Trying to live on candy bars is not a good idea. The immediate rush of a sugar fix may give you a short-term boost in energy. But once the buzz wears off, you are usually left feeling “blah” and listless. Do it repeatedly and the real health problems start: everything from obesity to increased risk of diabetes.
According to Dan Undersander of the University of Wisconsin, some of the high-concentrate, low-fibre diets being fed to lactating dairy cows are the bovine equivalent to the candy bar diet. He says throwing some good grass silage into the mix may be just the thing to remedy the problems.
Undersander is well-known to dairy and forage producers in Western Canada. For 22 years, he has been the extension and research forage specialist at the University of Wisconsin and is frequently invited to travel north of the border to share his thoughts and research. He is a strong proponent of grass silage, either grown and harvested separately or in combination with alfalfa.
“The biggest benefit to feeding grass silage,” he says, “is that it offers the opportunity to reduce the non-fibre carbohydrates (NFCs) that are commonly found in rations that are high in concentrate and corn silage. Compared to corn silage and concentrate, grass silage has more fibre but that increased fibre is more digestible. It is also digested faster — about two per cent per hour versus about one per cent for the fibre in both corn and alfalfa.”
Undersander has found that typical NFCs for alfalfa and corn silage run at 27.5 per cent and 37.5 per cent, respectively. For grass silage, it ranges from 11.5 per cent for orchardgrass all the way up to 22.5 per cent for perennial ryegrass. The neutral detergent fibre (NDF) is typically a lot higher in grass silage, with values between 47 per cent — this time perennial ryegrass is at the low end of the scale — and 60 per cent, compared to alfalfa and corn silage at about 40 per cent. The digestibility of the NDFs in grass silage is also a lot higher than alfalfa at 55 to 68 per cent.
The reason for the increased digestibility of grass silage is found in the nature of the lignin that binds to cellulose fibres in the plant, hardening and strengthening its cell walls. The lignin in taller plants which have sturdier stems, like corn and alfalfa, is made up of different sub-units than those
found in grasses, making it harder to break down and digest.
Undersander believes reducing the NFCs fed to dairy cattle and upping both the level and rate of fibre digestibility have several advantages. The first has to do with herd health.
“You have to remember that cows are ruminants,” he says. “They are made to digest fibre. Without enough of it, they end up with excessive acid and upset stomachs.”
This leads to other problems.
“About 25 per cent of the dairy cows in the Midwest United States suffer from mild to serious lameness,” says Undersander. “Of these, we estimate that close to half are lame because of too much NFCs and not enough effective fibre in the diet.”
This is a problem that is amplified by feed particle size that is too fine and “sorting” — where cows only eat the portion of the available feed which is lowest in fibre.
Rob Berry, business development specialist for dairy with Manitoba Agriculture, Food and Rural Initiatives (MAFRI) agrees.
“When starches break down too readily in the rumen it decreases the pH, leading to a die-off of the bacteria that digest fibre,” says Berry. “As they die, the bacteria release toxins that are absorbed into the bloodstream and that in turn affect the horn-producing tissue in the hooves.”
Lameness in turn leads to lower levels of feed intake — up to 15 pounds per day less in the case of severely affected cows and significant decreases in milk production (30 pounds per day, according to Undersander).
Because lameness in dairy cattle is a complex issue that can have many causes, including genetics, stage of lactation, stall design, stocking density and handling methods, research in this area poses many challenges. Undersander has yet to see conclusive evidence of grass silage leading to reduced levels of lameness. However, the link between excessive levels of NFCs and lameness are well established and he remains convinced that good grass silage in the ration is part of the solution.
Grass silage can also serve to improve butterfat content. Berry says the fibre in grass silage is converted by the rumen bacteria into acetates which the liver then processes into fatty acids which show up in the milk. Undersander’s has found the dietary fibre provided to lactating dairy cows can be upped by two per cent while still maintaining intake and production. So if a producer is looking for an economical way to add a couple of tenths of a percentage point of butterfat content, including some grass silage in the ration may be the way to go.
What is the best grass to use for silage and is it better grown alone or in combination with alfalfa? Growing grasses and legumes together is simplest, Undersander says, especially when talking silage. If both crops are growing in the same field, the stand will typically produce more in the year of establishment, the hay will dry down more quickly and the risk of winterkill appears to be lessened. As well, it means having only one silage bag or pile open at a time, instead of having one for alfalfa and another for grass. That said, it is not easy to get just the right mix of both in the same field. Undersander targets about 30 to 40 per cent grass in the silage mixture on a dry matter (DM) basis. Sometimes, either the grass or the alfalfa does not perform up to expectations and the resulting mix is out of the optimum range.
As for the most desirable grasses for dairy rations, Undersander says it depends on where your farm is located and what type of climate you are dealing with. In the drier regions of Western Canada, where producers may only take one cut, smooth brome or meadow brome may well have their place. The problem with these two forages, in his experience, is they produce heavily on the first cut and do little on subsequent ones. Therefore in multiple-cut systems — for example in the eastern Prairies — other grasses are probably worthy of consideration. Tall fescue, orchardgrass and meadow fescue are three Undersander recommends. Tall fescue will produce more of its total yield in later cuts and has higher NFCs than orchardgrass at 14.5 per cent. Timothy may also have a place in cooler and wetter regions, although its seasonal distribution, like bromegrass, is not ideal. However, Undersander cautions there is more variability between grass varieties than what producers are used to seeing in corn or soybeans, for example. So they should be very careful in selecting varieties that have good resistance to diseases and high yield potential for their areas.
“About 25 per cent of the dairy cows in the Midwest United
States suffer from mild to serious