Broadly speaking, ruminants are genetically optimized to eat pasture grasses, legumes, and browse from bushes and trees. Goats are more tailored to browse than grass, sheep do reasonably well on both, while cattle are primarily grass grazers.
In the last hundred or so years, commercial livestock operations have shifted fairly heavily to a CAFO model (concentrated animal feeding operation) where the ruminants are not eating pasture, but are eating hay of various forms and grains without leaving fairly tight confines where they live out their lives. This type of feeding has some notable effects on dairy animals and their milk and its quality.
It is preferable to feed ruminants on high quality pasture, even dairy animals which have high energy needs from their feed, even if supplementation is needed to help them keep good body condition while producing milk or feeding their young. This can be a challenge, as that requires vastly more land than a CAFO, it requires more management, and places the animals further from the milking parlor at times. Some modern dairy breeds have been eating grain and CAFO-style feed for so long that they have a difficult time on pasture, although many heritage dairy breeds still thrive well on pasture.
Good milk starts with good pasture, and high quality feed if supplementation is needed. A dairy that desires to produce high quality, safe and nutritious milk should focus on pasture quality. In some grazing systems, the ranchers don't even really call themselves ranchers, they call themselves graziers and think of themselves as pasture-growers first. The animals will thrive if the pasture is well cared for. This is a useful philosophy for dairies, where successful pasture management make the final product – milk – easier to produce well and incur lower input costs.
While all grazing methods may require supplemental feed for the animals, especially in cold weather, a good grazing system should produce as much pasture as possible for the dairy animals during the year to lower the cost of milk production and to increase the health of the animals and the quality of the milk. There are several methods:
This method consists of having open pasture land, and just letting the ruminants roam where they like on it and eat pasture plants as they see fit.
Pros
Cons
Rotational grazing splits a pasture up into a number of paddocks, and the animals are moved at least a few times per year to allow a grazed paddock to recover and regrow.
Pros
Cons
Management-intensive grazing is a newer method, part of the umbrella of “regenerative agriculture." It takes rotational grazing to it's logical conclusion, by dividing the pasture up into small paddocks that may only be large enough to fit the animals for a single day or so, and have them moved to a new paddock usually daily. The amount of pasture plant eaten is monitored, and each paddock typically gets at least 30 days of rest after being grazed before the animals are rotated back onto it. This can result in fantastic pasture productivity.
Pros
Cons
Feed requirements depend upon the type of ruminant and the stage of lactation. For cows, generally they need around 18% protein in their feed. Most of the feed should consist of grasses, with some legumes added in. During peak milk production or during winter time, the energy content may need to be increased, possibly using grains as a supplement to achieve this depending on the circumstances. Cows need a little less than 1 kg of feed per day to maintain their own body weight when they are not lactating or under stress (such as cold winters), but the feed and water requirements can increase by multiples for many high-milk-production breeds during the height of lactation.
Some suggested feed requirements and proportions for dairy cows can be found here.
It's important to frequently evaluate the body condition of your animals to ensure they are in a healthy range. Body conditions are generally set between 1 and 5 in fractional increments so they can be standardized Cows should score 2.5 to 4.0 at all times, tending toward 3.5 before breeding and at the start of peak lactation. As the lactation period ends they should ideally score no less than 2.5, and have a dry period where they can recover their body condition higher again before the next lactation cycle. Sheep are similar, between 2.0 and 4.0, with similar fluctuation between lactation cycles to stay healthy.
A good tutorial on evaluating sheep for good body condition (which likely applies well to goats) can be found here.
Body condition scoring for cows is a little more complicated, but a good visual tutorial can be found here.
Dairy animals have perhaps the highest and most demanding diet requirements of any farm animal on Earth. Especially when it comes to raw milk, “only the very best” feed and diet is a good philosophy. There are subtleties to the feed, however, which can have an impact on the taste, quality and even appearance of the milk.
Fermented feeds such as silage and haylage are enticing because the fermentation provides a preservation effect that makes the feed last longer, as well as being a little easier on animals' digestive systems due to the pre-digestion effects of fermentation. The issue is that it is difficult to control exactly what microorganisms were doing the fermentation, with clostridia family bacteria frequently participating. These enter the gut, pass out via the manure, and some of that inevitably ends up near or in the teat canal of the lactating animals, and will cause late blowing defects in certain types of cheese. In some cheese types, such as Parmiggiano Reggiano, fermented feeds are banned for this reason, as the risks are too high. Unfortunately, pasteurization of milk does not destroy clostridia spores, so this problem is not confined to raw milk.
Depending on the final use of the milk, fermented feeds may need to be skipped.
Not all pasture grasses are created equal. Legumes and grasses are not equal. Grain and pasture diets are not equal. They each have pros and cons. Grain is usually high energy, but it is hard on the rumens of dairy animals, and it lacks carotenoids and other vitamins and minerals that grasses provide. Legumes like alfalfa and clover provide more energy than grasses, but too much of them can cause bloating and should be used in moderation. Grasses don't provide as much energy, but they and their dried equivalents should be the foundation of a good diet for cows and sheep, for example.
“I can taste what the goat was eating!” This kind of statement unfortunately can be true at time. If a ruminant gets into an onion patch, it will come through in the milk. The species of grasses, legumes, and also the mix of grains and hay for supplementation needs to be controlled and adjusted at times to produce not just quality milk, but good-tasting milk. Goats in particular have a habit of eating whatever they can get their little mouths on. Not all bad milk tastes come from the feed, however – if the male goats are near the female goats, the milk will taste strongly “goaty” due to hormonal effects induced by their presence.