by Tamara Scully
The importance of cow comfort is not only an animal welfare concern: it impacts productivity, longevity, and the bottom line at the dairy. Comfortable cows are not only cows free from pain, they are cows that are housed in an environment that maximizes their genetic potential. The Cow Comfort Conference, hosted by Cornell Cooperative Extension North Country Regional Ag Team, was recently held in Syracuse, NY. The conference offered participants a comprehensive overview of dairy cow comfort concerns facing the industry.
One of the main issues in dairy barns today is overstocking. Stocking density can have detrimental effects on comfort, as cows are forced to compete for limited resources, such as comfortable stalls, food when they want it, and freedom from social pressures. Discomfort isn’t only due to pain — from lameness, mastitis or other health concerns — it is due to stress, and causes behavioral changes that result in reduced milk output and quality.
Mac Campbell, PhD candidate at the W. H. Miner Agricultural Research Institute, presented a workshop discussing his research on the interaction between stocking density and the feeding environment in the dairy barn. While overstocking increases the utilization of fixed cost resources, “overstocking consistently compromises the cow well-being,” he said. “It all comes down to the economics,” and whether the cow impacts from increased stocking density over 100 percent are enough to negate the increased overall herd milk production driving overstocking on many dairies.
There is some controversy over how much overstocking is too much. It can depend upon management, with good management able to negate some of the stress impact on cows. Every cow has a basal level of stress, which is the response to basic life requirements. The body has to be able to keep itself alive. The next level of stress involves the intermediate stressors associated with calving, reproduction and lactation. The cow environment adds the third level of stress.
It’s the environmental stressors which are multiplied in overstocked barns. The social hierarchy, with dominant and subordinate cows interacting, becomes more pronounced as crowding and competition for resources increases. The cow’s biological reserve is increasingly needed to respond to these environmental stressors, and as they mount, other bodily functions become unbalanced. Milk yield, reproductive success, and immune function become compromised.
Stressors and diet
The feeding environment can be a significant stressor. When low fiber diets are fed, the incidence of subacute ruminal acidosis (SARA) increases. Physically-effective fiber (peNDF) can play a role in counteracting this concern. The peNDF estimates the portion of fiber that stimulates chewing behavior, and is related to particle matter size and fiber content.
In overstocked situations, an increase in peNDF will result in more normal rumen function, and lesson the risk for SARA, Campbell said. His research examined two nutritionally equivalent diets, but with two different sources of forage fiber, fed to cows in a four-row barn. Cows were held at either 100 percent stocking density, or 142 percent stocking density.
“Significant interaction with stocking density and fiber formulation” was found, Campbell said.
When overstocked, the cows had the worst SARA response when fed the diet lower in peNDF. When compared to the cows that weren’t overcrowded, but fed the same low peNDF diet, the overstocked cows’ response was “exacerbated,” Campbell said.
When straw was added to the diets, it resulted in a decrease in SARA even in the overstocked situation. Diet can overcome some negative impacts associated with stocking density. A lower fiber diet itself is a negative risk factor, but not as much of one as the increased stocking density.
“Stocking density is actively contributing more to SARA than diet itself,” he said.
Even in overstocked situations, cows will maintain the same level of intake, but their feeding behaviors will need to change in order to meet those intake requirements, Campbell said. Coming back from the parlor, cows want to eat. But a high stocking density will cause a latency in eating, as less dominant cows seek out available stalls for resting.
If stalls aren’t clean, these cows won’t lie down and ruminate. They will ruminate standing up, but the quality of this rumination is not the same, and will increase the risk of SARA. While the total overall time spent eating and ruminating did not change in the 142 percent stocking density situation, the amount of pH buffering is probably what causes an increase in SARA, Campbell said. In overstocked situations, increasing the efficiency of resources by having the stalls ready when the cows come back from milking can decrease the risk of SARA.
“Location is very important for us,” he said. “Cows in an overstocked situation, they maintain their intake, but they alter their feeding behavior,” and are at greater risk of SARA.
If feed is not available when a cow wants to eat, SARA can increase, if the barn is overstocked. In a 142 percent stocking situation, with reduced access to feed, SARA rates increased. But in 100 percent stocking density studies, feed restriction itself did not increase SARA.
SARA risk increases the more time the rumen is below pH 5.8. Rumen pH decreases at the beginning of the day, and as cows ruminate throughout the day, the rumen pH increases. The increase in pH reduces the risk of SARA. Altering feeding practices to combat the risk early in the day would be one management change that can have a positive effect in an overstocked situation, Campbell said. Feeding different diets throughout the day, with added fiber in the second feeding, could help to combat the SARA risk associated with overcrowding. Having feed available at night in overcrowded barns may be beneficial, too.
Since overstocking is a reality, determining its actual impact and finding ways of decreasing the negative effects can lead to practical management changes and increased herd productivity. Farmers can assess how their environments serve to increase cow stress. Looking at clean stall availability, feed management practices, and overall cow comfort can lead to changes that can counteract the negative effects of overstocking.
A change in grouping strategies, so that first lactation cows are kept separated, can reduce social stressors. Increasing feed pushups, every 30 minutes for two hours post-feeding, is also a beneficial practice. Making sure that feed is available at all times, so subordinate cows can get to the feed when needed, can help.
“Give the cows that come up later access to the same feed,” Campbell said.
Stalls that are too small, improperly bedded for comfort, or not kept clean are concerns. Inadequate barn ventilation is also an environmental stressor. A chaotic environment is detrimental.
Overall, studies find that stocking densities over 120 percent lessen productivity, as “cows can’t make up” the lying time, and the resulting decreases in milk output, changes in reproduction, and increases in health issues will impact profitability. But this number can be variable, as good management practices — to negate the detrimental impacts seen in overstocking — can be the deciding factor in high-density situations.