Gastrointestinal nematode and lungworm infections in organic dairy calves reared with nurse cows during their first grazing season in western France.

The rearing system of dairy calves with nurse cows has been developing since 2010 in organic farms in western France. This system allows cow-calf contact until a weaning age close to the natural weaning for cattle and is characterized by an early turnout for calves at around one month of age with their nurse cows and a first grazing season with mixed grazing of calves and adults at a ratio of 2-4 calves per nurse cow. The objectives of this study were to assess the gastrointestinal (GIN) and lungworm infections in such reared calves and their variability during the first grazing season. Faecal egg count (FEC), pepsinogen (PEP) concentration and Ostertagia ELISA optical density ratio (ODR) were determined in calves (n = 497) at housing in 33 groups from 24 farms in 2018, and in calves (n = 405) and nurse cows (n = 199) throughout the 2019 grazing season in 41 groups from 20 farms. For lungworm infection, information was obtained during 2019 through the recording of coughing episodes along the grazing season and the Dictyocaulus ELISA ODR determination at housing both in calves and nurses. Results indicated that the level of GIN infection was overall low for calves during the first grazing season with PEP and Ostertagia ODR group-average values ranging from 0.97 to 1.6 U Tyr and 0.23 to 0.71 ODR respectively. No anthelmintic treatment being given in any group of calves. Ostertagia ODR values increased with the duration of the grazing season (>240 d) and with the ratio calves/nurse (>2). GIN parameters for nurses remained fairly stable during the grazing season with mean FEC, PEP and Ostertagia ODR group-average values of 13 epg, 2.28 U Tyr and 0.81 ODR, respectively. Antibodies against lungworms were detected in 3-62 % of calves depending on the duration of grazing, but only 6% of calves showed a coughing episode. The dilution effect due to the mixed grazing of resistant (nurse cows) and susceptible (calves) animals associated with predominant milk diet of calves during the first months of grazing in combination with protective grazing management allow calves to be turned out at an early age without using anthelmintic treatments. Further studies are needed to assess the GIN infection dynamics during the second grazing season in weaned heifers.

Rearing system with nurse cows and risk factors for Cryptosporidium infection in organic dairy calves.

Rearing dairy calves with nurse cows has been increasingly adopted by French farmers especially in organic farming and is characterized by a fostering of two to four calves during the first month of life by an unmilked lactating cow. This type of rearing remains poorly documented regarding its impact on calf health, such as cryptosporidiosis. The objectives of our study were to describe practices related to rearing dairy calves with nurse cows and to evaluate the prevalence, intensity and risk factors for Cryptosporidium infection in calf neonates. Between January and September 2019, the rearing practices of calves were described in 20 organic French farms and faeces were sampled once from 611 animals aged between 5 and 21 days. Cryptosporidium oocyst shedding was identified by modified Ziehl-Neelsen technique and scored semi-quantitatively (score 0-4). The risk of excretion (score 0 versus 1-4) was analysed using multivariate logistic regression models. This cow-calf rearing system usually consisted of a first phase with the dam, followed by an optional phase of artificial milk feeding (calves being fed with whole milk of the farm) and a final phase of fostering by a nurse cow. Each nurse was suckled from one to five calves of close age with a fostering age of 8 days on average. The oocyst shedding prevalence was 40.2 % and similar to classically reared calves, but the intensity of shedding and the prevalence of diarrhoea appeared to be lower. The identified six risk factors for oocyst shedding were: born in the last two thirds of the birth order, born between January and July versus August and September, calf with its dam in the barn versus on pasture, having an artificial milk feeding phase versus being with the dam only, and contact between peer calves and notably the presence of an oocyst excretory calf fostered by the same nurse. These results emphasize the role of the environment for the direct and indirect contamination, particularly that related to the accumulation of oocysts from previous or peer calves facilitating the faecal-oral route of transmission. This highlights the crucial role of the premises used intensively during the winter and spring months with higher densities of calves in the barn compared to outdoor situations promoted by this rearing.