This experiment was carried out using 397 newly born Friesian Holstein
calves to study some of hair coat characteristics during the different seasons up to
one year of age and their relations to some physiological parameters and animal body
weight. Hair coat measurements involved field observations (coat depth, density,
curliness and luster) and laboratory measurements (fiber density, fi er length, fiber
crimping and fiber shedding). Physiological parameters dealt with rectal temperature,
skin and hair temperature and respiration rate. In the present study, hair coat characteristics of calves showed strong
seasonal variations. Coat type was short, more medullated, less del se and h ad a
very few number of crimps in summer, whereas in winter it was dense, long and low
in percentage of medullated fibers. Physiological parameters showed higher values in summer tha~ those in winter
season. Temperature gradients of rectal temperature and each of sk n temperature,
mid point coat temperature and surface coat temperature showed a higher value fer
insulation during winter season than those of summer. Daily weight gain showed high positive correlation (P<0.01) with fiber density
(0.611), fine undercoat length (0.603), coarse undercoat percentage (0.719), coat
depth (0.838), curliness (0.734) and belly cover depth (0.775). It could be concluded that the seasonal fluctuations in hair coat
characteristics might be regarded as one means of animal adaptability to the
environmental factors which surrounded the animals. Such fluctuations had also
strong correlations with the physiological responses of animal body as well as with
daily weight gain.