Because of costs associated with the construction and maintenance of freestall barns, dairy farmers may limit the number of feeding and resting places available for cows in order to maximize utilization of facilities. Facility design, such as whether there are two or three rows of stalls per feedline, may also influence the number of cows that have to share a particular resource. However, the impact of overcrowding on cow behavior, welfare and productivity should be considered.
At pasture, dairy cows tend to synchronize their grazing and lying behavior – that is, most cows will eat or lie down at the same time. Indoors, such synchronization may be less pronounced, but it is often still evident and may be strongly influenced by management procedures such as the delivery of fresh feed or time of milking. The synchronization of dairy cattle behavior, along with a limited number of feeding and lying places, means not all cows will be able to eat or lie down at once.
Studies that have investigated the effects on cow behavior of a limited number of freestalls found the total lying time of cattle over a 24-hour period was reduced because of overcrowding. Even at relatively low overstocking rates (25 percent overcrowding or 1.25 cows per freestall), Wierenga and Hopster found reductions in the total daily lying times of some cows. At low overstocking rates, the lying times of only low-ranking cows seem to be affected, while at higher overcrowding rates the lying times of all cows are affected.
Under conditions of one stall per cow, very often 90 percent or more of the cows are in the stalls during the night and very few cows stand inactive in the alleys at any time throughout the day. However, time spent standing inactive in the alleys is significantly higher in overcrowded conditions, and this is particularly evident at night.
Furthermore, overcrowding may lead to cows (particularly low-ranking cows) lying in the alleys at night when all stalls are occupied, but cows are highly motivated to lay down. This aberrant behavior has obvious implications for cow cleanliness and the risk of mastitis.
Reduced daily lying times and increased time standing on hard surfaces are behaviors associated with increased rates of hoof lesions and lameness. Hence, a reduction in lying time (and consequently increased time spent standing in the alleys) as a result of overcrowding may increase the risk of lameness, with obvious implications for cow welfare and productivity.
Furthermore, adequate rest is necessary to ensure high production, and blood flow to the udder is increased when cows are lying down. Cows also tend to ruminate (chew their cud) when lying down compared to when standing up, so maximizing lying time is also important for optimizing rumination time.
Disturbed rest leads to physiological changes in cattle usually indicative of stress and are likely to affect cow health and milk production. Therefore, to maintain high levels of production, health and welfare, it is essential dairy cows are able to optimize their time spent resting.
Overcrowding the feeding area
Friend et al. found time spent eating was not reduced until only 0.1 meters of feeding space per cow was provided (space allowance ranged from 0.5 meters to 0.1 meters per cow), and Collis et al. found total feeding time did not change when feeding space was gradually reduced from 1.05 meters to 0.15 meters per cow.
Similarly, Wierenga and Hopster found overcrowding the number of feeding places by 25 to 55 percent had almost no consequences on eating time. It was suggested the limited effect of overcrowding on total eating time may be due to the relatively short amount of time cows spend eating each day (around four hours), which would enable a cow to easily compensate for changes in the opportunities to eat that occur as a result of overcrowding.
However, in contrast to findings from earlier studies, more recent research by DeVries et al. found when cows had access to more feeding space (1.0 meter versus 0.5 meters of feeding space per cow), cows increased their feeding activity throughout the day and especially during the 90 minutes after fresh feed was provided.
At 30 percent overcrowding of headlocks (1.3 cows per headlock), Batchelder found reduced daily dry matter intakes (DMI) and substantially fewer cows eating during both the hour following milking and following delivery of fresh feed. Interestingly, Batchelder also found overcrowded cows spent significantly less time ruminating during a 24-hour period than did cows not overcrowded.
Huzzey et al. found for both post-and-rail and headlock feed barriers, overcrowding resulted in reduced feeding times and increased time spent standing inactive in the feeding area. These changes were most obvious during the times of peak feeding activity (within 60 minutes following the delivery of fresh feed).
Mentink and Cook compared freestall pens with two or three rows of stalls per pen, which provide for very different amounts of feed space per cow when freestalls are stocked at similar rates. These authors found the extra feed space per cow in a two-row pen improved access to feed at peak feeding times.
All cows are motivated to access feed when fresh feed is delivered, but when feeding space is inadequate, some cows may be prevented from feeding at the time of fresh feed delivery and, consequently, may be forced to shift their feeding time. Research has indicated cows will sort a total mixed ration (TMR), and hence feed quality declines throughout the day. Thus, cows that are forced to delay their feeding time because of overcrowding may consume a poorer quality diet.
Furthermore, when cows do not have access to feed when they want to eat, they may overeat following a period of feed deprivation. This could happen when cows have limited access to feed because of overstocking. Increased feeding competition may reduce intake and increase feeding rate, possibly increasing the risk for metabolic problems such as left-displaced abomasums and subacute ruminal acidosis.
Increased aggression in the feeding area when cows are overcrowded has also been noted. Aggression could have consequences for hoof lesion development and lameness. Shaver also suggested the potential for laminitis may be greater when overcrowding of freestalls coincides with limited feeding space (as is often the case). This is because cows may spend more time standing on concrete rather than lying in stalls and consume fewer but larger meals or have reduced feed intake.
It is important to realize that even when freestalls are not overstocked, social and environmental factors may still reduce the number of available or preferred resting places. For example, stalls in some locations may not be used because of close proximity to a water trough, high volume of cow traffic or location in a draft.
Low-ranking cows will also prefer not to use a stall adjacent to a higher-ranking cow, and a cow lying in a stall may occupy part of a neighboring stall with their legs, head or back, which would prevent another cow from lying down in the vacant stall. Thus, the implications of overstocking resting and feeding areas for cow behavior, health, production and welfare should be carefully considered. PD
References omitted due to space but are available upon request.
—From Buckeye Dairy News, Vol. 8, No. 4
Naomi Botheras, Animal Welfare Program Specialist, Ohio State University