Heat stress is detrimental across many, if not most aspects of animal agriculture. Heat stress can have direct effects on the animal, effects on their environment and effects on the feedstuffs they consume. The work presented here will address direct effects on the animal (using dairy cattle) and effects on their feed (using pigs). Dairy cattle were chosen to study direct effects on the animal because they exhibit unique metabolic adaptions during heat stress. One adaptation of interest is a heat-stress induced state of hyperinsulinemia and hypoglycemia while self-limiting feed intake. In regards to effects on feedstuffs, high ambient temperatures are associated with elevated concentrations of mycotoxins in cereal grains. Mycotoxins are problematic because, at sufficient concentrations, they induce specific, toxic effects. Zearalenone is one such mycotoxin that is particularly problematic for swine, as it is a potent phytoestrogen. As such, it can reduce productivity by disrupting reproductive processes. Although these topics are disparate, the overarching goal of this work is to improve agricultural animal productivity during periods of heat stress. Overall, the three objectives of this thesis were to: 1) isolate the production-related effects of hyperinsulinemia with hypoglycemia from heat stress, 2) determine whether glucose supplementation during heat stress could improve or rescue milk production during heat stress, and finally, 3) investigate reproductive tract morphology following different durations of zearalenone consumption in peri-pubertal gilts. The first experiment compared the effects of thermoneutral, thermoneutral + hyperinsulinemic-hypoglycemic clamp (HHC), environmental heat stress, and heat stress + euglycemic clamp (EC) on milk production, milk components, and circulating glucose concentrations. Milk production, as expected, did decrease under heat stress when compared to thermoneutral conditions. Milk production during the HHC was intermediate, which was likely the result of the induced hypoglycemia. Interestingly, the glucose infused during the EC did not improve milk production over heat stress. Baseline blood glucose concentrations declined during heat stress, and those concentrations measured during the thermoneutral period were correlated with the change in blood glucose (from thermoneutral to heat stress). In the second experiment, zearalenone (6 mg) was fed to peri-pubertal gilts for 0, 7 or 21 days. Gilts were monitored daily for observable signs of zearalenone toxicity, and tissues were harvested after 21 days of treatment. No differences in the lengths or weights of any portions of the reproductive tract were observed. Likewise, there were no differences in body weight, carcass weight, dressing percent or liver weight. In summary, heat stress has varied effects on livestock production and the ultimate outcomes are not always predictable. Future work will be aimed at defining the factors that contribute to this variability. / Master of Science / Heat stress can have direct and indirect consequences that affect the efficiency of livestock production. The overall objective of this work is to improve agricultural animal productivity during periods of heat stress. The first study compared milk production, milk characteristics and blood glucose concentrations in the presence or absence of heat stress. Aspects of productivity were also measured when insulin and/or glucose were administered in a manner that mimicked either heat stress or thermoneutral conditions. Heat stress did cause a decline in circulating blood glucose, feed intake, and milk production. Infusion of insulin during thermoneutral conditions caused a decline in milk production but not in feed intake. As a way to compensate for the naturally low circulating glucose during heat stress, glucose was infused during heat stress in the last portion of the experiment. Simply infusing glucose to return the animal to pre-heat stress concentrations did not improve milk production. Further work is needed to determine factors (other than feed intake) that limit milk production during heat stress. The second study investigated whether the mycotoxin, zearalenone, affects the size or weight of the pig's reproductive tract. If differences existed, they would be indicative of potential problems with the function of those tissues. Young female pigs consumed zearalenone for 0, 7 or 21 days and tissues were evaluated 21 days after the experiment began. No changes in tissue weights or lengths were observed. Future experiments should be aimed at determining the concentration and duration of exposure at which zearalenone becomes problematic for young, female pigs.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/107483 |
| Date | 07 January 2022 |
| Creators | Stewart, Jacob Wesley |
| Contributors | Animal and Poultry Sciences, Rhoads, Michelle, Clark-Deener, Sherrie, Rhoads, Robert P. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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