Those familiar with raising dairy calves know well that the weaning transition is a critical time, which, if not managed well, can lead to stress and ultimately lost growth performance, increased disease, and reduced animal well-being. But what physiological factors are at play during this transition phase, and which management practices can help to support the calf into adulthood? To address these questions, a new review article published in Applied Animal Science by a renowned professional animal scientist translates the latest science on this topic, illuminating what is happening to calves during this time and outlining the best management tips for supporting calf health and performance.
"The weaning period for dairy calves is inherently stressful," explained Bill Weiss, PhD, PAS, editor in chief of Applied Animal Science. "Solid food completely replaces liquid feed, and, often, housing and social structure are changed concurrent with the diet change. Calves are starting to develop functional rumens, and their metabolism is changing from that of essentially a nonruminant to a ruminant. These stresses often result in decreased growth rates, increased disease risk, and undesirable behavioral changes such as decreased resting time. This review discusses the physiological and metabolic changes that occur at this time and how improper management practices and nutrition can adversely affect those changes."
The review's author, James K. Drackley, PhD, PAS, of the University of Illinois Urbana-Champaign College of Agricultural, Consumer and Environmental Sciences at Urbana, Illinois, USA, first emphasized different physiological and developmental occurrences through weaning, including expanding gut fill, rapidly growing a body-proportionate reticulorumen and gastrointestinal tract, and developing the ruminal epithelium--all of which influence a calf's ability to stabilize rumen pH for fiber digestion and absorb volatile fatty acids (VFA).
"The most important factor in preparing the calf for weaning is developing the rumen so that the ruminal microbiome can ferment solid feeds and VFA can be absorbed," explained Drackley, "and starter intake plays the key role in this development because fermentable carbohydrates lead to butyrate and propionate production that stimulates rumen epithelial development."
"A common recommendation for weaning is for the calf to eat one kilogram per day of starter for three consecutive days before weaning," acknowledged Drackley. "However, to reduce the chance of growth slumps at weaning, I recommend that large-breed calves consume 1.5 kilograms per day of starter for three consecutive days, and small breeds consume one kilogram per day. The age of calves when weaning occurs depends on the amount of starter intake, increasing as milk feeding decreases."
A new review article calls attention to physiological and management factors contributing to dairy calves' stress during weaning, emphasizing that managing starter quality, time and rate of weaning, forage and water availability, overlapping stressors, and acidosis through the transition can help promote calf welfare and growth performance (Credit: James Drackley).
The review also covers various management factors that can affect the weaning transition. "These include poor starter quality or composition, weaning too early or too quickly, relying on conserved forage too much, poor water management, amplifying stressors around weaning, and acidosis," said Drackley.
Many characteristics contribute to a high-quality starter feed, including appropriate ingredients, chemical composition, and physical form. "Offering a high-quality starter and weaning later and in steps rather than abruptly allows for the best results," stated Drackley. "Considering that, I recommend feeding legume hays to no more than 10% of total intake, but starter intake and average daily gain may improve from consuming around 5% or less of chopped grass hay or straw."
Meeting the nutrient requirements also entails adequate water availability for a weaning calf, especially as the rumen's microbial ecosystem develops. In addition, the article echoes previous recommendations of avoiding combining weaning with vaccination, dehorning, and other upkeep stressors. The final factor of calves struggling described by Drackley, but maybe one of the most common, is acidosis.
"Acidosis is the excessive accumulation of VFA and lactate in the rumen that overwhelms the underdeveloped absorption and buffering abilities of calves after weaning," explained Drackley. "Research shows that supplementing small amounts of forage benefits starter intake and growth rates, and may improve the rumen environment to help prevent acidosis."
Weiss detailed the major takeaways of the article and emphasized its effect, saying, "Weaning should be based on amount of starter intake, rather than age. The review discusses how the proper nutrient composition and physical form of the starter can encourage starter intake and how excess forage access will discourage starter intake. The benefits of gradual versus abrupt weaning are discussed, as is the importance of providing adequate, clean water. This review provides practical recommendations that, when applied, will reduce weaning stress."
The weaning transition in dairy calves may be challenging, but adopting these care practices may lead to an easier weaning process for caretakers and promote calf performance and welfare.
The article appears in the June issue of Applied Animal Science.
This research was presented at the ARPAS Symposium: From birth to lactation, as part of the American Dairy Science Association 2024 Annual Meeting. Register for the 2025 American Society of Animal Science and Canadian Society of Animal Science Annual Meeting to join the ARPAS Symposium: Water requirements for crop production, beef production, swine production, and meat processing facilities.
