Recently, I attended a meeting where the presenter spoke glowingly about a new miracle product his company was marketing. His PowerPoint slides dutifully showed fancy tables and graphs, but as I looked around the room, I noticed that some folks were beginning to nod off. We’ve all been there before, and what time was lunch, anyway? I heard the speaker state his product would increase forage yield by 20% during the slow periods of spring and fall when the forages were hardly growing. Only 20%? But then I started to think about this number and suddenly sat up very straight. It may not seem like much … but his numbers actually indicate that the effective yield boost was much, much larger than it first appears.
Let’s do calculations on two situations where this comes into play. (I’ll express all numbers on a dry matter (DM) basis.)
First scenario: a grazing situation. It’s early spring, and in a field of 2.4 acres, our grass pasture is just coming out of dormancy. We want to graze animals on that field, but we also want to follow good grazing practices and maintain a residual forage mass of 1,000 pounds per acre – which means that we move the animals off when they graze the forage down to 1,000 pounds per acre. But it’s only early spring – the grass is growing slowly, and the field only contains a total mass of 1,500 pounds per acre. Since I want to protect a residual of 1,000 pounds per acre, that leaves only 500 pounds per acre of forage available for grazing. This available forage is an important number because it’s the actual amount of feed we can graze. Therefore, the entire field of 2.4 acres contains 1,200 pounds of available feed (= 500 x 2.4).
My flock consists of 65 ewes in early lactation weighing 154 pounds (70 kilograms). If I assume a DM intake of 4% bodyweight, the entire flock needs a total of 400 pounds of feed DM each day. Thus, the 1,200 pounds of available forage in my field will provide three days of feed (= 1,200 divided by 3).
Still with me? Good, because now let’s apply the miracle product to the field and do some arithmetic.
Let’s assume this product indeed stimulates a 20% boost in forage yield. But 20% of 1,500 pounds per acre is only 300 pounds per acre, which may not seem like much, so let’s examine it further. The 20% boost means that the total yield increases from 1,500 pounds per acre to 1,800 pounds per acre. Now we subtract the 1,000 pounds per acre of residual forage we want to protect. The leftover forage – the available forage – increases from 500 pounds per acre to 800 pounds per acre (= 1,800 - 1,000). Which means that the available feed supply for my entire field of 2.4 acres jumps from 1,200 pounds to 1,920 pounds – an increase of 60%.
Since my sheep consume 400 pounds per day, that miracle product increased grazing time on that field from three days to nearly five days. Not bad.
What happened? Well, although the product increased yield of the entire field by only 20%, we are reserving a baseline residual amount of forage that we can’t touch – the field’s maintenance requirement, if you will – so all the additional yield was allocated to the forage leftover for production. Thus, a relatively modest 20% increase in the total forage quickly translates into a whopping 60% increase in the forage available for production. That’s something to ruminate about.
Speaking of ruminating and maintenance, let’s look at the second scenario: a nutrition situation with lactating ewes grazing early high-quality grass. Here, the issue is the low DM percentage in the early grass. Let’s alter that by 20% and see what happens.
Some background: Young grass growing in the very early spring is vegetative and highly nutritious, but it’s also very short with a low DM percentage, often as low as 13%. Here in the Pacific Northwest, we call this forage “washy” because it doesn’t support good production even though animals graze it voraciously. Its high level of water dilutes the nutrients so much that animals can’t consume enough energy and protein to support good lactation or growth.
Take a deep breath – lots of numbers ahead. Also, bear with me as I am going to switch to metric values, because all the reference tables are in metric and the numbers would become quite cumbersome if they were in pounds and ounces. However, the principles are exactly the same, especially the conclusion.
Let’s look at the energy needs of a 70-kilogram (154-pound) mature ewe raising twins in early lactation. Basic nutritional principles tell us that our lactating ewe requires calories for two things: maintenance and production (in her case, production = lactation). The highest priority is maintenance, and any calories she consumes must first satisfy those maintenance needs. Then, any leftover calories are used to synthesize milk. We can estimate the ewe’s maintenance requirement by looking at a reference table in the 2007 Small Ruminant NRC, which lists that a 70-kilogram ewe in maintenance requires 0.62 kilograms of TDN. That’s our baseline.
Here are two additional items from the scientific literature: An adult ewe will take approximately 30,000 bites per day on pasture, and her average bite contains 70 milligrams of DM. (For comparison, a penny weighs 2,000 milligrams = 2 grams.) Yes, 30,000 bites – researchers have actually spent time counting them. But really, what else does our ewe have to do except eat, sleep and chew cud?
But I digress. If our ewe takes 30,000 bites that each contain 70 milligrams DM, her daily DM intake is 2,100,000 milligrams (= 2.1 kilograms), which equates to 3% of her bodyweight (= 2.1 divided by 70 as a %). This intake level falls within the expected range for a lactating ewe. If the high-quality grass contains 70% TDN, her TDN intake is 1.47 kilograms (= 70% of 2.1 kilograms). Subtracting her maintenance requirement of 0.62 kilograms leaves 0.85 kilograms of TDN that she can use for lactation.
Here is where we make a change of 20%. Let’s change our grazing management slightly to allow the grass to grow a little longer and increase its DM percentage by 20% – say from 13% to 15.6%. We can accomplish this by simply waiting until the grass grows to 8 to 10 inches before grazing rather than putting sheep out when it first turns green.
Now let’s recalculate. Because the 20% increase in DM may not seem like much …
Our ewe will take the same number of bites – 30,000 – but now each bite contains 20% more DM, which is 84 milligrams rather than 70 milligrams. This gives our ewe a daily DM intake of 2.52 kilograms. Since the forage still contains 70% TDN, our ewe’s TDN intake is now 1.76 kg (= 70% of 2.52 kilograms). Now we subtract her maintenance requirement of 0.62 kilograms. This leaves 1.14 kilograms of TDN that she can use for lactation – a 34% increase in energy available for production over the 0.85-kilograms TDN in the shorter forage.
Let’s review. By delaying grazing slightly in early spring so the grass grows taller and increases its DM percentage by a modest 20%, we boost the amount of energy available for lactation by 34%. That translates to considerably more milk for those twins, faster growth, earlier marketing and perhaps better body condition in the ewes.
When I hear a salesperson claim that such-and-such a miracle product will double or triple my yield, I tend to be a wee bit skeptical. We’ve all been down that road before. But if someone states in a straightforward manner that a product or technique can increase yield by 20%, then I listen very carefully indeed.
