The distribution of calving hours in the dairy cow was described and a
nalyzed through a 2 550 sample relative to 3 breeds: Holstein, French-
Friesian, Montbeliarde (table I). Calving data (n = 2 031) from suckli
ng cows were used for comparison. All the data concerned cows kept in
stanchion stables during the winter period (October to March) in 2 exp
erimental farms in the mountain area of central France. The observed d
istributions for dairy cows differed from that of suckling cows, which
was more homogeneous; differences were observed between farms, but no
t between dairy breeds within farms (fig 1 and table I). The rhythm of
the presence and activity of cowmen explains the major pattern of cal
ving hours (tables III and IV). In the dairy cow, the mean diurnal fre
quency of occurrence of calving was higher when cowmen were absent (46
.4/1 000) than when they were present (35.3/1 000); the lowest frequen
cy occurred during milking (28.9). Difficult parturitions occurred mor
e frequently at daytime human interventions being scarce at night (fig
2). Consequently, diseases linked to calving concerned more daytime p
arturitions. We could not prove any effect of the lactation rank, the
milk yield in the first week, or calf sex or birth weight.