standing forage for cattle is a gener- al recommendation. The minimum amount of standing forage required for recovery from grazing varies depending on the plant community and eco-region.” The next step is to calculate the
number of available animal days per acre. An animal unit consumes approximately 26 pounds of forage per day. Let’s assume we have 50 cows
that collectively will consume 1,300 pounds of forage per day (50 x 26 = 1,300). If we estimate 4,000 pounds of forage per acre and there are 150 acres in the pasture, we have a total forage production of 600,000 pounds (150 x 4,000 = 600,000). We want to use 25 percent which
gives us 150,000 pounds of available forage (600,000 x 0.25 = 150,000). Dividing the amount of avail-
able forage by the daily herd con- sumption tells us that we have 115 grazing days in that particular pasture (150,000 ÷ 1,300 = 115). Events such as drought, grasshop- pers or armyworms could change this number. Constant monitoring is necessary. “An important piece of informa-
tion required for adjusting stocking rates is the potential forage produc- tion of a pasture or an ecological range site,” says Ortega. “What can we expect in terms of forage produc- tion in an average year? For an ex- ample, a Kleberg bluestem pasture may produce 4,500 pounds per acre of dry forage in an average rainfall year. If by June, at the end of the spring growing season, we do not receive 5 to 6 inches of properly dis- tributed rain and a standing forage crop of 2,200 pounds per acre, we know there may not be more than 2,600 pounds of forage in October, even if we get 10 inches of rain in September.
tscra.org
“This is far below the poten-
tial forage productivity of 4,500 pounds per acre and is a situation that should trigger the fi rst destock- ing decision.” The next question is: How much
to destock? “That depends on how much standing crop you have and what is the target minimum amount of forage you want to maintain to allow recovery,” says Ortega. “Culling 20 to 25 percent of the
mother cows might be appropriate. If the market is good, you might want to wean early and market all of your calves. Then in October when you measure the quantity of standing forage again, you will know how many animal units can be maintained without overusing the pasture. “Fall measurements show the
amount of forage available for graz- ing until the next growing season which is spring of the following year,” Ortega continues. “Number of grazing days can be estimated for the pasture in which the measure- ments were made and depending on the amount of available forage, you may decide to destock once again. Destocking may include the previous year heifers and maybe, additional mother cows. The abil- ity to maintain a certain number of mother cows to rebuild the herd when forage availability improves is one way to survive droughts.” Every rancher should have the
ability to determine the residual forage required for soil protection and forage recovery when moisture becomes available. For example, Ortega destocks
in South Texas when Kleberg blue- stem-dominated pastures reach 750 pounds per acre. If stocking rates are properly managed, this amount of production occurs only in severe droughts. In average or high rainfall
years, these pastures will produce 4,000 to 6,000 pounds of dry for- age per year.
Trigger No. 3 — animal body condition scores It’s fairly easy to assess body
condition scores (BCS) when check- ing cattle, and they are good indi- cators of forage quantity and qual- ity. Body condition scores in cows should be maintained at around 5 and they should be between 5 and 6 at calving. Heifers should have a body condition score of 6 when calving. Monitor cattle closely because once a cow drops a body condition score, it takes a lot of feed to get her back to her original condition. “Supplementation may be used
strategically when body condition scores start declining because of low forage quality,” says Ortega. “The quantity of available forage should be enough to fulfi ll dry mat- ter requirements of the cattle and supplement should take care of the quality problem. We want the sup- plement to have an additive effect, and under no circumstances should it substitute for the lack of forage.” To survive droughts and to
maintain pastures for long-term productivity, we must learn to rec- ognize the triggers for destocking. Vacating a pasture at the correct target amount of residual forage protects the soil from erosion and increases water infi ltration and re- tention when rain occurs. There is a signifi cant difference
in plant growth following a rain- fall event between pastures that have the proper amount of residual cover versus those with mostly bare ground. A pasture with a residual forage cover will recover faster and help keep a cow-calf producer in business.
April 2014 The Cattleman 87
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