Contributions à l'amélioration du diagnostic et de la gestion du transfert de l'immunité colostrale chez les veaux viandeux sur le terrain | Contributions to the improvement of diagnosis and management of colostral immunity transfer in beef calves under field conditions

Transfer of colostral immunity (TCI) can be defined as the process through which maternal immunoglobulins are transfered to the calf through colostrum. The importance given to the acquisition of an adequate TCI for the calf health and productivity has long been recognised. TCI can be assessed by the measurement of the calf serum IgG (direct method) or by measuring other parameters correlated with serum IgG concentration (indirect method). The success of TCI depends on several factors, the most important being colostrum quality and quantity and feeding delay. Practically, colostrum quality remains the most difficult factor to deal with. Indeed, quality is very hard to estimate because it is influenced by several factors such as breed, parity and individual. As for the TCI, colostrum quality can be assessed by direct and indirect methods. The study first aimed at evaluating the quality of colostrum produced by four beef cattle breeds and to compare the results with measurements realised with a Brix refractometer. Beef cows produced a high quality colostrum without any significant negative impact of breed or parity. An IgG1 concentration lower than 50g/L was measured in less than 10 % of colostrum samples. Refractometric measurements and colostrum IgG1 concentrations were strongly correlated even if correlation coefficients obtained for breed and parity were significantly different. Brix percentage identified for beef cattle for the IgG1 50 g/L value was slightly higher compared to those described for dairy cattle in other studies. In order to correctly classify a beef cow colostrum as a good quality product, concentrations of 75 g/L and 100 g/L were preferred to the 50 g/L concentration used for dairy cows; indeed, beef cows produce less of a more concentrated colostrum. The use of 25.5 % and 26.9 % Brix percentages allows to correctly classify high quality colostrum based on IgG1 concentrations of 75 g/L and 100 g/L, respectively. The second aim of the study was to compare the accuracy of four refractometers (Atago, Atago ATC, Wolf ATC and digital ATC refractometers) for measuring serum total protein (STP) concentration and to assess the efficacy of TCI using the 16g/L serum IgG concentration threshold. In addition, the assessment of TCI by means of the gamma-glutamyl transferase (GGT) activity and gammaglobulins concentration was also performed. Refractometric measurements of STP were highly correlated with those obtained with the biuret method frequently used as the laboratory method. The four refractometers presented a similar accuracy for STP assessment despite a significantly higher bias for the Wolf ATC refractometer. When considering the 16 g/L serum IgG threshold, STP concentrations of 56, 58, 54 and 56 g/L were measured for the 7 Atago, Atago ATC, Wolf ATC and digital ATC refractometers, respectively. For reasons of simplicity and convenience, the concentration of 56g/L could be used for the four refractometers without losing much accuracy. The GGT activity only reflected colostrum uptake by the calf whereas gammaglobulins concentrations were highly correlated with IgG. The last objective of the study was to evaluate, under farm conditions, the efficacy of a bovine concentrated lactoserum (Locatim®) to prevent neonatal diarrhoea. The administration of Locatim® did not significantly affect the incidence, duration or severity of diarrhoea. Serum IgG concentrations of control animals did not differ significantly from treated groups. Only the concentrations of IgG specific to E. coli CS31A strain were significantly higher in treated animals compared to the control group. The absence of significant effect of Locatim® can be explained by the high prevalence of Cryptosporidium parvum in studied farms and the adequate immunity transfer observed in most calves. In conclusion, beef cows produced a high quality colostrum regardless of breed or parity. Under field conditions, the use of Brix and clinical refractometers allows a quick, easy and reliable evaluation of colostrum quality and TCI. Refractometers have proved to be effective tools which can be easily used for implementing TCI management program. The use of a concentrated bovine lactoserum such as Locatim® is not justified when adequate TCI is observed or when neonatal diarrhoea is caused by pathogens against which lactoserum is not effective. The use of such lactoserum is therefore justified when specific antibodies contained in Locatim® can be effective in farm conditions. The study opened numerous perspectives both from practical and theoretical points of view. A large scale field assessment of colostrum quality and TCI in Belgian Blue cattle but also in other beef breeds would allow estimating the current situation and identifying the main factors which may influence colostrum quality and TCI. The joint assessment of colostrum quality and TCI is currently possible with a single type of refractometer but the development of other applications would increase the interest for using such tool in practice. The development of more efficient colostrum replacers and supplements would pave the way to an interesting alternative in case a high quality colostrum is lacking in a farm.