Data (n = 1725) were collected from 613 primiparous and multiparous Charola
is cows managed in an experimental herd over a 10-year period. The objectiv
es of the study were to describe the variability in the re-establishment of
postpartum reproductive activity. The duration of the postpartum anoestrus
period was estimated from progesterone concentrations in weekly blood samp
les, and from daily detection of oestrous behaviour. Oestrous behaviour was
first observed 71.9 days (+/- 27.2 S.D.) post-calving, and a first positiv
e progesterone concentration (greater than or equal to 1 ng/ml) was observe
d at 68.7 days (+/- 25.5 S.D.). There were differences in the chronology of
these events: a first positive progesterone test was detected before she f
irst oestrus in 51% of the cases. The duration of the first oestrous (25.6
+/- 16.4 days) and ovarian (2.8 +/-0.9 weeks) cycles varied according to th
e chronology of the events. Year and period of calving, calving difficulty
and parity (interacting with suckling status) significantly affected the du
ration of the postpartum anoestrus period. These results also showed an imp
ortant effect of individual female on the duration of postpartum anoestrus
with a repeatability of 37% for the interval to the first oestrus and 60% f
or the interval to the first positive progesterone test. (C) 2001 Elsevier
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