Are your rations environmentally friendly?

When you and your nutritionist develop a ration formulation strategy, do you consider the potential environmental impact of that ration? Adjusting ration formulation strategies will be a primary method to help you comply with existing Concentrated Animal Feeding Operation (CAFO) and Comprehensive Nutrient Management Plan (CNMP) regulations. It can also address a dairy's ammonia emissions. The goal is straightforward: Your rations should provide the opportunity for profitability from your herd while minimizing nutrient excretions in manure. Research and on-farm observations indicate you can improve income-over-feed-cost by making these adjustments in most situations.

Nitrogen (N) and phosphorus (P) are the nutrients grabbing the most interest. Your ration should meet the animals' requirements without feeding excess quantities of N and P. Yes, you do have to feed slightly above requirements to account for the daily variations in forage dry matter, feed mixing and delivery, dry matter intake and milk production that occur on dairies. But your overall objective is to maintain milk production while increasing the efficiency of nutrient use.

Dairy cows have a very simple response when N and P are fed in excess of requirements: They excrete the excess in the manure. So you're spending money on feed to help increase the quantity of N and P excreted by cows. This is a poor use of your feed dollar and can increase the acres needed for manure spreading if you're applying manure based on N and P application rates.

We looked at 81 rations in commercial dairy herds that were averaging about 85 pounds of milk per cow. The average daily N excretion was about 1 pound per cow per day, but the range was 0.75 to 1.4 pounds of N.

The amount of fecal N excreted is relatively fixed with the diets we feed our herds. But the  amount of urinary N varies greatly, and it's the source of most ammonia N volatilized into the atmosphere. Figure 1 shows the relatively constant output of fecal N across a range of N intakes at similar energy intakes, but there's a linear increase in urinary N with increasing N intakes. To reduce excess N excretion into the environment, balance herd diets so milk N output is at least equal to urinary N excretion.

 

Working with your nutritionist, evaluate your rations to identify opportunities to reduce N and P. This person knows what factors enter into your ration formulation process. There could be good reasons why your ration N and P levels may be different from the guidelines we're suggesting.

The simplest way to asses P status is to look at the percent P in your rations. The 2001 Dairy NRC publication says rations for lactating dairy cows containing 0.32 - 0.38% P (dry matter basis) will meet her nutrient requirements. These values will change in herds with either high or low dry matter intakes.

You can evaluate the N status of your herd in a number of ways:

As N is fed in excess of requirements, MUN will go up. Many milk cooperatives provide routine bulk tank MUN data on the loads of milk shipped from a dairy. Some herds get MUN data as part of their DHI test day information.

We obtained the monthly DHI herd MUN data for 822 herds in New York and Pennsylvania tested in July or August. Here is what we found:

All of these MUN values are the average for the whole herd. MUN levels of less than 8 mg/dl may suggest an N deficient animal with potentially reduced rumen digestibility and microbial yield.

Fact check

You can use the following guidelines to make a quick assessment of the N and P status of your lactating cows' ration:

These values are a starting point, and your herd values may deviate from them at times. For example, ration P may increase if canola meal is a good feed buy and replaces some of the soybean meal in a ration. Ration CP or MUN may be higher than these guidelines when you feed high protein forages with high levels of soluble protein. Still, the above guidelines are realistic long-term targets for New York dairy herds.