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ST. CLOUD, Minn. - A great deal of research has been done on the effects of stocking density of lactating cows, but Peter Krawczel of the University of Tennessee and his cohorts are taking the subject to new depths.
In addition to analyzing previous research conducted on existing facilities around the world, they are conducting studies that look deeper into the pros and cons.
On Nov. 30 Krawczel presented "Interaction of Stocking Density, Productivity and Cow Comfort: What to Consider on Your Farm," during the Minnesota Milk Dairy Expo. Krawczel, an assistant professor in animal science, first reviewed existing studies, then turned his attention to current research.
Krawczel pointed out the importance of rest to a lactating dairy cow, noting that a cow typically spends 10 to 14 hours a day lying and resting. Research has shown that rest is priority, with cows opting to decrease feeding and social behavior time in order to rest. In overstocked situations, cows demonstrate less time before lying down. They come back from milking, skip feeding and lie down as a way of competing for stalls.
"Cows value rest the most," Krawczel said. "They'll give up meals to rest."
As overstocking increases, lying time decreases. Although overstocking can create an illusion of good stall comfort, it likely will result in decreased milk yield and may represent an increased risk of environmental mastitis.
"How much can we overstock? 120 percent is about the tipping point," Krawczel said.
Increased competition at the feed bunk also causes negative effects, among them decreased feeding time, aggression, increased standing time and a shift in feeding times. Those effects are greater at post-and-rail bunks, versus headlocks, since dominant cows have less ability to chase submissive cows away. Overstocking also causes increases in feeding rate, as cows try to consume feed in limited time.
Increased stocking densities also resulted in decreased rumination in the stall, versus in the alley, as cows were unable to access a stall to rest.
Overstocking affects heifers more than mature cows as dominant cows display territoriality in the use of freestalls, preferring those nearest the feed alley. Subordinate cows avoid stalls previously occupied by dominant cows. Research has shown that overcrowded conditions - from a subordinate perspective - may exist even at lower stocking densities.
In research that paired cows and heifers in one study, heifers suffered more milk loss than cows, due to reductions in resting and rumination activity.
Looking at preliminary evidence from on-going trials, Krawczel said four treatments were used in one study. A control group was stocked at 100 percent at both the feed bunk and stalls. A feed bunk group was at 160 percent stocking density at the feed bunk and 100 percent at the stalls. The freestall group was at 100 percent density at the feed bunk and 160 percent at the stalls. The both group was at 160 percent stocking density at both the feed bunk and stalls.
As expected, lying time decreased considerably for both the freestall and both groups (1.7 and 1.4 hours per day, respectively), and also decreased by a lesser amount (half-hour) for the feed bunk group which had to fight for feeding time.
"Is it better to provide stalls or feeding space? We're still working through the data, but overall access to freestalls appears to be the big thing," Krawczel said. "But, we should probably consider the quality of rest, more than the hours."
A non-invasive approach to assessing sleep in dairy cows - similar to sleep studies in humans - applied electrodes to various locations on the cow's poll, head and neck. It studied eye and neck muscle movements to observe sleep patterns of cows in box stalls. Sleep was divided into drowsing, non-REM sleep and REM sleep. Those categories, along with minutes of rumination per day, were studied as they related to stage of lactation.
When one cow in the study came down with E. coli mastitis, the patterns were analyzed, with rumination severely limited on day 1 and day 2, but bouncing back on day 3. Drowsing time increased while REM dropped considerably while the cow was sick.
Using a collaborative grant from the USDA, the study found that cows in confined spaces were subjected to either 24-hour sleep deprivation or 24-hour lying deprivation. In the sleep deprivation study, cows were nudged awake every time they tried to sleep. A grid was used to prevent cows from lying down in the second study.
Researchers are currently working through the data to determine the effect on milk production and recovery, and how it would apply to pens of cows. As expected, lying time increased drastically for both treatments after the deprivation. Daily milk production decreased the day after lying deprivation, but stayed fairly steady for sleep deprivation.
Krawczel next addressed the effects of inadequate feeding environments, noting especially sub-clinical stresses of overstocking. While cows may be able to use reserves to handle overstocking as a single stressor, a combination of stocking density and dietary stressors can cause negative effects.
"It comes back to where cows are ruminating," Krawczel said. "There's a decrease in rumination in freestalls. They're ruminating while standing. Saliva is on the barn floor, rather than being swallowed."
Although not studied as much, Krawczel said the importance of behavioral and physiological responses of dry cows to stocking densities. A historic perspective on the effect of stocking density on DMI intake of dry cows indicated that stocking rates greater than 90 percent, with headlocks, results in decreased intake.
Stocking densities of 80 percent of stalls and headlocks result in lost milk for the first 83 days in milk. For each 10 percent increase above 80 percent, there was a 1.6 pound/day milk decrease. Metabolic disorders - milk fever, ketosis, DA and RP - also increase in overstocked cows. As expected, heifers are most severely affected by overstocking as they have to fight to gain access to the feed bunk.
In conclusion, Krawczel said it's important to recognize the relationship among management, stocking density and productivity - and that producers need to think about quality of lying time, not just total hours.[[In-content Ad]]

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