Abstract
Simple SummaryPhysiological responses to heat stress are affected by breed. Therefore, crossbreeding genetically improved lines with tropically adapted breeds of pigs may be a strategy to attenuate the impact of high ambient temperatures on pig production. Although some studies have evaluated thermotolerance in tropically adapted breeds, it is not yet clear to which extent improved tolerance to heat stress is a consequence of a greater ability to equilibrate thermogenesis and thermolysis, or if it is a consequence of decreased growth performance. Although there was no interaction for performance, thermoregulatory responses, and blood parameters, our results evidenced that ambient temperature effects on carcass parameters were modulated by the pigs’ genotype. Because protein deposition significantly decreased in response to high ambient temperature in commercial pigs, and was not affected by ambient temperature in Piau crossbred pigs, our study suggests increased thermotolerance of Piau crossbred pigs.The study aimed at evaluating the effects of high ambient temperature (HT: 30 °C) on the thermoregulatory responses and performance of commercial and Piau crossbred (Brazilian Piau breed sires × commercial genotype dams) growing pigs. Commercial and Piau crossbred pigs were reared under thermoneutral (TN: 22 °C) or HT conditions during a 14-day experimental period. Feeding (daily) and animals (beginning and end) were weighted to obtain performance parameters. Skin and rectal temperatures, respiratory rate, and blood parameters were also measured. At the end of the trial (day 15), the animal’s backfat thickness (BF) and loin eye area (LEA) were measured. No interaction (p > 0.05) between the genetic group and ambient temperature was observed for any performance trait. Irrespective of ambient temperature, Piau crossbred pigs had a similar feed intake (ADFI, 2615 g/day, on average; p > 0.05), lower daily weight gain (ADG, −234 g/day; p < 0.01), and a higher feed conversion ratio (FCR, +0.675 g/g; p < 0.01). There was interaction (p = 0.01) between genotype and ambient temperature for the LEA that decreased significantly in response to HT in commercial pigs (−6.88 cm2) and did not differ in response to ambient temperature in Piau crossbred pigs (29.14 cm2, on average; p > 0.05). Piau crossbred pigs had greater BF (+7.2 mm; p < 0.01) than commercial pigs. Regardless of the genetic group, exposure of pigs to HT resulted in decreased ADFI (−372 g/day; p < 0.01), ADG (−185 g/day; p < 0.01), and a higher FCR (+0.48 g/g; p = 0.01). Ambient temperature did not affect lipid deposition. Pigs at HT had an increased respiratory rate (+38 bpm; p < 0.01) and a long-lasting increase in skin and rectal temperatures compared to TN pigs. Total concentrations of triiodothyronine (T3) and thyroxine (T4) were not affected by ambient temperature in commercial pigs, whereas Piau crossbred pigs kept at 30 °C had a transient decrease in both hormones at day 2 (p < 0.01). Serum cortisol concentrations were not affected (p > 0.05) by genotype nor ambient temperature. In summary, Piau crossbred pigs had lower efficiency using nutrients for growth in association with increased lipid deposition when compared to commercial pigs. In response to HT, commercial pigs had a decreased LEA, whereas no effect was observed for Piau crossbred pigs. Apart from that, commercial and Piau crossbred pigs had a similar magnitude of thermoregulatory responses activation in response to HT, evidencing their innate survival-oriented function.
Highlights
Ambient temperatures above the thermoneutral zone for growing pigs (15 to 25 ◦ C) [1]can be a source of extensive financial loss in production systems by affecting the performance and welfare of pigs [2,3,4]
Animals were evaluated at a similar initial body weight (BW) and age that consisted of 71.2 ± 1.94 kg BW and 108 ± 7 days old for commercial genotype pigs, and
Piau breeds pigs hassuggested been suggested as a strategy to thermotolerant select thermotolerant genotypes crossbred pigs had growthgrowth performance
Summary
Can be a source of extensive financial loss in production systems by affecting the performance and welfare of pigs [2,3,4]. Renaudeau et al [5] reported that physiological responses to heat stress are affected by the breed of pig. According to Carabaño et al [7], heat-tolerant animals are those that, under high ambient temperature, maintain homeothermy by balancing heat production and dissipation without productive and reproductive losses. Teixeira et al [8] suggested in a previous study a greater heat-tolerance in Piau pigs than commercial pigs, due to the decreased magnitude of feed intake impairment and preserved feed conversion rate of the native Brazilian breed at high ambient temperatures. Rosé et al [9] and Gourdine et al [3] showed genetic variation in the thermotolerance of pigs, suggesting an improvement in this trait by genetic selection
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