| Abstract |
Two experiments were carried out to investigate the adaptive response of goats to seasonal variation and exposure to solar radiation. The first experiment includes 45 Baladi goats (23 and 22 2-3 years old does in winter and summer, respectively) and 30 male kids (18 and 12 1-year-old Baladi male kids in winter and summer respectively) . Adult does were divided into three groups according to their physiological status i.e. dry, pregnant (during the last third of pregnancy) and lactating (2-3 weeks after kidding). The number of does in winter was 9, 8 and 6 and in summer the number was 10, 8 and 4 does, respectively. The second experiment was carried out on 6 dry does in summer to study the physiological responses of adult goats to exposure to solar radiation for 4 hours. In each experiment the following parameters were measured:
1- Ambient temperature (AT), black body temperature (BBT) and relative
humidity (RH%) were recorded with measuring physiological responses.
2- Thermorespiratory and cardiac measurements:
Rectal (RT) , Ear (ET) and skin (ST)temperatures, respiration rate (RR) and pulse rate (PR) were measured and temperature gradients i.e. RT-AT, ST-AT, RT-ST and RT- ET were calculated.
3- Blood and plasma measurements:
Haematocrit value (Ht%), plasma volume (PV), blood volume (BV) plasma total proteins (TP), plasma albumin ( A1 ) , plasma
globulin (G1), A/G ratio, Na+ , K+ plasma concentrations and plasma aldosterone level were measured.
4- Productive traits: Litter size, mortality rate, kids birth weight, weaning weight, weaning age, marketing weight, marketing age, number of kids weaned/doe, kg body weight weaned/doe and daily gain were collected for does conceived in summer and winter. Animals were fed on hay and a concentrates according to their body weight requirement on a ration containing approximately 14% crude protein, 3% crude fat and 15% crude fiber. During winter (from December to April), animals offered were Egyptian clover, (Trifolium alexandrinum) ad-libitum, while during the period from May to the end of November, rice straw was offered ad-libitum. Animals were allowed to drink fresh water ad-libitum twice daily.
Results obtained indicated that:
First experiment: Effect of seasonal variation:
1- Effect of seasonal variation on kids:
The increase in AT from 16.6 oc (55.6% RH) to 32 c in summer (45% RH) caused a significant increase in RT, ST, ET, RR and PR, meanwhile significant a decrease in temperature gradients occurred. Chronic increase in AT during summer increased significantly PV% and BV% due to a significant increase in colloid osmotic pressure (AI and A/G ratio), while GI decreased significantly, the result was insignificant significant an increase in TP. No seasonal changes were found in TP, aldosterone, Na+ K+ to be to the and daily gain. However, plasma Na+ and K+ tended lower in summer than in winter which may be due increase in PV.
2- Effect of seasonal variation on does:
Higher AT in than summer in winter caused a significant increase in RR and ET while no significant changes occurred in RT and ST. Temperature gradients ST-AT and RT-ET were significantly higher in winter than in summer, while RT-ST did not differ significantly between seasons. Similar results were found in dry does, while in pregnant and lactating does ET and ET-RT as well as RR of pregnant does did not differ significantly between seasons. The overall mean PR did not differ significantly between seasons, but it was significantly higher in summer than in winter in dry does while a reverse insignificant trend was noticed in pregnant and lactating does. Haematocrit value did not differ significantly between seasons either in overall mean or in dry, pregnant and lactating does. Season had no significant effect on PV and BV (as an absolute value or as a percentage of body weight) which was due to an insignificant seasonal variation in pregnant and lactating does, while PV% and BV% of dry does were significantly higher in summer than in winter. Plasma TP was significantly higher in winter than in summer due to higher GI meanwhile Al was almost unchanged causing an insignificant reduction in A/G they were insignificant, while a significantly higher Al ratio in winter. Similar trends were found in pregnant does but in winter than in summer was observed in dry does. On the other hand, lactating does had significantly higher Al and A/G ratio in summer than in winter. No significant seasonal variation was found in aldosterone, Na+ and K+ K+ concentrations, but there was a tendency of a reduction in during summer in all groups which was more obvious in dry and pregnant does than in lactating ones. It was clear that Na+ was higher in summer than in winter in dry does, while opposite trend was found in pregnant and lactating does.
Environmental conditions in both seasons are suitable for goat production so at there no significant were effect of season on productive traits of goats. Data obtained on kids and does revealed that kids may be less tolerant to changes in AT than does because they had wider range of body temperature, higher PR in summer, higher and lower PV% and BV% in and summer winter respectively. Kids also showed higher Al and A/G ratio summer (which was in consistency with lactating does) and higher seasonal changes in plasma Na+ and K+ than does.
3- Effect of physiological status:
In both seasons, RT was higher in lactating does than in dry and pregnant does (being significant in winter). In summer, RT-ST in, higher in lactating was does than pregnant does while dry does was in-between. There was significantly opposite trends in PR in summer and winter where dry does had higher and lower PR than lactating in and winter, respectively. In summer, PV% and BV% were significantly pregnant higher in dry does than in ones due Na+ although to higher plasma concentration pregnant does had higher Al and A/G ratio than dry ones. In Second experiment: Exposure to solar radiation:
Before exposure, BBT and RH% were 35 oC and 52.5% while after exposure they were 46 oC and 27%, respectively.
Exposure to solar radiation caused significant a increase in RT, ST, ET, RR and PR, while it reduced significantly temperature gradients except RT-ST.
No significant changes occurred after exposure to solar radiation in PV%, BV%, plasma proteins (TP, AI, Gl and A/G ratio) and plasma aldosterone, Na+ and K+ concentrations. However, there was an insignificant reduction in aldosterone, Na+ and K+ concentrations indicating that animals were suffering from heat stress.
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