Forage Choices for Feeding Dairy Cows

Posted: November 5, 2005

Grasses are one of the predominant forages harvested in the northern and western regions of Pennsylvania.

Opportunities exist in these areas to harvest high quality grass forages, however, producers face challenges in preserving quality grasses due to their quick maturation period. As grasses mature, the NDF percentage increases rapidly, resulting in lower quality forage. In order to maintain milk production with grass feeding, more expensive rations may need to be formulated.

Preservation methods of forages impact the nutritional quality of the feed and potentially impact how much dry matter the animal may consume. Silage is the principal method for forage preservation in Pennsylvania as well as in the northeastern United States. Including hay in rations may allow opportunities for more flexible harvesting schedules; however, little information is available comparing silage versus dry hay in diets of dairy cows.

In general, grass silage contains more non-protein nitrogen in soluble protein, or nitrogen readily available to rumen microbes compared to forage preserved as hay. Hay has a greater potential for rumen protein to escape rumen microbial protein degradation and enter the lower digestive tract. Regardless of preservation method energy is required for microbes to utilize nitrogen. Rations need to be formulated so that available energy is compatible with nitrogen availability.

Compatibility of energy and nitrogen results in greater ruminal ammonia utilization and increased rumen microbial protein synthesis. Microbial protein can supply up to 60% of the daily protein needs of the cow. It is therefore very important to balance dairy rations that include complementary nitrogen and energy sources.

We conducted a study to evaluate grass hay and grass silage based diets and their impact on dry matter intake, milk production and milk components. Eight high producing Holstein dairy cows were used in this study. Four rumen cannulated animals were included. Diets were formulated to be 50 percent forage, 50 percent concentrate.

The primary ingredients included 25 percent grass hay or silage, 25 percent corn silage and approximately 25 percent ground corn. Other ingredients included heat-treated soybean meal, canola meal, liquid sugar, cookie meal, cottonseed hulls and alfalfa hay. Urea was added to the hay diets in order to give the hay diets similar soluble protein levels as the silage diets. The total mixed ration was balanced for carbohydrates and nitrogen fractions and for the needs of cows producing 90 pounds of milk.

The chemical composition of the forages used is shown in Table 1. and results of our study are shown in Table 2. The two treatments were: grass silage or grass hay based rations. Cows provided the silage diets consumed more than the cows fed the hay diets. This increased intake did not result in additional production of milk or any differences in milk fat or protein yield. Greater efficiency in feed utilization Energy Corrected Milk/DMI (ECM/DMI) was observed in the hay diets. Ruminal pH and ammonia concentrations did not differ across diets (data not shown). Rumen microbes degrade feed nitrogen sources to ammonia and then use this ammonia for microbial protein synthesis. Ruminal ammonia concentrations observed in this study indicate that the carbohydrate and protein fractions were synchronized regardless of forage preservation method.

Table 1: Chemical Analyses of Forages

Grass Silage Grass Hay Corn Silage
DM (%) 38.2 93.2 37.3
CP (%) 11.2 7.5 7.2
Sol Pro (%DM) 7.4 3.0 3.7
NDF (%) 67 65 40.5
ADF (%) 42.4 38.3 22.4
NFC (%) 15.4 22.4 42.0
NEL (Mcal/kg) 1.03 1.08 1.61

Table 2: Dry matter intake (DMI), milk production, mill components and feed efficiency of cows fed grass silage versus grass hay diets

Silage Diet Hay Diet
DMI (lbs) 50.10 43.09
Milk Production (lbs) 85.14 85.97
ECM/DMI 1.50 1.86
Milk Fat (%) 3.4 3.43
Milk Protein (%) 3.07 3.07

In conclusion, regardless of forage preservation method, if nitrogen fractions and carbohydrate fractions are well balanced in dairy rations milk production may be maintained on grass based rations. Various carbohydrate sources were used in the diets, corn, sugar, cookie meal, resulting in a more consistent energy source for the rumen microbes. Balancing rations by using different carbohydrate sources may have economic benefit to farmers when considering availability and cost of common energy sources in dairy rations. Rations that include hay also gives producers more flexibility to create well balanced, synchronized diets regardless of the harvested forage quality. It is very important to balance both nitrogen and energy sources in dairy rations to result in consistent, healthy rumen function and maintenance of milk production and components.

Neil Brown, Ph.D. Candidate, Dairy Nutrition, Department of Dairy and Animal Science, Penn State