Abstract #321

# 321
Chromium supplementation alleviates heat stress in growing pigs.
Fan Liu*1, Jeremy J Cottrell1, Danni Wijesiriwardana1, Fletcher W. Kelly1, Pietro Celi2,1, Brian J. Leury1, Frank R. Dunshea1, 1Facultry of Veterinary and Agricultural Sciences, the University of Melbourne, Parkville, VIC, Australia, 2Faculty of Veterinary Science, the University of Sydney, Camden, NSW, Australia.

Reduced insulin sensitivity is a characteristic of heat stress (HS) in pigs. Therefore the aim of the experiment was to investigate the effect of chromium (Cr) supplementation in ameliorating HS due to its properties augmenting insulin sensitivity. Thirty-six gilts (Large White × Landrace, 29 ± 4 kg) were randomly assigned to 2 diets containing 0 (control) or 3200 ppb Cr picolinate (400 ppb Cr). After 14 d supplementation pigs were allocated to 8 d thermoneutral (20°C; TN) or cyclic HS (8h/d 35°C) (n = 9/group). Production performance was recorded in the thermal exposure period. Respiration rate (RR) and rectal temperature (RT) were measured at 0900, 1300 and 1600h daily, and blood gas was measured on d 7. Area under the curve (AUC) of glucose and NEFA was studied in an intravenous glucose tolerance test (n = 6/group) on d 8. Data were analyzed by ANOVA in Genstat. In TN pigs fed Cr diet had higher ADFI (2.0 vs. 2.3 kg, P < 0.05), but ADG was not improved (0.63 vs. 0.69 kg, P = 0.26). Heat stress decreased ADFI by 35% and ADG by 84% (both P < 0.001) and no effect of Cr was observed. Heat stress increased RT (38.8 vs. 40.0°C, P < 0.001) and RR (34 vs. 155 breaths/min, P < 0.001). The increased RR led to reductions in blood CO2, bicarbonate and base excess in HS (all P < 0.05). Collectively the results indicate that heat treatment resulted in a “heat stressed” state. Besides, HS increased glucose and decreased NEFA AUC (both P = 0.05), suggesting reduced insulin sensitivity. Compared with control diet, Cr pigs had lower RT (40.2 vs. 39.9, P < 0.05) and RR (173 vs. 136, P < 0.01) under HS, indicating an amelioration in the level of HS experienced in Cr pigs. Chromium did not alter the glucose AUC in HS, although Cr reduced the glucose “basal to peak” increment in TN (4.15 vs. 2.55 mM, P < 0.05). Besides, Cr tended to increase NEFA recovery (20 to 90 min) rate and AUC in HS (both P = 0.09), indicating that Cr facilitated lipid mobilization in HS. In summary, pig growth performance was not improved by Cr during HS, possibly because of the severe reduction in ADFI. However, dietary Cr mitigated the physiological responses to HS, including lipid mobilization. Therefore, an inclusion of 400 ppb Cr may reduce HS in growing pigs.

Key Words: chromium, pig, insulin