SHEARING AND SHELTERING INFLUENCE ON SEVERAL PHYSIOLOGICAL PARAMETERS IN SHEEP

Transcription

1 SHEARING AND SHELTERING INFLUENCE ON SEVERAL PHYSIOLOGICAL S IN SHEEP Pennisi P. 1 ; Biondi L. 1 ; Giudice E. 2 ; Lanza M. 1 ; Nicosia S. 3 ; Piccione G. 3 1 Dipartimento di Scienze Agronomiche, Agrochimiche e delle Produzioni Animali Università degli Studi di Catania 2 Dipartimento di Scienze Mediche Veterinarie Università degli Studi di Messina 3 Dipartimento di Morfologia, Biochimica, Fisiologia e Produzioni Animali Università degli Studi di Messina Abstract The pattern of several physiological parameters such as body temperature, respiratory rate, heart rate, haematocrit, Hb content, which are closely related to thermoregulatory potential, have been investigated with the purpose to assess shearing and sheltering influence on thermoregulation. Thirty clinically healthy and well-fed yearling ewes, Comisana breed, aged 8 months, underwent this trial. 7 days prior to the beginning of this study, all subjects were equally distributed in three groups with different sheltering conditions: group A was kept in an outdoor pen, group B was kept in a pen equipped with a shady net (80% of shading) and group C was kept in an outdoor sheepfold with an attached paddock. As to feeding conditions, groups A and B were fed daily on: hay (2 kg), wheat straw (1 kg), wheat concentrate (0.5 kg) and water ad libitum; the remaining ewes grazed on a wheat stubble pasture for 6h/day, and were sheltered during midday warmer hours. Through a simultaneous monitoring equipment (Schiller Argus Tm 7) and a blood collection by means of a jugular venipuncture parameters assessment was carried out for each subject before shearing and during the following five days at a fixed time during morning. A Student T test was applied to determine any statistic significance between groups and within each group. Statistically significant differences were observed for all parameters under investigations. These results suggest that shearing is brings about adaptive responses, which are influenced by shelter conditions as well. More specifically, obtained results underline that shading net provides a more comfortable microclimatic environment. Introduction Ovine breeding is mainly exposed to environmental factors (climatic and dietary) variability and to their interaction. It is well known that to maintain body temperature constant, an animal has to satisfy the condition of stationary equilibrium, in which the metabolic production of heat is equal to its loss. The thermoneutral zone has been defined as The range of ambient temperature within which metabolic rate is at a minimum, and within temperature regulation is achieved by non-evaporative physical processes alone (Bligh and Johnson, 1973). The breadth of the thermoneutral zone depends on age, species and breed, level of nutrition and fleece (Yousef, 1987). The breadth of the thermoneutral zone which is significantly correlated to fleece length in the sheep (Hecker, 1983) presents a lower critical temperature (LCT) of 4 C (Slee, 1987) which increases to 28 C after shearing (Ruckebusch, 1986). At an environmental temperature lower than body temperature, heat dispersal through conduction, radiation and evaporation should be aided by the absence of fleece: in fact, at an environmental temperature of 30 C, the shorn sheep disperses 50% more through evaporation than the unshorn sheep (Bettini and Ferrara, 1987). The ability to regulate temperature is an evolutionary adaptation that allows homeotherms to function in spite of variation in ambient temperature (Baker, 1989); this ability also allows temperature to be used as a signal to control physiological processes. The pattern of some physiological parameters (body temperature, respiratory rate, heart rate, haematocrit and haemoglobin content) have been investigated to evaluate the role played by the fleece and the influence of sheltering on thermic homeostasis maintenance in Comisana ewes breeded in Sicily.

2 Materials and methods Thirty clinically healthy and well-fed yearling ewes, Comisana breed, aged eight months, were used. Seven days prior to the beginning of this study, all subjects were equally distributed in three groups of 10 subjects with different sheltering conditions. Group A was kept in an outdoor pen. Group B was housed in a fenced area equipped with a 80% shading net assembled with green plastic wires and sustained by frame made of steel tubes; the shading net was 2.5 m height from the ground level. Group C was kept in an outdoor sheepfold with an attached paddock. As to feeding conditions, groups A and B were fed daily on: hay (2 kg), wheat straw (1 kg), wheat concentrate (0.5 kg) and water ad libitum; the remaining ewes grazed on a wheat stubble pasture for 6h/day, and were sheltered during midday warmer hours. On each subject through a simultaneous monitoring equipment (Schiller Argus Tm 7) body temperature, heart and respiratory rate were measured. A blood sample collected by means of a jugular venipuncture was used for haematocrit (microhaematocrit method) and haemoglobin (in U. V spectrophotometry) assessment. Parameters assessment was carried out for each subject before shearing and during the following five days at a fixed time during morning. The statistical elaboration of the data for each parameter was based on the average values obtained at each day of test. A Student T test for paired data within each group and for not-paired data between groups was applied to point out statistical significance among mean values of studied parameters. Results and conclusions Figures 1-5 show the pattern of body temperature, respiratory rate, heart rate, haematocrit and haemoglobin content studied on the different experimental conditions for A, B and C groups. Environmental temperature during the experimental period was unchanged (min: 19 C, max: 25 C). Data elaboration pointed out statistically significant differences for all the parameters recorded on each group. On shearing day all the subject were within the thermoneutral zone (-4 C +28 C) and heat production and heat dispersal mechanisms were equivalent. After shearing animals actived quickly heat production mechanisms for the raise of lower critical temperature (LCT). Different environmental conditions influenced the pattern of the studied parameters in each group. Body temperature showed a statistically significant increase on shearing day in sheltered ewes (groups A and B) (P<0.0001; P<0.001) and a statistically significant decrease (P<0.01) in grazed subjects (group C), compared to immediately after shearing. Wind cooling action could determine a remarkable convection heat loss higher than heat production. Five days after shearing group A body temperature was higher (P< 0.01) than groups B and C body temperature. Natural shelter in the pasture and shading net formed a more thermic comfortable microenvironment compared to group A, which were exposed to direct effect of solar radiation. Respiratory rate shows a similar trend in respect to the above parameter. The day after shearing respiratory rate shows a statistically significant increase in groups A (P<0.01) and B (P<0.03) and a statistically significant decrease in group C (P<0.01). Thermic polypnea is functional to disperse through evaporation heat stored in sheltered groups as results of body temperature raise. Vice versa, body temperature decrease in grazed subject (P<0.01) is responsible of a respiratory volume decrease to a minimum value able to provide gas exchanges (Johnson, 1982). In sheep, painting is the major evaporatory heat loss mechanism and respiratory frequencies tend to follow closely the heat loss by evaporation (Hales and Brown, 1974). In non-sheltered sheep respiratory rate can be 56% higher than in sheltered sheep due to direct effect of solar radiation (Silanikove, 2000). Heart rate showed an increase in group A compared to groups B and C (P<0.001) due to stress caused by the direct effect of solar radiation. Heat stress induces haemodynamic adaptations: the organism produces an higher quantity of heat dispersed by an enlarged peripheral vascular system.

3 Both haematocrit and haemoglobin content show higher values in grazed sheep (group C) compared to groups A and B (P<0.01), due to a lower water availability during pasture compared to sheltered animals which have water ad libitum. Obtained data show that different micro environmental conditions, such as sheltering, can highly influence thermoregulatory mechanisms resulted from shearing and take part in productive performance and in welfare (Silanikove, 2000). Simple shading net can defend sheep from direct solar radiation, especially in Mediterranean areas, producing a microclimate able to minimize heat stress in sheared sheep. References Baker M. A., 1989 Effect of dehydration and rehydration on thermoregulatory sweating in goats. J Physiol Lond 417: Bettini T. M., Ferrara L., 1987 Ambiente e adattamento. In: Bettini TM (ed) Elementi di scienza delle produzioni animali, Edagricole, Bologna: Bligh J., Johnson K. G., 1973 Glossary of thermos for thermal physiology. J Appl Physiol 35: Hales J.R.S., Brown G.D., 1974 Net energetic and thermoregulatory efficiency during panting in the sheep. Comp Biochem Physiol 49A: Hecker J. F., 1983 Climate physiolog. In: The sheep as an experimental animal. Academic Press. London: Johnson K.G., 1982 Susceptibility of sheep to adverse weather: physiological responses to cold and the effects of hypothermia. In: Proceedings of a seminar on Losses of sheep after chaining due to adverse weather. Editors: Baker S.K., Chapman H.M., Williams I.H., 1-7. Ruchebush Y., 1986 Physiologie Pharmacologie thérapeutique animales. Maloine S.A. ed. Paris. Silanikove N., 2000 Effect of heat stress on the welfare of extensively managed domestic ruminants. Livestock Production Science 67: Slee J., Sheep. In: Johnson H.D.(ed) Bioclimatology and the Adaptation of Livestock, Elselvier, Amsterdam, Oxford, New York, Tokyo: Yousef M. K., 1987 Principles of bioclimatology and adaptation. In: Johnson HD (ed) Bioclimatology and the adaptation of livestock, Elsevier, Amsterdam, Oxford, New York, Tokyo:

4 Table 1. Average values of body temperature, respiratory rate, heart rate, haematocrit and haemoglobin, together with their standard deviations, studied on different experimental conditions for group A. Body temperature ( C) 39.40± ± ± ± ± ±0.14 Respiratory rate (b/min) 59.9± ± ± ± ± ±3.43 Heart rate (b/min) 98.0± ± ± ± ± ±3.89 Haematocrit (%) 28.4± ± ± ± ± ±2.09 Haemoglobin (g/dl) 9.84± ± ± ± ± ±0.3 Table 2. Average values of body temperature, respiratory rate, heart rate, haematocrit and haemoglobin, together with their standard deviations, studied on different experimental conditions for group B. Body temperature ( C) 39.32± ± ± ± ± ±0.2 Respiratory rate (b/min) 49.7± ± ± ± ± ±1.94 Heart rate (b/min) 100.8± ± ± ± ± ±3.91 Haematocrit (%) 28.2± ± ± ± ± ±2.65 Haemoglobin (g/dl) 9.90± ± ± ± ± ±0.8

5 Table 3. Average values of body temperature, respiratory rate, heart rate, haematocrit and haemoglobin, together with their standard deviations, studied on different experimental conditions for group C. Body temperature ( C) 39.4± ± ± ± ± ±0.29 Respiratory rate (b/min) 59.6± ± ± ± ± ±1.64 Heart rate (b/min) 100.4± ± ± ± ± ±2.70 Haematocrit (%) 27.5± ± ± ± ± ±2.04 Haemoglobin (g/dl) 9.86± ± ± ± ± ±0.6