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Sulfur deficiency and toxicity in livestock is associated with decreased performance and diseases. However, little is known about the diagnostics of sulfur status in dairy herds. The objectives of this study were to describe sulfur concentrations in feed rations in German dairy herds, to assess associations between feed sulfur concentrations and health and milk yield, to determine suitable laboratory diagnostic methods of sulfur status, and to propose reference values for the assessment of sulfur status in different sample media.
Between 2006 and 2014, a total of 569 dairy herds were visited. Blood, urine, and hair samples were obtained from 10 animals per group in the groups -3 to 0, 0 to 1, 3 to 5, and 15 to 18 weeks post partum (p. p.) (farms > 200 animals) or -3 to 0, 0 to 5, and 6 to 20 weeks p. p. (farms ≤ 200 animals). Pooled whole blood, serum, plasma, urine, and hair samples (n = 5663) were analyzed by ICP-OES. The sulfur content of the total mixed ration (TMR) of the group -3 to 0 weeks p. p. was determined in a certified feed laboratory (n = 625). Data analyses were performed using ANOVA, Chi-squared test and Spearman-correlation. Reference values were determined using the 2.5% and 97.5% percentiles.
Median sulfur concentration in the feed rations was 2.3 g/kg dry matter (DM). Deficiency (< 1.6 g/kg DM; 31% of farms) and oversupply (> 4.0 g/kg DM; 11% of farms) of sulfur in feed rations were regularly diagnosed. Sulfur deficiency was associated with reduced milk yield (p < 0.001), retained placenta (OR = 1.74; p = 0.037), milk fever (OR = 2.68; p < 0.001) and silent heat (OR = 2.56; p = 0.014). Positive correlations were found between sulfur concentration in feed rations and sulfur content in urine (r = 0.50), serum (r = 0.17), plasma (r = 0.18) and whole blood (r = 0.16). Reference values for sulfur diagnostics in dairy herds were proposed.
Diagnostics of sulfur status in dairy herds is relevant for veterinary practitioners and can be performed using TMR analysis and clinical laboratory parameters. Urine can be considered a short-term parameter, serum, plasma, and whole blood as intermediate parameters, and hair as a long-term parameter for the evaluation of the sulfur status.