With dry conditions across much of the western United States, grazing regrowth on irrigated alfalfa fields is likely in fall grazing plans for many producers. Alfalfa is a fairly drought tolerant crop and will produce forage in dry conditions. However, alfalfa has several challenges to grazing from animal and plant health perspective.
With its high soluble protein content, alfalfa can easily cause bloat in cattle so cattle should be monitored closely, especially the first few days of grazing. One of the keys to reducing bloat when grazing alfalfa is to not create situations that would cause large swings in forage intake. Any situation that would cause cattle to become overly hungry before or while grazing alfalfa can be problematic.
One method to mitigate the incidence of bloat is to adapt cattle to the alfalfa slowly. First move cattle to the alfalfa field after the morning grazing bout on grass pasture, this way the rumen is full and cattle will not consume large amounts of alfalfa right away. Another method is to only allow cattle access to the alfalfa field for a few hours each day for the first few days so that cattle are consuming other grass forage. However, monitor cattle as some may learn after a few days that they will get access to the alfalfa and wait to eat until then. A third method to mitigate bloat is the use of a feed additive called poloxalene. The compound acts as a surfactant in the rumen to inhibit frothy bloat and can be delivered in a feed supplement or mineral mix. A combination of these methods will likely provide the best bloat prevention.
Grazing alfalfa after a light freeze, especially followed by warm days, can increase bloat problems because freezing ruptures plant cells releasing more soluble proteins. Cattle should be monitored closely when temperatures approach freezing and possibly removed from alfalfa until night time temperatures return to normal.
Alfalfa can also contain high levels of phytoestrogens that can negatively impact reproductive performance of females. Fall-calving cows or fall breeding heifers could be negatively impacted by grazing alfalfa in the fall. However, research studies indicate that phytoestrogen levels generally only reach problematic levels with fungal infection of the alfalfa plant. Water stress did not result in increased phytoestrogens in alfalfa. Therefore, if plant disease measures have been implemented, the concern for phytoestrogens interfering with female reproductive performance is low.
Besides potential issues with the cattle, grazing alfalfa can cause issues with the plant. There are two types of alfalfa: those for hay and those for grazing. This does not mean that you cannot use either type for the other situation, but it does mean that additional care should be taken. Varieties for hay production are bred to produce high quality tonnage based on infrequent complete harvesting of above ground plant material, which then allows the plant to regrow and put down more energy reserves into the roots. But hay production varieties have poor grazing tolerance due to the frequent removal of above ground plant material by the cattle. Hay varieties can also have more bloat potential. In contrast, grazing varieties were bred to withstand more frequent removal of above ground plant material by cattle resulting in a more persistent stand. Grazing varieties are also less bloat prone, but not bloat free. The grazing management system needs to be adjusted to the type of alfalfa.
Alfalfa regrows from the crowns which are at the soil surface and heavy hoof traffic can damage the crowns. Grazing management plans need to take this into account and consider such things as soil moisture conditions and repeated trampling of plants. Removing cattle if the soil becomes soft from moisture and rotating cattle to new areas of the field to reduce trampling are ways to minimize damage to crowns.
In contrast to overnight frost, a killing freeze followed by cold days can significantly reduce bloat problems, but also reduces the nutritive value of the forage. Grazing killed alfalfa should occur in the few days/weeks after the killing freeze to capture as much of the nutritional value as possible. Additionally, hoof traffic on frozen ground causes less damage to alfalfa crowns.