Pastures provide forage, which is the foundation of dairy cow diets. The higher the quality of any forage – essentially meaning the more it can be fermented and converted into energy in the rumen – the greater the value of the pasture and its contribution to a dairy’s profitability. At the heart of extracting the most from pasturing dairy cows is the dairy farmer’s ability to optimize forage quality during a growing season while not over-grazing and damaging pastures.
In most parts of the country, pasturing cows is seasonally limited – cows can’t be run out on pasture all year long. Even with managed intensive grazing, dairy farms must still bring cows into a confined environment for part of the year to keep them fed, healthy and productive. Winter snow covers the ground in many regions, making grazing impossible. Where snow is not an issue, growth of grass still comes to a near standstill due to cold weather and shortened daylight hours, which is absolutely crucial to photosynthesis and plant growth.
Like any living organism, a plant’s singular biological purpose is to reproduce and propagate. Perennial pasture grasses and legumes have a growth cycle with the most nutritional herbage – high in protein and low in fiber – being produced at the beginning of a season. As forages grow and mature, their nutritional value declines as they lignify and flower or go to seed. In doing so, they spoil the party for livestock nutrition.
Milk production for dairy cows is primarily a function of feed intake, forage quality and balanced nutrition. Two significant challenges for any dairy that grazes a herd is keeping the quality of the forage from degrading to a point where it’s no longer nutritional enough to produce a desired level of milk and also knowing how much dry matter and nutrition is coming from the pastures on any given day throughout the grazing season.
For many dairy farmers, having milk cows that spend a good deal of their lives grazing on well-managed and productive pastures is an environmentally friendly and profitable way to dairy. In regions with good soils and dependable water, high quality pastures allow dairy farmers to optimize feed tonnage and forage quality. Well-managed intensive grazing of dairy herds can result in improved milk-revenue-over-feed-cost margins.
It should be understood that cows consuming pastures should be receiving adequate nutrition that will support a desired level of milk production. While it’s tempting during times of low milk prices to reduce purchased feed costs, the grass that is taking the place of the grains must be highly digestible. Many pastures, due to previous poor management, do not have the ability to provide a consistent supply of high quality forage week in, week out over the summer months. Cows should not be put on pastures with a goal of easing life for the dairy farmer.
Dairy farmers must look at pasture grass the same way as for hay or haylage. Just as the quality of hay and haylage varies with maturity, pasture grass will be at its nutritional best in the early vegetative stage. Farmers must develop an expert eye as they watch the length of grass on any given day. They also must know what types of grass varieties are in the pastures. Grasses are not the same. They grow at different rates and have different nutritional values at different stages of growth. The most productive pastures will have a diversified variety of grasses and legumes that will be at different stages of growth throughout the season rather than all grass coming to maturity at the same time.
Even small changes in nutrient content of pasture grasses will have a profound effect on milk production since so much of the diet is coming from this single feed source. Imagine that you would replace half of your grain concentrate with forage. You may save a dollar per cow per day on grain costs but what will happen to milk production? Make money or lose money? You can quickly see that the quality of the forage will have a profound impact on net income when switching to a pasture program.
Cows are big animals that consume between 30 and 50 pounds of dry matter each day depending on if they’re dry or lactating. Lush pasture grasses are 80 percent to 85 percent water. For a cow to consume 40 pounds of dry matter in a day she must eat about 200 pounds of grass. Dairy farmers and nutritionists must be able to calculate how many cows can be grazed on a given amount of acreage before grass runs out.
A general rule of thumb is that a well-managed pasture should be able to produce an average of about one ton of dry matter per acre throughout the growing season. The cow mentioned already who is consuming 40 pounds of dry matter per day will consume over 1,200 pounds of dry matter in a month – well within the expected 2,000 pounds that the acre can produce. Therefore, generally, farmers who are contemplating grazing a herd of milk cows should plan on having a minimum of an acre of pasture per cow.
This is fine as long as the pastures hold up. As long as there’s enough rainfall to keep the grasses growing, a pasture can support a herd of cows for many weeks. When the season gets warmer and rainfall slows down, cows can quickly over-graze a pasture. Dairy farmers must learn how to manage the pastures based on weather and how the grass is holding up. Over-grazing pastures will stress the root systems, impacting their ability to remain healthy. Weeds can quickly invade a pasture that is stressed.
Pastures vary from farm to farm and region to region. One style of grazing may work better on one farm than on another. It must be approached on a farm-by-farm basis. The decision to pasture cows should be heavily based on the realistic economics of income-over-feed-cost that the dairy will realize from pasturing cows.