Alpacas thrive on simple grass pastures and ordinary grass hay. But some grasses are better than others and some should be avoided.
Know your area
Not every region of the country can grow the same grasses. Some grasses thrive in the northeast, while others stay dormant. The following will be for what performs well in the southeast, although some of the grasses that do well here do well in other areas, too. There are two basic types of grass - cool season and warm season.
Cool season grasses
These grasses grow during the cool part of the year - spring and fall in the south when daytime temperatures are between 60 and 75 degrees F. The most common forage grasses are orchard grass, timothy, fescue, annual and perennial ryegrass, winter wheat and bluegrass. An orchard grass with a little timothy mix works very well in the southeast.
Orchard grass is very palatable, and the better varieties are persistent. (Persistent is the term used to describe how well a forage survives grazing. Also, grasses, although many are perennial, are not immortal. So if they live many years and recover well from repeated grazing, they are persistent).
Annual ryegrass works very well to seed in the early fall and grows very quickly to provide forage for late fall. Being an annual, it must be reseeded yearly.
Fescue is one of the most common and popular forage grasses, but most fescue varieties should be avoided. See further down on grasses inappropriate for alpacas. However, there are varieties of fescue that are inoculated with hypo-virulent strains of endophytes that may work well with alpacas.
Warm season grasses
When temperatures get to 80 to 85 degrees, the cool season grasses growth slows dramatically, actually going dormant if the temperature is high enough. Warm season grasses are the answer and thrive between 80 and 95 degrees during the day.
Common warm season grasses are bermuda, millet, sudan grass and bahia grass.
The most popular forages are the many varieties of bermuda. There are many turf varieties of this grass, but the forage varieties exhibit very fast growth and actually get tall enough to cut for hay. There are a couple of varieties that are very tolerant of cold weather and do well in the upper mid-west up to Indiana and Illinois.
County Extension Agent
This is the person who's going to tell you which grass variety works best in your specific area. You can fill them in on what basic grass does well for alpacas and which ones don't and the agent will tell you which variety, when to plant, and how many pounds of seed to the acre. The agent is also the one to turn in your soil sample to see what amendments (fertilizer) your soil will need for the type of grasses you will plant. The county agent is an incredibly valuable resource and what they don't know, they can find out as virtually all of them are on first name basis with half the PhD's in the nearest University.
There are other plants in addition to grass that alpacas can eat that can be mixed in with the grass.
One of the most common is clover. There are short, medium and tall varieties. The common white dutch clover is a short variety but is not a vigorous forage. The talls are mostly for haying and the mediums as Goldilocks would say are "just right". They grow well enough to be useful as forage and some varieties are very persistent.Alfalfa tastes soooo good the animals will selectively eat it ...until it dies.
Alfalfa is one of the highest protein forages available, but is prone to insect problems. For a forage pasture that your alpacas will graze, insecticide spraying is probably not an option, but would be necessary if you wanted much alfalfa in your pasture. A little mix won't work well either. Alfalfa tastes soooo good, the animals will selectively eat it, to the exclusion of all else, until it dies. Also, and most importantly, alpacas can have problems if the alfalfa is more than 20% of your pasture. The calcium content is very high and supplemental phosphorus will be necessary to prevent problems.
Forage chicories have lately had good results with sheep. I tried it. It grew well. Despite my pleading about how great the stuff was, my alpacas wouldn't touch it even at the point of starvation.
Despite their common use, there are two grasses that should be avoided.
Fescue is a fantastic grass. It is hardy, drought resistant, remains green in the winter and grows very well. Much of this success is due to a symbiotic existence with an endophyte. An endophyte is a fungus that grows internally - inside the plant. The fescue gives it a home and the endophyte provides additional nutrients for the fescue. The endophyte also produces compounds that affect pregnant and lactating camelids. The effects and symptoms are virtually identical to problems that mares have who have been fed fescue. The common problems are agalactia, thickened placentas, and ...tough fetal membranes The common problems are agalactia (milk related problems. E.g. low milk production, no milk, slow to let milk down), thickened placentas and on camelids the fetal membrane which envelopes the cria will be very tough. Not all fescue will have endophytes, but if the fescue is tall or in moist or naturally foggy areas, it will. Males have no problems with it, so your "boy" pastures would be OK.
There are fescue seeds that are endophyte-free. They don't grow as well as regular fescue, since the endophyte supplies nutrients. Also, after a while, they naturally become "infected" with the endophyte, so you're back at square one.
There are some new varieties with a hypo-virulent strain of endophyte. A hypo-virulent strain means that it is not as toxic, if at all. So its infected with an endophyte already, but its natural toxins that it produces do not have the bad effects with horses, and presumably, with alpacas.
The other popular grass to avoid is perennial rye. This is not the same as annual rye. Perennial rye can cause ryegrass staggers - a bad reaction that can lead to death.