A challenged faced by all dairy cows after calving is negative energy balance (NEB), where energy demands are not being met by intakes.
Although turning cows out to spring grass is important in a grass-based grazing dairy system, it can create a number of dietary challenges.
Spring turnout of dairy cows can result in butterfat depression and fertility issues.
However, negative effects can be reduced by balancing rumen function and energy supply, according to Dr. Richard Kirkland, ruminant nutritionist for Volac Wilmar Feed Ingredients.
Negative energy balance
Grazed grass is important within the a grass-based dairy system, but early grazing can pose a number of challenges to cows and farmers.
Early grass is often of lower feeding value and has a low dry matter (DM) content.
Outlining the impact that this can have on cows, Dr. Kirkland said: “As cows transition from a controlled winter ration to grazed grass, the rumen has to adapt to the differing and more-variable forage source.
“The diet change alone can cause challenges to rumen function and milk production stability.
“Additionally, the low fibre and rapid fermentability of early, leafy grass growth can disturb the rumen’s pH balance and cause the grass to pass through the digestive system too quickly, increasing the risk of acidosis.”
He explained that while early grass is high in energy, variable spring grazing conditions make it harder for energy supply to be consistently maximised, with a drop in fertility and milk production key risks.
Dr. Kirkland added that during early lactation, cows cannot eat enough to meet the high energy demands of milk production, leading to a negative energy balance.
This means they rely on body fat stores to support the genetic drive for milk production, resulting in a loss of body condition.
He noted that research from the University of Nottingham indicates that for each 0.5-unit loss in condition during this period, conception rates can fall by around 10%.
Supplementation
To offset this energy deficit, cows will be offered concentrates to increase energy supply, but there is a limit on how much can be used in order to reduce the risk of the rapidly-fermentable starch pushing down rumen pH, and with it, increasing the risk of acidosis and low milk fat.
He continued: “Digestible fibre sources such as soya hulls, citrus and sugar beet pulp will help balance the starchy energy sources and aid rumen function and milk fat, though offer less of the rumen tickle factor than higher-fibre forages.
“With lower energy concentration than cereals, the greater bulk of forage sources will limit the potential to deliver those vital additional megajoules.”
He has recommended using a combination of digestible fibre sources and rumen-protected fat supplements in buffer rations to help drive milk production and support fertility in early lactation.
“In contrast to other ingredients, rumen-protected fats are not fermented in the rumen and contain around 2.5 times the energy content of cereals.
“This makes them an ideal choice to sustain energy supply at grass where conditions can be unpredictable on a daily basis,” Dr. Kirkland said.
