You know the tongue-in-cheek adage: When milk prices rise, farmers milk more cows. When milk prices fall, farmers milk more cows.
As rules of thumb, the logic seems sound. When milk prices are high, farmers try to maximize profits. When milk prices are low, farmers still try to maximize pounds of milk production to maintain cash flow.
The problem is that over-stocking pens often comes with a cost. That’s particularly true in the late dry period and right after calving when dry matter intake is crucial to cow health. But it also applies to lactation groups once cows have over-come the stress of calving and negative energy balance.
Analysis by Albert De Vries, a dairy scientist with the University of Florida, shows that some overstocking might be economically warranted at times. But changes in milk and feed prices do affect the most profitable levels of overstocking. And he notes: “Animal welfare is reduced above approximately 20% overstocking. There will be a tradeoff between profitability and welfare in some situations.”
Lying time is reduced as stocking density increases above one cow per stall, and starts to be really affected when it reaches 150%. And lying time equates to milk production. Several research studies show that there is about a 1.1 to 1.5 lb/cow/day decrease in milk production for every 10% increase in stocking density.
Studies show first-calf heifers that are housed with older cows are much more affected by over-stocking than older cows. “Similarly, when stocking density was higher, the lame cows in the pen suffered greater losses in milk yield than the healthy cows,” De Vries says.
Milk production isn’t the only thing that suffers. Conception rates will also fall, even when pens are overstocked by just 20%. “A herd with a 120% stocking density, conception rates are on average 2 percentage points lower (say from 40% to 38%) than in herds that were not overstocked,” he says. Milk fat can also fall and somatic cell counts rise as stocking density increases.
Diminishing return. De Vries says stocking density economics appears to follow the classical law of diminishing returns. The reason: Every additional cow reduces the performance of all the other cows already in the pen.
Milk production for the entire pen continues to increase as more cows are added, up to 150% stocking rate. But as milk prices fall or feed costs increase, the profitability of that additional milk is affected. His analysis shows that a milk price of $14/cwt and feed costs at 10¢/lb of dry matter, the most profitable stocking rate is one cow per stall.
As milk prices improve and feed costs remain stable, the optimal stocking density does go up. At $16 milk, the most profitable stocking rate rises to 120%. And if milk prices rise to $18 with stable feed prices, the optimal stock rate rise to 140%.
“Note that this is stall stocking density; feed bunk space is not considered a limiting factor [in this analysis],” he says. If bunk space is limiting, increasing stocking density becomes more and more problematic as more cows are added to pens.
“With low income over feed cost, one should not overstock… With today’s tight margins, keeping fewer cows seems to be the right thing to do, but it is counter-intuitive for some people.”
For more information, read De Vries study from the 2016 Florida Dairy Production Conference.