To Graze or Not to Graze?

Brittany Davis Ph.D., Research Animal Scientist

Jennifer Weinert-Nelson Ph.D.; Animal Scientist Research Associate

Tracy Hamilton Agriculture Research Technician

It has been a very interesting year as far as winter weather, or the lack thereof in the state of Kentucky. We started with the late December polar plunge leaving most livestock producers thinking it was going to be a long winter of frozen automatic waterers and hoping there would be enough hay from an already pretty tight supply. Fortunately, the pattern subsided and since then we have had many sunny and very windy days with above normal temperatures for the season. With warmer temperatures has come a little earlier start to the growing season for most perennial plants including our pastures. Grass has been greening up since the end of February and most of us are ready to park our tractors and take advantage of some early grazing opportunities. Our cattle are also noticing the green, green grass and are demanding access. Every cattle producer has their own strategies of determining when it is time to graze in the Spring, and there is no right or wrong way. However, there are some pasture and animal considerations that should be acknowledged when making these management decisions.

Pasture Considerations at rst glimpse of green grass in the spring a er long winter months is a beautiful sight! It signals that the need for feeding supplemental forage is coming to an end and grazing is right around the corner. However, spring pasture management can present a number of challenges, and the decisions we make now can impact the productivity and quality of our pastures later in the grazing season and even in future years.

Avoiding overgrazing is one of the primary challenges associated with spring pasture management (Figure 1). Defoliation during overgrazing removes a large percentage of the stem and leaf material available to perform photosynthesis in the plant. ose green parts of the plant act as solar panels capturing sunlight and converting it into energy. Removing too much plant material through overgrazing can reduce photosynthetic e ciency and capacity, limiting the ability of pasture grasses to produce energy needed for re-growth and lowering pasture yield in later months of the grazing season. In the spring, the risk of overgrazing increases if pastures are grazed too early before enough forage has accumulated and animals quickly deplete the available grass. Fluctuations in weather can also create potential for overgrazing. In some years, early spring temperatures are warm (as they have been this spring), but that does not mean that above average (or even average) conditions will continue over the course of the full spring season. If cooler temperatures return later in spring, pasture growth will slow, and pastures that provided adequate forage during those earlier warmer months may no longer be able to support your herd.

In addition to depressing pasture productivity, overgrazing can lead to a reduction in vegetative cover and a greater percentage of bare ground in pastures. Decreased competitiveness and persistence of grasses due to overgrazing can leave pastures vulnerable to weed invasion. Not only are weeds often an eyesore, but they can decrease the overall nutritional quality of pastures, and some can even be toxic to grazing cattle. Once weeds have infiltrated a pasture stand, eliminating them from pastures can be time-consuming and costly.

Decreased vegetative cover due to overgrazing can also be detrimental to soil health. Impacts of overgrazing on pasture soils in the spring are compounded by characteristically wet weather conditions. Grasses growing in wet and muddy soils have less wear tolerance and are prone to trampling. These combined stressors can have negative environmental implications. When vegetative cover in pastures is reduced below 70%, there is a greater potential for soil erosion and nutrient runoff. It is difficult for pastures to recover from these effects of overgrazing without reseeding or renovation, which can confer significant costs to producers.

Animal Considerations

Early Spring grass is like candy to cows. They will eat and eat and eat for several days until they have a stomachache just like we do when faced with an endless supply of our favorite sweet treat. It is true that cows are typically able to regulate their intake to avoid gut disturbance, toxins, or disease, but early Spring grass is the exception to that rule. I think we are all familiar with the geyser of wet green feces coming from the rear of our cows after transition to grass. Hopefully, for your sake, you weren’t standing too close when observing this! The facts are that there are several nutrition, performance, and health challenges when transitioning from stored forages to lush Spring pastures that producers need to consider in our management decisions.

Lush green spring pasture is NOT a balanced diet. As perennial pastures break dormancy in the spring, we often see a rapid green up. Rapid grass growth requires fast nutrient and water uptake by the plant. As a result, our first spring pastures are quite different in nutrient and moisture content in comparison to the stored forages being fed through the winter and even what we typically expect from the same pastures later in the spring season. The first grass growth can contain as high as 85% moisture and only 15% dry matter (DM; Figure 2). The DM portion includes ALL of the nutrients available to the animal including sugars, proteins, and fiber. In comparison, pasture grasses later in the Spring often provide 30% DM and stored forages like hay provide 85% DM. This dietary transition is probably one of the most dramatic a cow will face over the year and if managed incorrectly can dramatically impact rumen function and lead to loss of performance and even increase risk for disease.

Cattle appetite is limited to rumen capacity. The rumen is the largest digestive organ (20 – 30 gallons) in the cow’s body, but it still can only hold so much plant material. When cattle chow down on early spring pasture the rumen will fill up with water before they can consume enough to get the fiber and nutrients they need. If a 1200 lb cow needs to consume 2.5% of her body weight in pasture DM to meet her energy requirements she would normally consume 30 lb of pasture DM or 100 lb of fresh forage per day. In early spring, that same cow would have to consume double that or 200 lb of pasture to get to the same DM consumption. This is an impossible task for the cow and can lead to nutritional restrictions and decreased performance.

It is also important to note that nutrient composition is often unbalanced in spring pasture with higher protein, moderate energy, and low fiber. Balanced protein and energy in the diet are essential for supporting optimal animal health and performance. Adequate fiber intake is important for maintenance of the rumen fiber mat and rumination behavior. The rumen fiber mat is made up of long plant fiber material and microbes and is essential for maintaining a normal digestive passage rate to allow for optimum nutrient utilization (Figure 3). Without it, digesta passes too quickly through the gut resulting in decreased nutrient utilization, unsatisfied cows, and you guessed it – the dreaded fecal geysers. The fiber mat also stimulates rumination or cud chewing, allowing for saliva production that provides minerals and buffers that help to maintain a healthy rumen environment. These nutrient imbalances and limitations on DM and fiber are most concerning when cattle have increased nutrient demands like spring calving cows that not only have to produce milk to support their calf, but also maintain body condition for re-breeding or recently weaned calves from fall cows. Lack of fiber and nutrition can result in digestive disturbances, performance limitations (milk production, re-breeding, gain), metabolic issues, and even increased susceptibility to disease and parasites.

QUICK TIPS FOR TRANSITIONING FROM HAY TO EARLY SPRING PASTURE:

Be Patient: Initial grazing of forage should not start until plants are 8 –10 inches tall. Research has shown that >60% loss of total forage yield can occur if early spring grass is grazed too early. One week of early grazing in the spring can translate to 3 weeks of lost grazing in the fall. It just isn’t worth it.

Be Mindful of Overgrazing: Overgrazing early in the spring can also lead to decreased forage production later. Moving livestock through pastures a little faster allows for only a few inches of grazing at a time which prevents overgrazing and also will allow you to get through all your paddocks before pastures get too mature.

Supplement Fiber and Nutrition: Consider supplements to better meet nutrient requirements during transition. These can include concentrate and/or high Mg mineral supplements. If there is still residual dry grass from the fall (4 – 6 inches) there may already be enough fiber for your cattle to consume and balance the spring lush forages. If not, provide hay for a minimum of 2 weeks when transitioning to allow for adequate DM intake and to support a healthy and productive rumen and animal.

Respect Mother Nature: No matter how hard we try as producers to predict the future and support our cattle, the biggest challenge we encounter is Mother Nature. Don’t ever assume that green grass means winter is over. As we have experienced over the last few years, she always sends us a surprise when we least expect it. Always be prepared with a backup plan.

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A three-year research study was conducted using Fescue 7 at Morehead State University. Researchers measured cow body condition scores, calf weights, hair shedding, body temperature, and cow behavior. Cows provided the Fescue 7 mineral had significantly better body condition scores, quicker hair shedding, lower body temperature and grazed more frequently during the heat of the day. We believe that our research shows that Fescue 7 mineral can be an effective tool in combating heat stress associated with fescue toxicosis.”

Dr. Patricia Harrelson Associate Professor of Animal Science at Morehead State University

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“Some years ago, we lost almost an entire calf crop due to the fescue. Needless to say I was looking for answers. One thing I did was attend the Alliance for Grassland Renewal workshop and learned a lot of things, which we have instituted as common practices on our farm and farms we rent. However, I didn’t want to get rid of the Kentucky 31 because I’m a seedstock producer and I felt that if I did away with the Kentucky 31 I could possibly be selling cattle to people that couldn’t handle the hot grass. So I opted to just do a better job of managing the grass that covers most cattle country in my area. The second thing I did was look up a mineral salesman I had talked to a year prior by the name of George Speigelhalder. That conversation changed the landscape of our operation forever. He introduced me to Gro-Tec mineral and a product called Fescue 7. Without going into great detail this stuff is a gamechanger. Not only did it help tremendously with the fescue but it also cut down our pinkeye and foot rot problems. Sent our breed back rates on the high 90% range.”

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Toxin Infested Fescue? WE

A three-year research study was conducted using Fescue 7 at Morehead State University. Researchers measured cow body condition scores, calf weights, hair shedding, body temperature, and cow behavior. Cows provided the Fescue 7 mineral had significantly better body condition scores, quicker hair shedding, lower body temperature and grazed more frequently during the heat of the day. We believe that our research shows that Fescue 7 mineral can be an effective tool in combating heat stress associated with fescue toxicosis.”

Dr. Patricia Harrelson Associate Professor of Animal Science at Morehead State University