Trimming Ration Protein Cuts Cows' Ammonia Production

By Ron Johnson, Dairy Editor
Thursday, January 4, 2007 11:47 AM CST

Dairy farms' ammonia production is coming under increasingly close scrutiny.

Cows produce ammonia through their manure and urine, so researchers are looking at ways to trim that production. Tweaking rations might be one way to do just that.

Michel Wattiaux, in the UW-Madison Department of Dairy Science, talked about "Monitoring Apparent Ammonia Nitrogen Loss" during the recent Arlington Dairy Day. He was among a team of researchers who studied ration changes, collected manure samples and had them analyzed for their nitrogen losses at the UW-Platteville Pioneer Farm.

Cut protein bills?

One finding was that dairy producers might be able to cut their protein bills and not lose much milk production. That's assuming that dairy farmers are overfeeding protein to begin with.

Trimming the amount of protein fed can do something else, too. It can lessen the amount of manure cows produce, and it can lessen the amount of nitrogen that's in the manure.

Previous studies have found that ammonia nitrogen losses on dairy farms begin right after an animal excretes manure or urine. These ammonia losses, Wattiaux explained, continue right on through manure handling, storage and application.

But estimating these ammonia losses can be tough to measure under research settings. And, they can vary widely.

A study conducted in 2001 found that cutting the amount of nitrogen in dairy cows' rations can also cut the amount of nitrogen that goes into the atmosphere, the researcher noted. In that study, reducing the amount of protein - and thus the amount of nitrogen in the ration - by 10 to 15 percent lowered the amount of nitrogen being lost into the air by 25 to 30 percent.

What's more, a study done in 2004 that Wattiaux was involved in, found that cows "performed as well on 16.5 percent crude protein diets compared to 18 percent crude protein diets," he related.

Verification sought

So in the study at UW-Platteville, Wattiaux and three other researchers set out to see if they could verify some of those earlier findings. But there was a new twist to their study. They wanted to look at ammonia nitrogen losses "under farmlike conditions."

They compared the impact of feeding cows the recommended amount of protein in their rations compared to 10 percent more than recommended. Plus, they looked at nitrogen losses from cows on the north side of the freestall barn compared to the south side. And, they compared nitrogen losses by month of the year, from January to December.

The UW-Platteville barn used in this study consisted of 80 stalls arranged in two rows. As might be expected, it had a concrete floor. Oat straw was used as bedding.

Two cow groups

Two groups of cows were created. Cows were randomly put into either the "green" group or the "blue" group. They went into the stalls two to three weeks after they calved.

Each month, some of these group-fed cows were switched from the north side of the barn to the south side. Meanwhile, some stayed where they'd been.

Also once a month, some of the cows went off the lower-protein ration and onto the one higher in protein. And, some of the cows stayed on their present ration.

Two rations were formulated, each designed for cows making 90 pounds of milk a day. One followed National Research Council (NRC) recommendations for crude protein and contained 16.5 percent crude protein. The second ration was formulated to be 1.5 units higher than recommended, so it contained 18 percent crude protein.

Forage in the rations consisted of equal amounts of corn silage and haylage, plus balage. These rations also contained ground high-moisture corn, cottonseed, soybean meal, bloodmeal, and the usual vitamins and minerals.

Cows were fed twice a day, after milking. Balage was not part of the mixed ration, but was topdressed twice a day.

Manure tested

All the manure produced each day was collected after the alleys were scraped, then tested for its nitrogen content. In addition, the researchers recorded the temperature of the manure. Finally, they recorded the barn's temperature every hour.

They found several things from this study. One was that changes in silos, grain mixes and balage created "wide variation" in the amount of crude protein in the cows' rations. "For example," said Wattiaux, "substituting alfalfa and corn grain when running out of corn silage led to large increases in nitrogen intake and nitrogen emission."

Little milk impact

But they also found that lowering the ration's crude protein from 18 percent to 16.5 percent of the ration's dry matter lowered the nitrogen loss through manure by 20 percent. What's more, lowering the crude protein by 1.5 percent did not hurt feed intake and had virtually no impact on milk production.

Cows fed the 16.5 percent protein ration produced an average of 70.84 pounds of milk per day during 178 days. Those fed 18 percent protein in their ration averaged 69.74 pounds of milk per day over the course of 177 days. That's a difference of 1.1 pounds of milk per day.

Cows getting the 16.5 percent protein ration ate 52.8 pounds of dry matter each per day. Those getting the 18 percent protein ration ate 53.9 pounds of dry matter per day. That's a difference of 1.1 pounds per day.

MUN measured

The researchers also measured the milk urea nitrogen (MUN) of the cows' milk. For those eating the lower-protein ration, MUN was 16.3 milligrams per deciliter. For cows on the higher-protein ration, MUN was 18 milligrams per deciliter.

Measuring milk's urea nitrogen content is a way to monitor a cow's protein utilization. MUN is considered an accurate reflection of how much nitrogen is absorbed by the cow but not used for growth or synthesizing milk protein.

In addition, cows fed the ration containing 1.5 percent less crude protein produced less manure. Those getting the 16.5 percent protein ration produced an average of 168.7 pounds of manure per day. Those on the 18 percent protein ration produced an average of 172 pounds of manure per day.

Total nitrogen in the manure of the lower-protein ration cows was 3.4 percent, Wattiaux reported. It was 3.6 percent for cows on the ration containing 18 percent crude protein.

Alfalfa: More manure

Another finding from this study was that "Manure production increased considerably during the months alfalfa was included in a higher proportion in the ration," Wattiaux said.

Most of the nitrogen lost from the manure escaped during the first four hours after excretion. Manure from cows fed the higher-protein ration lost 24 percent of its nitrogen during that time. Meanwhile, manure from cows fed the ration lower in protein lost 20 percent of its nitrogen during the first four hours.

Wattiaux said the study's results "suggest" that nitrogen losses from the manure were "strongly" influenced by three factors. One factor was the level of nitrogen in the ration. Another one was the alfalfa haylage-to-corn silage ration of the ration.

The third factor was the average monthly temperature in the freestall barn. Nitrogen losses ranged from a low of 77 grams per cow per day during February, to a high of 191 grams per cow per day during September.

In addition, apparent nitrogen losses were a bit higher on the north side of the barn compared to the south side. On the north side, the nitrogen loss was measured at 21.8 percent. On the south side of the barn it was measured at 22.1 percent.

Not all the nitrogen losses from the manure can be attributed to the differences in the amount of protein these cows were fed, Wattiaux pointed out. But he said 73 percent of the difference "could be explained" by differing amounts of nitrogen in the rations.

Comments »

Comment on this story

Comments will be approved within 48 hours

Name:

Email: (optional)

Comments:

Image Verification: (Case sensitive)