By: Pat Johnson and Roger Gates, SDSU Extension
It has been a very long winter and we are waiting impatiently for signs of spring to occur. There’s nothing like green grass to remind many of us how much we love the livestock business. In the midst of market highs and lows, droughts, blizzards, and floods, it is encouraging to remember how reliable the progression of seasons is. Every year at green up, grass managers must make decisions about when and where to begin grazing. Considerations include hay reserves, the cost of purchasing additional feed, and the impact of early grazing on pasture grasses. How long should you continue to feed stored forages, to delay the impact of grazing on pastures? How early can you turn out, relieving the cost of feeding? Which pasture do you graze first? The answer to these questions is: It depends! You may have several options, depending on your pasture resources, your stored feed resources, and your ability to be flexible in your grazing options.
You may want to utilize one or more of the following options:
Continue feeding livestock a few weeks longer
If you have the feed reserves available, feeding livestock a little later into spring provides your pasture grasses with time to shift from dependency on reserves to utilizing photosynthesis for energy. If grazing is initiated too early, production for the balance of the growing season can be reduced.
Graze tame grass pastures earliest
Access to pastures planted with introduced cool-season grasses, such as crested wheatgrass and smooth brome, provides early season flexibility and avoids early grazing on native pastures which may compromise production later in the season. These pastures are typically ready to be grazed 2 or more weeks before native pastures.
Flash grazing winter pastures
A recent study demonstrated that native winter pastures could be grazed in mid-May at about 25% relative use without a decrease in stockpiled winter forage. Exceeding 25% use or extending grazing into mid-June, however, could reduce forage in those pastures that you will need next winter.
Wait to graze native pastures until grass is “ready”
Research suggests that grass plants are most vulnerable to grazing before they have formed three new leaves. Knowing how many growing degree days are required to reach the 3-leaf stage provides a general “rule-of-thumb” about plant development. The date that grasses reach the 3-leaf stage varies considerably, so examining the important plants in your own pasture is recommended. One way to come up with a date to begin examining your grasses is to use “growing degree days” (GDD, base 32 degrees after March 1). GDD is calculated for each day as (Tmax Tmin)/2 – Tbase, where Tbase is 32. GDD is then summed for all days after March 1. For introduced grasses, the 3-leaf stage generally requires accumulation of about 500 GDD; many native cool-season grasses require about 1200 GDD. The calendar date when these growing conditions occur varies considerably from one location to another and from year to year. For example, climate data from the weather station at Oral, SD indicates the average date at which 1200 GDD accumulate is May 28. For Nisland, SD, average date for 1200 GDD is June 1. Recently, 1200 GDD accumulated as early as May 11 in Oral and May 21 for Nisland. Growing degree day data for South Dakota weather stations can be accessed using the SDSU Climate website. In general, for tame pastures, examining crested wheatgrass or smooth bromegrass plants might begin as early as mid-April. Mid-May might be a reasonable date to start examining native cool-season grasses such as western wheatgrass and green needlegrass.
One last thought
A “rule-of-thumb” which should be remembered at turn-out is “never graze the same pasture at the same time of the year, two years in a row.” While many operations, of necessity, have a calving pasture which is grazed at the same time of the year, every year, most operations can vary where cows and calves begin grazing after calving is completed. The management goal is to distribute defoliation pressure on desirable species to different times of the season in different years. If a pasture is grazed at the same time every year, the vigor of plant species which are most vulnerable at that season will be reduced and they may eventually be eliminated from that pasture.