||The present study was planned to detect the variation in some metabolic parameters related to milk formation and production within different seasons of the year. In addition, it was aimed to minimize the adverse effect of high environmental temperature during summer months by increasing the ability of heat dissipation to optimize metabolic rate and process of milk formation within the economic limits.
The field part of the study was carried out at the dairy experimental farm belonging to the Department of Animal Production, Faculty of Agriculture, Benha University.
Chemical assays of some metabolic parameters and milk constituents were performed in the laboratories belonging to the same Department belonging to the Faculty of Agriculture, Benha University
A total number of 12 cross bred cows (Friesian X Balady) and 13 buffalo cows of three lactations (first, second and third) were subjected to the study. Animal's age ranged from 23 to 55 in cows and from 25 to 65 in buffalos. Average body weight ranged from 254 to535 Kg in cows and from 449 to728 Kg In buffaloes.
Animals were kept in well ventilated stable that was cleaned in the morning after the milking and during the time of grazing. After grazing time animals were kept under shed offering the diet up to the sundown after which all animals were moved to the stable. During summer months animals were grouped into two groups. The first group were allowed to graze from 9 a.m to 2 p.m then kept under shed from 2 pm to 6 am the time of sundown then kept in the stable over night. However animals of second group were allowed to graze during the period from 9 am to 2 pm then kept in the stable provided with system of water tubes at 1.5 meter over the animals ended with nozzles to allow spray water over the animal body surface for 15 minutes per hour to increase dissipation of body heat by evaporation. Ration, was offered to animal's ad-libitum after grazing time and all over night. Water was also offered ad-libitum.
The ambient temperature and relative humidity were estimated by data logger every 30 minutes allover day and night in both the stable and outdoors. The temperature humidity index (THI) was calculated
Rectal temperature, udder and milk vein temperatures were estimated at three times daily (at 6:00 am, 2:00 pm and 7:00 pm a) during two days per week using infrared thermometer
Animals were monthly weighed after the morning lactation to the nearest kilogram.
Cows and buffaloes were hand milked twice daily (at 7 am and 2 pm.) and milk yield was recorded, in kg, for each milking time then calculated as daily milk yield. Milk samples were collected from each milking time every last 15 day per month all over the experimental period. Analysis of collected milk samples were performed after collection time to estimate total solids, total protein, fat ash and lactose percentages
Blood samples of approximately 10 mL were individually withdrawn by puncture of jugular vein using sterile vasecutainer needle Samples were collected in sterile evacuated tubes containing heparin. Samples were monthly collected after calving up to the end of the experimental period
Blood plasma samples were exposed to chemical colorimetric analysis in to determine: total proteins, Albumin, total lipids, total cholesterol, plasma calcium plasma and phosphorus, alkaline phosphates GOT and GPT. Number of RBCs and WBCs were counted
Results obtained could be summarized as follows:
1. No stressful effect was found during the period from December to April months, but mild stress effect was found during May and June months as will as during the period from September to November. On the other hand the period started from the first of June up to the end of August is considered a period of sever stressful effect.
2. Rectum temperature was found to be more sensitive to ambient temperature. It is obviously and significantly decreased during the period from December to April (during winter and early spring). The rate of decrease was higher in buffaloes than in dairy cows.
3. It was obviously noticed that milk vein temperature in both cows and buffaloes. Was almost higher than udder temperature in all months of the year and all estimation times.
4. Generally estimation of temperature for each organ was higher at 2pm than at either 6am or 7pm for both buffaloes and cows.
5. In all organs of buffaloes and cows the temperatures were at its lowest value during winter months (from December to February) and early spring (March). While were at its highest value during summer months (from June to August) and early autumn (September).However, at all times organs temperatures were physiologically controlled at their normal limits.
6. Averages of daily milk yields were higher during winter season than during falls. On the other side, daily milk yields averages were at its lowest value during summer. However, during summer were increased as a result of increasing the rate of heat dissipation by applying spray of water above the body surface of the animals. This reached an average approximately equal to that obtained during spring and autumn.
7. Higher negative regression coefficient value in dairy cows was detected between daily milk yield and milk vein temperature (-0.53) while the higher positive regression coefficient value in buffaloes was detected between rectal temperature and daily milk yield (0.28). However, the lower positive regression coefficient value in dairy cows was found between rectal temperature and daily milk yield in cows (0. 18) and between milk vein temperature and daily milk yield in buffaloes (0.12).
8. Variations exerted in average body weight due to treatment applied were of no significant magnitude in dairy cattle cows. However average body weight of buffalo cows was significantly affected by treatment. Significant effects due to the season of the year were found on the average body weights of both dairy cattle and buffalo's cows.
9. Applying water spray above the body surface of lactating experimental (dairy cattle or buffaloes) increased most milk constituents estimated. The rate of increment varied according to factors studied.
10. Lactation numbers in dairy cattle cows significantly (P