اثرات تغذیه و سن بر روی خصوصیات الیاف بز کرکی رائینی

Introduction: Cashmere is a very fine fiber that is produced by secondary hair follicles in cashmere goat. Based on American test and material association description, cashmere is fine fiber in Asian Indian goat hair follicles with diameter lower than 30 microns. Cashmere is growing as “under coat” in cold season and it shedds during the time from late winter until early spring. It is estimated that 68 goat breeds produce cashmere fibers in the world. Cashmere goats are originated from Asia. The important countries that can produce a large amount of cashmere are China, Mongolia, Iran, Turkey, and India. Total production of cashmere is estimated to be 5mt. During the last decades, due to the economic importance of cashmere, USA, Australia, and NewZealand joined to the cashmere producing countries. Many researchers reported that cold climate is suitable for production of quality cashmere. In this research, effects of nutrition and age on histological characteristics of Raeini Cashmere goat were studied in Tabriz, East Azerbaijan.
Material and methods: For this research, 24 female Raeini cashmere goats were selected. The goats were selected from Baft Raeini cashmere goat breeding and husbandry station. Goats were fed individually   and were treated for 8 months of study based on feeding levels (Maintenance, 0.7 M, 1.4 M, and 1.8M) and age (6 months and 18 months) on fleece growth. The trial was conducted at the khalat-Pushan Research Station, University of Tabriz. The goats allocated to four feeding levels: M (goats fed to maintain live weight, 0.7M (goats fed to lose 3Kg live weight from February to September), 1.4M, and 1.8M (goats fed to gain live weight). Patches of fleece from defined areas were repeatedly shorn at 4 weekly intervals from the right mid side of each goat. For follicle study, in the fist, 120cm² of left side of animals was marked firstly; then, these region fibers shaved by electrical shaver. Shaving was repeated monthly (for four weeks). Skin biopsy was taken monthly from left mid side of skin of abdomen. samples were fixed in 10% formalin. Paraffinized block were prepared and then, they are sectioned as serial section in 8-micron thickness. Histological sections were stained by sak pic method (reference ????). Results were analyzed by analyses variance and paired t-test.   
Results and discussion: This research results, showed that there was no significant effect of feeding level or age on weight of cashmere and hair per area, secondary follicle activity, cashmere length, and yield (p < 0.05). Fleece and live weight for young goats were significantly less than that of old goats (p < 0.05). Result were appeared that mean cashmere diameters of patch shorn in September of goats fed M, 1.4M and 1.8M were significantly greater than that of goats fed 0.7M (p < 0.05). In group feeding more than maintenance requirements, results indicated no increase in cashmere production. Average fiber diameter of cashmere in June was higher than in May. Results of this research indicated that there are not any significant differences between different levels of feeding and age on fiber growth rate (p < 0.05). The highest fiber production and the maximum mean of fiber growth rates (1.64 and 1.48 g/120cm² / 28 days) were observed in June and July. Secondary to primary follicle ratio of all goats was 12.60. Study of secondary follicles ratio showed that different levels of feeding cannot reduce number of secondary follicles. Many researchers reported that increase in feeding levels to over maintenance rate cannot increase cashmere growth rate. This research results confirmed by previous studies. it was reported that feeding limitation can reduce diameter of cashmere, but there is not any increasable effect during over maintenance feeding and an increase in dietary protein. This research indicated that cashmere diameter was more in two-years old goat than one-year old goat cashmere diameter. These   results were similar with reports of Klor et al. (1993), Rafat (1997), and Salehi (1997). Increase in diameter of wool fibers with increasing in the age of animals was reported in sheep and goat. In other studies, it is shown that effect of age on diameter of Norway cashmere goats was significant (p < 0.05). Results of our research show that diameter of cashmere in Raeini goats increases at June. Similar results are illustrated in Kerman (with the same age and sex). The weight of produced fibers / body surface was the same in four feeding treatment groups, but diameter of cashmere was different. Numbers of secondary follicles   increased in April. Minimum weight of fibers was observed in April in all of the treatments, which may be because of low activity of follicles in this month. Variation of cashmere diameter and cashmere growth rate can explain differences in total cashmere production. Changes of feeding level from under maintenance to high levels cause increase in cashmere diameter. This study appeared that diameter of cashmere fibers can have reaction to feeding rate. Accordingly, energy has important effect on growth of hair and cashmere. The animals with low energy diet produce low amount of cashmere, Other researchers have opposite idea. According to their statement, there are not any difference in partition for nutrient between primary and secondary follicles. This research result showed that increase feeding cannot increase cashmere production. Jia et al (1995) reported that increase of diet net protein has not any important effect on cashmere goats production in Spain. In other study using unpregnant goat it has been indicated follicular activity and fiber growth is not under influence of pregnancy and milking. However, some researches showed that reproduction condition of animal, as pregnancy and milking, has effect on cashmere fiber growth.  
Conclusion: Generally, results of this study showed Raeini cashmere goats in East – Azarbayjan climate did not show any fundamental changes in diameter and length of cashmere in comparison with Raeini cashmere goats which reared in Kerman province.