Effect of high ambient temperature and genotype on thermoregulatory responses and gene expression in various tissues in growing pigs
Résumé
Heat stress (HS) in pig production is a critical problem in
temperate countries during summer but also in tropical areas
where pig production dramatically increased over the past 2
decades. Physiological and metabolic adjustments resulting
from the thermoregulatory responses to HS have negative consequences
on pig productivity and health. The objectives of this
experiment were to improve knowledge on the mechanisms
underlining heat tolerance by comparing thermoregulatory
responses in 3 different pig genotypes (G). This experiment
was performed on a total of 36 castrated male pigs: 1 genotype
sensitive to HS (Large White [LW]), 1 genotype tolerant to
HS (Créole [CR]), and a cross between LW and CR pigs. Pigs
were housed at 24°C for 10 d and thereafter at 32°C for 5 d.
The temperature (T) transition from 24 to 32°C occurred on d
0 at a constant rate of 2°C/h. Pigs had free access to water and
feed. Body T and respiratory rate were measured on d –7, –4,
and –3 at 24°C and on d 1, 2, 3, 4, and 5 at 32°C. Eighteen pigs
(6 per G) were slaughtered on d –2 (before the T transition) and
on d 5. At slaughter, blood and 3 tissue samples (backfat [BF],
longissimus dorsi [LD], and liver [LI]) were collected. A transcriptome
analysis was performed on blood and tissues using
a semicustom 60K microarray (GPL16524). Blood hormones
and metabolites were also measured. The T × G interaction
was not significant (P > 0.05) for feed intake and thermoregulatory
responses (except for skin T). Whatever the G, HS had
a significant negative effect on voluntary feed intake (–200 g/d
on average). The T increase resulted in an increased rectal and
skin T and respiratory rate within the first 24 to 72 h of exposure
and in a subsequent recovery phase characterized by
a rapid decrease of these thermoregulatory responses. Plasma
glucose, lactate, glycerol, and albumin concentrations were
significantly reduced under HS but creatine concentration increased
at 32°C. Thyroid hormone (triiodothyronine and thyroxine)
concentrations were reduced at 32°C. Irrespective to
the G, a considerable number of differentially expressed genes
(false discovery rate < 0.05) were found by comparing blood
(13,807), LD (6,261), BF (5,236), and LI (435) samples collected
at 24°C with those collected at 32°C. A first functional
analysis revealed that most of the significantly differentially
expressed genes especially in BF and LD were involved in the
regulation of the oxidative phosphorylation pathway.