Forty years ago, a farmer might have been able to build a freestall barn for $750 per stall, and a cow cost about $1,000. Today, the same farmer might pay $2,000 to $2,500 to build that same freestall, and the cow costs about $1,000. Hence the attraction of putting more cows in a stall today. As fixed costs per stall increase, increasing milk per stall makes sense. Running another cow through a parlor will likely increase milk production per parlor stall, too, but there is one critical difference between this and increasing cows per free stall. Increasing cows per parlor stall usually does not negatively affect the other cows in the herd, while increasing cows per freestall almost always negatively affects the other cows in the herd. Negatively affecting some or all of the other cows can easily wipe out the gains of adding cows to a fixed number of stalls.   
    There is research to quantify some of these claims. Increasing stocking density above one cow per stall likely reduces production by 1.7 pounds of milk per cow per day for every 10% increase in density (for example, 120% to 130%). Butterfat production may decrease by about 0.04 pounds per day for every 10% increase in stocking density. Conception rates may decrease by 0.1 percentage points for every 10% increase in stocking density. All of these assumptions, though based on research, will vary from farm to farm. There are other negative effects that unfortunately do not have a lot of research behind them but will most likely occur. Some of the more significant are: increased reproductive and non-reproductive culls, increased somatic cell count and clinical mastitis, increased lameness, reduced rumination, increased heat stress, decreased feed efficiency and increased health disorders. At least five of the six Compeer/Zoetis “Big Six” factors affecting profitability (milk per cow, somatic cell count, pregnancy rate, cow death rate and calf death rate) are likely to be negatively affected by increased stocking density.   
    The big problem is this: The effects of increasing stall density can be hard to evaluate. The main reason is that most of the negative effects are long term, while the positive effects of more milk sold per stall are short term. The farmer sees the immediate increase in the milk check but does not necessarily see the effects of long-term negative effects on the cows. For example, a two percentage point drop in pregnancy rate will have only moderate short term costs but could easily cost $0.10 per hundredweight on a long-term basis. Reduced performance becomes the new normal and is accepted as an acceptable cost of increased stocking density.
    Another problem with increasing stocking density is that it is more profitable to increase stocking density when the margin between milk price and feed price is greater. Unfortunately, human nature makes us want to increase milk per stall the most during periods of low milk prices not high milk prices. While this may intuitively make sense, in reality this is precisely the time not to increase stall stocking density on most farms.
    Increasing stall stocking density is an attempt to dilute the fixed costs of the stall or pen. However, how does one define fixed cost per stall? Things like interest cost are easy to quantify, but what about depreciation and labor? Do more cows in the pen result in faster depreciation? In most cases, the answer is probably, to some degree, yes. But most of the time depreciation is considered a fixed cost. The same is true for labor. More cows in the pen will, to some degree, increase labor requirements. How one models depreciation and labor costs will significantly affect the economic projections of increasing stall stocking density and thus complicates the decision.
    There is, of course, another consideration. The negative effects of increasing stocking density are mostly due to a decrease in the long-term welfare of the cow. Ouch. How would the consumers of our products feel about this? Truthfully, we all know there are always tradeoffs between the natural state of animals in the wild and food production, but what are the limits and what is acceptable to our market?
    We veterinarians often find ourselves as the primary cow advocate in discussions about increasing farm profitability. We sometimes are on the losing side when decisions regarding cow welfare versus expected increased profitability are weighed. This may be OK, but ultimately cow welfare is what makes money on a dairy, not milk per stall. Usually a very small negative change in cow welfare has large costs. Every veterinarian may not understand the economics of milk production, but having your veterinarian at the table when contemplating an increase in stall stocking density is almost always a good idea, because the decision is more complicated than just numbers.
    Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minn. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.