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The annual cycle in coat growth and shedding rates was investigated in Holstein and Syrian x Holstein cattle (3.1-6.2% relationship to the Syrian) under natural conditions in three different climatic regions of Israel. Hair quantity, coat thickness, and hair diameter were tested monthly on an area of 100 cm2 on the thigh. 541 samples were taken during 1 year. Cows were tested in two herds in the Jordan Valley (mean annual temperature 23�_C), one herd in the Coasral Plain (mean annual temperature 20.4�_C), and one in the Jerusalem area (mean annual temperature 17.5�_C). Hair quantity and coat thickness in the Jordan Valley were very- significantly smaller than in the other two regions. A clear cycle was observed in these three factors. Weight of hair reached the peak In January, then decreased to 50% of the maximum weight during April-Nay and increased again during May-June, reaching 75% of the maximum weight. From October hair growth continued, to the peak in January. Variations in coat thickness differed from those in weight of hair during summer, when coat thickness stayed lox and stable until autumn. Hair fibre diameter was lowest between December and March, then increased sharply until June. Hair quantity and coat thickness decreased more and faster in the Jordan Valley. These results show that day length is not the only factor influencing the annual cycle of hair quantity and coat thickness but that, apparently, the air temperature? are of influence too. In this experiment hair diameter was influenced only by variations in day length. |
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