An experiment was conducted with dairy cows to study the partitioning of excreted purine derivatives between urine and milk and to quantify the endogenous contribution following the isotopic labeling of microbial purine bases. Three lactating cows in their second lactation that had been cannulated in the rumen and the duodenum were fed a mixed diet (48:52, roughage/concentrate ratio) distributed in equal fractions every 2 h, and duodenal flow of purine bases was determined by the dual-phase marker system. Nitrogen-15 was infused continuously into the rumen to label microbial purine bases, and the endogenous fraction was determined from the isotopic dilution in urinary purine derivatives. Urinary and milk recovery of duodenal purine bases were estimated at early (wk 10) and late (wk 33) lactation by the duodenal infusion of incremental doses (75 and 150 mmol purine bases/d) of RNA from Torula yeast. Each period was 6 d, with RNA being infused during the last 4 d, followed by measurement of the flow of purine bases to the duodenum. The isotope dilution of purine derivatives in urine samples confirmed the presence of an endogenous fraction (512 +/- 36.43 micromol/W0.75 or 56.86 mmol/d) amounting to 26 +/- 3.8% of total renal excretion. Total excretion of purine derivatives in urine plus milk was linearly related to the duodenal input of purine bases, but the slopes differed (P < 0.005) between lactation stages resulting in a lower equimolar recovery in early (y = 58.86 (+/-3.89) +0.56 (+/-0.0164) x; r = 0.90) than late lactation (y = 58.86 (+/-3.89) + 0.70 (+/-0.046) x; r = 0.80). Excretion of purine derivatives through milk represented a minimum fraction of total excretion but responded significantly to the duodenal input of purine bases. No differences between lactation stages were detected, and variations in milk yield did modify significantly the amount of purine derivatives excreted through the milk.

Bovine paratuberculosis (PTB) is a chronic granulomatous enteritis, caused by Mycobacterium avium subsp. paratuberculosis (MAP), responsible for important economic losses in the dairy industry. Current diagnostic methods have low sensitivities for detection of latent forms of MAP infection, defined by focal granulomatous lesions and scarce humoral response or MAP presence. In contrast, patent infections correspond to multifocal and diffuse types of enteritis where there is increased antibody production, and substantial mycobacterial load. Our previous RNA-Seq analysis allowed the selection of five candidate biomarkers overexpressed in peripheral blood of MAP infected Holstein cows with focal (ABCA13 and MMP8) and diffuse (FAM84A, SPARC and DES) lesions vs. control animals with no detectable PTB-associated lesions in intestine and regional lymph nodes. The aim of the current study was to assess the PTB diagnostic potential of commercial ELISAs designed for the specific detection of these biomarkers. The ability of these ELISAs to identify animals with latent and/or patent forms of MAP infection was investigated using serum from naturally infected cattle (n = 88) and non-infected control animals (n = 67). ROC analysis revealed that the ABCA13-based ELISA showed the highest diagnostic accuracy for the detection of infected animals with focal lesions (AUC 0.837, sensitivity 79.25% and specificity 88.06%) and with any type of histological lesion (AUC 0.793, sensitivity 69.41% and specificity 86.57%) improving on the diagnostic performance of the popular IDEXX ELISA and other conventional diagnostic methods. SPARC and MMP8 showed the highest diagnostic accuracy for the detection of animals with multifocal (AUC 0.852) and diffuse lesions (AUC 0.831), respectively. In conclusion, our results suggest that quantification of ABCA13, SPARC and MMP8 by ELISA has the potential for implementation as a diagnostic tool to reliably identify MAP infection, greatly improving early detection of MAP latent infections when antibody responses and fecal shedding are undetectable using conventional diagnostic methods.

Grazing cows could produce milk with a higher proportion of polyunsaturated fatty acids, which is beneficial to human health, compared with non-grazing cows, though grazing alone could compromise milk production. Under oceanic climate conditions, a study involving 15 dairy cows, fed total mixed ration (TMR)ad libitumin combination with different grazing times of 12 h (TMR12), 6 h (TMR06) and zero grazing time (TMR00) with the aim to evaluate different strategies on the fatty acids profile of milk and milk production. No differences were seen between the treatments with respect to milk yield (34·4±6·3 kg/d) or milk protein content (30·4±1·8 g/kg). The milk produced by the TMR12 cows had less total fat (36·2 vs. 38·2 g/kg) and saturated fatty acid (FA, 69·39 vs. 71·44 g/100 g FA) than that produced by the TMR00 cows. The concentration of vaccenic acid in the TMR06 and TMR12 milk was twice that of the TMR00 milk (4·22, 4·09 and 2·26 g/100 g FA respectively). Linear increases in conjugated linoleic (CLA) and linolenic acids were observed with increasing grazing time. Pasture was an important source of FA especially C18:3 for TMR06 and TMR12 cows. Under oceanic climatic conditions, the grazing of dairy cows as a complement to feeding with TMR can improve the FA profile of milk and increase its CLA content.