Thermogenic and digestive responses of ad libitum fed pigs to α2-adrenergic stimulation with guanfacin in different thermal environments

Abstract

Guanfacin, an α2-adrenoceptor agonist, reduces heat production in cold-stressed, but not heat-stressed animals. Growth rate, feed intake, metabolic rate, ileal and fecal digestibility were measured in 16 pigs, housed in neutral (20.4 ± 1.7°C), hot (32.7 ± 1.6°C) or cold (6.6 ± 1.4°C) environments. For ileal digestibility determination, pigs received 80 mg kg–1 d–1 followed by 3 × 40 mg kg–1 d–1 of guanfacin or saline, within their own environment, in a cross-over design. Fecal digestibility and heat production were measured over 7 d with treatments applied in a cross-over design of two periods. Oxygen consumption (VO2) was determined by open circuit respiration calorimetry. Cold-housed pigs had higher feed intakes (P < 0.05), but not growth rates, compared with those in the thermoneutral environment. Pigs in the hot environment had lower feed intakes, weight gains and heat production (P < 0.05) and higher rectal temperatures (P < 0.05) compared to those in the other two environments. Guanfacin did not reduce heat production in swine in any environment. Pigs in the cold and neutral environments had lower (P < 0.05) fecal dry matter (DM) digestibility. Pigs in the cold had lower fecal gross energy (GE) digestibility (P < 0.05) compared to those in the hot, and lower fecal crude protein (CP) digestibility (P < 0.05) compared to those in the neutral or hot environments, probably due to changes in digesta retention in the large intestine. Temperature did not affect ileal digestibility of DM, GE, CP and amino acids. Guanfacin did not affect fecal digestibility, but increased ileal DM and GE digestibility (P < 0.05) across all temperatures, possibly by affecting smooth muscle contraction and rate of passage. Increased ileal energy digestibility without a change in heat production suggests an improvement in utilization of DE in response to guanfacin. Key words: α2-adrenoceptor agonist, digestibility, pig, environment, heat production, ileum