The effects of overcrowding on the behavior of lactating dairy cows in free-stall housing systems
Overcrowding is commonly seen among free-stall dairy operations in order to increase herd size without altering facilities. Overcrowding occurs at stocking densities greater than 100%. Overcrowding at the feedbunk is defined as greater than one cow per headlock or less than 0.6 m of linear feedbunk space per cow. Overcrowding at the resting space is defined as providing less than one stall per cow. At maximum capacity, 48.5% of free-stall farms in the US provided less than one stall and 67.9% provided less than 0.6 m of feedbunk space per animal (USDA, 2010). These crowded environments interfere with time budgets of cows by disrupting lying and feeding behaviors. A normal behavior time budget for a lactating dairy cow includes 3-5 hours of eating per day (Grant & Albright, 2001). As stocking density increased, time cows spent feeding decreased while feeding rate increased. This may alter intake during these feeding bouts. Increased feeding rate may increase the risk for ruminal acidosis and displaced abomasums after calving. Aggressive interactions among animals resulting in displacements from the feedbunk also occur more frequently in overcrowded pens (DeVries et al., 2004). Providing 0.5 m of feeding space as opposed to 0.1 m of feeding space resulted in 60% less space between animals and 57% more aggressive interactions while feeding. Subordinate animals are most affected as they will often be displaced from the bunk by a dominant animal. Feed quality tends to decline throughout the day as TMR is sorted, and submissive cows will ultimately consume a poorer quality diet after waiting for feed bunk access. A typical lactating dairy cow will rest for 12-14 hours per day to meet her daily time budget (Grant & Albright, 2001). Cows prioritized rest, and will choose to rest rather than eat when both lying time and feeding time are limited (Munksgaard et al., 2005). At stocking densities of 150%, cows spent 1.7 hours/day less lying relative to those housed at 100% (Fregonosi et al., 2007). These data may help explain the positive relationship between milk production and free stall availability described by Bach et al. (2008). Krawczel et al. (2008) reported average time standing idly in the ally also increases at stocking densities above 110%, which is associated with an increased risk for lameness.
Keywords: overcrowding, free-stalls, stocking density