To test the hypothesis that Cu metabolism in dairy cows is affected by dietary starch concentration and additional sulfur S and Mo, 60 Holstein-Friesian dairy cows that were [mean ± standard error (SE)] 33 ± 2.5 days postcalving and yielding 41 ± 0.9 kg of milk/d were fed 1 of 4 diets in a 2 × 2 factorial design experiment over a 14-wk period. The 4 diets had a Cu concentration of approximately 15 mg/kg of dry matter (DM), a grass silage-to-corn silage ratio of 1:1, a dietary starch concentration of either 150 g/kg of DM (low starch, LS) or 220 g/kg of DM (high starch, HS), and were either unsupplemented (-) or supplemented (+) with an additional 0.8 g of S/kg of DM and 4.4 mg of Mo/kg of DM. We found an effect of dietary starch concentration on mean reticular pH, which was 0.15 pH units lower in cows fed the high starch diets. The addition of S and Mo decreased intake by 1.8 kg of DM/d, an effect that was evident beginning in wk 1 of the study. Mean milk and fat yields were 37.0 and 1.51 kg/d, respectively, and were not affected by dietary treatment. We found an effect of dietary starch concentration on milk protein concentration, protein yield, and urea nitrogen, which were increased by 2.8 g/kg, 0.09 kg/d, and 2.1 mg/dL, respectively, in cows fed the high starch diets. We found no effect of dietary treatment on either cow live weight or body condition. Mean plasma Cu, Fe, and Zn concentrations were 15.3, 42.1, and 14.4 µmol/L, respectively, and were not affected by dietary treatment. In contrast, we found an interaction between dietary starch concentration and Cu antagonists on plasma Mo, where feeding additional S and Mo increased plasma Mo to a greater extent when cows were offered the high versus low starch diet. We also found that increasing dietary starch concentration increased serum ceruloplasmin activity, but serum haptoglobin concentration was not affected by dietary treatment. The addition of S and Mo decreased hepatic Cu concentration, whereas in cows fed the higher dietary starch concentration, hepatic Cu concentration was increased over the period of our study. We concluded that increasing dietary starch concentration decreases rumen pH and increases milk protein yield and hepatic Cu concentration, whereas feeding additional S and Mo decreases intake and hepatic Cu concentration.

Background: Oversupply of dietary copper (Cu) is common among UK dairy herds, but studies on the long‐term outcomes of this oversupply are scarce. Methods: A longitudinal study was undertaken to determine the long‐term implications when 80 Holstein‒Friesian heifers with a mean (±standard error) age of 4.1 ± 0.1 months and a mean liveweight of 137 ± 2.4 kg were fed a recommended (R; 16 mg/kg dry matter [DM]) or high (H; 32 mg/kg DM) dietary Cu concentration until 6 weeks prior to calving. Results: Hepatic Cu concentrations in both treatment groups were elevated into the ranges used to diagnose chronic Cu toxicity in cattle at 6.9 months of age (798 ± 46.4 mg/kg DM for H vs. 643 ± 35.4 mg/kg DM for R), with associated evidence of liver damage. Hepatic Cu concentrations then returned to normality but remained higher ( p < 0.001) for heifers fed H than for those fed R and were associated with a reduced ( p = 0.044) conception rate to first and second services (73.7 ± 8.05% for H vs. 91.2 ± 7.68% for R). Limitation: This retrospective analysis identified pre‐study liver damage, which may have affected results. Conclusions: Supplying Cu in excess of requirements resulted in liver damage and reduced conception rates.

Excessive copper (Cu) supplementation is common on dairy farms worldwide, despite a growing body of research highlighting the risks of over-supplementation, including liver damage, impaired growth, and reduced fertility. However, diagnosing Cu toxicity remains challenging due to the liver’s allostatic regulation of blood Cu levels and debate surrounding toxicity thresholds. This study utilised secondary data from a longitudinal study conducted between September 2016 and September 2018 involving 80 replacement Holstein–Friesian heifers. Data was utilised to generate receiver operating characteristic curves which established liver Cu thresholds associated with suboptimal liver function and fertility. Results indicated that hepatic Cu concentrations exceeding 167 mg/kg of dry matter (DM) were associated with reduced conception rates to first service, while concentrations above 260 mg/kg of DM reduced conception probability to first and second services. Hepatic Cu concentrations exceeding 322 mg/kg of DM were linked to impaired liver function, as evidenced by elevated serum glutamate dehydrogenase activity. In contrast, a toxicity threshold value could not be generated for plasma Cu, underscoring its inadequacy as a biomarker. The fertility thresholds identified in this study may be more closely related to optimizing Cu levels for animal performance rather than indicative of liver Cu toxicity, suggesting the need for further research.

Excessive copper (Cu) absorption in calves may increase the risk of excessive hepatic Cu accumulation, likely driven by their elevated pre-ruminant absorptive capacity, with the potential for harmful Cu accumulation leading to adverse health and productivity outcomes. However, quantitative data across the weaning transition remains limited. This study utilized secondary data and bio-banked samples from 35 Holstein–Friesian bull calves to estimate hepatic Cu retention coefficients pre- and post-weaning. Although mean hepatic Cu concentrations remained broadly stable throughout the study, between 311 and 675 mg/kg of DM, changes varied by developmental stage: calves experienced hepatic Cu accumulation of 2.5 mg of Cu/kg of DM/d pre-weaning but a net reduction of 1.8 mg/kg of DM/d post-weaning. Pre-weaning calves exhibited a hepatic Cu retention coefficient of 81% compared to post-weaning calves, where the hepatic Cu retention coefficient was 5%. This reduction in absorptive capacity is consistent with increased rumen development and greater antagonism from dietary sulfur and molybdenum. Hepatic steady-state Cu intake requirements were estimated at 3 mg/kg of DM pre-weaning and 15 mg/kg of DM post-weaning. These findings demonstrate that the pre-weaning period represents a phase of high Cu retention and heightened susceptibility to hepatic Cu accumulation, even when dietary Cu meets current recommendations. Refining Cu feeding guidelines to more accurately reflect developmental stage and rumen maturation may help prevent excessive hepatic Cu loading while maintaining adequate mineral supply.

Weaning is a time of acute stress for the piglet, as it transitions from dependence on the sow and her milk to social and nutritional independence (Weary et al. 2008). This coincides with a change ...