In most cases, when freestalls are overstocked,
bunk space is restricted simultaneously. Caraviello et
al. (2006) reported that bunk space per cow was one
of the most important explanatory variables affecting
pregnancy status at 150 d postpartum, although it was
not found to be significant in the current model.
In the present study, a longer VWP was associated
with improved conception rate. Caraviello et al. (2006)
found a positive relationship between length of the
VWP and first-service conception rate. Foote (1978)
found that cows serviced before 50 d postpartum had a
lower conception rate than those serviced after a longer
postpartum period. Also, cows in an Ovsynch group
with VWP >76 d had a greater conception rate than
cows with a VWP between 60 and 75 d (Pursley et
al., 1997). In contrast, Schneider et al. (1981) observed
that cows serviced very late after calving (93 ± 17 d)
had lower fertility than cows serviced earlier (72 ± 18
d). The maximum VWP in the present study was 80 d
postpartum, so the efficacy of a VWP greater than 80
d postpartum is subject to greater uncertainty because
of extrapolation.