43 (2) : , 1997

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1 43 (2) : A cta Zoologica S inica 3 ( ) ( ) ; ( ) ; 17 2 ; ( Bos grunniens) % m ( Yu et al. 1992b 1993a 1993b 1993c) m ; (No )

2 2 : 179 : (7 ) (6 ) (8 : 00) (20 : 00) 10 15ml 1 % 0115ml 1 % 0115ml ( - 25 ) 112 : (1992a) L H/ hcg 125 I - hcg hcg 0120 ng/ 8121 % ( n = 10) % ( n = 5) % : ( Yu et al. 1993b) 4102 pg/ % 7165 % ( n = 10) % ( n = 2) 17 2 : ( Yu et al. 1993b) 5101 pg/ % 4189 % ( n = 10) % ( n = 2) 113 ( x) ( SD) Student s t : ( ) ; ( ) : ; : 10 (2414 %) (4115 %) 1 6 (1416 %) ; 9 : ; ; : / 1 3 ( ) ;

3 ( ) 015cm 1 017cm 2 3 ( ) cm ; cm 1 ( ) 019 1cm ; ng/ ml ; 5 ( - 5) - 2 ( ng/ ml) ; - 1 (0 ) ng/ ml pg/ ml ; 8 6 ( - 8-6) ( pg/ ml P > 0105) - 2 ( pg/ ml) ; - 1 (0 ) ( pg/ ml) pg/ ml ( 1) Fig. 2 Changes of plasma luteinizing hormone Fig. 1 Changes of plasma progesterone and concentrations during oestrus in yak 17 2oestradio1 concentrations around oestrus in yak ng/ ml (0 ) ( ng/ ml) ( P > 0105) ; 10 ( ng/ ml P < 0101) 11 ( ng/ ml)

4 2 : 181 ( P > 0105) ( ng/ ml) ; 17 ( ng/ ml P > 0105) 1 (015 1 ) ( Y 46 ) ( 3) 3 3 Y 46 Fig. 3 Changes of plasma luteinizing hormone concentrations during oestrus of yak No ( 1981) ( 1980) ( ) ; ( Yu et al1 1993b) (7 10 ) ( 3 ) Hunter (1986) Webb (1980) (Berardinelli et al ; Gonzalez2Padilla et al. 1975) Dodson (1988) 17 2

5 ; ( Yu et al. 1993a 1993b) ( Walters and Schallenberger 1984) ( Carr 1972) : a. 2 : : Berardinelli J. G. R. A. Dailey R. L. Butcher and E. K. Inskeep 1980 Source of circulating progesterone in prepubertal ewes. Bio. Reprod. 22 : Carr W. R Radioimmunoassay of luteinizing hormone in the blood of zebu cattle. J. Reprod. Fert. 29 : Dodson S. E. B. J. Mcleod W. Haresign A. R. Peters and G. E. Lamming 1988 Endocrine changes from birth to puberty in the heifer. J. Reprod. Fert. 82 : Gonzalez2Padilla E. J. N. Wiltbank and G. D. Niswender 1975 Puberty in beef heifers. J. A ni m. Sci. 40 : Hunter M. G. J. A. Southee B. J. Mcleod and W. Haresign 1986 Progesterone pretreatment has a direct effect on GnRH2induced preovulatory follicles to determine their ability to develop into normal corpora lutea in anoestrous ewes. J. Reprod. Fert. 76 : Walters D. V. and E. Schallenberger 1984 Pulsatile secretion of gonadotrophins ovarian steriod and ovarian oxytocin during the periovulatory phase of the oestrous cycle in cow. J. Reprod. Fert. 71 : Webb R. G. E. Lamming and N. B. Haynes 1980 Plasma progesterone and gonadotrophin concentrations and ovari2 an activity in postpartum dairy cows. J. Reprod. Fert. 59 : Yu S. J. Y. M. Huang and B. X. Chen 1992b Postpartum ovarian function in yak cows as revealed by concentra2 tions of progesterone in defatted milk. Recent A dvances in A ni mal Production proceeding of the Sixth A ni mal Science Congress of A A A P. 3 : 93. Yu S. J. Y. M. Huang and B. X. Chen 1993a Reproductive patterns of the yak. I. Reproductive phenomena of the female yak. B r. Vet. J. 149 : Yu S. J. Y. M. Huang and B. X. Chen 1993b Reproductive patterns of the yak. II. Progesterone and oestra2 dio1217 1evels in plasma and milk just before the breeding season ; also during normal and short oestrous cycles. B r. Vet. J. 149 : Yu S. J. Y. M. Huang and B. X. Chen 1993c Reproductive patterns of the yak. oestradio1217 during pregnancy and the periparturient period. B r. Vet. J. 149 : III. Levels of progesterone and

6 2 : 183 ( Abstract) CHARACTERISTICS OF REPROD UCTION AND RELATED HORMONE CHANGES AROUND OESTRUS IN YAK YU Si2Jiu CHEN Bei2Heng ( Depart ment of Veterinary Medicine Gansu A gricult ural U niversity L anzhou China) The reproductive characteristics of 42 multiparous yaks around oest rus were examined by clinical observation and rectal palpation. Concent rations of plasma progesterone and oestradiol217 in 6 subjects during this period were measured by radioimmunoassay ( RlA) and luteinizing hormone was analyzed by radioreceptor assay ( RRA). At t he beginning of the breeding season all examined animals showed oestrus2like pro2oestrus signs for 1 5 ( ) days before they were in heat. The length of oestrus was ( ) days in the animals mated at the beginning of oestrus or in early oestrus (78 %) ; it lasted days in those animals which were mated in late oestrus (12 %). Ovulation oc2 curred hours from the onset of oestrus. The baseline level of oestradiol217 before the first oestrus was pg/ ml ; a peak of pg/ ml occurred 8 6 days before oestrus which was similar to that on the day of oestrus ( pg/ ml P > 0105) ; it declined to the baseline level at the end of oestrus. The baseline level of pro2 gesterone before the first oestrus was ng/ ml ; a small peak of ng/ ml appeared 2 days before oestrus ; it then decreased and maintained at a low level until the end of oestrus. The reason of the temporal increase in oestradio1217 and progesterone before the first oestrus might be a transition to the normal cyclic activity at the beginning of the breeding season. The baseline level of luteinizing hormone plateau appeared hours after the onset of oestrus with a maximum of ng/ ml occurred at 14th hour ; it declined to the baseline level at the 17th hour. Key words Yak Reproductive characteristic Progesterone Oestradiol217 Luteinizing hormone Around oest rus