The aim of this study was to compare the effects of cryopreservation at approximately -196 °C in liquid nitrogen (N) and freezing at approximately -20 °C in a freezer, on the viability and survival of eight different mastitogenic bacteria inoculated in milk. Bacteria were frozen at approximately -20 °C in a freezer and cryopreserved at approximately -196 °C in liquid nitrogen. An effective preservation method was needed for follow-up samples from cows identified in the South African National Milk Recording Scheme (NMRS) with somatic cell counts above 250 000 cells/mL milk. The organisation responsible for sample collection of the NMRS milk samples also provides producers with liquid nitrogen for their semen flasks at the collection sites. This existing mode of storage and transport could therefore be utilised.Ten samples of each organism were thawed and cultured bi-weekly until week 18 for both temperature treatments. An additional sampling was performed at week 30 for samples frozen at approximately -20 °C. Freezing and cryopreservation did not impair subsequent isolation of Streptococcus dysgalactiae, Streptococcus uberis, Enterococcus faecalis, Staphylococcus aureus (STH) (phage type lytic group III) or Sta. aureus (STA) (phage typed, other than lytic group III). Survival was indicated by the isolation of bacteria from samples, and viability by the strength of growth of the bacteria isolated. The survival of Streptococcus agalactiae decreased after week 12 and Escherichia coli after week 16 of freezing, but both organisms survived under cryogenic preservation until week 18. Coagulase-negative staphylococci survived until week 18 for both freezing and cryogenic preservation.Both storage methods could thus contribute to the improvement of a pro-active approach towards udder health management in South African dairy herds.

Objective: To evaluate a human radioimmunoassay (RIA) and equine and high-range porcine (hrp) species-specific ELISAs for the measurement of high serum insulin concentrations in ponies. Samples: Serum samples from 12 healthy nonobese ponies (7 clinically normal and 5 laminitis prone; 13 to 26 years of age; 11 mares and 1 gelding) before and after glucose, insulin, and dexamethasone administration. Procedures: Intra-and interassay repeatability, freeze-thaw stability, dilutional parallelism, and assay agreement were assessed. Results: Assay detection limits were as follows: RIA, < 389 μU/mL; equine ELISA, < 175 μU/mL; and hrp ELISA, 293 to 8,775 μU/mL. Mean ± SD intra- and interassay repeatability were respectively as follows: RIA, 6.5 ± 5.1 % and 74 ± 3.4%; equine ELISA, 10.6 ± 11.0% and 9.0 ± 4.6%; and hrp ELISA, 19.9 ± 172% and 173 ± 16.6%. Freezing and thawing affected measured concentrations. Dilutional parallelism in the RIA was only evident when insulin-depleted equine serum was used as a diluent (percentage recovery, 95.7 ± 274%); in the ELISAs, dilutional parallelism was observed when a zero calibrator was used. Agreement between RIA and equine ELISA results was good for samples containing concentrations < 175 μU of insulin/mL (bias, −18.5 ± 25.5 μU/mL; higher in RIA). At higher concentrations, assay agreement was poor between RIA and equine ELISA results (bias, −185.3 ± 98.7 μU/mL) and between RIA and hrp ELISA results (bias, 25.3 ± 183.0 μU/mL). Conclusions and Clinical Relevance: Agreement among results of the 3 assays was variable, and dilutional parallelism was only evident with the RIA when insulin-depleted equine serum was tested. Caution is recommended when evaluating high insulin concentrations measured with the RIA or ELISAs.