Response of cows with osteomalacia grazing sub-tropical native pastures to phosphorus supplementation with loose mineral mix or feed blocks.

Osteomalacia outbreaks often occur in cattle grazing native pastures in regions with endemic phosphorous (P) deficiency. This study evaluated the responses of two groups of cows, initially with clinical signs of chronic P deficiency, to P supplements (100 g P/kg) offered ad libitum for 13 weeks as a loose mineral mix (LMM group) or the same mineral mix offered as blocks (BMM group). Half of the cows in each group were categorized as 'with' or 'without' severe osteopenia according to a test that depended on the resistance to penetration of a needle through the left lateral process of the L4-L5 lumbar vertebra. The groups grazed two paddocks that were switched each 3 weeks. The liveweight, supplement intakes, and the P-concentrations in soil, forage, blood, and external cortical bone (ECB) of the ribs were measured. The bicarbonate-extractable P in soil was 3.5 mg/kg. The mean of total P in forage (0.95 g/kg/DM), inorganic P in serum (iP, 0.96 mmol/L), and total P in the ECB of the ribs (85 mg/mL) at the beginning of the experiment were all low and consistent with severe chronic P deficiency. The P supplementation allowed clinical recovery in 18/20 cows with their serum and ECB P and calcium approaching normal values and in the two remaining cows the only sign was abnormal gait. Cows consumed more of the LMM than BMM supplement (means 8.3 and 6.6 g P/day, respectively). After 13 weeks cows initially classified as 'with severe osteopenia' and supplemented with LMM had higher (P < 0.05) final liveweight (difference = 21.6 kg), iP (difference = 0.74 mmol/L), bone Ca (difference = 65.7 mg/mL) and bone P (difference = 26.5 mg/mL) concentrations and lower (P < 0.01) final serum Ca/iP ratio (difference = -0.65) than cows with severe osteopenia but supplemented with BMM. The treatment of severe P deficiency cows grazing P deficient sub-tropical grasslands by P supplementation for 13 weeks was more effective with LMM than BMM.

Frequency of Neospora caninum-specific antibodies in bulk milk from dairy farms from Mar y Sierras Dairy Basin, Argentina.

The aim of this study was to describe the prevalence of Neospora caninum based on the detection of specific antibodies in bulk tank milk (BTM) from dairy cattle farms in the Mar y Sierras Basin by using an enzyme-linked immunosorbent assay (ELISA). A total of 98 BTM samples from 49 dairy farms were collected during autumn and spring of 2019. Additionally, 147 paired individual milk and serum samples were collected from two dairy farms to assess the prevalence within-herd by ELISA and indirect fluorescent antibody test (IFAT, serum samples). Additionally, 12 individual serum samples were also assessed to test the agreement between IFAT and ELISA (total serum samples 159). Noteworthy, 100 and 91.84% of 49 dairy farms were positive in the BTM in autumn and spring, respectively. For the within-herd individual samples, a good agreement between serum and milk results was obtained for ELISA and IFAT (0.86-0.90). This is the first study in Argentina in which milk samples were tested to determine the N. caninum infection status at herd and within-herd levels in dairy farms, providing a base for further research.

Delayed-type hypersensitivity skin test against Neospora caninum in heifers with undetectable specific antibodies.

Delayed-type hypersensitivity (DTH) has been used in human and veterinary medicine as a skin testing for evaluating in vivo cell-mediated immune responses (CMIR). Whereas CMIR is a key process to control intracellular pathogens, its value at identifying cattle exposed to the abortigenic intracellular coccidian parasite Neospora caninum is unknown. In this work, we have evaluated a DTH skin testing in cattle exposed to N. caninum and still seronegative. Female calves were experimentally sensitized by subcutaneous (SC) inoculation with live tachyzoites of N. caninum (NC-Argentina LP1) in sterile phosphate-buffered saline (PBS) (group A; n: 8) whereas other calveswere mock-sensitized with PBS (group B; n: 6). Two DTH skin tests were performed by intradermal inoculation with a soluble lysate of N. caninum tachyzoites (NC-Argentina LP1) in the neck region at 60d and 960 d after sensitization. Skinfold thickness at the intradermal inoculation site was measured at 0, 24, 48 h post each DTH skin test and skin biopsies taken for microscopic evaluation. Specific N. caninum antibodies kinetics was evaluated all throughthe experiment. We found that whereas N. caninum specific antibodies remained below the ELISA cut-off, a distinctive skinfold thickness increase was detected in sensitized animals (group A) at the DTH skin test site, showing induration, swelling and inflammatory infiltration. Mock sensitized animals (group B) showed no skinfold thickness growth and lacked specific antibody response. Thus, N. caninum DTH skin testing could be a useful diagnostic tool for the detection of CMIR during N. caninum infection in non-humoral responders.

Frequency of Neospora caninum infections in beef cow-calf operations under extensive management.

The aim of this study was to evaluate the frequencies of Neospora caninum horizontal and vertical transmissions in beef cow-calf operations under three different extensive management systems: group A: 0.75 head per hectare pasturing on natural grass; group B: 1.1 head per hectare on natural grass and improved cultured pastures; and group C: 2 head per hectare on natural grass, improved cultured pasture and whole corn silage. Serum samples from 72 multiparous cows assigned to each beef cow-calf operations were obtained every 3 months during 2 years. A group of 30 replacement heifers from each group were tested similarly since they were 10-21 months old. Twenty four, 20 and 34 calves from groups A, B and C respectively, were bled before colostrum intake and again 6 months later. The samples were analyzed by indirect fluorescence antibody test (IFAT) for detection of total IgG against N. caninum at a serological titre ≥ 200 for multiparous cows and replacement heifers, and a serological titre ≥ 25 for calves. Serum samples from seropositive cows were assessed by ELISA to evaluate the avidity of their specific antibodies. There were no differences in the proportion of seropositive cows from groups A, B and C at the beginning of the trial (p>0.05). Interestingly, the lowest serological titres in seropositive cows from all groups were observed during the first trimester (p<0.05). Although seropositive cows had medium to high avidity antibodies, suggesting chronic infection; seroconversion associated with low antibody avidity was found in 2, 3 and 3 seropositive cows from groups A, B and C. All replacement heifers remained seronegative. No abortions were recorded but 2, 1, and 2 calves from groups A, B and C were seropositive before colostrum intake, respectively. Seropositive calves born from cows having intermediate or high avidity remained with the same serostatus at 6 months of age. Even under varying extensive management conditions, both N. caninum horizontal and vertical transmission methods do occur in beef cow-calf operations.