Cryptosporidiosis is regarded as a major concern for the dairy industry as it primarily affects neonatal calves, contributing to increased morbidity and mortality rates. Although cryptosporidiosis is found on various farms worldwide, it is more prevalent in intensive dairy production systems. It has a significant impact on calf health and production resulting in economic losses and increased treatment costs for farmers. On-farm hygiene management, rehydration therapy, and treatment with substances such as halofuginone lactate and, more recently paromomycin sulphate, are most often relied on for the prevention and control of cryptosporidiosis. Despite these efforts, the current methods remain ineffective, highlighting the need for an alternative approach. Additionally, the zoonotic potential and worldwide distribution of cryptosporidiosis raise public health concerns, especially in children and individuals with a compromised immune system. Since no effective treatments are available for humans or animals, the focus has shifted to natural, plant-based alternatives as a potential treatment option. Among these, plant alternatives such as garlic have shown beneficial antimicrobial properties and health benefits to animals such as water buffalo calves and mice, while also providing a more sustainable and environmentally friendly approach.
     The present study investigated the benefit of including different garlic extract inclusion levels in the milk replacer of pre-weaned dairy heifer calves on starter feed intake, skeletal growth, weight gain, health parameters, and veterinary intervention. Furthermore, the presence of Cryptosporidium oocysts was investigated to determine if the inclusion of garlic extract would result in reduced oocyst counts in the faeces of infected calves. In this trial, forty-five Holstein heifer calves (32.607 ± 4.944 kg birth weight) were randomly allocated to one of three treatment groups (n = 15): control (CON), garlic extract (1 g/calf/day) in the milk replacer (G1), and garlic extract (2 g/calf/day) in the milk replacer (G2). Calves were raised in individual outdoor pens and weaned at 70 days of age.
     No difference in weaning weight, average daily gain, total skeletal growth, starter feed intake, and feed conversion ratio was observed among treatment groups. Additionally, no differences were observed in health scores, veterinary intervention, and faecal oocyst counts. However, calves in the G2 treatment group had higher weekly live weights during weeks three to five, higher skeletal growth on days 18, 35, and 70, and lower overall average faecal scores, indicating reduced diarrhoea severity. They also required less treatment during week three compared to calves in the CON group. Despite these observations, the inclusion of garlic extract in the milk replacer had no overall beneficial effects on the growth performance or health of cryptosporidiosis-infected calves compared to untreated, infected calves.
     Therefore, further research is required to determine if higher garlic inclusions would result in improved growth and health or for an alternative natural, plant-based treatment to manage and treat calves infected with cryptosporidiosis on dairy farms.