So we're running about 85 head on stockpiled forage right now in central Nebraska. We had about 10" of snow recently, and I just moved the cattle this morning. We're back grazing through a long quarter (160 acres, 1 mile long), that's divided into 3 lanes. We had a severe drought this year, so we didn't get as much growth as we wanted but we have plenty.
We grazed 100 large commercial cow calf pairs last spring, about 1300-1500lbs each plus 200lb calves (monsters, way too big...but not our herd). We also cut some hay and then the grass shut down from the severe drought and heat until the fall (its a cool season 6 species mix and 3 legumes).
Now we're running the grass finishing herd on the early growth stage grass....this can be important. If it's too mature and rank it won't be as palatable and may have extremely low feed value...yes seed heads are energy, but the sugars in young grass act as a preservative...its a debatable topic.
The cows grazing weigh about 1100-1200lbs and we have some steers out there as well, mostly Galloway but some hereford crosses. We're selling grass FAT animals on Wednesday. I would estimate we have at least another 8 weeks of standing feed. We usually mob the animals, but since the snow we pulled the back fence and are allowing them to go south into areas they have already grazed (back/strip grazing). They go for the orchard grass first, then the bromes. Obviously the dicots lose all leaves in the winter, so there is little feed provided by the legumes in the winter.
Its important to have animals that still have good grazing instincts. Buy animals that fit your system, or select towards your ideal system. If you go buy Holstein calves from the sale barn, they may have no grazing instinct left and none taught. This can lead to a disaster. Animals need shelter in a storm, not a building....a dry creek or gulley works great. A good hill or windbreak is perfect.
The animals do have to work harder to graze with snow on the ground, but if its not crusted too hard and is under 12", they will still graze. If you are running dry cows, then good stockpiled grass is sufficient even in a good snow. However if you have calves on the cows, or are trying to keep gain on a finishing animal (we expect our cows to take the calves through to march, and are still selling finished animals)...some additional hay goes a long way when there's snow. We feed a bale of alfalfa every other day, rolled out across the pasture so they all can eat (prbly 1500lb bale, mid quality alfalfa) There is almost no waste, and the protein boost helps with the stockpiled forage. If we didn't have any snow, we would not feed any hay (as we have been doing for most of the year). Rolling it out, or forking from a wagon, spreads the nutrition as well.
Pugging- yes plugging can be of concern. However, only when the snow melts. If you start to get pugging, move them faster in smaller areas. They will spoil less forage and create less damage. If the snow melts slowly, and freezes at night pugging is of no concern. One of the reasons we pulled the back temporary fence was to help prevent pugging. It gives us more time to move the animals if pugging becomes a concern.
We have been running about 275 head hair sheep and 30 goats on stockpiled forage as well. However, with small ruminants they can go downhill fast. We feed them every other day when there is no snow (1 bale of cool season mixed grass/legume hay prbly 1600lbs forked into piles from a moving wagon). We feed them 1/2 a bale everyday when there is snow. With sheep, you can finish the lambs in the fall, so you're only taking breeding animals thru the winter. Thus a slightly higher hay expense can be justified. Additionally, we feed the hay on a 12 acre field that is not in permanent pasture....so we are fertilizing the field by feeding all over the place. We will grow specialty organic corn this spring and harvest many times the value of the hay in that crop....cutting out a lot of very fuel intensive steps commonly used in farming.
Carrying capacity depends on region and productivity. We have extremely productive ground due to over a decade of mob grazing. The neighbor has a field that can't grow anything without anhydrous ammonia. Lean on the side of caution, or expect to buy hay if you underestimate. Feeding some hay can be beneficial if you are building your fertility and organic matter, but it is expensive and fuel intensive (plus lots of work). Planned grazing is of great benefit, if nothing else it will allow you to estimate carrying capacity as you go. There is no equation that will give you anything more than an estimate of carrying capacity, experience and observation is the best way to calculate carrying capacity.
I'll try and shoot a video this afternoon of our grazing system.