|CHAPEL, NICHOLE - Purdue University|
|BYRD, CHRISTOPHER - Purdue University|
|LUGAR, DREW - Purdue University|
|MORELLO, GABRIELA - Purdue University|
|BAUMGARD, LANCE - Iowa State University|
|ROSS, JASON - Iowa State University|
|SAFRANSKI, TIM - University Of Missouri|
|LUCY, MATTHEW - University Of Missouri|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2017
Publication Date: 7/18/2017
Citation: Chapel, N.M., Byrd, C.J., Lugar, D.W., Morello, G.M., Baumgard, L.H., Ross, J.W., Safranski, T.J., Lucy, M.C., Johnson, J.S. 2017. Determining the effects of early gestation in utero heat stress on postnatal fasting heat production and circulating biomarkers associated with metabolism in growing pigs. Journal of Animal Science. doi: 10.2527/jas2017.1730.
Interpretive Summary: Elevated core body temperatures in gestating pigs can have lasting effects on offspring development and future productivity. Specifically, in utero heat-stressed pigs have an increase in teratogenic tendencies (i.e., reduced head size, organ weights), as well as reduced feed efficiency, carcass gain efficiency, and altered nutrient partitioning during the finishing phase resulting in enhanced adipose accretion rates at the expense of lean tissue. Furthermore, we have determined that basal core body temperature ‘set-point’ is permanently elevated for in utero heat-stressed pigs during the growing-finishing phase of production, regardless of changes in ambient temperature. Previously, we suggested that the in utero heat stress induced increase in basal core body temperature ‘set-point’ is a consequence of increased metabolic heat production. Therefore, study objectives were to determine the effects of in utero heat stress on fasting heat production and circulating blood biomarkers associated with metabolism in growing pigs. Based on our previous observations of increased core body temperature ‘set-point’, we hypothesized that in utero heat-stressed pigs would have an increase in fasting heat production and associated blood biomarkers during the growing phase of production compared to their in utero thermoneutral counterparts. As a result of this study, we determined that fasting heat production per kilogram of body weight was increased by 16.5% in the in utero heat-stressed pigs compared to the in utero thermoneutral controls. In addition, circulating levels of triiodothyronine (active thyroid hormone) were 19.5% greater in the in utero heat-stressed pigs compared to the in utero thermoneutral pigs, and this may be one mechanism by which fasting heat production is increased in in utero heat-stressed pigs. To conclude, the increase in fasting heat production may have implications towards postnatal production efficiency in pigs gestated during hot summer months.
Technical Abstract: The study objective was to determine the effects of in utero heat stress (IUHS) on postnatal fasting heat production (FHP) in growing pigs. Based on our previous observation of increased postnatal core body temperature ‘set-point’ in IUHS pigs, we hypothesized that FHP would be greater during postnatal life. Pregnant first parity gilts were exposed to thermoneutral (TN; n = 4; 17.8 ± 0.1°C) or heat stress (HS; n = 4; cyclical 28 to 38°C) conditions from d 30 to 60 of gestation. At weaning (21 d of age), two median weight male pigs (1 barrow and 1 boar) were selected from each litter [n = 8 in utero thermoneutral (IUTN) and 8 IUHS pigs], and then housed in TN conditions (22.3 ± 0.1°C). Blood samples were collected at 8, 9, and 10 wks of age to analyze thyroxine (T4) and triiodothyronine (T3) concentrations. Pigs were acclimated to an indirect calorimeter for 1 wk prior to testing. At 12 wks of age pigs were fasted for 24 h and indirect calorimetry was performed on individual pigs over a 23 h testing period to determine FHP and the respiratory quotient (RQ) in three intervals (0900-1700 h, 1700-0000 h, 0000-0800 h). Body weight was determined before and after testing and was similar for all pigs (P = 0.77; 37.0 ± 0.5 kg BW). Data were analyzed using PROC MIXED in SAS 9.4. No boar versus barrow differences were observed with any analysis. Overall, FHP/kg BW and FHP/kg BW0.60 were greater (P < 0.04; 16.5 and 12.1%, respectively) in IUHS compared to IUTN pigs. Fasting heat production per kg BW and FHP/kg BW0.60 were greater (P < 0.01; 19.8 and 19.8%, respectively) from 0900-1700 h compared to 1700-0000 h and 0000-0800 h, and greater (11.6 and 10.9%, respectively) from 1700-0000 h compared to 0000-0800h. Respiratory quotient did not differ by in utero treatment (P = 0.51; 0.72 ± 0.01); however, RQ was increased (P < 0.01; 13.0%) from 1700-0000 h compared to 0900-1700 h and 0000-0800 h. No other FHP and RQ differences were detected. Although no in utero treatment differences were observed for T4 (P = 0.11; 52.2 ± 6.2 ng/mL), overall T3 was greater (P = 0.04; 19.5%) in IUHS versus IUTN pigs. In summary, FHP and circulating T3 were increased in IUHS pigs and this may have implications towards postnatal production efficiency in pigs gestated during hot summer months.