Weaning management of beef-suckler calves: health implications

Bernadette Earley Mark McGee

In Irish grass‑based, spring‑calving suckler systems, calves are typically weaned in autumn. This often coincides with a change in weather, reduced grass availability, additional handling, housing, vaccination and sometimes transport or sale. The resulting stress response in the calf, especially when several of these stressors occur concurrently, can temporarily suppress immune function, increasing susceptibility to bovine respiratory disease (BRD). Research conducted at Teagasc Grange has investigated the impact of weaning-related stress on the physiological and immunological responses of calves.

Why weaning causes stress

Weaning itself primarily exposes calves to two key stressors:

1. Psychological stress: separation from the dam and disruption of the cow–calf bond,
   and changes in social grouping.
2. Nutritional stress: loss of milk often coupled with transition to silage and concentrates.

Additional stressors usually occur at or around weaning due to management practices, rather than weaning per se:

Environmental stress: movement from pasture to indoor housing, if housing coincides with weaning.

Physical and handling stress: handling, vaccination, regrouping, transport, commingling animals, castration, or dehorning when these procedures are carried out at the time of weaning.

These combined stressors lead to suppression of the immune system, making calves more susceptible to BRD/pneumonia-causing viral pathogens (such as bovine respiratory syncytial virus (BRSV), parainfluenza-3 virus (PI3), and bovine herpesvirus-1  BoHV‑1/infectious bovine rhinotracheitis (IBR)), and several bacterial species (including Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis). Environmental factors associated with housing such as poor ventilation, draughts, fluctuating temperatures and overcrowding can further increase disease risk. Research studies at Teagasc Grange have investigated:

1. The impact of weaning with and without simultaneous housing.
2. The effect of weaning on immune cell function.
3. The role of pre‑weaning concentrate supplementation.
4. The influence of dam proximity to calves at weaning on immune responses.

Together, these studies provide clear, evidence-based guidance for reducing stress at weaning.

Experiment 1: Abrupt weaning of suckler calves with immediate housing versus abrupt weaning with housing deferred for 35 days

The objective of this experiment was to evaluate the effects of delaying housing after abrupt weaning, compared with immediate housing, on physiological stress responses and immune function in suckler calves. Thirty‑six spring‑born suckler beef calves (mean live weight 279 kg; age seven months) previously grazing with their dams were abruptly weaned and allocated to one of two post‑weaning housing treatments. Half of the calves were housed immediately after weaning and offered an indoor diet (grass silage ad libitum + 1 kg supplementary concentrates following gradual adaption), while the remaining calves were returned to familiar pasture, with housing deferred for 35 days. Dams were relocated at a sufficient distance such that the vocalizations of either group could not be heard by the other.  At weaning, both groups of calves showed increases in rectal temperature, cortisol (the primary stress hormone), and markers of inflammation known as acute phase proteins, confirming that abrupt weaning from the dam elicited an acute stress response.

Calves that were immediately housed after weaning experienced a more severe and prolonged disruption of immune function. Total white blood cell and lymphocyte numbers, key components of sustained and targeted immune defence, remained reduced for extended periods in these calves. This indicates a temporary but prolonged impairment in their ability to mount effective immune responses against viral and bacterial pathogens. Cell‑mediated immunity, assessed by interferon‑γ production (an important mediator of antiviral defence), was also reduced on days two and seven following weaning in immediately‑housed calves, further highlighting suppressed immune competence during this period. In addition, neutrophil numbers, which are short-lived white blood cells involved in rapid, first line defence, were lower between days 14 and 35 post-weaning, suggesting a sustained alteration of normal immune cell dynamics rather than a short‑lived stress response.

In contrast, the calves returned to familiar pasture after weaning showed evidence of a shorter‑term and more transient stress response. Neutrophil numbers increased on days two and seven post‑weaning. This pattern reflects an acute stress response consistent with mobilisation of first‑line immune defences, followed by recovery while calves remained in a familiar environment. Cortisol concentrations in this group increased again when housing was introduced later, demonstrating that housing itself represented an additional stressor. However, this delayed housing event resulted in only a brief immune disturbance, characterised by increased leukocyte and neutrophil numbers and reduced lymphocyte counts and interferon‑γ production two days after housing. Importantly, these changes were short-lived and less pronounced than those observed in calves housed immediately after weaning. Overall, these findings indicate that combining abrupt weaning with immediate housing places a greater and more sustained stress on the calf’s immune system. In contrast, delaying housing after weaning reduced the severity and duration of immune disruption, allowing calves more time to adapt and recover before housing. Despite the immunological differences, no significant effects on clinical health outcomes were observed between treatments.

Experiment 2: Effect of abrupt weaning versus non-weaning at housing on suckler calf immunity

The objective of this experiment was to compare the immunological and physiological responses of abruptly-weaned calves with those of non‑weaned calves that remained with their dams as both groups transitioned to indoor housing. Sixteen spring‑born suckler beef calves (mean live weight, 310 kg; age 7-8 months) previously grazing with their dams were used. Eight calves were abruptly‑weaned and separated from their dams at the time of housing, and eight non‑weaned control calves were housed indoors together with their dams. Abruptly-weaned calves showed a clear acute stress response, with significant increases in total white blood cell (leukocyte) numbers and neutrophils two days after housing. No changes were observed in the non‑weaned control calves, indicating that housing alone did not trigger a stress response when calves remained with their dams. Despite the increase in circulating immune cells, abruptly-weaned calves showed evidence of immune suppression at the same time point, including reduced proportions of key immune cell populations involved in disease protection (e.g. CD4+ and CD8+ T lymphocytes, γδ T cells (WC1+) and MHC class II+ lymphocytes). These cells play an important role in recognising and responding to viral and bacterial infections. Their reduction indicates a temporary weakening of immune defence following abrupt weaning. Additionally, neutrophil function was also impaired in abruptly-weaned compared to non-weaned calves. Neutrophils from weaned calves had a reduced ability to engulf pathogens (lower phagocytic capacity) and lower expression of L‑selectin (CD62L), a protein required for neutrophils to move in the bloodstream to sites of infection. Overall, the findings demonstrate that abrupt weaning at housing induces a rapid but short‑term disturbance in immune function, affecting both the number and effectiveness of key immune cells. In contrast, calves housed with their dams maintained stable immune profiles throughout the housing transition. This helps explain why calves that are abruptly-weaned at housing are at greater risk of respiratory disease in the immediate post‑weaning period. This also has implications for vaccine effectiveness at weaning as the temporary suppression and functional impairment of key immune cells may reduce the calf’s ability to mount an effective protective response to vaccines administered during the immediate weaning period.

Experiment 3: Impact of pre‑weaning concentrate supplementation on immune, acute phase and behavioural responses to abrupt weaning

The objective of this experiment was to determine whether pre‑weaning concentrate supplementation could reduce the immune, acute phase protein, and behavioural disturbances associated with abrupt weaning and subsequent housing. Twenty spring‑born, suckler calves (mean live weight, 258 kg; age, 6.6 months) were allocated to either a concentrate‑supplemented (1.0 kg/calf daily) group or a non‑supplemented control group for 26-days prior to weaning. After the 26-day supplementation period, all calves were abruptly weaned from their dams and housed indoors. Following weaning, both groups showed reductions in immune cell markers, including CD4+ T lymphocytes and WC1+ (γδ T cells), and a decrease in lymphocyte percentage on day two. These changes indicate a short‑term suppression of adaptive immune function immediately after weaning. However, the reduction in WC1+ cells, a lymphocyte subset important in early immune defence in cattle, was significantly greater in non-supplemented calves, showing that these animals had a more pronounced immune suppression. By day seven post‑weaning, CD4+ lymphocyte percentages had not only recovered but increased above baseline levels in the concentrate-supplemented calves, indicating faster immune recovery and improved immunity. In contrast, no such recovery was observed in non-supplemented calves, indicating a more prolonged period of immune suppression. Post-weaning, supplemented calves spent more time lying suggesting a less stressed state compared with non-supplemented calves. Overall, the findings demonstrate that feeding concentrates before weaning can buffer calves against the immune disturbances and behavioural responses typically associated with abrupt weaning and housing.

Experiment 4: Physiological and molecular immune responses to weaning: effects of dam proximity

The objective of this experiment was to examine if dam proximity during weaning influences physiological stress indicators and molecular immune markers in suckler calves. Prior to weaning, twenty‑eight suckler calves (14 steers and 14 heifers; mean live weight, 270 kg; age, seven months) were housed indoors with their dams. At weaning, calves were either penned adjacent to their dams, allowing visual and auditory contact through a metal barrier but prevented from suckling, or penned away from their dams with no visual or auditory contact. After weaning, all calves showed clear signs of acute physiological stress, most evident in changes to white blood cell populations. Neutrophil numbers increased sharply, while lymphocyte numbers decreased, resulting in a marked rise in the neutrophil‑to‑lymphocyte (N:L) ratio. Calves penned away from their dams had higher neutrophil counts and higher N:L ratios, indicating a greater physiological stress load associated with the complete separation. Allowing calves visual and auditory contact with their dams helped reduce, though not eliminate, the immune disruption associated with weaning. At the molecular level, weaning resulted in the activation of several key inflammatory and immune‑related genes indicating that the immune system entered a highly activated state in response to weaning stress. Calves weaned without dam visual or auditory contact experienced the greatest immune disruption, while adjacent penning helped moderate the stress response.

Conclusion

Collectively, these experiments demonstrate that abrupt weaning induces a measurable physiological stress response and short‑term immune suppression in suckler calves, with the magnitude and duration of this response influenced by how weaning is managed. Interventions including delaying housing relative to weaning, pre‑weaning concentrate supplementation, and maintaining visual and auditory contact with the dam during weaning were shown to moderate stress responses and support immune function. Together, these findings highlight the importance of adopting low‑stress, evidence‑based weaning strategies, coupled with the avoidance of concurrent stressors (e.g. transport, commingling animals, castration) to protect calf health, enhance resilience during a high‑risk period for bovine respiratory disease, and reduce reliance on antibiotic treatments.

Compiled and edited by Mark McGee and Paul Crosson, Teagasc, Grange Animal & Grassland Research and Innovation Centre, and first published in BEEF2026 – Driving Sustainable Performance, additional reading from BEEF2026 is available here.