Alternative Measures of Physiological Stress in Nursery Pigs and Broiler Chickens
Farm animals face a variety of stressors during commercial production practices, and economic necessities and ethical considerations require mitigation strategies to help animals cope with stressors that might otherwise reduce animal performance or lead to morbidity. In swine production, arguably the most stressful period of a pig’s life is the first several weeks following weaning (nursery period), where pigs must rapidly adapt to a host of environmental and physiological stressors. In broiler chickens, exposure to environmental temperatures above their comfort zone is a considerable stressor. Accordingly, several studies were conducted with the objective of developing alternative ways to measure physiological stress in nursery pigs and broiler chickens. These alternative methods may improve the ability of animal scientists to measure physiological stress and thereby aid in development of mitigation strategies. Nursery pigs frequently struggle with diarrhea and other intestinal diseases characterized by increases in intestinal permeability. Therefore, several studies were conducted to evaluate the use of non-metabolizable carbohydrates (lactulose and mannitol) as a non-invasive measure of intestinal health in weanling pigs. In Exp 2.1 and Exp 2.2, an aspirin-induced model of intestinal permeability was explored and the excretion pattern of lactulose and mannitol in urine over a 48 h urine collection period was determined. Aspirin at 15 mg/kg BW increased the excretion of lactulose over that of pigs given 0 or 30 mg/kg of aspirin, and therefore has potential to be used to induce intestinal permeability in nursery pigs. The excretion of lactulose and mannitol peaked at 4 h post-oral dose with a solution of lactulose and mannitol and was primarily complete by 8 h post-oral dose. In the few published reports of the lactulose and mannitol test of intestinal health in weanling pigs, the dose of lactulose and mannitol has varied considerably, raising questions as to the comparability of the results. Accordingly, in Exp 3.1, the impact of variation in the dose of lactulose and mannitol was explored, and pigs given the lowest dose at 0.2 g/kg BW lactulose and 0.02 g/kg BW mannitol had large numerical decreases in lactulose excretion warranting further investigation. Pigs in Exp 3.1 also demonstrated low urine recovery rates (50% successful urine collection averaged over the 3 urine collection time points) which were postulated to be due to the stresses associated with urine collection in metabolism cages combining with the stresses of weaning. Therefore, in Exp 3.2, an alternative urine collection procedure was developed that utilized a urine collection pad held in place by an elastic wrap. Results from Exp 3.2 with urine collected either by metabolism cages or via the urine collection pads indicated that the urine collection pad held promise as an alternative urine collection method that would not require the use of metabolism cages. Accordingly, the use of the collection pad was evaluated as part of a lactulose and mannitol test of intestinal health in group-housed nursery pigs in Exp 5.1. In brief, in Exp 5.1, pigs were weaned, transported for 12 h in a livestock trailer, and fed five treatment diets for 14 d post-weaning. The treatment diets were designed to evaluate the additive effects of L-glutamine and a combination of prebiotics and probiotics as potential antibiotic alternatives to aid in mitigating stress associated with weaning and transport. After two weeks of treatment diets, common diets were fed through market-weight. Urine collection pads were used on 40 pigs (8 pigs per treatment) on d 5 and d 12 post-weaning, with pigs allowed to remain in their familiar group pen during the urine collection period, and urine collection success rates averaged 84% across collection days. This improvement over that of Exp 3.1 may indicate that the use of a urine collection pad may improve the ability to obtain urine from pigs shortly after weaning. Considerable variation in the excretion of lactulose and mannitol was still observed similarly to that seen in Exp 3.1 and precluded statistical differences among dietary treatments. An increase in urine collection length was postulated to be one potential way to reduce that variation. Additional responses to the nursery diets fed in Exp 5.1 are discussed in Chapters 4 and 5. In broiler chickens, measurement of physiological heat stress is limited by the existing techniques which have considerable disadvantages. Therefore, in Chapter 6 a simple surgical procedure is detailed that allows small data loggers to be placed into the abdominal cavity of anesthetized broiler chickens. After a period to allow the chickens to recover from the surgery, these data loggers can record the internal temperature of the chicken at user-defined intervals and have the ability to gather large amounts of internal body temperature data in a wide variety of research settings. A more traditional measure of physiological heat stress in chickens is measurement of the temperature of the cloaca with a thermometer. Therefore, to compare the two methods, values from implanted data loggers were compared to values obtained by measuring the temperature of the cloaca in Exp 6.1 and Exp 6.2, and in general, the two methods yielded similar results. Since surgery to implant data loggers is not always possible or practical, in Chapter 7 the development and evaluation of an equation to predict the internal temperature of broiler chickens was investigated. In Exp 7.1, broiler chickens were exposed to four ambient temperatures each day for four days. The surface temperature of the chicken’s face was measured with a thermal imaging camera, while internal temperature was measured with data loggers as in Chapter 6. The resulting prediction equation contained the significant explanatory variables of the surface temperature of the face, the sex of the chicken, and the number of days of heat stress exposure. Accordingly, the accuracy of the prediction equation was evaluated in Exp 7.2, where chickens were exposed to the same 4 ambient temperatures and temperatures of the face and the internal body measured as in Exp 7.1. The prediction equation developed in Exp 7.1 was then used with the inputs of the facial surface temperature, sex of the birds, and number of days of heat stress exposure from chickens in Exp 7.2 to calculate a predicted internal temperature. This predicted internal temperature was then compared to the internal temperature as measured with data loggers in Exp 7.2. While the accuracy varied by experimental day and ambient temperature, the predicted internal temperature averaged 0.32°C greater than the measured internal temperature. Therefore, while the prediction equation shows considerable promise as a non-invasive metric of physiological heat stress in broiler chickens, refinement of the equation may be required in future studies before internal temperature may be predicted with the accuracy desired in a research setting. In conclusion, the lactulose and mannitol urinary test of intestinal health requires more research before wide-spread use but has considerable promise as a non-invasive test. Surgical implantation of data loggers to measure internal temperature of broiler chickens enables precise measurement of physiological heat stress in broiler chickens, and further research may enable accurate prediction of internal body temperature of broiler chickens without requiring invasive measurement techniques.