I can’t count the number of times I have been asked this question or better yet, “can you come to my place and tell me how many animals I can raise?” The question I have to ask is how much grass do you have? Of course no one knows or has even asked themselves this important question so let’s look at where we can go to begin the process.
On pages 114 and 115 of the Soil Survey of Williamson County there is Table 6 Rangeland Productivity. This table lists every soil type for the county and the potential for annual production depending on the growing conditions. This would assume only range type plants and typical plant compositions are listed in the description of each soil series at the front of the book. A natural question arises, “what about coastal bermudagrass?” Since this assumes that the range plants are not fertilized we would also say that unfertilized coastal bermudagrass would respond similarly or slightly better. If the coastal is fertilized then we can increase the productivity of the plant, generally producing two times as much forage as without fertilizer.
Looking at Table 6 in the Soil Survey we can see for example that a Branyon (BrA or BrB) Blackland soil can produce 7,000 lbs of dry matter in a favorable year, 5,500 in a normal year and 4,000 in an unfavorable year. This would be the amount of forage produced if all the forage was cut and then dried and weighed. So it represents a total harvest for the year. You can find your soil type in the Soil Survey Maps!
Next, according to Range Scientists and Conservationists we can only expect to effectively use or consume 25% of the forage produced commonly known as “harvest efficiency.” 25% is consumed by the animal, 25% is lost to natural disappearance, and 50% is necessary for soil protection and future forage production.
So taking our previous example a Branyon Blackland soil in a normal year at 5,500 pounds of forage and only using 25% then we have 1,375 lbs of forage to consume per acre per year. A standard animal unit is considered to be a mature cow (1,000 lbs.) with or without calf consuming 26 pounds of forage per day (6 goats equals one mature cow). One acre produces 1,375 lbs divided by 26 lbs equals 52.88 days of grazing. 365 days divided by 52.88 equals 6.9 acres per animal unit per year in a normal year on a Branyon Blackland soil.
An Eckrant soil (EaD or EeB) produces only 1400 lbs of forage in a normal year. 25% yields 350 lbs of forage to consume divided by 26 lbs per day equals 13.46 days. 365 divided by 13.46 equals 27.11 acres per animal unit per year.