Spring is in the air, and cattle and farmers alike are eager to start the grazing season. Timing that delightful move is critical, as spring grazing management sets up both yield potential of the pasture and the amount of gain achievable for calves and yearlings.
How early is too early?
Livestock should go out on pasture when grasses have fully developed three to four new leaves. Turning out earlier than this is very stressful on the plants. Perennial forages rely on carbohydrates stored in their root systems to fuel regrowth when they break dormancy (Figure 1). The plants do not refill those carbohydrate stores until they have enough leaf area to produce more sugar than they need to grow. By waiting until grasses have three to four fully developed new leaves, those plants are given a chance to put energy back into the roots. The plants will draw on those reserves again to recover from grazing. If cattle go out to pasture too early, the plants have not been able to refill their root reserves and there is no energy to draw on when grazing takes their leaves away. This early spring stress will reduce pasture yields for the rest of the grazing season. If livestock are turned out too early year after year, weeds that begin their growth later in spring than grasses may be able to out-compete the forage plants.
Figure 1. Root carbohydrate reserves change during grass regrowth
How late is too late?
Waiting too long can have negative effects on livestock production. Spring grass growth is very rapid, and it is easy for pasture maturity to get ahead of animal consumption. Once plants enter their reproductive stages, feed quality and palatability decline quickly. This reduces gains in young stock and milk production in cows with calves at foot. For the first grazing rotation, cattle should be moved quickly through paddocks to nip the tops off everything, which will delay the onset of reproductive growth stages. The second rotation through the paddocks will be slower and make more use of the grass that is there. Many producers manage forage quality by taking a first cut of hay (or haylage) off part of their pasture ground and bringing those acres back into the grazing rotation in the late spring or summer once the plants have recovered and grass growth has slowed.
One way to check whether grasses are too mature is to grab a handful and slide your hand along the leaves. If the grasses are coarse, sharp, or cut your hand they are very mature and are no longer palatable to cattle. Another quick test: would it feel nice to walk barefoot through that paddock (avoiding cow pies of course)? Young stock are even fussier eaters than mature cows. Their mouths and muzzles are more sensitive, and they do not like being poked in the face by their food. To keep intakes and gains up, graze plants frequently enough to keep them in a vegetative state. Maintaining grass quality also reduces the need for energy and protein supplements, which saves money.
What about wet pastures?
Spring grazing often involves managing wet conditions. Pugging (also called poaching) is hoof damage that creates divots in a pasture and exposes grass roots and bare soil. This kind of damage can reduce pasture yields, and the uneven surface may make haying operations difficult. Not grazing during these wet conditions is an option, but with rapid spring grass growth delayed grazing makes managing grass quality even more difficult. Research in Ireland has shown that cattle with unrestricted access to pasture spent only 37% of their time grazing (Kennedy et al., 2012). Livestock do the least amount of pugging damage to a field when they are grazing. Other activities, such as visiting the water trough or mineral source, lying down, or socializing cause more damage.
Researchers studied restricting the amount of time that cattle spent on pastures to try to reduce pugging damage. They found that cows can eat their daily forage dry matter intake during two 3-hour periods each day, and spend 98% of their time on pasture grazing under this type of management (Kennedy et al., 2012). This has led to the development of a management technique called on/off grazing, where cattle are let out to graze for three hours in the morning, then brought into a barn or dry lot until they are turned out to graze for another three hours in the afternoon or evening. For each grazing interval they are only given access to the amount of grass the herd can eat in that time, so it is a modified form of strip or block grazing. The Irish study showed that when cows were not restricted in the time they could graze, pugging damage resulted in 20% less grass yield compared to the on/off grazing management.
Another way to minimize pasture damage is to use several gates. If the herd enters the paddock through one gate and leaves through a different gate the traffic through each gate area is cut in half. This decreases the amount of pugging and soil compaction around gates. Leaving behind more residual grass can also help protect the field from pugging damage. In tame pastures, leaving 10 – 15 cm (4-6 in.) might be appropriate under wet conditions.
Waiting to let cattle out to pasture until the grasses have three to four full leaves reduces stress on the plants and contributes to higher pasture yields all season. Managing fast spring growth to keep grasses in a vegetative state will maximize gains on pasture. Wet ground in spring is a challenge, but careful management can prevent field damage and maximize forage quality for the rest of the season. Getting the timing of turn-out right sets up the pasture for success.
References
Kennedy, E., O’Donovan, M., Delaby, L., and Boland, T. 2012. Strategies to increase the length of the grazing season for spring and autumn calving cows. Teagasc Technology Updates.
