Pasture & Range: November 2000 Other Pasture & Range Articles

Keeping grazing records to make grazing management and forage unit decisions can be very useful. Grazing records track grazing period and recovery period days, grazing cycles, seasons of use, and much more. All of those things are helpful, but we want to talk about using grazing records to record grazing days per acre (GDA) and using GDA to determine other factors, such as cost per GDA, estimated yields, and paddock comparisons.

On the Noble Foundation's Controlled Rotational Grazing Unit (CRGU), we have kept grazing records, including GDA per paddock, for many years. GDA as recorded is a quantitative yield of a given paddock that helps us assess paddock forage management and serves as a reference in future seasons.

Table 1 is a summary of several actual GDA records from the CRGU. The paddocks were bermudagrass-based and overseeded to 'Maton' rye and 'Marshall' annual ryegrass. Some were fertilized our usual way, as outlined in the table. Although we thought our fertilizer rate was satisfactory, we wanted to see whether our GDA, and thus beef yield, could be measurably and economically increased by doubling our usual nitrogen input per acre. In addition, we kept GDA records to partition winter pasture yields from summer pasture yields. Winter pasture GDA from cows was from stockpiled bermudagrass.

By accumulating and interpreting the GDA record, we can ascertain several things for the CRGU. Costs per acre for the various fertilizer applications, which are in pounds per acre (nitrogen-P₂O₅-K₂O), are as follows: 118-46-62, $49; 100-0-0, $28; 200-0-0, $56; and 218-46-62, $75. Costs include per-acre charges of $2.50 per application in our case. We can use these figures to calculate cost per GDA and other factors. For example, fertilizer input costs for growing winter pasture in the usual fertilizer case was $49 per acre to yield 245 steer GDA. Part of that yield comes from lush early bermudagrass that grows in May as a mix with the late winter pasture. Cost per steer GDA for fertilizer was $0.20 ($49 ÷ 245) when all phosphorus and potassium cost was applied to the winter season. Part of phosphorus and potassium costs could be charged to the summer grass. The usual rate of fertilizer applied to the unit is considered upper-level management for optimum production efficiency. In the doubled fertilizer case, the cost was $75 per acre to yield 338 steer GDA. Cost per steer GDA for fertilizer was $0.22 ($75 ÷ 338). Therefore, in this comparison, there was a small increase in cost per grazing day: only $0.02. We could judge that the increase in cost would be more profitable in the long term. On all forages, our steers have averaged about 1.9 pounds of average daily gain (ADG) throughout their time on the unit. On that basis, fertilizer cost was $0.11 and $0.117 per pound of gain, respectively, for the usual and doubled fertilizer cases. Both are quite acceptable.

This example is just one of many from this table, and we could continue this line of interpretation with other examples to gather information to better manage forage economics.

In table 1, several important grazing records are shown. Winter pasture steer GDA production is greater than summer GDA production, illustrating the importance of season and pasture type. Steers contributed an average of 63 percent of total actual GDA, as reported. Since stocker cattle enterprises are usually more profitable, the higher that figure, the better the profit potential. Doubling fertilizer inputs increased yields in almost all cases, but not all were judged potentially profitable. For example, thirty-five steer equivalent GDA more with twice the fertilizer on winter pasture in our case is not profitable. The added winter yield mentioned before came from lush winter pasture and did not include the stockpiled bermudagrass grazing by the cows. The winter pasture stubble and the stockpiled bermudagrass the cows ate did not contribute to an increased yield from more fertilizer. However, the total of 267 more GDA for all winter and summer forage could have been more profitable. Later in the report, we'll talk about converting cow unit GDA to steer equivalent GDA.

The GDA presented for steers and cow units is actual but can be converted to equivalent total steer GDA or equivalent total cow unit ADG for more uniform comparisons by using averaged charts available in the livestock and pasture industry. I prefer, when possible, to make these estimates from known cattle weights or estimates and realistic estimates of forage intake. For example, our cow-calf units averaged 1,400 pounds yearly, calculated by adding the weight of the cow to that of the calf and prorating it over 365 days. At an estimated consumption of 2.5 percent of body weight, those units would consume an average of 35 pounds per day. Our steer units averaged about 500 to 550 pounds long-term, and at a consumption of 3 percent of body weight, they would consume about 15 pounds per head daily. The steer GDA equivalent from the cow GDA is the cow unit forage intake divided by the steer unit forage intake, e.g., 35 ÷ 15 = 2.3 steer GDA per cow GDA. Total steer equivalent GDAs are reported in the table. That estimate was derived by adding actual steer GDA to estimated steer ADG equivalents from the cow GDA. For example, from the left columns in the winter pasture row, we can calculate that 245 steer GDA + (122 cow GDA x 2.3 steer GDA per cow GDA) = 526 steer equivalent GDAs. This estimate gives us a potential figure of total steer GDA if cows are not included and steers are the only grazers. The reverse calculation can be made to convert steer GDA to cow GDA.

We can take this process a step further and estimate possible pounds of beef per acre. Our steers averaged 1.9 pounds of ADG long-term. Thus, the example is 526 steer GDA x 1.9 ADG = 1,001 potential pounds of beef per acre. This type of estimation can be done on any yield reported in the table, whether actual or equivalent GDA.

An interesting projection comes from the 1,052 equivalent steer GDA: 1,052 GDA x 1.9 ADG = 1,999 potential pounds of beef per acre at a cost of about $150 per acre for seed and fertilizer, and thus a cost of $0.08 per pound of projected gain. That outcome is exceptionally good, and these records indicate it might be feasible in our case, but we would proceed with caution, monitoring weather closely. A more realistic long-term ADG for a yearling might be 1.5 ADG to get a projected potential beef yield of 1,578 pounds per acre. Some of our paddocks with usual fertility have yielded over 1,200 pounds of beef per acre, so at a higher fertilizer rate, perhaps 1,578 pounds of beef per acre is a realistic goal in a good year.

We can take this type of GDA data and estimate total forage consumed (produced). If a steer averages 15 pounds of forage intake per GDA, then 15 pounds x 526 steer GDA = 7,890 pounds of estimated forage yield from winter pasture and one month of bermudagrass mixture. We know by research and experience that this yield is possible and realistic.

If we judged that pasture used 150 pounds of actual nitrogen to grow the forage yield of 7,890 pounds, we could calculate estimated pounds of grass per pound of nitrogen. For example, 7,890 pounds of grass ÷ 150 pounds of actual nitrogen = 53 pounds of grass per pound of nitrogen, which is a good conversion in pasture. A usual conversion is 25 to 35 pounds of grass per pound of nitrogen, including the deduction for check plot yield (no fertilizer).

In addition, GDA or projected forage yield per acre can be used to judge stocking rates for alternative livestock enterprises such as cattle, sheep, horses, or goats.

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