| BSE is a fatal disease, which is relevant to age of animals. Its latent period is generally from 2 to 8 years. The cattle infected with BSE prions usually show its clinical syptoms at ages of 4 to 6 years old. At present, the pathogenesis of BSE is generally believed to be due to the change from normal prion protein (PrPc) to the abnormal prion protein (PrPsc). In the latent period of BSE, the pure beef is condidered to be not harmful to consumer's health, as the muscle tissue is not a source of infectious prions, even the infectious tissue such as brain or sprinal cord contain normal prions. Therefore, the beef products younger than 24 months seem to be safe. As soon as the ban of beef import from low BSE risk coutries is withdrawn for politic rensons, the beef restrictively from younger than 24 month cattle will be effective to prevent BSE entering China.Telomere is the special terminal-structure of eucaryote chromosomes, which has a close relation with the cell aging. Large quantities of experiments have proved that repeated sequence of telomere disappeared gradually as the increase of the age and cell mitosis, which has resulted in the progressive shortness of the telomere.Southern hybrid technology was applied in this experiment to detect the length of telomere of 130 cattle samples in order to investigate the relationships between the length of telomere and muscle tissue, species, sex, age respectively. A regression equation has been bulit for predicting the age of beef as a technical reference for estimating the age of cattle according to the telomere length of fresh beef.the four trials were done in this paper, and their results can be concluded as follows:(1) It implied that the length values of telomere of meats sampled at the neck, ex-leg, shoulder, rib, hind leg, buttock of Simmental cattle of 56 days were not obviously different(P>0.05).(2) Meat samples of Luxi Yellow cattle and Limousin aged of 12 to 36 months were tested for their lengths of telomere, then no significant difference(P>0.05) was found between two specics; and it seemed that there was not significant influnce of animal species on the length of telomere.(3) It was discovered that there was extremely significant difference(P<0.01) in the length of telomere between bull and cow of Luxi Yellow cattle and Limousin at the age of 18 months; moreover cow had longer telomere than bull.(4) Because of the sex difference significantly influencing the length of telomere, only bull were choosed as the experimental material to carry on the regression analysis. In this experiment, according to study on Simmental, Luxi Yellow cattle and Limousin bull from 56 days to 72 months, their length of telomere becomed shorter with the increase of age. It took on a quicker shortness before maturity while a gradually slow shortness after maturity, and the degree of shortening seemed imbalance. On the other hand, the regression equation of bull telomere length with age was biult: Y =-1.5854ln(X)+19.556, and R2=0.9784 (X represented the age, and Y showed the corresponding telomere length). This research showed that we could use the same regression equation to estimate the beef age from different species and sampled positions; whereas for the samples from different sexes, we must deal with them according to cow and bull individual respectively; besides, the length of telomere becomed shorter with the increase of age, which might be a possibility to estimate the individual age of cattle. In this experiment, it was proved that the shortness of the length of telomere was extremely remarkable before 36 months old, which was benefitial to estimate the age younger than 24 months for BSE. As a whole, it was very useful for practical application to estimate cattle age of beef products by the length of telomere.
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