"An important element of the dairy cow’s diet, starch is often overlooked, but is a key component throughout the cow’s life" - Debby Brown, Dugdale Nutrition’s veterinary technical manager.
From a young calf to a bulling heifer, from an early lactation cow to a dry cow, starch is a crucial component of any dairy cow's diet.
The presence of starch is crucial, according to Debby Brown, the veterinary technical manager for Dugdale Nutrition, even if requirements and quantities may alter during various periods.
As propionic acid, a result of starch digestion, affects the metabolism of glucose and insulin, starch is a crucial component of the diet of dairy cows. An overabundance of carbohydrates in the diet coupled with inadequate forage in terms of protein and fibre would result in acidosis. However, a lack of starch in the diet may have an effect on condition, digestion, production, and fertility.
"Farmers tend not to realise how vital starch is to the dairy cow's diet and can sometimes have a negative opinion of it, believing too much starch will induce acidosis, resulting in them cutting starch from the diet totally," Mrs Brown explains. As a result, almost nothing is stimulated."
Looking at all of the diet inputs and calculating how much starch is in the concentrate feed, how much is going into the blend, and where the other sources of starch are on-farm is important to get an overall diet value. The main sources of starch in the diet are barley, wheat, and maize, with barley and wheat having a greater impact on rumen microbes than maize, making them the main sources for rumen development.
"From the standpoint of a milking diet, the amount of supplemental starch required in the diet is dependent on the forage available, as maize or wholecrop silage will already contain some starch," she explains.
The presence of starch in the food is depending on the animal's life stage and is critical to the animal's many biological functions at different periods. Ms Brown concludes that nutrition is all about balance, not extremes.
"It all comes back to balance and need since there is no use in eliminating it completely. It must be appropriate at each stage."
As a calf ages, its rumen develops to start digesting feed once weaned off milk because starch encourages the growth of the rumen papillae. It helps the rumen develop by combining the starch typically present in concentrates with grass and straw.
Forage and straw are crucial for rumen size and expansion, while the papillae are responsible for absorbing energy. Starch is necessary for developing those papillae in a calf's diet. Mrs. Brown explains that if starch is not provided in adequate amounts or from appropriate sources, it can cause delayed development of the rumen and slow adjustment and maturation of the calf over time.
This can lead to slower weaning of calves and slower adaptation to silage or grass rations. "This has knock-on effects on the maturation of animals into heifers, affecting age at first calving and milk production at first lactation," she said.
It is important to continue feeding postpartum heifers starch as it maintains mastoid development and digestion. However, Ms Brown said care should be taken not to feed too much starch to heifers, lest they become overweight. "It's all about balance, but you definitely need some starches in your diet during the growing and later stages of pregnancy," she says.
Early lactation cows
Starch is especially important for cows in early lactation as it promotes energy metabolism and thus fertility, so starch is important for hormones related to oestrus detection and conception. "If the cows aren't milking as well as they should be, one of the first things I look at is how much starch they're getting, especially if the cows aren't doing well early in lactation," she said. Starch is less important in late lactation cows, depending on rumen conditions, but more important closer to calving, Ms. Brown said.
The dry cow
Starch is important for the development of ruminal papillae in dry cows. If a dry cow gets too much starch and concentrate in the lactation ration, the rumen can become damaged, Ms Brown said. However, without enough starch to feed, she says, the rumen shuts down because the rumen papillae cannot develop. Ms Brown said this phase was about balance as the rumen needed to recover and prepare. "You want it to recover, so you have to be on a lower starch diet than the milking diet. But you still need some starch to prepare the rumen for the next lactation," she says.
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