16 Sept 2025
Emma Bleach PhD, FRASE discusses the importance of colostrum and transition milk in the early days of a calf’s life.
Emma Bleach
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Image: SGr / Adobe Stock
Rearing well-grown and healthy replacement heifers, to calve for the first time at 24 months of age, should be a key strategic aim of dairy producers (Cooke et al, 2013). And we must be rearing dairy heifers with the resilience to cope with the demands of life in the lactating herd for at least two years, to repay the costs of rearing (Boulton et al, 2017).
On commercial dairy farms, many calves (80% according to Mahendran et al, 2022) are separated from their dam within the first 24 hours of life. These calves receive their colostrum feeds (the first or second milking of the cow) and then most are abruptly switched on to milk feeds, which are often a milk replacer (Denholm et al, 2023).
With this, an abrupt change in nutritional value of the feed offered to the newborn calf takes place; protein and fat concentrations are much higher in colostrum, while lactose content is lower (Godden, 2008) and, depending on the milk replacers offered, protein and fat sources may not be of 100% dairy origin (Thornsberry et al, 2016).
However, naturally, milk produced by the cow during three to four days postpartum is characterised by a gradual change in composition from colostrum to whole milk (Godden, 2008; Blum and Hammon, 2000); this milk is termed transition milk. The importance of timely (within six hours of birth) delivery of sufficient (10% to 12% of bodyweight; Godden, 2008) colostrum to the newborn calf is very well-established.
This first feed facilitates passive transfer of immunoglobulins from the cow to the calf, providing protection while the calf develops its own adaptive immune system. Timeliness is critical as the efficiency of absorption of antibodies quickly declines and once colostrum has been consumed, the mechanisms of antibody uptake are switched off (Stott et al, 1979). Without any colostrum consumption, spontaneous gut closure is complete by 24 hours after birth (Stott et al, 1979; Fischer et al, 2018). With this in mind, is there any value to additional feeds of colostrum or transition milk?
Although macromolecules such as immunoglobulins are no longer absorbed following gut closure and their concentrations are declining as colostrum is diluted with the onset of milk synthesis, these molecules may have important local roles during the immediate neonatal period (Hammon et al, 2020).
In addition, colostrum and transition milk are much more than just antibodies (Blum and Hammon, 2000; Godden, 2008). A plethora of potentially bioactive molecules are present, the significance of many of which remains to be established.
Examples of these molecules include those with antimicrobial activity, such as lactoferrin and lysozyme (McGrath et al, 2016); oligosaccharides that may provide support for the growth of beneficial bacteria (Fischer-Tlustos et al, 2020); and local regulators of gut development, such as the growth factors, insulin-like growth factors 1 and 2 (Hammon et al, 2020). These factors are present in both colostrum and transition milk at higher concentrations than in whole milk.
The long-term importance of colostrum is reported by DeNise et al (1989), who demonstrated that higher immunoglobulin concentrations in newborn heifer calves (reflective of colostrum intake) had a positive influence on the yield of milk and milk fat content.
Faber et al (2005) also report long-term effects in their heifer calves that were monitored into first and second lactation. Those fed 4L produced more milk in both lactations (9,907L versus 8,592L and 11,294L versus 9,642L, respectively). These effects may be a result of improved calf health during the neonatal period, but given the enhanced nutritional value and the presence of bioactive molecules, other factors may also be at play.
With regards to feeding transition milk, Van Soest et al (2020) found increased growth in calves from birth to weaning, when they were fed transition milk or a milk replacer enhanced with colostrum, compared to the same milk replacer alone, purported to be an effect of the higher energy content of these feeds. However, in a follow-up study, feeding transition milk was found to increase villi development in all sections of the small intestine as a result of enhanced epithelial cell proliferation (Van Soest et al, 2022). Other studies have shown beneficial effects of transition feeds on calf health (Conneely et al, 2014).
Thus, providing transition milk as a follow-on feed to colostrum for the newborn calf may help lay a stronger foundation for dairy-bred calf performance.
However, practicalities on farm may make this difficult to achieve. While 76% of the respondents to the survey of Denholme et al (2023) would feed colostrum/transition milk if benefits became evident, others highlighted potential issues with the practicality of feeding transition milk, such as the inconvenience of collection and storage, the need for changes to calf-rearing facilities and potential disease risks leading to the need for additional pasteurisation capacity or alternative means of preservation (Denholme et al, 2025). So, are there alternatives?
Two studies involving the use of a transition milk powder have shown positive results. In the first study, feeding dairy heifer calves the transition milk powder (Transformula from Bonanza Calf Nutrition) for 10 days after their colostrum feeds on the day of birth, compared with colostrum then a skim-based milk powder, showed no beneficial effects on calf growth from birth to 12 weeks of age.
There were also no effects on age at first calving. However, during first lactation these heifers produced more milk (8,625L versus 7,678L) and a greater weight of fat and protein (617kg versus 532kg; Bleach and Gauld, unpublished).
In the second study, treatment calves were fed the transition milk powder for three weeks following colostrum feeds, while the controls received a skim-based milk replacer after colostrum feeds. In this study, the calves that received the transition milk replacer had a greater daily liveweight gain than the control calves.
Using the transition milk replacer rather than transition milk gives consistency in the product offered to calves and removes the concerns over cleanliness of the product. The results look promising, but the mechanisms of action of the transition milk replacer remain to be determined.
Key take-home points:
Emma Bleach is a senior lecturer in animal science in the Agriculture and Environment Department at Harper Adams University. She teaches subjects related to dairy production systems and the underlying science that supports them. Emma’s main research focuses on improving rearing systems for dairy-bred calves.
