast to CON pigs, HEAT pigs displayed increased (P < 0.01) drinking but decreased feeding and lying in contact with other pigs from d 1 to 3, and similar drinking and feeding but increased (P < 0.01) lying with contact behaviors from d 8 to 10. With the exception of subordinate pigs exhibiting less (P < 0.05) frequent standing/walking behavior than the dominant or intermediate pigs on d 1 to 3, frequency of behaviors for both recorded time periods did not differ among pigs due to social status, regardless of treatment. The concentration of plasma haptoglobin in HEAT pigs on d 7 compared with d 0 increased (467 vs. 763 mg/L; P < 0.05), whereas cortisol and pCBG decreased (274 vs. 235 nmol/L and 11.4 vs. 9.9 mg/L, respectively; P < 0.05) as a result of treatment. The free cortisol index (total cortisol/pCBG) was greater (P < 0.05) in HEAT pigs on d 14 than on d 0 or 7. Hepatic CBG mRNA level was not affected by treatment. On d 14, HEAT pigs had plasma cortisol, pCBG, and haptoglobin concentrations similar to those of CON pigs. These results indicate that measured behavioral and physiological responses were not related to social status, and decreased circulating levels of cortisol and pCBG in pigs following a 7-d exposure to elevated temperature may not be determined by hepatic CBG mRNA expression.

The cortisol response to ACTH in pigs, heritability and influence of corticosteroid-binding globulin

“…Apart from immune stimuli, haptoglobin can also be released in response to other stressors like hot ambient temperature (Heo et al, 2005), transport (Piñeiro et al, 2007b) or unpredictable feeding practices (Piñeiro et al, 2007a). In the present study, haptoglobin levels were unrelated to cortisol levels.…”

“…It is noteworthy that CBG, which is a protein of hepatic origin like positive and negative acute phase proteins, displays reduced concentrations in cases of inflammatory conditions (Garrel, 1996), and thus varies in the opposite way to haptoglobin. These opposite variations have also been observed in pigs, in inflammatory (Carroll et al, 2003) as well as in other stressful conditions (Heo et al, 2005;Piñeiro et al, 2007a and2007b).…”

Changes in endocrine and neurochemical profiles in neonatal pigs prenatally exposed to increased maternal cortisol

“…Therefore, it is assumed that the decrease of CBG levels in newborn piglets may result from direct inhibition of fetal hepatitic CBG biosynthesis by elevated maternal cortisol exposure during both mid-and late gestation. This decrease in CBG and the unchanged total cortisol levels indicate a higher amount of biologically available free cortisol, which is also found in animals under conditions of chronic stress (Kim et al 1999, Stefanski 2000, Heo et al 2005.…”

Physiological responses of growing pigs to high ambient temperature and/or inflammatory challenges

“…Conversely, some studies have reported a decrease in plasma concentration of cortisol in pigs exposed to hot conditions. Heo et al (2005) observed low circulating levels of cortisol in 20-30 kg BW pigs exposed to 32 °C. In addition, Kim et al (2009) reported that cortisol levels were 22% lower in growing pigs exposed to 40 °C when compared with pigs kept at 24 °C.…”