Some Mammals Require Dietary Carbohydrate

But they’re ruminants, and we aren’t

I’ve been busy since the last post. I’m grateful for the opportunities I’ve been given, but it is a challenge! I made a commitment (dare I say a “resolution”?) to post items to this blog on the 1^st and 15^th of each month. Looks like I’ll miss this one by just a bit. I’ll try to get back on track for the next post, although the next few weeks will include presentations at the Douglas County Livestock Association’s Spring Livestock Conference on April 9^th in Roseburg, Oregon and at the Small Farm Trade Fair in Madras, Oregon on April 16^th.

Since my last post I’ve given a presentation, attended a conference, and tried to work my way through a couple of books. And I’m constantly being reminded of just how much we have to do to before “the system” is fixed.

I spoke to the Crook County Stock Growers Association’s Annual Banquet on March 19^th. The event was held at the at the Crook County Fairgrounds in Prineville, Oregon. The well attended event was, in part, a fund-raiser for their Beef For Kids initiative. They are striving to get good-quality, locally-grown beef back on the menus of Crook County public schools. A truly worthy goal. I know that the cattlemen in Malheur County are already engaged in a similar initiative, and I hope we’ll see this effort spread throughout the nation. The “food” we provide to our school children via our school meal programs is truly abysmal. And the chance to repeat the message, in various ways, that animal products are fundamental to human health should never be missed. My presentation, “Food For Thought,” was well received. Several folks kindly shared their personal experiences with me. I was grateful that I could again direct people to the sources of information that have so profoundly changed my own life. Eventually I found myself standing in the dinner line next to a long-time friend. Suddenly I became aware of one of the paintings that were hung on the wall over the pass-through from the kitchen. Oh, the irony!

Figure 1:How to fatten a hog, and a human!

I also attended the Oregon Forage and Grassland Council’s 2011 Annual Meeting in Albany on March 24^th. This year’s keynote speaker was Neil Lane, an Australian dairy farm management consultant from Intelact. He shared a wealth of information about pasture-based dairy management in Australia and New Zealand. What he tried to impart to us can have an immense impact on the Pacific Northwest. Our environment is unique to North American. The potential for grass-based animal agriculture in our region is huge. We have progressive grass farmers here, but there’s room for many more!

“We don’t manage paddocks – we manage tillers!”

                                                                                  - Neil Lane

Now a clump of perennial ryegrass might look like a single plant, but it’s actually a collection of tillers. While each tiller has its own leaves and roots, it is connected to neighboring tillers at its base. These tillers share water, nutrients and carbohydrates via this connection. A newly-established ryegrass plant consists of one tiller until it reaches the 3 leaf stage. If there is a low tiller density, sunlight will penetrate to the base of the sward. This stimulates the production of daughter tillers. These daughter tillers grow from buds in the leaf axil, appearing first as small one leaf tillers growing inside an older leaf at the base of the plant. This older leaf soon dies and disappears. The new tiller continues to put out leaves and soon becomes a separate tiller with its own root system. Each new leaf emerges on the opposite side of the tiller to the previous leaf.

Figure 2. A ryegrass tiller with 3 1/2 leaves (from Guest, 2008)

A perennial ryegrass tiller maintains a maximum of 3 live leaves. As each new leaf emerges after this 3 leaf stage, the oldest leaf dies. Maximum perennial ryegrass yield is achieved by allowing the tillers to grow to 3 leaves as each subsequent leaf is bigger than the previous leaf. The 1^st leaf contributes 15–20% of total pasture biomass, the 2^nd leaf 30–35% and the 3^rd leaf 45–50% with little difference in metabolizable energy content between the 1^st and 3^rd leaf (Figure 3).

Figure 3. Leaf stage vs. yield (from Guest, 2008)

Provided water is not limiting, leaf growth rate is controlled mainly by temperature. Perennial ryegrass will usually grow a new leaf every 6–7 days in the warm, sunny days of early fall, but could take 10–13 days or more in the colder, shorter days of mid to late fall.

Tillers form glucose and then other water soluble carbohydrates (WSC) in the leaves via photosynthesis. These WSC (also known as Non-Fiber Carbohydrates, or NFC) are used to provide energy for ongoing growth and respiration. The availability of WSC in ryegrass tillers has a marked effect on the plant’s re-growth potential and ability to persist after grazing. When the fourth leaf emerges and the oldest leaf dies, there is no further build up of plant WSC levels (Figure 4). Proper grazing management must take into consideration this relationship to promote improved utilization and production. Improved pasture utilization and production will lead to optimal profit.



Figure 4. Leaf stage and water soluble carbohydrate levels (from Guest, 2008)



Studies have shown that it is best to use leaf appearance intervals

to decide when to graze, not pasture height.

- Kelly Guest, 2008

Grazing at the 3^rd leaf stage doesn’t just improve pasture production and utilization. It also improves animal performance. Proper rumen function requires at least as much NFC as Ruminally Degradable Protein (RDP) in the herbage eaten. If there is too much RDP, it is converted to ammonia in the rumen. This excess ammonia needs to be detoxified to urea and excreted in urine. This process requires energy, and can have a negative effect on both production and reproduction in the grazing animal. Green growing pasture contains more than enough RDP for any ruminant’s requirements, but the NFC are frequently limiting. Recent research has shown that the ratio of RDP to NFC becomes more balanced after the 2-leaf stage, as NFC levels increase with re-growth, while RDP levels decline due to leaf maturity. The ratio of RDP to NFC can be as high as 5:1 at the 1^st leaf stage, declining to 1:2 at the 3^rd leaf stage. The levels of minerals in perennial ryegrass change markedly with re-growth, too. Potassium, which is usually at levels far in excess of the animal’s requirements, declines, while calcium and magnesium, important for milk production, increase with re-growth to the 4-leaf stage. One indicator of appropriate mineral status for performance of dairy cows is the ratio of potassium over calcium and magnesium. This ratio should be below about 2.2 to reduce the incidence of grass tetany and other metabolic problems. The ratio falls from about 6 at the 1^st leaf stage, to below 2.2 at the 3^rd leaf stage. Another indicator of appropriate mineral status is the ratio of calcium to phosphorus. The recommended ratio for milking cows is above about 1.6:1. In perennial ryegrass this ratio changes from about 1:1 at the 1^st leaf stage, to over 2:1 at the 3^rd leaf stage.

Table 1. Nutrient values of perennial ryegrass herbage at different leaf stages. (Donaghy, 2005)

There is abundant evidence of farmers increasing their profitability by using leaf stage for grazing management. But new ideas aren’t always embraced by the farming community. If the New Zealanders are lagging in their adoption of this philosophy, as Neil told us, then how long will it be before it’s adopted in the US? Seven-plus dollar a bushel corn may help the adoption rate!

Figure 5: Spring in Western Oregon

References:

Donaghy, D. and B. Fulkerson. 2005. ‘Principles for developing an effective grazing management system for ryegrass-based pastures’. Press release Dairy Research and Development Corporation, Tasmanian Institute of Agricultural Research. http://www.crtkyneton.com.au/seeds/heritageseeds/dairy-pasturemanagement.pdf

Guest, K., 2008. “Pasture Phase Farming – More Than a Passing Phase: A Handbook to Ryegrass Management on the Esperance Sandplain.” Lemon, J., J. Ryan, M. Ryan, N. Witham, and J. Lucey, Eds. South East Premium Wheat Growers Association. http://www.sepwa.org.au/pastures/book.html