Dr. Bill Weiss, Dairy Specialist, Ohio State University
This year's rainy spring had negative effects on the quality of first cutting hay crop forages. Rain either delayed cutting, caused substantial weather damage to mowed crops that could not be removed quickly from the field, or forced farmers to harvest hay or silage at improper moisture contents.
Delayed harvest means that forages were more mature when they were eventually cut. Fiber (NDF) and lignin concentrations increase and protein and energy decrease as forages mature. The negative effects of maturity are greater for grasses than for legumes. Rations should be formulated to contain adequate, but not excessive concentrations of forage NDF (usually between 18 and 21% of dietary DM). High concentrations of forage NDF in diets reduce DM intake and milk production. Intake depression becomes substantial when diets have more than about 25% of the DM as forage NDF. If forages have high NDF, diets should contain less forage. For example, if corn silage makes up 25% of dietary DM and has 44% NDF, it will provide 11% forage NDF (0.25 x 44). If alfalfa has 40% NDF and the dietary target is 21% forage NDF, the diet should contain 25% alfalfa (21% in total diet - 11% from corn silage = 10; 10/0.40 = 25% alfalfa). If the alfalfa contained 50% NDF, then the diet should contain 20% alfalfa (21 - 11 = 10; 10/0.5 = 20%). Additional supplemental protein may be needed because of the lower concentration of protein in the more mature forage.
Weather damage reduces the concentrations of protein, energy, and soluble carbohydrates, and increases the concentration of fiber. These changes are caused by rain leeching away soluble compounds and concentrating the less soluble compounds. Although the cause of quality loss is different for weather damage and maturity, the results are the same - DM intake decreases. Indeed, depression of intake can be greater in weathered forages than mature forages because of the development of mold and other anti-quality factors. The same diet modifications as described above should be made when weather-damaged forages are fed.
Silage made with too much moisture because of poor wilting conditions can undergo an abnormal fermentation. Wet silage (especially when moisture is >70%) can have high concentrations of acetic and butyric acids and a low pH and often adversely affects intake. About the only solution to this problem is to feed less of the poorly fermented silage. Some experiments have shown positive effects on intake when wet silage with low pH is treated with sodium bicarbonate (2 to 4% of silage DM) immediately before feeding. Positive results were reported for corn silage only, not hay crop silages.
Hay baled with too much moisture usually becomes moldy and heats. Heat-damage reduces the digestibility of energy and protein, but proper diet formulation can minimize those effects. Effects of mold are more complicated. Moldy alfalfa hay that contained no detectable mycotoxins reduced intake by dairy heifers (approximately 300 lb of body weight) but not beef steers (about 600 lb of body weight). Cattle in both experiments sorted against severely molded hay. Moldy hay also can contain mycotoxins which may adversely affect health and production. Because of the risks, moldy hay should not be fed to high producing dairy cows. Several commercial binding products are available, but their value has not been proven in controlled experiments with dairy cows.
Recommendations for feeding low quality hay crop forages
1. Have the forage analyzed. Concentrations of NDF and available protein are important quality measures. Alfalfa with > 44% and grasses with > 53% NDF can reduce milk production.
2. If possible, feed lower quality forages to animals with lower nutrient needs, such as growing heifers and late lactation cows. Feed early lactation cows the highest quality forage available on the farm.
3. If forage quality is poor because of high NDF concentrations, reduce the amount of forage in the diet but ensure that the diet still contains adequate NDF. Diets with >25% of the DM as forage NDF usually reduce intake.
4. If forage quality is poor because of a bad fermentation (wet silage), reduce the amount of that particular silage in the diet. Neutralization of the acids in wet silage with sodium bicarbonate may help increase intake.
5. If forage quality is poor because of mold (wet hay), intake may be poor and toxicity risks are present. This type of forage should not be fed to high producing cows and may or may not be acceptable to other types of cattle. Moldy hay can increase sorting which may increase ruminal acidosis. Other than not feeding or severely limiting the amount fed, little can be done to overcome the problems with moldy hay.