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Growth rate of 60 Lori-Bakhtiari single male lambs were assigned to a
completely randomized design with two factors. The factors were tail status
(with and without fat tail) and fattening period ( 75,90, 105 days). Lambs were alternately docked by the use of rubber rings at the begining of the second day of birth. Lambs were weaned at 90±5 days of age and randomly divided into three groups of 75, 90 and 105 days of feedlot while being kept in individual boxes. The results showed that tail status did not influence the preweaning trait. Docked and undocked lambs were not significantely different for weaning as well as daily gain from birth to weaning. Daily weight gain, final weight, and thus total weight gain during the fattening period were influenced by tail status, so that daily weight gain, final weight and total weight gain of docked male lambs were significantly higher than yhouse in undocked male lambs (P<0.05). Docked lambs were significantly superior in feed conversion as compared to undocked lambs. Feed efficiency in docked lambs was 1.28 percent higher than in undocked lambs (P<0.05). The length of the fattening period had significant effect on gain and final weight, but did not influence daily live weight gain and feed conversion during the fattening period. In conculsion, in order to increase production through increasing final weight, daily weight gain and improvement
of feed conversion during the fattening period, docking togheter with 75 days of fattening period in Lori-Bakhtiari lamb is recommended.