---

NORWOOD-YOUNG AMERICA, Minn. - Unlike people, dairy cows are more likely to give up eating and social time in favor of resting time. That's one result of studies to observe the effects of overcrowding on cow health and productivity. Peter D. Krawczel of the University of Tennessee presented the findings at the Carver County/University of Minnesota Dairy Expo & Trade Show on Feb. 20.
Krawczel began his presentation with a discussion of the typical time budget of a lactating dairy cow. Basic behavioral needs include three to five hours/day eating, 10 to 14 hours/day lying (resting), two to three hours/day standing/walking in the alley (grooming, agonistic, estrous activity), and a half hour/day drinking, for a total of 20.5 to 21.5 hours/day needed. That leaves 2.5 to 3.5 hour/day for milking, herd health checks, etc.
Overstocking reduces a cow's ability to practice natural behaviors, but may improve economic returns on facility investments, making the question "What is optimal stocking density to avoid compromising health and productivity?"
Krawczel put it another way, "Are we taking advantage of the cow and her natural abilities or are we just taking advantage of the cow?"
The studies found that cows have strong behavioral needs to rest. They'll sacrifice feeding time to make up lost resting time and will spend more time waiting in alleys to lie down than eating when barns are overstocked. Further, it was found that they're unable to recover from deprivations of two to four hours, such as being locked in headlocks. They'll alter their behavior for the next four days to make up for it.
Benefits of adequate rest include reduced stress on hooves, greater blood flow to the uterus, lower cortisol, increased bGH, and greater milk yield-about 3.5 pounds for each additional hour.
Although they spend less time eating, overstocked cows eat about 25 percent faster-but ruminate an hour a day less.
In addition, overstocked cows experience greater pathogen load in the environment, greater teat end exposure, and may experience immune suppression. Preliminary data indicates that clinical mastitis events per lactation increased significantly when overstocking reached the 140 percent level.
Similarly, negative impacts were observed in reproduction as a result of overstocking. Decreased bunk space-24 inches down to 12 inches-was associated with linear decreased percentage of cows pregnant at 150 days in milk, dropping from 70 to 35 percent. Overstocking of stalls in breeding pens was associated with reduced conception rates. The reason appears to be greater aggression at feeding, reduced lying time, and reduced compliance with synch programs.
With studies carried out at various levels of overstocking, research seems to suggest a maximum level of 120 percent before negative effects outweigh any positives.
Krawczel left the group with the message that the relationship between milk yield and stall availability/resting time is evident, but the effect is variable; reproduction is negatively affected by overcrowding at the feed bunk and in stalls; and that detrimental effects on the time budget may explain the impact of the stocking density. Detrimental effects, especially related to reproduction, contribute to cows leaving the herd.[[In-content Ad]]

---