The use of mid-infrared spectrometry to estimate the ration composition of lactating dairy cows.

The composition of cow milk is strongly affected by the feeding regimen. Because milk components are routinely determined using mid-infrared (MIR) spectrometry, MIR spectra could also be used to estimate an animal's ration composition. The objective of this study was to determine whether and how well amounts of dry matter intake and the proportions of concentrates, hay, grass silage, maize silage, and pasture in the total ration can be estimated using MIR spectra at an individual animal level. A total of 10,200 milk samples and sets of feed intake data were collected from 90 dairy cows at 2 experimental farms of the Agricultural Research and Education Centre in Raumberg-Gumpenstein, Austria. For each run of analysis, the data set was split into a calibration and a validation data set in a 40:60 ratio. Estimated ration compositions were calculated using a partial least squares regression and then compared with the respective observed ration compositions. In separate analyses, the factors milk yield and concentrate intake were included as additional predictors. To evaluate accuracy, the coefficient of determination (R2) and ratio to performance deviation were used. The highest R2 values (for kg of dry matter intake/for % of ration) for the individual feedstuffs were as follows: pasture, 0.63/0.66; grass silage, 0.32/0.43; concentrate intake, 0.39/0.34; maize silage, 0.32/0.33; and hay, 0.15/0.16. Estimation of groups of feedstuffs (forages, energy-dense feedstuffs) mostly resulted in R2 values >0.50. Including the parameters milk yield or concentrate intake improved R2 values by up to 0.21, with an average improvement of 0.04. The results of this study indicate that not all ration components may be estimated equally accurately. Even if some estimates are good on average, there may be strong deviations between estimated and observed values in individual data sets, and therefore individual estimates should not be overemphasized. Further research including pooled samples (e.g., bulk milk, farm samples) or variations in ration composition is called for.

[Evaluation of sulfur status in dairy cows in Germany]. / Untersuchungen zur Schwefelversorgung von Milchkühen in Deutschland.

OBJECTIVE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION AND CLINICAL RELEVANCE: 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.