Lowering Feed Costs
Recent corn price increases have left animal nutrition researchers looking for alternatives that maintain milk production
When corn prices rise, you can rein in feed costs without sacrificing milk production. The key to successfully replacing starch from high-priced corn is using non-forage fibre, research has shown.
Recent corn price increases have resulted from competing uses and growing global demand, leaving animal nutrition researchers to look at ways to lower costs. In dairy rations, starch is a major energy component, and corn is the predominant starch source in much of Canada and the U.S. Other grains, such as barley, may be a more common starch source in areas where corn is not as readily available.
Starch is used to formulate today's energy-dense rations needed by high-producing cows. Starch fermenting in the cows' rumens produces volatile fatty acids and contributes to the growth of rumen microbes to generate microbial protein. When digested by cows, microbial protein contributes to milk production and maintaining energy balance and body condition.
Too much starch fermentation can lead to health issues such as ruminal acidosis. Digestion rates depend on starch concentration, how much of it is exposed -whole corn is less exposed than cracked corn, which is less than ground corn-and the extent the starch is bound to the kernel's other components.
Current milking ration starch content recommendations vary. Rations are typically in the 23 to 30 per cent starch range, with an optimum suggested at 24 to 26 per cent.
During the last 10 years or so, a lot of interest has developed in partially replacing corn in rations with alternative feed ingredients. These are primarily from non-forage fibre byproduct feeds such as dried distillers grains, beet pulp, citrus pulp and soybean hulls. They have much lower starch concentrations than corn.
South Dakota State University researchers, known for their expertise in feeding dried corn distillers grains to dairy cattle, have reported on an experiment investigating the effect of reducing starch in the diet to 20 per cent from 29 per cent. The four diets used in the experiment are shown in the table on page xx.
The amount of distillers grains in the four diets was zero, seven per cent, 14 per cent and 21 per cent. The table shows other ingredient changes the researchers made to try to keep composition of the diets as consistent as possible.
As they increased the amount of distillers grains, however, total fat content rose to 5.48 per cent in the diet with 21 per cent distillers grains from 4.35 per cent in the diet with no distillers grains. This resulted from the distillers grains' fat content.
After six weeks of being fed different diets, cows had no statistical difference in milk production or fat and protein in terms of both yield and percentage content in milk. Cows did reduce their dry matter intake (DMI) as the amount of starch in their diet decreased and the amount of soybean hulls and distillers grains increased. DMI declined to 22.9 kilograms per day on the 20 per cent starch diet from 25.6 kg per day on the 29 per cent starch diet.
The researchers calculated feed efficiency based on energy-corrected milk per DMI. It increased to 1.61 from 1.47 as the starch level decreased and total neutral detergent fibre (NDF) increased.
Decreased DMI can be linked to increased NDF above 32 per cent dry matter, although this relationship is far weaker with non-forage NDF than with forage NDF.
This study's results tend to agree with other reports that it is possible to replace starch in diets with non-forage fibre sources from distillers grains and soybean hulls. Several other studies agree with this one that a drop in DMI as a result of distillers grains inclusion need not affect milk yield. One Alberta study found a 10 percentage point drop in starch concentration did not affect milk yield, possibly due to the increased fat content and highly digestible NDF in distillers grains.
The economics of lower starch diets pay off when corn prices are high. When they lowered starch to 20 from 29 per cent, the South Dakota researchers calculated feed costs decreased to $3.49 from $4.91 per cow per day-a savings of $1.42.
These savings highlight the need for more low-starch diet studies, particularly below 21 per cent starch and for longer terms. Most studies like this one have not lasted for a full lactation, but many U.S. herds are achieving good milk production with starch levels as low as 15 to 19 per cent.
If you are thinking of adopting a low-starch ration, watch for decreased milk production, decreased body condition, reduced milk protein and increased milk urea nitrogen (MUN). When using distillers grains, regularly monitor the product's nutrient variability, including sulphur levels in the whole ration at high feeding rates. Starch digestibility of all ingredients plays a key role in successfully implementing a lower starch ration.
Anne Laarman is a graduate student, department of animal and poultry science, University of Guelph, Brian McBride is a professor, department of animal and poultry science, University of Guelph, and Tom Wright, is OMAFRA's dairy cattle nutritionist.
References: Ranathuga, S and others. 2010. Replacement of starch from corn with non-forage fiber from distillers grains and soyhulls in diets of lactating cows. J. Dairy Sci. 93:1086-1097. Zhang, S. and others. 2010. Effects of feeding alfalfa hay on chewing, rumen pH, and milk fat concentration of dairy cows fed wheat dried distillers grains with solubles as a partial substitute for barley silage. J. Dairy Sci. 93: 3243-3252.
Various starch containing diets used in the study at South Dakota
This articles first appeared in the October 2011 Ruminations column of the Milk Producer magazine.
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