– Jeff Lehmkuhler, Extension Beef Cattle Specialists, University of Kentucky
Several county Ag Agents have reported producers asking what to do supplement-wise for grazing livestock with the slow pasture growth this spring. A lot of this is related to the fact that we are roughly 100 growing degree days less this year than the same time frame a year ago. Combine this with the wet weather leading to muddy feeding conditions, producers were happy to see cows begin to pick grass. Low hay stocks also contributed to producers pulling hay away a bit prematurely. Cooler temperatures has resulted in slow pasture forage growth and cows are nipping it off faster than it is growing. This situation has led to several questions regarding supplementing grazing cattle under these conditions and I’ll try to share a few things to consider.
1) No free lunch – Grazing energy expenditure based on research is significantly greater than the energy required to walk, stand, and other activities. A cow grazing an acre would expend more energy than simply walking that same distance. The energy to raise the head, prehend forage, chew and swallow are all energetic costs.
2) Low forage availability – The National Research Council (NRC) beef cattle nutrient recommendations publication has reviewed the scientific literature related to grazing energy expenditure. Models have been developed to account for energy expended during grazing in relation to forage dry matter availability (see previous Grazing News article https://grazer.ca.uky.edu/content/when-start-feeding-hay). When forage dry matter (DM) availability falls below 2,000 lb per acre or approximately less than 6 inches in height with 90% ground cover, dry matter intake may be reduced which will negatively impact performance. Maintaining pasture sward to be greater than 3-4 inches in height should ensure there is at least 1,000-1,200 lbs DM/acre pasture forage availability. At 1,000-1,200 lbs DM/acre, research indicates DM intakes will be about 90% of normal.
3) Providing Free-choice Supplements when pasture is limited – Offering free-choice supplements during low forage availability is a situation that in many instances can lead to digestive and metabolic disorders. When forages are limited, over consumption of free-choice supplements can occur. The name is important “supplement” not “replacement”. In many free-choice supplement toxicity cases, it has almost always occurred when forage availability was limited. This same over-consumption can occur with liquids such as molasses and distillers condensed syrup. Use free-choice supplements when forage availability is not severely limited for best results.
4) Hay – Hay would be the preferred “replacement” to pasture forages. Even though the lower sugar content and other factors such as rot and mold will make it less palatable to grazing livestock, hay is the most logical substitute. Having access to higher quality hay will provide some replacement of pasture forages. Granted the intakes may be low as they seek pasture forage. Low hay intakes of 5-10 lbs of hay intake can replace 25-50 lbs of fresh forage intake. Enticing hay intake could be done by adding liquid molasses to bales while also boosting nutrient content slightly.
5) Supplements – Limit-fed supplements can be used to provide nutrients to cattle grazing pastures that are short, but won’t lower their forage DM intakes when forage is limited a great deal. Two intake regulation systems are involved, metabolic and gut fill. Gut fill will often be driving the cattle to graze even though nutritionally they may not need the nutrients. For instance a supplement that is mostly soyhulls, wheat middlings and some corn gluten feed would likely have about 78-80% TDN. Lush, lowly lignified pasture will contain about 65-70% TDN. The math suggests that for an energy exchange, 1 lb of supplement as mentioned would provide the energy of about 1.15 lb of pasture forage DM or lower forage DM needed by about 15%. As forage becomes more mature, lower in quality, the exchange becomes more significant. Consider mature pasture forage that is 58% TDN. It would take 1 lb of supplement would replace about 1.34 lbs of pasture DM. This is a bit simplified, but it should illustrate that the rumen fill sensors could still signal cattle to eat more even though pasture forage intake could be reduced 15-30% while still meeting nutrient needs with supplementation. On another note related to item 3 above is supplementation can provide energy that the cattle need due to the increased physical activity while attempting to fill the rumen with pasture forage. Early spring conditions with lactating cows and low pasture availability can lead to excessive Body Condition loss as the cows activity levels are high. Hilly terrain and steep terrain increases the energy expended.
6) BCS – Don’t let spring calving cows lose more than 1 body condition score from calving to breeding IF they calved in a BCS of 5. If they calved at a condition less than 5, they should be maintained and not lose additional condition to ensure optimal breeding opportunity. Thin cows at calving that continue to decline in body condition are at a much higher risk to not rebreed.
7) Economics – Some of the supplements being mentioned by agents as a replacement for pasture forage are in a “form” of convenience. One pays for this convenience. For instance, a cube that may cost $300/ton that can be poured on the ground with minimal feed loss may be the feed of choice of some. But consider this, a soyhull:corn gluten mix may only cost $200/ton. That means one could effectively waste 1/3 of the feed on the ground, which is highly unlikely, and still breakeven. Be certain to do your homework on supplements and the nutrient content to purchase nutrients wisely. Some may contain adequate mineral that removing the free-choice mineral supplement will offset the higher feed cost. Supplements may contain higher levels of “roughage” products such as cottonseed hulls, peanut hulls, rice hulls and other low energy feedstuffs to prevent digestive upsets. Find out the nutrient content and suggested feeding rates and compare these to alternative nutrient dense feedstuffs.
As the temperatures increase pasture forages will rebound quickly. Adequate soil moisture will aid in pasture forage growth and this will be a short-lived challenge. However, these same basic principles can apply during forage dormancy induced by heat and low precipitation periods. As mentioned by one of our agents working with a client this spring, don’t overlook the potential for consumption of toxic weeds when forage availability is limited. Happy forage managing this spring/summer.