“If you feed more starch and less fibre, within reason, you’ll reduce manure”
More milk with less feed and less manure. That’s the ideal balance on a dairy farm. Bill Weiss has been trying to find it, with some surprising results.
Weiss, a professor in the Department of Animal Sciences at Ohio State University, told the Western Canadian Dairy Seminar here last month about a 20-year study which involved feeding 70 different diets to lactating Holstein cows. The data was collected using 314 observations.
The cows in the study ate between 10 to 30 kg of feed a day and produced between 60 to 80 kg of milk. The diets included between 40 and 80 per cent forage.
Some cows were on rations that included no corn silage, while others ate rations where all forage was corn silage. The fibre in the diets averaged around 32 per cent but ranged from 25 to 46 per cent. The protein average was 17 per cent but ranged from 11 per cent to 21 per cent.
Manure and urine output were both weighed and sampled each day during the tests.
On average, lactating cows produced about 45 kilograms of feces and about 24 litres of urine a day. The research team determined cows that produced more milk were also producing more urine and feces.
Weiss said there was a huge variation in the study. Some cows were producing 20 litres of urine a day, while others were producing 60 litres. Some cows produced 20 kg of feces a day while others produced 70.
Weiss then combined the data sets of the most efficient and inefficient cows and the amount of manure they produced.
The researchers found that for every additional pound of milk produced, the cow would generally produce an additional pound of manure, but Weiss emphasized that there was tremendous variation in those numbers.
The concentration of fibre, the concentration of protein and the concentration of corn silage as a percentage of forage all had an impact on the amount of manure produced. For every unit of increase of non-digestible fibre concentration, cows produced a small increase of manure each day.
The researchers found that increasing protein in the diet significantly increased the cows’ urine production while decreasing the fecal output. This result in a zero net effect, so protein was determined not to be a major player in manure production.
Starch and fibre
By contrast, starch and fibre had a major influence on manure production. Low-starch, high-fibre diets produced the most manure, while high starch and low fibre produced the lowest ranges of excretion.
“This is economically important. Milk production was unaffected, so you can feed for good milk and still get less manure production,” Weiss said. Corn silage had the largest effect. Feeding it resulted in little change to the fecal output, but a large drop in urine output and resulted in a lot less manure produced.
Cows that are overfed potassium and sodium will produce more urine, Weiss said. “For every one per cent change in potassium, you get about 25 litres more urine. If you feed more starch and less fibre, within reason, you’ll reduce manure.”
However, too much starch can have a negative impact on the cattle. More-digestible corn silage diets result in less manure without affecting milk production.
Weiss said good-quality forage with a reduced byproduct diet may also reduce manure.
“On average, a one-unit increase in diet digestibility will reduce manure output for lactating cows about 1.3 kg per day,” he said.
Byproduct diets which may include new feeds such as dried distillers grains, may be rather inefficient and pass through the rumen too quickly. “If they’re not digested to the maximum, they’re going to result in more manure,” Weiss said.