The effect of hay steaming on forage nutritive values and dry matter intake by horses
Take home message: Steaming should not replace the primary goal of feeding hay with low mold and dust concentrations. However, in the absence of such hay, steaming represents a viable management strategy for reducing mold and dust concentrations in moderately moldy hay and can be used to increase forage intake when feeding low mold hay.
In an effort to avoid rainfall, or in the presence of adverse weather conditions, hay is often baled prior to achieving recommended moisture concentrations, resulting in mold development and reduced forage quality. Horses are highly sensitive to mold and dust particles from hay and bedding, and inhalation of mold or dust particles can result in respiratory problems. To reduce the number of airborne mold and dust particles released during feeding, current management strategies include soaking hay in water for no more than 60 minutes prior to feeding horses diagnosed with respiratory disorders. Unfortunately, soaking also leaches essential nutrients, including non-structural carbohydrates, dry matter and minerals including phosphorous (P), potassium, and magnesium.
Hay steaming is widely accepted in Europe and is gaining popularity in the U.S.; however, little is known about the impact steaming has on forage nutritive value and intake. This factsheet will focus on the results of a research study that investigated the effect of steaming on forage nutritive values, mold concentrations and total suspended particulate (TSP; an indicator of dust concentration), and forage intake by adult horses.
Two alfalfa-orchardgrass mixed hays were evaluated: a low and moderately moldy hay. Six mature horses were used to evaluate preference of steamed and unsteamed hay. Three horses were assigned to each hay type (either low or moderately moldy hay) for five days. Horses were switched on day 6 to the other hay type. Each day, one bale of each hay type was sampled for forage quality (pre and post-steaming) and steamed for 90 minutes using a commercial hay steamer (Figure 1). Two flakes of steamed or unsteamed low or moderately moldy hay were weighed and offered simultaneously to each horse in individual hay nets. Horses were allowed access to the hay for 2 hours (Figure 2). Remaining hay was then collected and 2 hour dry matter intake (DMI) was calculated. Six additional bales of both hay types were used to evaluate the effect of steaming on TSP. Flakes of unsteamed or steamed hay were agitated in an electric cement mixer, and TSP were recorded every min for 30 minutes (Figure 3).
Steaming increased hay moisture and therefore reduced dry matter to 77 and 81% for low and moderately moldy hay, respectively (Table 1). This increase in moisture would make steamed hay more susceptible to mold formation and have deleterious effects on forage nutritive value if not fed and consumed soon after steaming.
In both hays, steaming reduced P content by 16 and 17% (Table 1). Although P was leached during the steaming process from alfalfa-orchardgrass mixed hays, it is unlikely to be deficient in horse diets. However, a P deficiency could be observed if feeding steamed hay with a lesser initial P concentration. Calcium is not water soluble and therefore steaming could further magnify Ca:P ratio imbalances, mostly with pure alfalfa hay.
Steaming reduced water soluble (WSC) and ethanol soluble carbohydrates (ESC) by 13% and 27%, respectively, for moderately moldy hay, but had no effect on low mold hay. The mold content of moderately mold hay is indicative of hay that was likely baled at a greater moisture content and may have heated after baling. It is possible that heat produced from the molding process in the moderately moldy hay may have increased the availability of the WSC and ESC fraction, making these soluble carbohydrates more prone to leaching during the steaming process. We believe this process did not occurred in the low hay and likely contributed to the difference in post-steaming soluble carbohydrate fractions between the hay types.
Total suspended particulate (TSP; a measurement of "dust particles") of moderately moldy hay was reduced by 91%, but TSP in low mold hay was not affected by steaming. Unfortunately, there are no established guidelines for the maximum amount of TSP that is acceptable in horse feed. Steaming reduced mold concentrations in both hays by ≤ 91%. Many researchers agree that horse feed should contain no more than 500,000 cfu/g of mold. Others have also demonstrated that steaming reduced mold content in hay and Recurrent Airway Obstruction-affected horses fed unsteamed hay exhibited an increase in clinical signs associated with the disease while those fed steamed hay did not. This suggests that horses affected by respiratory diseases may benefit from the reduction in mold and dust particles associated with steaming hay.
Dry matter intake of low mold hay was increased by steaming; horses ingested 1.4 pounds of unsteamed and 4.4 pounds of steamed hay. Dry matter intake of moderately moldy hay was not affected by steaming. Mold in hay has been negatively correlated with feed intakes in livestock. While steaming decreased amount of the viable mold present, the process did not physically remove the mold from the forage. Therefore, if mold had an unpalatable flavor or off-taste, its mere presence, whether dead or alive, likely affected forage intake rates. It is theorize that the elevated mold content of the moderately moldy hay was enough to produce an off-taste, which resulted in equal amounts of hay consumption both pre and post-steaming. For hay with lesser mold concentrations, steaming increased the 2 hour DMI of the hay. The steaming process increased the moisture content of the hay, likely softening its texture and making it more palatable.
Is there a relative advantage of steaming versus soaking hay in water? Soaking hay in water for less than 60 minutes to reduce dust and mold particle inhalation by the horse should be less costly compared to purchasing a steamer and steaming hay for 90 minutes. The hay steamer purchased for this trial cost $1,600 plus added shipping and handling (ordered June 2011). However, hay soaking may be more labor intensive compared to steaming, yet both methods present users with difficulties, especially during winter months in northern climates (i.e. wet hay can freeze). Furthermore, because nutrients are leached when hay is steamed and soaked, care should be used when disposing of remaining water. There are two apparent benefits hay steaming offers over hay soaking. The steaming process killed the mold and increased forage DMI of hay with lesser mold concentrations. However, it is unknown if any benefits exist to feeding dead versus alive but wet mold-contaminated hay to horses. Regardless, neither management strategy should replace the primary goal of feeding hay with low mold and dust concentrations.
Table 1. The effect of steaming on forage nutritive values (on a DM basis, except DM), mold counts, total suspended particulate (TSP) and dry matter intake (DMI) in moderately and low mold alfalfa-orchardgrass mixed hay.
|Moderately moldy||Low mold|
|Unsteamed||Steamed||% Change||Steamed||Unsteamed||% Change|
|TSP, μg/m3 kg DM-1||758||345||-91||406||257||NS*|
|DMI, Lbs./2 hours||2.9||2.7||NS*||4.4||1.4||+216|
|*NS = not statistically significant|
Reviewers: Roy Johnson, Kim Otterson, Tom Tweeten
Scientific Citation: Earing, J.E., M.R. Hathaway, C.C. Sheaffer, B.P. Hetchler, L.D. Jacobson, J.C. Paulson, and K.L. Martinson. 2013. The effect of hay steaming on forage nutritive values and dry matter intake by horses. Journal of Animal Science. 91: 5813-5820.