Grazing and the end of the growing season

Molly Reichenborn, range management specialist

September is here, the first frost is on the horizon, and the growing season will be winding down in the coming months across Kansas. With the transition to the dormant season comes a key time for grazing planning, whether you are ending your grazing season in the coming months, grazing stockpiled grass during the dormant season, or using a combination of strategies to support your herd throughout the year. Keeping a few considerations in mind can support the productivity of your grass resources into the winter and the following years.

Watch grazing height: Knowing the beginning and ending grazing heights for your grass pastures is key to understanding your available forage and setting up your pastures to be productive in the following year. Leaving adequate residual height protects the soil surface from erosion, preserves capacity to capture and retain soil moisture, and avoids stressing plants to the point of depleting root reserves, which will reduce future stand productivity.

If your grazing season is ending at or near the end of the growing season, your ending grazing height should ideally be determined at the beginning of the growing season. Stocking rate can then be managed throughout the season with this target in mind to avoid over- or under grazing. The second best time is now to take a look at the height of your grass stand on your pastures and adjust your end of season grazing accordingly. Leaving approximately 50% of the total season production as standing forage at the end of the grazing season is the rule of thumb for grass stands.

For native grass stands, this roughly translates to different minimum ending grazing heights depending on your dominant grasses (Table 1). If you’re already below the target grazing height or expect you’ll graze below this target by your planned shipping date, consider moving up plans to destock to preserve remaining cover and avoid reducing stand productivity for the next growing season.

Table 1. Recommended minimum grazing height for native rangeland types.

Native Forage Type	Minimum Grazing Height
Tallgrass	6 to 8 inches
Mixed-grass	4 to 6 inches
Shortgrass	2 to 3 inches

 

If you’re grazing cool season pasture grasses this fall (e.g., fescue, brome) or grazing stockpiled tame forage over the fall and/or winter, leaving at least 3 to 4 inches of residue until the following growing season is typically recommended to preserve stand productivity and health. Some tame forages (e.g., bermudagrass) can tolerate grazing heights as low as 2 to 3 inches. Although plants can be grazed without concern for affecting growth during the dormant season, adequate residual still needs to be maintained to protect the soil surface and capture precipitation until the following growing season.

Take stock of winter forage availability: If you plan to graze stockpiled grass over the winter, estimate your available forage now to ensure you have an adequate supply, acquire supplemental feed if necessary, or reduce your herd size if needed.

The amount of forage produced each year depends on several factors, including precipitation, soil conditions, and management practices. The forage type also heavily influences how many pounds of forage you can expect per inch of height in your grass stand (Table 2). Based upon the expected pounds per acre for your stand, you can estimate how much forage you have available to graze during the dormant season.

Example: If you are planning to graze stockpiled fescue on 20 acres and measure 12 inches of available forage, and you expect to leave 4 inches of residue, you have 8 inches of available forage. Assuming that the fescue stand produced 200 pounds per inch per acre x 8 inches of available forage, you have = 1,600 pounds per acre, which translates to 32,000 pounds of total available forage over 20 acres. With a continuous grazing approach on fescue, you can expect your herd to harvest 30-40% of the available forage, with the rest lost to factors such as trampling, avoidance of cow patties, etc., during the grazing period. If you assume 35% harvest efficiency of 32,000 pounds, 11,200 pounds of the total available forage can be grazed. With a herd of 30 cows consuming 2.5% of their body weight per day each weighing approximately 1,200 pounds, each cow will consume about 30 pounds of dry matter forage per day. Based on 11,200 pounds of available forage divided by the 900 pounds of forage intake per day for the entire herd, your fescue pasture can support the herd for approximately 12 days.

Table 2. Estimates of dry matter forage produced per inch per acre (lbs/inch/acre) for several forage types.

Forage Type	Low	Medium	High
Tallgrass	120-160	160-230	230-300
Mixed-grass	70-120	120-160	160-230
Shortgrass	30-40	40-50	80-120
Brome or fescue, fertilized	100-200	200-300	300-400
Bermudagrass, fertilized	150-250	250-350	350-450