Effect Of Cold Stress On Physiological, Biochemical And Endocrinological Values In Fasting Weaned Lambs

In the event of heavy snow or cold current in the northern region of Xinjiang, it results in lowand/or large extend decrease in temperature. Due to the extreme cold and the lack of forage, grazing sheepespecially lambs with weaning stress and not yet mature, lead to poor resistance to disease and cold, andhigh mortality. To understand the effect of acute and chronic exposure to cold on the basic vital signs,blood biochemical indices and stress-related hormones, fasting and weaned lambs were used; moreover, toexplore the effect of ghrelin on both cold and starvation stress, exogenous ghrelin was administrated to thestress lambs.In order to understand the effects of acute cold exposure on lambs, Small Tail Han sheep lambs afterweaning about a week were used. The animals were fasted for24h before the experiment, and divided intowarm hunger group (WH group) and cold hunger group (CH group) based on the incomplete Latin SquareDesign. Basic vital signs, blood biochemical indexes and stress-related hormones at a series of time pointsbefore and after cold exposure in lambs was assayed. The results showed that heart rate (HR) wassignificantly higher in CH group than in WH group after cold exposure30,60and120min (P<0.01).Respiratory rate (RR) rose in CH group from30min after cold exposure until the end of the experiment,and it was significantly higher in CH group than in WH group (P<0.05). Plasma glucose level was sharprise in CH group after cold exposure15min, and maintained at high levels until the end of the experiment,and was significantly higher than that in WH group at the same time point(P<0.05).In order to explore the effects of chronic cold exposure on lambs, the same batch of lambs with acutecold exposure test was used. The animals were fasted for24h before the experiment, and divided into threegroups: warm hunger group (WH group), cold hunger group (CH group, exposed at-3.2~-17.8℃for32h)and cold feeding group(CF group, feeding at24h after cold exposure) based on the incomplete LatinSquare Design. The results showed that heart rate in CF group and in CH group after cold exposure untilreturn to warm pens (130±3.3beats/min) was significantly faster than that in WH group (70.7±1.3beats/min)(P <0.05), hear rate and outside temperature from-4.0~-17.8℃was found to show a significantnegative correlation(r=-0.522). Respiratory rate in both CF and CH group after cold exposure (24±0.6breaths/min) was significantly faster than that in WH group (19.2±0.5breaths/min)(P <0.05), and showedlow negatively correlated with air temperature(r=-0.314). However, re-feeding after24h of cold exposuredid not affect HR and RR in CF group. In survival lambs, body temperature were no significantly differentamong the three treatment groups. Plasma glucose levels in CH group at2,4,20and25h after coldexposure was significantly higher than those in WH group (P <0.05), then the level decreased to the samelevel in WH group at the same time point. In our experimental conditions, the correlation of otherbiochemical indexes and stress related hormones with cold stress was not found in lambs.To explore the effect of ghrelin, a newly discovered peptide hormone, on cold stress, ghrelin wasintravenously injected to25-hour-fast lambs at1h after cold exposure, and the animals had beencontinuously fasted and exposed to the cold environment for another1h. The results showed that plasmaglucose levels at each time point from10min to60min after administration in ghrelin group weresignificantly lower than that in control group (P<0.05), indicating that ghrelin may inhibit the elevation ofblood glucose induced by cold exposure. Respiratory rate from30min after ghrelin injection was significantly lower than that in control group (P<0.05). No significant difference was found in otherindexes between two groups.The results from this study indicate that acute and chronic cold exposure can affect basic vital signsand blood glucose level, and exogenous ghrelin may involve in the regulation of energy metabolism duringcold exposure in fasting lambs. We hope the results from this study could help to provide a reference forevaluate the extent of cold stress in livestocks.