الفهرس 
Review of literatureOnly 14 pages are availabe for public view
 |  | from | 218 |  |  |
| | | from | 218 | | |
Abstract
A total of 440 Friesian cows, 23 crossbred cows and 88 Egyptian buffaloes were examined for milk yield and milk fat % allover two years from January 1992 to December 1993 under the effect of local environmental conditions in Qalyoubia governorate.
1-The study revealed that the ambient temperature and relative humidity affect the milk production as follows :
- Milk yield of Friesian cows was dropped during hot months (summer) with a % of loss 25.8% than in cold months (winter) followed by crossbred cows and buffaloes.
- Milk fat % of Friesian cows was decreased during hot months, while that of crossbred cows and Egyptian buffaloes was slightly
affected.
2-Photoperiod is the second most important environmental factor influencing milk yield of dairy cattle. At 18 hr continuous light, the milk yield was increased by 1.57 kg/day, while fat % was not affected.
3-180 blood samples were analysed for levels of milk related hormones
(thyroxine and prolactin) and the following results were recorded :
- Thyroxine : was lowest at the beginning of lactation, then increased gradually with the progression of lactation period. Thyroxine not significantly increased with the rise of environmental temperature.
- Prolactin : peak level was recorded during early periods of lactation, while it was lowest during the late period of lactation. Prolactin levels increased significantly with the rise of environmental temperature.
4-Age of animals has visible effect on milk yield, where the milk yield of crossbred cows was highest at six to less than nine years of age, followed by cows at three to less than six years of age and lower yield occurred in cows over nine years of age.
5-Milk yield was highest during the first stage of pregnancy and was lowest during the last stage of pregnancy (7th month - drying off). On the other hand, the milk fat % increased with advancing of pregnancy stage.
6-Body conformation of dairy cattle affect the milk yield and milk fat as following :
▪Heart girth : Milk yield of Friesian cows was higher at smaller heart girth, whereas, the crossbred cows and buffaloes produced more milk when their heart girth was larger. Fat % revealed not significant correlation with heart girth.
•Paunch girth : Both milk yield and fat % of dairy cattle were higher when their paunch girth was larger.
Wither ,height The milk yield and fat % of dairy cattle were higher at higher wither height.
•Body length : Both milk yield and fat % of examined dairy cattle showed a little increase when the body length was larger.
•Pelvic width Milk yield and fat % increased. when the pelvic width measurements were larger.
7- It has been found that the total colony, coliform and E.coli counts were significantly declined after application of various premilking treatments such as washing and drying of teats with sterile towel, premilking iodophor 1% dip and drying with sterile towel.