الفهرس 
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Abstract
This study was carried out at Animal Production Research Institute in participation with Animal Production Department, Faculty of Agriculture, Moshtohor. The experimental work was conducted at Ali-Ezet farm- Meat Land Company- during summer (from Jun. to Sept. 1999).
This study aimed to improve productivity of European and exotic breeds under hot-humid summer conditions in Egypt. The experimental part wes conducted on 15 growing Holstein Friesian calves, aged about 8 months and weighted about 210 kg, assigned into 3 equal groups, kept separately under loose semi shaded yards, and fed ad-lib. at 8 am. (berseem hay, rice straw, great millet fodder and concentrate mixture).
The first group (G1) was used as a control group for G2 and G3. The second group (G2) was treated with spraying cooling system. The third group (G3) was treated with showering cooling system.
The mean results could be summarized as follows: - 1- Thermoregulation responses:
-Rectal temperature (RT) and respiration rate (RR) decreased significantly by using cooling systems in G2 and G3 comparing with GI, they were (38.94±0.01 and 38.94±0.01c° vs.39.0±0.01c°; and 50.02+0.34 and 49.94±0.34 r.pm vs. 52.78± 0.19 r.pm), respectively.
-Also, RT and RR increased significantly through M2 (Jul.) and M3 (Augu.) than that of M1 (Jun.) and M4 (Sept.).
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-Both of RT and RR affected by daytime; at 7am., they decreased significantly (p<0.05) for GI than those of G2 and G3. At 2pm. (under using cooling system), RT and RR of G2 and G3 decreased significantly than Cri. But, at 7pm. (after cessation of cooling systems), both of RT and RR of G2 and G3 increased significantly than GI.
2- Water consumption (WC):
-The water consumption (WC) decreased significantly (p<0.05) by the effect of cooling systems. And, the lowest WC was obtained in calves exposed to showering cooling system in G3 (35.15 L/d). Also, calves exposed to spraying cooling system in G2, had a lower WC (36.47 L/d.) than control shaded calves in G1(45.56 L/d.).
-Water consumption (WC) gradually increases significantly through experimental months from M1 (Jun.) to M4 (sept.). Whereas, the lowest value (34.75 L/d) was obtained in MI, and the highest one (42.82 L/d) was obtained in M4.
3- Dry matter intake (DMI):
-It did not affected significantly as a function of cooling water applications.
-Months affected significantly (p<0.001) on DMI, whereas, it increased gradually from M1 (Jun.) to M4 (Sept.) by increasing the requirements of the animals.
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4-Daily weight gain (DWG):
-Daily weight gain enhanced significantly (p<0.001) by cooling systems in G2 and G3 than in GI, they were (1.46 and 1.34 vs. 1.23 kg/d, respectively) whereas, spraying cooling system improved DWG more significantly than using showering by about 8.3%.
-Also, DWG affected significantly by month, whereas, DWG means of MI (Jun.) and M4 (Sept.) were higher than that of M2 (Jul.) and M3 (Augu.). The highest gain observed in M4 and the lowest one was obtained in M3. 5-Feed utilization (FU):
-Spraying improved significantly (p<0.05) FC and FE in G2 compared with GI. Also, as values, showering increased FC and decreased FE than G2, although, no significant statistical differences between them.
-Feed conversion (FC) increased gradually during the first three months, reached its maximum at M3 (from 5.48±0.112 for M1 to 7.8±0.128 kg DMI for M3) then, decreased then after at last month M4 (7.14±0.21 kg DMI). The opposite trend was observed for FE, which decreased until M3 (0.129±0.002 kg gain), then began increased in M4, where, reached to 0.141±0.004 kg gain. 6-Hematological responses:
-Using spraying cooling system improved significantly (p<0.05) Hb%, WBCS and TP. Whereas, using showering cooling system enhanced Hb% and TP without significant
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differences with spraying system, also it improved WBC a little lower than spraying. Control group recorded the lowest values in Hb%, WBC and TP. Also it had no significant difference in TL.
-Experimental months had significant (p<0.05) effect on Hb%. Whereas, M4 had the highest value than the others months, which had no significant differences between them. WBC’s increased gradually significantly from M1 to M4. TP increased significantly through MI and M4 and decreased in M2 and M3 (4.520.14 and 4.580.16 g/dl ver. 4.090.14 and 4.08±0.13g/d1, respectively). Whereas; experimental months had no significant effect on TL.
7- Hormonal responses:
-Using spraying system improved significantly (p<0.05) T4, T3 and testosterone than control group. Also, using showering system enhanced T4 and testosterone, without significant differences with the spraying system. Whereas, showering improved significantlyT3, but it was a little pet lower significance than spraying system.
-Experimental months affected significantly (p<0.05) on T4, T3 and testosterone. T4 improved significantly during M1 and M4, but it affected negatively by M2 (Jul.) and M3 (Augu.), without significant differences between each two months. Whereas, T3 recorded the highest significant concentration in M4 (Sept.), then in Mi (Jun.), and the lowest one was observed in M3. Testosterone concentration mean through M 1 was (4.350.57 ng/dl) and then it decreases through M2 and M3, without significant differences between these months (3.670.4 and 3.690.41 ng/dl, respectively), then after, it reached its maximum in M4 (6.480.38 ng/dl).