Effects of Overstocking on Cow Behavior, Welfare, and Productivity

Dr. Naomi Botheras, Animal Welfare Program Specialist, The Ohio State University 

Due to costs associated with the construction and maintenance of free stall barns, dairy farmers may limit the number of feeding and/or resting places available for cows to maximize utilization of facilities. Facility design, such as whether there are two or three rows of stalls per feeding line, may also influence the number of cows which 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 lay down at the same time. Indoors, such synchronization may be less pronounced, but is often still evident and may be strongly influenced by management procedures, such as the delivery of fresh feed and milking. The synchronization of dairy cattle behavior, along with a limited number of feeding and/or lying places, means that not all cows will be able to eat or lay down at once.

Overcrowding free stalls

Studies which have investigated the effects on cow behavior of a limited number of free stalls found that the total lying time of cattle over a 24-h period was reduced due to overcrowding (Friend et al., 1977; Wierenga and Hopster, 1990; Leonard et al., 1996; Dippel et al., 2005). Even at relatively low overstocking rates (25% overcrowding, or 1.25 cows per free stall), Wierenga and Hopster (1990) 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% 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 during the 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 (Wierenga and Hopster, 1990; Leonard et al., 1996). This aberrant behavior has obvious implications for cow cleanliness and the risk of mastitis.

Reduced daily lying times (Colam-Ainsworth et al., 1989; Leonard et al., 1994, 1996; Chaplin et al., 2000) and increased time standing on hard surfaces (Greenough and Vermunt, 1991; Singh et al., 1993) are behaviors that have been associated with increased rates of hoof lesions and lameness. Hence, a reduction in lying time (and consequently increased time spent standing in the alleys) due to 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 that are usually indicative of stress and which are likely to affect cow health and milk production. Therefore, to maintain high levels of production, health, and welfare, it is essential that dairy cows are able to optimize their time spent resting.

Overcrowding the feeding area

Friend et al. (1977) found that time spent eating was not reduced until only 0.1 m of feeding space per cow was provided (space allowance ranged from 0.5 m to 0.1 m per cow), and Collis et al. (1980) found total feeding time did not change when feeding space was gradually reduced from 1.05 m to 0.15 m per cow. Similarly, Wierenga and Hopster (1990) found that overcrowding the number of feeding places by 25 to 55% had almost no consequences on eating time. It was suggested that the limited effect of overcrowding on total eating time may be due to the relatively short amount of time that cows spend eating each day (around 4 hours), which would enable a cow to easily compensate for changes in the opportunity to eat that occur due to overcrowding.

However, in contrast to findings from earlier studies, more recent research by DeVries et al. (2004) found that when cows had access to more feeding space (1.0 m vs. 0.5 m of feeding space per cow), cows increased their feeding activity throughout the day and especially during the 90 min after fresh feed was provided. At 30% overcrowding of headlocks (1.3 cows per headlock), Batchelder (2000) found reduced daily dry matter intakes and substantially fewer cows eating during both the hour following milking and following delivery of fresh feed. Interestingly, Batchelder (2000) also found that overcrowded cows spent significantly less time ruminating during a 24-h period than did cows that were not overcrowded. Huzzey et al. (2006) found that 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 min following the delivery of fresh feed). Mentink and Cook (2006) compared free stall pens with 2 or 3 rows of stalls per pen, which provide for very different amounts of feed space per cow when free stalls are stocked at similar rates. These authors found that the extra feed space per cow in a 2-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 that cows will sort a TMR, and hence feed quality declines throughout the day. Thus, cows that are forced to delay their feeding time due to overcrowding may consume a poorer quality diet. Furthermore, when cows do not have access to feed when they want to eat, they may over-eat 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 (Shaver, 1997, 2002). Increased aggression in the feeding area when cows are overcrowded has also been noted (Olofsson, 1999; DeVries et al., 2004; Huzzey et al., 2006). Aggression could have consequences for hoof lesion development and lameness. Shaver (2002) also suggested that the potential for laminitis may be greater when overcrowding of free stalls coincides with limited feeding space (as is often the case), 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 free stalls 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 due to close proximity to a water trough or high volume of cow traffic, or because they are located 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/or feeding areas for cow behavior, health, production, and welfare should be carefully considered.

*A complete list of research references is available on request.