Page 353 - The Welfare of Cattle

330 the WeLfare of CattLe

at 131% and 142% (Krawczel et al., 2012). A separate study found notable neuroendocrine and meta-
bolic changes in cattle stocked at 200%, but mild overstocking of 120% did not produce any changes
in immune response, milk yield, or reproductive performance (Chebel et al., 2016).
Two separate studies found that cattle in confinement systems display more agonistic behavior
than those on pasture (9.5 vs. 1.1 per hour) (Miller and Wood-Gush, 1991), with peaks in aggression
occurring around delivery of fresh feed (O’Connell et al., 1989). These studies also noted synchrony
of feeding and lying behavior was diminished in confinement systems. Roca-Fernández et al. (2013)
reported cattle on pasture had longer feeding times than those in confinement (522 vs. 173 minutes),
but also lower milk production (20.1 vs. 27.0 kg/day). A separate study found a similar trend in
milk production and suggested cattle on pasture needed disproportionately more time to eat given
the generally lower nutritional density of pasture (Navarro et al., 2013). This might also explain the
tendency for pastured cattle to have increased standing times and decreased lying times relative to
cows housed in intensive systems. Thus, the discrepancies in agonistic behavior found between the
extensive and intensive housing systems are likely attributable to extensively reared cattle being
preoccupied with grazing and the much lower stocking densities typically found in pasture-based
systems.
Differences in feeding and social behavior are also sensitive to stocking rate. Increasing stall stocking
density (SSD) from 80% to 100% results in an increase in feed bunk displacements (Lobeck-Luchterhand
et al., 2015). Similarly, increased competition for bunk space leads to decreased feeding time, increased
idle time spent standing, and increased feed bunk displacements (Huzzey et al., 2006). Proudfoot and
colleagues (2009) echoed these results, finding displacements and standing time increased when the
ratio of cows to feed bins increased from 1:1 to 2:1. Other authors have reported a linear relationship
between displacement behavior and SSD in groups stocked at 100%, 113%, 131%, and 142%. The most
overcrowded cows in this study had drastically reduced lying times, as a result of increased competition
for stalls (Krawczel et al., 2012).
Stocking density represents only one aspect of pen management’s impact on social behavior
of cattle. Regrouping cows is a common practice as cows move from one phase of the production
cycle to the next. More frequent regrouping leads to increased feed bunk displacements, decreased
lying times, and transient losses in milk production (von Keyserlingk et al., 2008). Competitive and
agonistic behaviors also occur more frequently among cows subjected to frequent group changes
as opposed to those managed in an all-in/all-out model that maintain more stable group structures
(Lobeck-Luchterhand et al., 2014). These negative effects may not be borne equally by all cows.
Wierenga and Hopster (1990) found the impact on resting time on low rank cows is greater at rela-
tively low stocking densities (1.25 cows per stall), but others have failed to find an effect of social
rank (Fregonesi et al., 2007).
Changes in social behavior appear to interact with both stocking density and group composition.
For example, at 120% SSD, weekly pen moves increase feed bunk displacements, but do not alter
immune responses or several health and production measures, as long as heifers and cows have sep-
arate housing (Chebel et al., 2016). In free stall systems, it is very difficult to avoid group changes,
especially on smaller farms which may lack excess of pens. In these circumstances decreasing stall-
stocking density to 25% or 50% can mitigate increases in competitive behavior and negative effects
on lying time, although this may not be realistic on many commercial farms (Talebi et al., 2014).
Several caveats of the research on stocking density and group composition are worth mention-
ing. First, much of this research has relied on groups of animals (e.g., between 6 and 24 cows)
much smaller than those typically found on many commercial farms. It is therefore not clear how
translatable these research findings are to farms with larger group sizes. Moreover, the effects
of stocking density also apply to pasture-based dairies, yet very little research has investigated
the effects stocking rate have on social, feeding, and lying behavior in extensive systems. Unlike
intensive systems, forage production thresholds are likely to be the major factor limiting stocking
rates in pasture-based systems. More research is needed to understand how stocking density affects