Avoiding drought management

Here in South Texas the weather was hot (in the 100 degree range) back in the late spring and stayed that way through the summer.  A ridge of high pressure conspired to keep the hurricanes either well to the east or south of the Gulf Coast which a lot of folks were counting on to end the dry spell. It really stopped raining for us back in the winter of 2010 with only 2.5 inches recorded in January and nothing ex-cept traces of rain until 6.53 inches fell on my place in September (nearly all at once).

We have all read the drought management articles about how to survive the drought, what to cull, how to use nontraditional feeds and hays, how to feed them, etc. but we are just reacting to something we knew was going to happen again the last time it started raining. What I want to propose are two useful management tools to help avoid drought management. These are not something I have come up with; in fact one is an old grazing management tool that has been around for many years. The other is using a current climate forecasting technology and applying   to local rainfall data to decide the probability for long term rainfall conditions.

Stocking Rate. In my early Range Science classes stocking rate was determined by taking half of the available forage and determining how many days (or months) it would take a 1,000 pound cow to eat it. It was a useful estimate to decide how many days a group of cows could remain in the pasture without damaging the grass or the root system, allowing the plant ample time to regrow before regrazing the pasture. If you have read the articles in the agricultural press or run a few or many cows yourself, you will realize that the 1,000 pound cow is a thing of the past and that most cows are closer to 1,200 pounds or more. The problem with that is that those 1,200 lb. cows eat more than the 1,000 lb. cows (not quite 20% more but you get the point). So, a stocking rate set correctly for 1,000 lb. cows in 1950 or 1960 is woefully overstocked for 2011. Even more to the point is that very few of us even have a set of scales to weigh our cows.

You can get an  estimate of how much forage you have by clipping, drying and weighing the amount of forage from several areas of a fixed size (usually a square yard will do) across a pasture. These should be selected based on soil type, grass type and condition and represent average conditions for that period (even in a drought). An acre has 4,840 square yards so the more you measure the greater the accuracy, but at best this is only going to be an estimate of forage production. Combine all the clippings from one pasture and weigh on a scale (a letter scale works well here since the amount of forage will usually weigh in ounces) and let dry (an oven or a microwave is useful for this but placing a cup of water will keep the fire hazard to a minimum, but keep watch!). If you cannot dry or decide against it, just reduce the weight by what you consider the amount of moisture is in the clippings (green and growing – 70%, dry and brown – 30%). If you collected and dried 5 lbs of grass from 10 square yard samples, the average weight per square yard would be .5 lb. (8 ounces). Since we need to “take half and leave half” to allow the grass to regrow quickly after it is grazed (providing it rained), reduce the weight by 50% to .25 lbs. (or 4 ounces). There are 4,840 square yards in an acre, so multiply the .25 lbs. (per square yard) by the 4,840 (square yards per acre) to get the grazeable pounds of forage per acre, 1,210 lbs.

So how long will that last? Cows can consume somewhere between 2-3% of their body weight depending on the lushness of the forage, the dry matter content, the cow’s physiological state (bred or open or lactating), and a number of other considerations. Usually intake is considered to be 2.5% of body weight so a 1,000 pound cow will eat 25 pounds of forage. If we take the amount of grazeable forage per acre, 1,210 lbs., how many days will that acre support a cow? 48 days (1,210 lbs. divided by 25 lbs.). If the pasture is 10 or 100 acres the estimate is still the same. The size of the pasture (in acres) multiplied by the number of days an acre will support a cow will give you the total number of days a cow can graze it. If you have 100 acres in this pasture it can support a cow for 48 x 100 or 4,800 days (or 100 cows for 48 days). But we don’t have 1,000 pound cows, we have (at least) 1,200 pound cows and 2.5% of their body weight is 30 pounds. Now that acre will only support a big cow for 40 days. If the pasture is 100 acres it will support 100 big cows for only 40 days. If you leave the big cows in for 8 extra days you have done significant damage to the plants and their roots reducing their ability to regrow and remain viable. So consideration of cow size is important!

Cows don’t consume everything that is clipped and weighed and even if they did, unless the clipping was all one type of grass, there are differences in nutritional content and digestibility. All that has been measured is quantity of forage that is available for grazing. A friend of mine has a quality constant that he applies to his stocking rate in each pasture (acres/cow) to determine the number grazing days. After rains in the growing season he generally assigns a high quality constant (increasing the number of grazing days) but when the grass is dry and dormant or when it rains outside of the growing season he assigns a low constant (reducing the number of days) to keep from harming the grass.

It will help if you take a picture of your pasture that you clip (usually before you turn the cattle in to help you decide how long they should stay) and maybe put some sort of a measuring stick in the picture so you can develop a photo guide to compare with in future grazing decisions.

Drought Early Warning System (DEWS). I am not sure who coined this term or the system but I am attributing it to my good friend and mentor Leroy Foerster, a former Beef-master breeder and now a commercial cattleman using Beefmaster cows. I have known Leroy since 1988. Over the years Leroy has used short duration grazing based on rainfall data and his knowledge of grass growth. Since 1975 he has measured rainfall (averaging 31.36 inches annually). He uses a three month running average (based on the El Nino/La Nina episode rainfall ex-pectations, Table 1) to determine if he is above or below average in rainfall for that period of time. If he is below the average he initiates what he calls his drought early warning system meaning he looks to see how he might reduce his stocking rate, slow down his rotational grazing, early wean calves, cull older or less productive cows, or purchase feed (a last resort never exercised to my knowledge), etc. He does pay attention to the market, but he never has to sell cattle or purchase feed on a market already affected by drought sales.

In Table 1, he has compiled his average rainfall records by month on his ranch to the current status of the El Nino Southern Oscillation (ENSO or El Nino-La Nina episode conditions).  From this table he can determine if he can expect more or less rainfall than the long term average for the upcoming months. If he can expect more his DEWS management can be relaxed after the expected rainfall comes but if he can expect less he is ahead of the drought. By destocking early he has reduced the pressure on his pastures and there is more forage available for the remaining stock. In addition, by having numerous pastures to graze, there is always an opportunity that one might catch a random shower, even in a drought, and grow some grass. Measuring rainfall (and writing it down) is something most do.  But actually acting on it in a timely manner, using it as a drought management tool before the drought actually occurs, is not something usually done. Leroy also maintains, and I agree looking at long term rainfall results for many counties, that most “dry” periods extend beyond just one year. His data indicate that all the dry periods began with a DEW and since 1975 we have been under a dry spell 22% of the time!

Even though the table lists “best” and “worst” case episodes for historical rainfall, that doesn’t mean it will rain, only that it has. According to NOAA, from March until July this year the El Nino episode was in effect which should have provided average to above average rainfall. It would have except that a high pressure area kept tropical storms well away from Texas and the Gulf Coast. In August, La Nina conditions began which, al-though not the best in terms of rainfall could indicate near average for rainfall for October, November and January but below average rainfall for De-cember, February and March. Again, it is not predicting rain, just indicating what has happened, allowing one to make plans accordingly.

In this most recent drought I have been looking at rainfall records for the counties I speak in on drought management. One of the most interesting points is that about half of the years in the past 10 are considered dry (below average in terms of long term rainfall). When only 75% of the average rainfall was considered, only 2 out of the 10 years were below average (considered dry). That would of course translate into reducing stocking rates by 25% since 25% less rainfall grows 25% less grass. But if we didn’t have to buy or raise feed and hay every other year or early wean and sell cows to keep cost of feeding low maybe body condition scores would be better at breeding and calving, producing more and possibly heavier calves at lower cost.  Just a thought.