John Maday
Within limits, higher stocking rates can increase production while reducing fixed costs on a per-cow basis. At some point though, overstocking can negatively affect cattle welfare, feed intake, reproduction and productivity.
In a webinar this week hosted by the Dairy Cattle Welfare Council, Dairy Scientist Rick Grant, PhD., President of the William H. Miner Agricultural Research Institute in New York, outlined research to determine the practical limits of overstocking, and at what level the law of diminishing returns takes over. Dairy producers, Grant says, often walk a fine line between stocking rates that benefit profitability and those that negatively affect health, welfare and performance.
Grant defines overcrowding based on three main parameters:
Greater than one cow per headlock.
Less than 60 cm (24 inches) of linear bunk space per cow.
Less than one stall per cow.
Research has shown that about 58% of dairies provide less than 24 inches of bunk space and 43% use fewer than one stall per cow, Grant says.
Grant cites a Stall Stocking Density Calculator developed by dairy scientists at the University of Florida. The calculator allows the user to enter specific herd information including milk loss, conception rates, culling rates and milk and feed prices. In tests using a variety of scenarios, Grant says, the calculator indicates that 120% stocking rate is optimal for profitability. Maximum profit per stall occurs at greater than 100% stocking rate in 67% of the scenarios tested, and at greater than 120% in 42% of scenarios.
Grant describes excessive overstocking as a sub-clinical stressor in dairy herds. While not apparent through physical signs, sub-clinical stress leaves an animal less fit and able to respond to additional stressors. Farm-to-farm differences in response to overstocking, he adds, probably result from variation in other stressors present on farms.
Evaluation of stocking density, he says, requires understanding of how it affects natural cow behavior. On average, cows spend around 70 to 80% of their time either resting or feeding. They prioritize resting though, potentially at the expense of feeding time, and lying time decreases at higher stocking rates. Summarizing multiple studies, Grant says some show a linear decline in lying time as stocking density increases above 100%.
Others do not show much decline until stocking reaches 120%, but virtually all the studies show declines in lying time as stocking rates exceed 120%. If stocking density does not affect lying time, he adds, performance is less likely to be affected.
Crowded cows can, he says, adjust their feeding behavior somewhat, but at some point, overstocking results in greater aggression and displacement, changes in time of eating, fewer meals and faster eating. Younger cows, he says, become more likely to fall behind due to competition at the bunk.
Stocking rate, and its influence on feeding behavior also affects the incidence of sub-acute ruminal acidosis. In fact, research has shown that the feeding environment affects rumen pH as much or even more than the diet itself.
Research has shown that primiparous cows in an overstocked situation experience greater declines in dry-matter intake than multiparous cows. In a 2012 study, researchers gave primiparous cows a choice of eating a low-palatability, low-quality feed with no competition at the bunk or a high-quality feed with competition for bunk space from an aggressive older cow. Most, Grant says, chose the low-palatability feed over competing. Other studies have shown declines in milk production, conception rates and pregnancy rates as crowding increases. In a 2008 trial, researchers saw steady increases in milk production as stalls per cow increased from 0.4 to 1.6. Research also has shown that the spread in milk production between primiparous and multiparous cows widens as stocking rates increase, indicating that younger cows suffer more from overcrowding in mixed-parity pens.
Also, Grant says, research has shown that herds with high de novo fatty acid synthesis are associated with greater bunk space per cow.
Ideally, for management and consumer perceptions, Grant says farms would provide one stall for every cow in a freestall barn. That’s probably not economically feasible in many cases though, and he says good management can allow some moderate overcrowding.
The ideal stocking rate varies depending on the management system, but Grant generally recommends the following:
For lactating cows in four-row barns, keep stocking rates below 120%. In mixed-parity pens, stock at around 100% of capacity.
For lactating cows in six-row pens, reduce stocking rates to closer to 100%.
For close-up and fresh cows, stock at around 80% of bunk capacity, or about 30 inches of bunk per cow.
Always allow adequate access to feed, water and stalls.
Grant concludes with these points:
Optimal profit and cow well-being are achievable with outstanding management.
With overcrowding acting as a sub-clinical stressor, the economic effects of cattle well-being vary widely between farms.
We need to design facilities and manage cows in ways that optimize profit and well-being.
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