VetEnt Research, Te Awamutu, New Zealand.
School of Veterinary Science, Massey University, Palmerston North, New Zealand.
N Z Vet J. 2021 Jul;69(4):201-210. doi: 10.1080/00480169.2020.1861570. Epub 2021 Feb 11.
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 and spore counts identified herds likely to be affected by raised GGT activity in serum during autumn 2018 or 2019. In these herds, a pilot blood sample from 30 cattle was collected, followed by a full herd blood test within 2 weeks if in those 30 cattle one or more had GGT activities >300 IU/L. Individual MS production was measured within -5 - +12 days of a full herd blood test. Information about feeding spp. was collected from the farmer. Pooled sera from 10 randomly selected cattle from 10/11 farms with GGT >40 IU/L were tested for anti- antibodies.
The 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 activities > 40 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.
确定秋季奶牛面部湿疹（FE）引起的乳固体（MS）产量与肝损伤之间的关系，并确定血清γ-谷氨酰转移酶（GGT）活性预测产奶量损失的最实用截止值。
通过农场历史和孢子计数，确定了 2018 年或 2019 年秋季血清 GGT 活性升高的牛群。在这些牛群中，采集了 30 头牛的试点血样，如果这 30 头牛中的一个或多个牛的 GGT 活性>300IU/L，则在两周内对整个牛群进行血液检测。在全群血液检测后的-5 至+12 天内测量个体 MS 产量。从农民处收集关于 spp. 的喂养信息。从 11 个/个农场中随机选择 10 头/头血清 GGT>40IU/L 的牛的混合血清进行抗-抗体检测。
采用混合线性回归分析肝损伤与 MS 产量的关系。潜在的危险因素包括农场、牛龄、FE 风险期前最后一次牛群检测的 MS、牛的品种和 GGT 活性。随后，使用 40-400IU/L 的 GGT 活性阈值来表示不同严重程度的肝损伤。对于每个阈值，使用 herd test 数据的混合线性模型产生了高于或低于阈值的奶牛 MS 产量的估计边际均值差异。将动物超过阈值的患病率乘以每头奶牛的损失，即可获得每个截止值下每 100 头奶牛 MS/天的减少量。
农场间血清 GGT 活性>40IU/L 的动物患病率从 11%（45/488）到 96%（139/145）不等，个别牛的 GGT 活性从 3 至 6001IU/L 不等。从模型中可以看出，GGT 活性增加 100IU/L 与每头奶牛每天减少 0.011（95%CI=0.010-0.012）kg MS 相关。GGT 活性阈值为 40IU/L 与 MS 产量的关联最大，为 6.14kg MS/天/100 头奶牛。未发现明显的肝片吸虫或 Brassica 中毒。
肝损伤很可能是由 sporidesmin 毒性引起的，与 MS 的大量线性减少有关。在评估肝损伤对牛群产奶量的影响时，从业者在评估具有经济意义的面部湿疹时，应考虑阈值和超过阈值的动物的患病率。
