Submitted to: Meeting Abstract
Publication Type: Abstract only
Publication Acceptance Date: 10/23/2013
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Economic losses to the livestock industry due to heat stress (HS) are estimated to be greater than $2.0 billion annually. HS morbidity is linked to disruption of normal intestinal tract (IT) absorptive and barrier functions, is often manifested as decreased performance; however, extreme HS can have long-term negative impacts or result in mortality. HS models often consist of constant exposure to high heat, unlike the cyclical heat pattern pigs are exposed to during production. In addition, knowledge regarding the effects of HS on specific and non-specific immune function in pigs is lacking. The goal of this study was to compare two HS models, constant heat (CH) versus variable heat (VH), in terms of health and performance statistics, IT histology, and specific and non-specific immune responses. Pigs were divided into three treatment groups (n=12/group) at weaning (21 days old): CH, VH, and control (C). The HS period started 4 weeks later and lasted for 7 days. CH pigs were subjected to 33 degree C during the entire HS period. VH pigs were subjected to a repeated cycle of 40 degree C for 5 hrs then 25 degree C for 19 hrs. C pigs were maintained at 25 degree C. Pigs in both HS groups were stressed by our criteria. Both CH and VH animals had lower ADG and ADFI and higher respiratory rates and skin and rectal temperatures during HS compared to controls. Further, HS pigs experienced disrupted specific and non-specific immune responses. Natural killer activity, a measure of non-specific immune function, was lower in VH animals compared to control. Only HS pigs had lymphoproliferative responses to a sonicate of 12 different bacterial species isolated from the IT mucosa of healthy pigs. These lymphoproliferative responses serve as an indicator of IT barrier disruption and a measure of specific immune function. IT barrier disruption is supported histologically by IT architectural changes including desquamation and lower villus height and crypt depth in the jejunum of HS pigs on days 1 and 3 of HS. Both CH and VH temperature stresses are acceptable models of HS in this age pig; the VH design is more representative of what the commercial pig experiences. Future studies will apply the VH design to optimize HS mitigation at the level of the IT in order to strategically reduce the burden of HS and to quicken recovery following a HS event.