A giraffe mother does not simply switch off a tap when her calf stops depending on milk. Milk production involves living gland tissue, and bringing that production to an end requires a biological transition. Can the small molecules left in the milk reveal what is changing inside the mother?
In a 2026 study, Gideon Osthoff and colleagues examined milk collected from five giraffes during the later months of lactation. Many free amino acids became more abundant near the end, while several organic acids associated with energy metabolism declined. The milk was changing in composition, with a pattern consistent with the gland moving away from sustained production. Understanding exactly which cellular processes produced that pattern requires another step beyond measuring the milk.
Following an uneven transition
The samples came from animals involved in an existing fertility investigation in South Africa. Milk collection was therefore an opportunity within that work, rather than a tightly scheduled experiment designed from the outset to follow weaning. Calf ages were estimated, and sampling became less frequent as the wider investigation progressed.
The researchers grouped collections into three approximate stages: 9.4, 12 and 15.1 months of lactation. Those labels represent windows of time, not precisely matched birthdays. The same five mothers did not contribute equally at every stage, and some contributed repeated samples. At the final collection, milk from three mothers was light brownish; another attempt at about 16 months yielded no milk.
That design captures an otherwise difficult part of giraffe physiology. It also makes the timing less certain than a single date suggests. Differences among mothers and uneven sampling can contribute to differences among the stage groups. These observations cannot establish that all giraffes cease lactating at 15 months.
Separating milk into smaller chemical clues
The team removed larger components and analysed the filtered milk serum using liquid chromatography coupled to tandem mass spectrometry. Chromatography separates compounds within a mixture; mass spectrometry helps identify and measure them. The targeted analyses covered organic acids, amino acids and related compounds, including glutathione, a molecule involved in antioxidant protection.
This is a different question from asking how much total protein or fat milk contains. A free amino acid is a small molecule available for several processes, including protein production and breakdown. Its abundance does not directly tell us how much intact milk protein the calf receives.
The analytical distinction also matters within the study. Amino acids were measured against calibration standards. Organic acids were assessed using relative signals normalised to internal standards, as the methods describe. Their changes can therefore support comparisons between stages without treating every reported acid value as an equally secure absolute concentration.
When the researchers compared the combined chemical profiles, the earlier and latest samples separated. The intermediate samples spread between them: some resembled the earlier stage, while one was closer to the late group. That pattern fits a transition occurring at different times among mothers, rather than a uniform switch at one month of lactation.
Why fewer energy-related acids matter
Citrate and several other organic acids associated with the citric acid cycle declined in the later milk. That cycle is part of the cellular machinery that processes fuel and supplies materials for other biochemical reactions. A coordinated fall in related compounds made reduced energy and biosynthetic activity in the mammary gland a plausible interpretation.
Meanwhile, many amino acids increased. The authors considered whether these changes reflected greater protein turnover and redistribution of nitrogen as the gland approached the end of lactation. A mother no longer sustaining the same milk output may be breaking down or repurposing components of the production system.
Those explanations connect the observed chemistry to a biological process, but they remain interpretations. The team did not measure reaction rates inside mammary cells, trace labelled nutrients through the pathways, or directly observe gland tissue being remodelled. A molecule can accumulate because more is produced, because less is used, or because its movement between compartments changes. Milk concentrations alone do not choose among all those possibilities.
For the same reason, an increase in free amino acids does not show that late milk is nutritionally superior, nor that the calf receives more of them overall. The total amount delivered also depends on milk volume and nursing, neither of which was quantified as a nutrient-transfer experiment here.
An antioxidant hypothesis that did not pass its direct check
Some of the changing compounds participate in pathways linked to glutathione. That suggested a further possibility: antioxidant protection might become more prominent as lactation ended.
The researchers tested one part of this idea directly by measuring total glutathione. They found insufficient evidence for a significant overall increase or a clear linear trend. A higher average in the latest group than at 12 months did not establish the proposed progressive rise.
This negative result sharpens the story. Several chemical changes may be compatible with altered antioxidant activity, but the measured milk did not demonstrate a substantial increase in this particular antioxidant. A pathway diagram linking molecules together is a hypothesis about their relationships, not a measurement of every reaction along the route.
A window onto a process that needs closer following
The investigation establishes that giraffe milk near the end of lactation can differ markedly from milk collected several months earlier. It also identifies specific chemical changes that future work can follow in more animals, with matched sampling and clearer information about calf age, nursing and milk output. The possible influence of the immobilisation used during collection remains another uncertainty.
The useful finding is both biological and methodological: milk preserves evidence of a changing maternal system, yet understanding that system requires more than reading a list of rising and falling molecules. Here, the evidence supports a changing late-lactation profile. Explaining precisely how the mammary gland shuts down remains the next question.
Sources
G Osthoff, S Mason, E Davoren, F Deacon (2026). Targeted metabolomics of organic and amino acids in giraffe milk during mid- to late-lactation. Metabolomics. DOI: 10.1007/s11306-026-02455-z. Read the full paper.
