Forage quality of first cutting due to wet spring

Dan Undersander

University of Wisconsin-Extension

The record or nearly record high rainfalls we had during May 2004 made haymaking impossible. A few farmers on lighter soils got hay or haylage out in good shape but most did not. In addition, the rainy weather meant many cloudy days with little sunshine for photosynthesis to provide energy for growing forage and the cool weather also slowed growth. This combination of cool and cloudy weather has caused some unusual situations as far as the quality of the harvested forage.

A number of forage analyses from first cutting are coming back indicating low nitrogen. It is not unusual to see analyses that are 18% CP, 30% ADF, and 40% NDF instead of the 20% CP we would expect with such fiber levels. Lower protein than normal has occurred because nitrogen fixation in alfalfa and clovers was decreased. Nitrogen fixation requires large amounts of energy that comes from photosynthesis. Nitrogen fixation also requires oxygen in the root area which was limited in some soils due to water saturation.

In some cases, forage analyses may not report lower nitrogen content because much of the hay and haylage was lodged before it was harvested. This meant that only the top of the alfalfa plants were harvested and lower stems were left in the field. While lodging greatly reduced tonnage, it should have increased forage quality because the top portion of the plant is higher in leaf content which is high in energy and protein and the upper stems are more digestible than the lower stems.

Lodged forage may have elevated ash content. When alfalfa lodges the laying on the ground increases soil attached to the stems and attempts to pick up lodged forage will often include some additional soil. It is worthwhile to have the ash content check before balancing a ration.

Much of the forage from first cutting was rained on. This reduces forage quality by leaching protein and nonfibrous carbohydrates from the leaves. With one inch of rain more than 30% of the dry matter can be lost due to leaf shatter and another 10 to 15% of the dry matter is lost due to leaching. The two types of losses both result in high fiber, low protein and low nonfibrous carbohydrate (NFC) in forage.

Some farmers may have added lactobacillus or other inoculants to rained on hay in hopes of enhancing fermentation. While we would normally recommend adding lactobacillus to first alfalfa haylage due to low naturally occurring levels in the field, we definitely would not add it to any alfalfa that had laid in the field more than three days. After three days, the NFC has declined to the extent there is not enough food (substrate) to feed the microbes and adding more microbes does not increase fermentation.

Those who made alfalfa haylage should examine it carefully before feeding it. Lower NFC than normal may have resulted in poor fermentation. If the fermented haylage does not smell normal, watch for clostridia and other molds and bacterial that may cause animal health problems.

In addition, we should watch for the potential for mycotoxins in the forage. Mycotoxins are compounds produced by molds that affect animal intake and their immune system. The latter can result in elevated somatic cell counts in milk as well as predisposition the cattle to get other diseases. Mycotoxins are produced when the molds are stressed as can occur when forage lays in the field too long or in poor fermentation in the silo. There is no good test for these compounds. The antibody (Elisa) test kits tend to give a lot of false positives and HPLC only analyzes for a small number of the approximately 400 different mycotoxins so it frequently finds nothing simply because a different mycotoxin was present. The best management is to watch the cattle carefully and see if any changes occur when feed source is changed.

This spring was difficult and much forage is lower quality than desired but it can be fed and produce good milk levels with appropriate management. The key is to know what potential problems might occur and to watch for them.

Dan Undersander

June 2004

Undersander©2004