Failure of zinc supplementation to prevent severe facial eczema in cattle fed excess copper

Changes in serum and faecal zinc concentrations following supplementation with zinc sulphate heptahydrate of extensively grazed dairy cattle in New Zealand

AIMS

To examine the relationship in dairy cattle between serum and faecal Zn concentrations and daily intake of Zn supplemented with an oral drench; and whether total daily intake (TDI) of Zn in dairy cattle can be predicted from single measurements of Zn concentration in serum or faeces.

METHODS

A convenience sample of 20 animals from three stock classes (lactating cows, dry cows, heifers), that had not received Zn supplementation in the previous 60 days, was enrolled in the study. From Days -7 to -1, animals received no Zn supplementation. On Day 0, 15 animals per class were assigned daily drenching with increasing doses of ZnSO4.7H2O while five remained controls. From Days 0-6, treatment animals received 12.5 mg/kg LWT of Zn/day; from Days 7-13, 25 mg/kg LWT Zn/day and from Days 14-20, 37.5 mg/kg LWT Zn/day. Animals co-grazed within each stock class. Pasture, serum and faecal samples were collected at the start and at weekly intervals before each increase in Zn supplementation. Mixed and non-parametric models were used to assess treatment effects and whether daily intake of Zn could be predicted from Zn concentrations in serum and faeces.

RESULTS

Dosing with 0, 12.5, 25.0 and 37.5 mg Zn/kg LWT resulted in serum Zn concentrations of 12.1, 16.7, 27.2 and 35.8 µmol/L in heifers, 13.3, 17.1, 26.4 and 40.0 µmol/L in dry and 11.9, 12.1, 23.4 and 27.2 µmol/L in lactating cows. Dosing with the same amounts of Zn resulted in faecal Zn concentrations of 2.95, 21.72, 40.32 and 53.27 mmol/kg DM in heifers, 2.81, 23.77, 55.16 and 68.20 mmol/kg DM in dry and 3.00, 12.71, 34.86 and 57.53 mmol/kg DM in lactating cows, respectively. Treatment elevated serum and faecal Zn concentrations above controls (p < 0.001). Supplemented lactating cows had lower serum Zn concentrations than dry cows or heifers (p < 0.01). Supplemented dry cows had faecal DM Zn concentrations higher than heifers or lactating cows (p < 0.05). Analysis showed serum and faecal Zn concentrations could predict TDI of Zn (p < 0.001). Concentrations of Zn in faeces estimated TDI of Zn within a narrower predictive interval than serum Zn concentrations.

CONCLUSIONS AND CLINICAL RELEVANCE

Concentrations of Zn in serum and faeces were positively associated with TDI of Zn in dairy cattle and could predict TDI of Zn. When using serum and faecal Zn concentrations to estimate TDI Zn, stock class must be accounted for.

Comparison of a novel form of zinc with zinc oxide bolus licensed for prevention of facial eczema, and interaction with copper oxide in sheep

To evaluate a novel elemental zinc bolus compared with a registered positive control zinc oxide bolus and assess serum zinc concentrations following concomitant treatment with a capsule containing copper oxide needles. Forty Romney-cross ewes were randomly allocated in a 2 × 2 factorial design study. On Day 0, 20 ewes received novel boluses containing elemental zinc (Investigational Veterinary Product, IVP) while 20 received a zinc oxide bolus (control; CP). Half the animals in each zinc treatment group (n = 10) were treated with a copper oxide needle capsule [Copasure® - Ewe]. Weekly, from Day -7 to 56, all ewes were assessed for signs of photosensitization, and for 10 ewes from each zinc treatment groups, samples were collected for analysis of serum GGT activity, serum zinc concentrations, faecal zinc concentrations and on Days -7 and 56, liver copper concentrations. Multivariable random-effects models assessed the effects of zinc treatment, copper treatment, treatment interactions and time on all analytes. Regression models examined associations between serum and faecal zinc concentrations and GGT activity. Low spore numbers indicated low Pithomyces chartarum challenge. Serum zinc levels were significantly higher in the IVP than in the CP group [p < 0.0001] and varied by time [p < 0.001] and positively associated with faecal zinc concentration [p < 0.001]. Copper treatment did not affect serum zinc [p = 0.82] or faecal zinc [p = 0.92] concentrations. Liver copper concentrations did not differ between zinc treatment groups on Day -7 [p = 0.6] or Day 56 [p = 0.95]. Only the CP/no copper group had no increase in liver copper concentrations.

Quantification of zinc concentrations in serum, milk and faeces of dairy cattle as a measure of effective zinc supplementation for management of facial eczema

AIMS

To investigate the relationship between Zn concentrations in serum and those in milk or faeces, and to assess the ability of the Zn concentrations in milk, serum and faeces to predict intake of ZnO in dairy cattle.

METHOD

Seventy cows from one commercial farm in the Waikato region of New Zealand received one of seven dose rates (0, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 g/100 kg bodyweight (BW)) of ZnO given by oral drench, every morning, for 7 consecutive days. Every afternoon, milk and blood samples were collected from all cows. Free-catch faecal samples were collected during the afternoon milking on 3 days throughout the trial.Linear mixed models were used to assess the relationship between the concentration of Zn in serum and that in milk, and in faeces, respectively, and the relationship between dose rate of ZnO and concentrations of Zn in serum, faeces and milk, respectively. Receiver operating characteristic curve analysis was used to determine the ability of the Zn concentration in serum, milk and faeces to predict that a cow had been treated with a dose of ZnO ≥2.5 g/100 kg, the industry-recommended dose rate needed to protect against facial eczema.

RESULTS

A 1-µmol/L increase in Zn concentration in milk was associated with a 0.14 (95% CI = 0.11-0.17) µmol/L increase in Zn concentration in serum. Zn concentration in faeces was scaled by its SD; a 1 SD increase was associated with a 1.83 (95% CI = 0.54-3.12) µmol/L increase in zinc concentration in serum. Zn concentrations in serum and faeces increased with increasing dose rates of ZnO. No differences in Zn concentrations in milk were noted between animals dosed with 1.5-3.5 g ZnO/100 kg BW, inclusive. At the optimal threshold of Zn concentration in serum to predict protective ZnO intake (22 µmol/L), the sensitivity was 0.76 (95% CI = 0.69-0.82) and specificity 0.85 (95% CI = 0.80-0.89). For the concentration of Zn in faeces, the optimal threshold was 17.36 mmol/kg, with a corresponding sensitivity of 0.84 (95% CI = 0.84-0.85) and specificity of 0.85 (95% CI = 0.73-0.94). At the optimal threshold for the Zn concentration in milk (76.6 µmol/L), the sensitivity was lower than the other two sample types at 0.59 (95% CI = 0.52-0.67), but with a similar specificity of 0.84 (95% CI = 0.79-0.88).

CONCLUSIONS AND CLINICAL RELEVANCE

The concentration of Zn in milk shows promise as an initial screening test to identify dairy farms that do not provide adequate zinc to provide protection against FE.

The cellular and molecular toxicity of sporidesmin

The fungal metabolite sporidesmin is responsible for the hepatogenous photosensitising disease facial eczema in livestock. Toxicity is due to a sulfur-bridged epidithiodioxopiperazine ring that has wide biological reactivity. The ways in which the toxin causes hepatobiliary and other tissue damage have not been established. Hypotheses include direct interaction with cellular thiols including protein cysteine residues or production of reactive oxygen species resulting in oxidative stress. Comparison with the cellular effects of the structurally related compound gliotoxin suggests additional mechanisms including interaction with cell adhesion complexes and possible downstream consequences for regulated necrosis as a response to tissue injury. Revision of hypotheses of how sporidesmin affects cells has the potential to generate new strategies for control of facial eczema including through identification of proteins and genes that are associated with resistance to the disease.