Most fast growing, immature green plants are high in nitrogen and low in energy and this causes performance problems.
The more rain, the more fertilizer, and the less sunlight intensity and hours exposure, the more this is true. The less mature the plant, the more this is true.
Most of the excess nitrogen is in the form of non-protein nitrogen (such as urea), and not true protein. NPN requires excellent rumen microbial function and high levels of starch energy for protein synthesis to take place in the rumen of cattle.
If energy levels are low and forage NPN levels are high, there is a large amount of ammonia formed from the excess nitrogen, a condition known as alkalosis. This ammonia is absorbed through the rumen wall into the blood stream and depresses most bodily functions, including overall health and gains.
On lush spring pasture, stockers often start showing negative health effects a full four to eight weeks before seed heads begin to develop on the fescue, blue grass, brome, and other cool season (C3) grasses, cereal grains and legumes.
East of about Oklahoma City, the more green that was available during the fall, winter and early spring, the more quickly and severely the signs related to alkalosis show up in the herd when spring comes.
At our place in Tennessee just south of Interstate 40, we often see mouth-breathing yearlings by 11 a.m. before mid-April at 70 degrees, following a warm night. At the same time, we see short yearlings breaking with pink eye. Within a week or so, we notice a majority of the cattle are not shedding the long winter hair. The more and the earlier the green forage arrives, the sicker the cattle become.
Wheat-pasture calves in the fall on "good" years show similar problems. In years with plenty of rain and plant growth, wheat-pasture calves make good gains up to four pounds per day for forty-five to sixty days and then hit a wall where gains often slow to one-half pound per day. The major culprit is high NPN and low plant energy as the number of hours of daylight decrease. As animal growth slows, the effects of excess ammonia formation become more pronounced if forage remains lush.
A small amount of energy supplementation is the band-aid. Two to four pounds of dry hay per head per day also helps substantially.
The cure, however, is more plant diversity and maturity, higher soil organic matter and mineralization, better water cycling, improved soil microbes and energy, and standing dry grass from last year’s growing season.
Also, part of the take-home message is that you never want to move hungry cattle onto lush, wet pastures with only one, two or three species of plants that are immature (no stems). Life has enough challenges without causing a wreck.
Health requires diversity with some age and loss of tenderness. A little maturity is a good thing.
I am often asked how many different plant species per acre would be considered an excellent diverse pasture. I really don’t know; however, I do think when we can see close to 150 different species per acre over a period of a year or two, we will be getting close to right.
Think about it.
The opinions of R.P. Cooke are not necessarily those of Beef Producer or the Penton Farm Progress Group.