Validation of the diagnostic accuracy of the 3M™ Petrifilm™ coliform and aerobic count plates to measure colostrum bacterial contamination on Scottish dairy farms.

A calf should receive 10-12 % of its bodyweight in high quality colostrum ( >50 g/L immunoglobulin) shortly after birth in order to confer passive immunity, with calves ideally receiving their first feed of colostrum in the first 1-2 hours of life (Godden et al., 2019). It is recommended (not validated) that total counts for bacteria and coliforms in colostrum should not exceed 100,000 colony forming units per mL (CFU/mL) and 10,000 CFU/mL, respectively. This study was conducted between March and September 2023. Eighty-five colostrum samples from 5 commerical dairy farms in Dumfries and Galloway in Scotland were purposively selected. Samples were collected from various stages during the colostrum harvest, storage and feeding process to provide multiple samples with variable (low, medium and high) bacterial contamination. The objective of this study was to validate the diagnostic accuracy of the 3 M Petrifilm™ Coliform Count Plate (CCP) and Aerobic Count Plate (ACP) for colostrum bacteriology. The Petrifilm™ Aerobic Count Plates were compared to 5 % sheep blood agar (SBA) (total bacteria counts, TBC), and the Petrifilm™ Coliform Count Plates were compared to MacConkey plates (MAC) (total coliform counts, TCC) and test sensitivity and specificity were calculated. Colostrum bacterial contamination was highly variable between farms (TBC median and interquartile range= 50,000CFU/mL and 546000CFU/mL; TCC median and interquartile range=100,750CFU/mL and 188,500CFU/mL). Overall correlation between the Petrifilms™ and reference plate measures was moderate (Spearman rho=0.38-0.47). The statistical accuracy of the Petrifilm™ systems and the test sensitivity were improved by lowering the bacterial cutpoint from 100,000CFU/mL to 91,000 CFU/mL for the aerobic counts plates and from 10,000CFU/mL to 1500 CFU/mL for the coliform count plates. The Petrifilm™ system could be used as a monitoring tool to provide quick and statistically accurate results for TBC and TCC but should not be seen as a comprehensive solution for poor colostrum hygiene.

Defining optimal thresholds for digital Brix refractometry to determine IgG concentration in ewe colostrum and lamb serum in Scottish lowland sheep flocks.

This research aimed to define thresholds for ewe colostrum and lamb serum Brix refractometer measurements in lowland Scottish sheep. This would facilitate the use of this convenient, sheep-side test, enabling quick and accurate identification of poor quality colostrum and prevention of failure of transfer of passive immunity (FTPI) in lambs. Secondary aims were to identify risk factors for poor colostrum quality and FTPI in lambs. Serum samples (n = 233) were collected from lambs between 24 and 48hrs after birth, from four lowland Scottish meat sheep farms. Pre-suckle colostrum samples (n = 112) were also collected from ewes on two of these farms. Farmers provided information on litter size, ewe body condition score, ewe breed and dystocia. Duplicate digital Brix refractometer measurements were compared with immunoglobulin G (IgG) radial immunodiffusion (RID) testing for all colostrum and serum samples. Receiver operating characteristic (ROC) curves were used to redefine thresholds for Brix testing in colostrum and serum. Linear regression models were constructed with colostrum and serum IgG concentration as the outcomes of interest. Colostrum and serum IgG concentrations were highly variable. The prevalence of inadequate colostrum quality (using <50 g/L IgG on RID) was 4.5% (95% CI = 1.5 - 10.1) and the prevalence of FTPI (using <15 g/L IgG in serum on RID) was 7.73% (95% CI = 4.64-11.93). A ewe's colostrum IgG concentration was significantly and positively associated with the serum IgG concentration of her lamb(s) (p = 0.02). ROC analysis defined a Brix threshold for adequate colostrum quality of > 22.10% (sensitivity 80% (95%CI=28.4-99.5), specificity 90% (95%CI=82.3-94.8)). ROC analysis defined a Brix threshold for serum of > 8.65% for adequate passive transfer of immunity in Scottish lambs (sensitivity 94% (95%CI=72.7-99.8), specificity 82% (95%CI=76.6-87.2)). To optimise passive transfer of immunity in lambs, we suggest that ewe colostrum Brix measurements be defined as 'poor' (<22%); 'fair' (22-26%) and 'good' (>26%); and lamb serum as 'poor' (<8%); 'fair' (8-9%) and 'good' (>9%). It is recommended that these tests are used as for flock screening, using samples from multiple animals.

Associations between putative risk factors and poor colostrum yield in Holstein Friesian cattle.

When dairy cows produce little or no colostrum, calves are likely to suffer from failure of passive transfer (FPT). Volume of colostrum produced by the dam may be affected by: nutrition; environmental conditions; time from calving to milking; parity; dry period length; calving difficulty; calf weight; calf sex; calf viability; cow BCS / body weight; milk production in previous lactation and dam health. While risk factors for poor IgG concentration in colostrum have been extensively studied, there is little published literature on low colostrum yields and associated risk factors. The aim of this observational study was to identify risk factors for poor colostrum yield in dairy cows and to quantify the effect of variation in those variables that the farmer can directly control (length of dry period, and close-up transition period nutrition) using inverse probability modelling. 439 animals from a single Scottish dairy farm were used as a convenience sample. First milking colostrum yield was measured by farmers using a graduated bucket. For each animal, risk factor data and meteorological data from the nearest weather were obtained. Decreased colostrum yield was associated with increasing daily temperature range, while increasing UV index, lactation number and number of days dry increased colostrum yield. Marginal effect models revealed that for each additional day of dry period, colostrum yield increased. Higher UV indices the month before calving were positively associated with colostrum yield, particularly in primiparous cows, and higher temperatures in the months before calving were positively associated with colostrum yield in all cows.