Forty bitches in anoestrus for more than six months from the last heat, with a 
serum progesterone level less than 1 ng/ml were subjected to oestrus induction 
trials using anti-prolactin drugs and levothyroxine, once daily orally for 20 
consecutive days. The mean serum progesterone level among them was found to be 
0.57 +/- 0.03 ng/ml. Out of 10 animals treated in each group, five (50%) in 
Group I (bromocriptine @ 50 microg/kg body weight), nine (90%) in Group II 
(cabergoline @ 5 microg/kg body weight), eight (80%) in Group III (thyroxine @10 
microg/kg body weight) and seven (70%) in Group IV (thyroxine @ 5 microg/kg body 
weight) responded by evincing proestrual bleeding. The mean (+/-SEM) time taken 
from initiation of treatment to onset of proestrual bleeding in Groups I, II, 
III and IV was 28 +/- 3.39, 13.44 +/- 3.12 (P < 0.05), 24.50 +/- 3.18 and 33 +/- 
2.21 days respectively. The mean (+/-SEM) duration of proestrus and oestrus in 
the treatment groups was 9.80 +/- 0.86, 10.11 +/- 0.68, 11.25 +/- 0.88 and 10.71 
+/- 0.68 days and 7.60 +/- 0.24, 8 +/- 0.29, 8.5 +/- 0.63 and 7.85 +/- 0.46 days 
respectively. The conception rate in relation to the number of animals 
responding to oestrus induction in the treatment groups was 80%, 78%, 63% and 
57%, respectively. The mean (+/-SEM) gestation length calculated from the last 
breeding date and litter size in the treatment groups varied from 60.50 +/- 1.55 
to 64.00 +/- 0.82 days and 5.14 +/- 0.34 to 6.40 +/- 0.40 respectively.