Maternal Cryptosporidium parvum Gp40 Vaccination in Limousin Calves: Field Safety, Performance Outcomes, and Risk Factors for Neonatal Diarrhea

Neonatal diarrhea due to Cryptosporidium parvum is a major health challenge in young calves, adversely affecting growth and farm productivity. A novel maternal vaccine (Bovilis Cryptium®) targeting the parasite’s glycoprotein 40 (Gp40) has been developed to boost specific Gp40 antibodies in colostrum, thereby enhancing passive immunity in calves. We conducted a field trial on a French Limousin beef cattle farm to evaluate risk factors for neonatal diarrhea and to assess the safety, immunogenicity, and efficacy of this Gp40 vaccine under real-world conditions. Pregnant cows were randomly allocated to either receive the Gp40 vaccine or serve as unvaccinated controls, with all cows receiving standard prenatal E. coli/rotavirus/coronavirus vaccination. Calves born to vaccinated (test) vs. control cows were monitored from birth until turnout to pasture for health outcomes, including neonatal diarrhea incidence and growth performance (average daily gain, ADG). The Gp40 vaccine was well-tolerated with no adverse effects observed, confirming its safety in the field. Calves from vaccinated dams had significantly higher plasma Gp40 antibody titers than controls (geometric mean 15.6 vs. 13.0 log, p < 0.001), demonstrating robust immunogenicity. Neonatal diarrhea incidence was lower in calves from vaccinated dams (3.5% vs. 13.8% in controls), although this difference did not reach formal significance (p = 0.09). Notably, maternal vaccination was associated with a significant reduction in diarrhea risk when passive immunity transfer was optimal (high IgG levels). Late-stage growth performance improved in the vaccinated group, especially in male calves: by 6–8 weeks of age, male calves from vaccinated dams were on average 7 kg heavier than controls (ADG 1.15 vs. 0.93 kg/day from day 47–63, p < 0.05). In summary, maternal Gp40 vaccination proved safe and elicited high colostral antibody titers, resulting in reduced neonatal diarrhea and a delayed but significant improvement in growth of calves. These field results support maternal C. parvum Gp40 vaccination as a promising strategy to mitigate cryptosporidial diarrhea and enhance calf performance, pending confirmation in larger cohorts.