SHOULD WEANING DURATION BE RECONSIDERED IN ELEVATED MILK FEEDING PLANS?

Weaning is a major physiological time for a young calf, especially when the calf is fed an elevated milk replacer feeding program (Khan et al., 2011; Steele et al., 2017; Wolfe et al., 2023; Drackley, 2025). There are several benefits to adopting an elevated milk feeding program; in a review, Ghaffari and Hammon (2026) outline several. These include an increase in energy and protein supply, insulin and IGF-1 signaling, mTORC1 activation, muscle and protein synthesis, average daily gain, feed efficiency, potential for structural growth, gastrointestinal development, and epithelial maturity. In addition, there are several benefits related to behavior and welfare. This includes decreased hunger-driven behaviors, increased satiety and locomotor play compared to restricted feeding programs where there may be increased vocalizations and cross suckling.

With higher milk allowance, there can be several drawbacks if not managed appropriately. These can include a decrease in starter intake, fermentation of short-chain fatty acids, and a delay in epithelial differentiation in the rumen. Depending on the weaning schedule or other factors around the time of weaning, there is an abrupt change in nutrients. When calves are fed a higher milk feeding allowance, the amount of total solids consumed by the calf is met through milk. Whereas in a lower milk feeding allowance, the calf will compensate for a decrease in solid intake from milk by increasing starter consumption. Therefore, depending on the duration of weaning, how abruptly milk is removed, or other factors, calves may not be prepared to ferment solid feed and utilize nutrients that are consumed through starter, or they may not consume enough starter to meet their demands for growth. Several factors during weaning decrease performance: poor starter quality, weaning too early, duration or graduality of weaning, feeding high amounts of forage, poor water management, stacking multiple stressors around the time of weaning, and ruminal acidosis (Drackley, 2025).

Ghaffari et al. (2026) published two articles, one evaluating plasma bile acid dynamics during a 3-week and 6-week duration of weaning, and the other evaluating plasma acylcarnitine and free fatty acid profiles during the same durations of weaning. Calves in both studies were provided access to an ad libitum milk replacer feeding system, allowing for a maximum intake of milk replacer at 25 L per day. Ad libitum access to water, concentrate, and hay. Before the start of weaning, milk replacer allowance was standardized across treatment groups to 12 L per day for all calves, and weaning began at week 8 of age. Calves in the 3-week weaned group received a total mixed ration (TMR), after weaning, beginning at week 12 of life, and calves in the 6-week weaned group received TMR beginning at week 15. Average body weight (BW) from week 8 to 16 was 135.7 kg (299 lb) for the calves weaned over 3-weeks and 131.7 kg (290 lb) for the calves weaned over 6 weeks . There were no differences in average daily gain (ADG) between the weaning durations with 1.12 kg/d (2.46 lb/d) for the calves weaned over 3-weeks and 1.14 kg/d (2.51 lb/d) for the calves weaned over 6 weeks.

Acylcarnitines are intermediate products involved in mitochondrial β-oxidation of fatty acids to create energy. In cows, elevated concentrations of acylcarnitines are interpreted as an indicator of impaired fatty acid oxidation, where there is an increase in non-esterified fatty acids, or incomplete β-oxidation, which can lead to an accumulation of acyl-groups into blood circulation. In calves fed milk ad libitum, increased concentrations of acylcarnitines reflect the supply of milk and fatty acids that the animal is receiving. During weaning, acylcarnitine concentration will decrease as the milk supply and fatty acid supply decrease.

Bile acids are involved in lipid digestion, enterohepatic cycling, gut-liver signaling, and host-microbial interactions. Plasma bile acids reveal metabolic remodeling that occur during weaning. They found no differences in plasma bile acids across sampling weeks or weaning duration and suggested that any observed differences in circulating bile acids were due to redistribution rather than overall changes in the total abundance. In the companion study, evaluating plasma acylcarnitine and free fatty acid profiles, the effects of weaning duration on fatty acid concentrations were selective and varied by week. A slower step-down weaning method extended the systemic availability of specific fatty acids during this transition window without altering the direction of metabolic maturation. Differences in plasma acylcarnitine and fatty acid profiles were due to age-dependent remodeling, indicating a progressive maturation of the rumen and a transition toward rumen-derived energy metabolism. In the calves weaned over 3 weeks, there was an elevation in medium-chain acylcarnitines during abrupt milk reduction, which the authors indicated was due to an acute lipid flux. This is the short-term movement of fatty acids. Overall, this suggests that metabolic maturation is primarily due to the development of organs, while gradual weaning may support stable oxidative adaptation in elevated milk feeding programs

My recommendation would be to consider how much milk is being fed, when creating a plan for weaning. Then adapt the duration of weaning and the number of steps down in milk based on the peak amount of milk that the animal was consuming. I would prefer a longer duration of weaning versus a shorter one, so that the animal can adapt to a new diet slowly, practically speaking. Ultimately, on farm we won’t be measuring bile acids or acylcarnitine to understand the success of our calf programs but we can use this type of data to help inform us on what is happening developmentally during these types of transitions. One question I still had after reading these papers was if elevated milk feeding increased plasma acylcarnitine concentrations, which can lead to increased NEFA, could we possibly be exposing the calf to some oxidative stress or not allow them to efficiently utilize nutrients? An interesting way to look at this might be to compare this to animals that are older and follow this same schedule. In theory, calves could be more developmentally prepared if allowed to develop over a longer period of time. Yet, we often increase the timeline on our replacement heifers to minimize their time on milk.

— Victoria Blaney

vblaney@whminer.com