A systematic review of the scientific literature on relationships between management practices used on dairy farms and herd somatic cell count (SCC) was undertaken to distinguish those management practices that have been consistently shown to be associated with herd SCC from those lacking evidence of association. Relevant literature was identified using a combination of database searches (PubMed, Medline, CAB, Agricola, and Web of Science) and iterative screening of references. To be included in the review, a manuscript had to be published after 1979 in French, English, or Dutch; study design had to be other than case report or case series; herds studied had to be composed of ≥ 40 milking cows producing on average ≥ 7,000kg of milk in 305 d; interventions studied had to be management practices applied at the herd level and used as udder health control strategies; and SCC had to be measured using electronic cell counting methods. The 36 manuscripts selected were mainly observational cross-sectional studies; 8 manuscripts dealt exclusively with automatic milking systems and 4 with management of calves and heifers and its effect on SCC in early lactation heifers. Most practices having consistent associations with SCC were related to milking procedures: wearing gloves during milking, using automatic take-offs, using postmilking teat dipping, milking problem cows last, yearly inspection of the milking system, and use of a technique to keep cows standing following milking; all were consistently associated with lower herd SCC. Other practices associated with lower SCC were the use of a freestall system, sand bedding, cleaning the calving pen after each calving, surveillance of dry-cow udders for mastitis, use of blanket dry-cow therapy, parenteral selenium supplementation, udder hair management, and frequent use of the California Mastitis Test. Regarding SCC of heifers, most of the consistent associations reported were related to interventions made during the peripartum period. Studies on automatic milking systems have frequently reported elevation of the herd SCC following transition to the new system. These elevations seemed to be mediated both by the lack of monitoring of chronically infected cows and by an elevated incidence of intramammary infections. By assembling the results reported in many different studies, this review generates a more comprehensive understanding of the management practices influencing SCC and highlights areas of SCC control knowledge that lack evidence of effectiveness.

Bedding can affect mammary health of dairy cows. The objectives of this study were to evaluate clinical mastitis incidence in cows housed on recycled manure solids bedding and, more specifically, to determine which pathogens were involved. We followed 26 recycled manure solids farms and 60 straw-bedded farms as a comparative group during 1 year (2018–2019). For each episode of clinical mastitis, defined as a visual alteration of the milk, with or without local or systemic signs of infection, producers sampled aseptically the affected quarter, provided some details about the animal, and sent the sample to the research team at the Université de Montréal. We received and analyzed 1,144 milk samples. The samples were cultured according to the National Mastitis Council guidelines and the different colony phenotypes were subsequently identified with mass spectrometry. In 54.6% of CM cases, a single phenotype of bacteria was cultured (pure culture), while two different phenotypes were found in 16.8% of the samples (mixed culture), and no growth was observed in 14.4% of the samples. Samples with three or more phenotypes were considered contaminated and were not included in the pathogen-specific analyses (14.3% of the submitted samples). The most frequently identified bacterial species in pure and mixed culture in farms using recycled manure solids were Streptococcus uberis (16.0%), Escherichia coli (13.8%), Klebsiella pneumoniae (13.2%), Streptococcus dysgalactiae (6.2%), and Staphylococcus aureus (3.4%). In straw farms, the most frequent species were S. aureus (16.6%), S. uberis (11.0%), E. coli (9.1%), S. dysgalactiae (8.0%), and K. pneumoniae (1.1%). The incidence of clinical mastitis (all cases together) was not higher in recycled manure solids farms (14.0 cases/100 cow-year; 95% CI: 8.3–23.7) compared with straw-bedded farms (16.3 cases/100 cow-year; 95% CI: 9.0–29.6). However, K. pneumoniae clinical mastitis episodes were 7.0 (95% CI: 2.0–24.6) times more frequent in recycled manure solids farms than in straw farms. Adjusted least square means estimates were 1.6 K. pneumoniae clinical mastitis cases/100 cow-year (95% CI: 0.8–3.4) in recycled manure solids farms vs. 0.2 cases/100 cow-year (95% CI: 0.1–0.6) in straw-bedded farms. Klebsiella pneumoniae clinical mastitis is in general severe. Producers interested in this bedding alternative need to be aware of this risk.

The primary aim of this work was to isolate common bovine digestive tract parasites in recycled manure bedding (RMS), as well as to determine the ability of current RMS preparation procedures to eliminate these pathogens. Other objectives were to assess whether any of the aforementioned parasites could be retrieved in bulk milk from dairies using RMS and to study whether the prevalence of these parasites differed among manure of cows housed on RMS versus on straw bedding. For the study, 27 RMS farms and 61 control farms were recruited. Samples of manure from the pre-pit and milk from the bulk tank were recovered from straw-bedding farms and RMS-based farms. In addition, samples from the manure solid fraction after liquid extraction, RMS before use, and RMS currently in use were recovered from RMS herds. Parasites were first detected by double centrifugation zinc sulfate flotation to enhance isolation of gastrointestinal protozoa, and by modified Wisconsin sugar flotation for the appraisal of gastrointestinal nematodes. Cryptosporidium parasites were confirmed by nested PCR amplification and sequencing of a portion of the gene encoding the small subunit rRNA. Results revealed a high prevalence of Cryptosporidium spp. (C. parvum, C. andersoni, and C. meleagridis, identified by PCR) and Eimeria spp. (mainly E. bovis and E. zuernii) parasites in both types of farms, with a larger proportion of manure samples from RMS-bedded farms testing positive for Cryptosporidium parasites compared with manure from straw-bedded farms. Both Cryptosporidium spp. and Eimeria spp. oocysts were found at every step of RMS preparation and transformation, showing that current RMS preparation strategies do not guarantee the destruction of protozoan parasites. Cryptosporidium parvum, a potential zoonotic risk for professionals in close contact with livestock, was found to be present in 32 out of 61 straw-bedded and 24 of 27 RMS farms. No protozoan parasites were found in any sample derived from bulk milk, neither by microscopy analysis nor by molecular methods.