On most dairies, colostrum management is treated as a short window right after calving. The first milking is collected, tested and quickly fed to the calf. But new research suggests colostrum quality is shaped weeks before it ever reaches the pail.
Research from Amanda Fischer-Tlustos examines colostrogenesis, the process that produces colostrum, and how nutrition, metabolism and mammary activity during the dry period influence what ends up in that first milking.
“We always talk about harvesting colostrum to feed the calves,” she said during a recent Dairy Health Blackbelt Podcast. “But how are the cows producing it?”
Her work suggests the answer starts much earlier than many farms think, with high-quality colostrum developing gradually in the weeks leading up to calving.
Looking Beyond IgG
Colostrum conversations often revolve around immunoglobulin G, or IgG. Because calves are born without functional immunity, they depend on these antibodies from colostrum to establish passive transfer.
While IgG remains the cornerstone of colostrum quality, Fischer-Tlustos believes focusing only on antibodies overlooks much of what makes colostrum biologically powerful.
“I wanted to focus on it more than just IgG,” she says. “There’s all these other things in colostrum aside from IgG. Not just when is IgG transferred from the serum into the colostrum prior to calving, but also when are the macronutrients starting to be synthesized, and when are bioactive compounds starting to be synthesized or transferred?”
These additional components include hormones, growth factors and specialized carbohydrates known as oligosaccharides. Although they exist in much lower concentrations than fat or antibodies, they can have meaningful effects on calf development.
“To me, the definition of a bioactive compound is something that is present in low concentrations compared to IgG or fat,” Fischer-Tlustos says. “But even though they’re present at low concentrations, they could still have a really big impact on calf development and physiology.”
Taken together, these compounds reveal colostrum as a complex biological package rather than simply the first milk produced after calving.
“It’s almost like the cow has tailored her colostrum to the calf’s needs,” Fischer-Tlustos adds.
A Staggered Timeline Before Calving
To understand when these components begin forming, Fischer-Tlustos followed a group of Holstein cows from dry-off through calving. The cows were dried off approximately eight weeks before their expected calving date, allowing researchers to monitor mammary changes throughout the dry period.
The team collected small samples of mammary secretions at regular intervals leading up to calving.
“We didn’t want to take too much, because then we could induce them into lactation, which would wreck our colostrum,” Fischer-Tlustos says.
What the team discovered was a surprisingly staggered timeline of colostrum formation.
Lactose and fat production, two hallmarks of normal milk secretion, began very close to calving.
“We found that lactose and fat really only start to turn on within about one to two days prior to calving,” she says. “And that makes sense to me. They kind of turn on with lactogenesis, which is milk production.”
Protein synthesis began slightly earlier.
“We found that protein starts to turn on about a week prior to calving,” Fischer-Tlustos says.
The timeline for IgG accumulation, however, followed a different pattern.
“When we looked at IgG, what we actually found was that it started to accumulate substantially in some cows even as early as six weeks prior to calving, and some cows were accumulating it even before that,” she says.
Because the cows in the study were dried off roughly eight weeks before calving, that means antibody accumulation began soon after the dry period started. The discovery challenged the assumption that the close-up period is the primary window for influencing colostrum quality.
“It kind of really started to reframe my thinking,” Fischer-Tlustos says. “We try to put in nutritional strategies or management strategies in the close-up period to try to drive more IgG transfer. But it made me think, maybe this isn’t the time we need to be looking at that.”
Further analysis reinforced the importance of early accumulation. Cows that began building IgG earlier in the dry period consistently produced better colostrum.
“The earlier it could accumulate in the prepartum secretion, the better the colostrum would be after she calved,” she says. “And we found that the more gradual or slowly that that accumulation could happen, the better for first milking colostrum.”
Giving the Udder Rest
While studying differences between cows, Fischer-Tlustos began looking at another important factor: mammary activity during the dry period.
Her team measured indicators of mammary metabolism including milk yield at dry-off, mammary blood flow and uptake of metabolic fuels such as glucose and acetate.
“These were kind of indicators of mammary activity during the dry period,” she says.
The findings revealed a counterintuitive relationship. Cows whose udders remained more active during the far-off dry period tended to produce poorer colostrum.
“We found that cows that had more mammary activity during the far-off period had worse colostrum production,” Fischer-Tlustos says.
Many producers have seen these cows in the dry pen. They are the animals that never seem to fully dry off.
“We see cows in the dry pen that are like three weeks dry, and they have huge udders and they’re leaking milk still,” she says. “And I think these are those cows that have a lot of difficulty drying off, and they’re not able to get into that rest and regeneration state, which coincides with colostrogenesis.”
High milk production heading into dry-off appears to intensify the problem.
“We also found, too, that the more milk the cow made at dry off, she had more mammary activity in the far-off period, and then worse colostrum,” Fischer-Tlustos says. “This is even more exacerbated for our high producing cows, which are typically our ones that have trouble drying off.”
Nutrition and Metabolism Influence Composition
Additional work examined how prepartum nutrition influences colostrum formation. Beginning roughly 19 days before calving, primiparous and multiparous cows were fed diets with either high or low energy density.
Interestingly, the dietary treatments did not significantly affect IgG concentration or total colostrum yield. However, they did alter several other components.
Cows fed higher-energy diets produced colostrum with greater concentrations of insulin, somatic cells and sialic acid. At the same time, they had lower concentrations of total oligosaccharides.
The metabolic drivers of colostrum production also differed by parity. In first-lactation cows, colostrum yield appeared more closely linked to circulating glucose levels. Multiparous cows showed a stronger association with hormonal signaling, particularly insulin.
According to Fischer-Tlustos, these differences suggest that cows in different stages of life may rely on different metabolic pathways to support colostrum synthesis.
Rethinking Dry-Off
Another management factor that may affect colostrum development is the way cows are dried off.
According to Fischer-Tlustos, abrupt dry-off remains common practice.
“I read a review paper from 2020 that said 75% of U.S. farms are practicing abrupt dry off,” she says. “So just dry off in one day. Which is, from my standpoint, concerning from colostrum production, but that’s also really concerning for milk production.”
The challenge, she says, is that cows may not receive enough time for the mammary gland to fully transition from lactation to regeneration.
“I was trying to think of an analogy, and the Olympics were on,” she says. “You have to think they are like a pro athlete. They need to rest. They can’t just go right into the next Olympics two months later. They need a rest and regeneration period.”
Without adequate rest, the mammary gland may remain partially active during the dry period, limiting its ability to accumulate antibodies and other compounds needed for high-quality colostrum.
From Harvesting Colostrum to Developing It
Taken together, Fischer-Tlustos’ research suggests the industry may need to expand how it thinks about colostrum management.
Rather than focusing solely on the harvest and testing of colostrum at calving, her findings highlight the importance of the weeks leading up to it. Successful dry-off, controlled mammary activity and adequate time for mammary tissue to regenerate all appear to influence how colostrum develops.
For dairy producers striving to deliver consistent, high-quality colostrum to newborn calves, the most important management window may begin much earlier than previously thought. Long before the calf is born and the colostrum is harvested, the cow has already been building it.
