nutrients provided, within reason
(Albright, 1993; Grant and Albright, 1995).
Cow space, cow density and distribution of
feed and water facilities all influence feed
intake. Feed intake generally will improve
when cows are allowed access to feed
when they want to eat, such as leaving the
milking parlour. Feed restriction can occur
under a number of conditions. Apart from
simply providing inadequate amounts of
feed daily, other common, but less obvious,
causes include excessive time spent in
holding areas, time spent in exercise lots
without access to feed and water, unstable,
highly fermented silage, poor ventilation,
slippery floors, inadequate or poorly main-
tained free stalls, rough feeding mangers,
and overcrowding that results in inadequate
stall or bunk space (Grant and Albright,
1995).
Menzi and Chase (1994) concluded
that 0.37–0.40 m of bunk space per cow
did not necessarily restrict feed intake.
Periods of full bunk use were few during a
24-h period. Herd 1 exhibited four periods
when the feed bunk was fully occupied.
These periods were brief, lasting only
approximately 15 min. Herd 2 had only
one brief point of restricted bunk space and
two periods of nearly full utilization of
feeding space. In both herds, peak feed
bunk usage was typically followed by a
rapid decline in feeding activity, parti-
cularly in Herd 2. Although current recom-
mendations for linear feed bunk space are
0.61 m per cow, research results and on-
farm observations of high-producing herds
with large group sizes indicate that 0.21 m
per cow is near the critical bunk space.
One should consider, however, the differ-
ence between minimum bunk space that
can be tolerated in existing facilities with
excellent management and desired bunk
space in newly designed facilities. Barns
tend to become overcrowded with time,
and underdesigning a barn with regard to
bunk space may not be advisable. The
actual optimal bunk space will be a
function of feed availability throughout
24 h, relative to when cows want to eat,
and the degree of crowding and competition
placed on the cows by grouping strategy.
Future research must focus on the rela-
tionships among feeding management,
bunk space and barn design with feeding
behaviour and feed intake of higher milk-
yielding dairy cattle.Bunk space for dairy heifersMuch less is known about the need for
feeding space and the feeding behaviour of
dairy heifers at various ages and body
sizes. Maintaining adequate growth of a
group of heifers, and also of the individual
heifers within a group, depends on the
housing and feeding system, and their
impact on comfort and feeding behaviour.
To achieve growth rates that allow parturi-
tion at 24 months of age requires that bunk
space should not limit feed intake.
Previous recommendations were based on
heifers with much slower rates of gain than
currently desired. Beef cattle research
indicates that an animal within a group is
able to maintain adequate growth rate, or
even exceed it, when allowed 0.15 and
0.13 m of feed bunk length per animal
under conditions of restricted feed intake
with daily gains of 1.45 and 1.07 kg day^1
(Gunter et al., 1996).
Recent research (Longenbach et al.,
1997) evaluated the amount of feed bunk
space required by dairy heifers at various
ages grown at uniformly rapid rates of gain
to achieve adequate size and body weight
for parturition by 24 months of age. Three
groups of heifers were defined by an
average age of 4, 11.5 and 17 months. Bunk
space of 0.15, 0.31 and 0.47 m per heifer
was evaluated. Heifers were fed a TMR at
restricted intakes to achieve an average
daily gain of either 0.82 kg (4 and 11.5
months of age) or 0.91 kg day^1 (17 months
of age). The authors concluded that, based
on the observed feeding and growth
responses for each group, the following
feed bunk space recommendations are
optimal for rapidly growing Holstein
heifers being fed a TMR in either a free stall
or loose housing system: 0.15 m for 4–8
months of age, 0.31 m for 11.5–15.5 months
of age, and 0.47 m for 17–21 months of age.Feeding Behaviour 371