| Popis: |
To determine the association between production of milk solids (MS) and liver damage from facial eczema (FE) in dairy cattle during autumn and to determine the most practical cut-off for serum gamma-glutamyl transferase (GGT) activity in predicting production loss.Farm history andThe association of liver damage and production of MS was analysed using mixed linear regression. Potential risk factors included farm, cow age, MS at last herd test before the likely FE risk period, breed of cow and GGT activity. Subsequently, GGT activity thresholds, from 40-400 IU/L, were used to indicate varying severities of liver damage. For each threshold, a mixed linear model using herd test data produced estimated marginal mean differences in MS production for cows above or below threshold. The prevalence of animals above threshold was multiplied by the per cow loss to obtain the reduction in MS/day/100 cows for each cut-off.The prevalence of animals with GGT activities40 IU/L ranged between farms from 11% (45/488) to 96% (139/145), and GGT activities for individual cows ranged from 3 - 6001 IU/L. From the model, an increase of 100 IU/L in GGT activity was associated with a decrease of 0.011 (95% CI = 0.010-0.012) kg MS/cow/day. A GGT activity threshold of 40 IU/L identified the largest association with MS production of 6.14 kg MS/day/100 cows. No evidence of significant liver fluke or brassica toxicosis was found.Liver damage was most likely caused by sporidesmin toxicity and was associated with substantial linear reduction in MS., When assessing the impact liver damage has on herd milk production, threshold and prevalence of animals exceeding threshold should be considered by the practitioner in assessing economically significant facial eczema. |
