3. RESULTS
To evaluate viral spread, viremia, and seroconversion, nasal and rectal swabs and serum and milk samples were analysed. Milk samples were collected from 21 out of 24 cows due to the presence of two primiparous cows (6 and 10) and a dry cow (19) (Table 1).
All nasal and rectal swabs and milk samples tested negative for SARS-CoV-2 RNA. The results of the analyses performed on the serum samples are reported in Table 1. All tested samples were BCoV-negative (MTN ≥ 4). Eight of the 24 samples (33%, 95% CI 14–52) were negative for SARS-CoV-2. Of the 24 serum samples, 11 (46%, 95% CI 26-66) were positive for SARS-CoV-2 nucleocapsid protein (range: 1.38–7.40), 14 (58%, 95% CI 38-78) were positive for SARS-CoV-2 spike protein (range: 1.60–249.00), and 13 (54%, 95% CI 34–74) were positive for SARS-COV-2-neutralising antibodies, with titres ranging from 1:20 to 1:160 (Table 1). Interestingly, six of the samples were from pregnant cows (46%, 95% CI 19–73) (5, 12, 17, 19, 20, and 23) (Table 1). Of the 13 animals with neutralising antibodies, 2 of 13 were aged 1–5 years (15%, 95% CI 5–49), 6 of 13 were aged 6–10 years (46%, 95% CI 36–98), and 5 of 13 were aged >10 years (38%, 95% CI 53–113) (Table 2). Of the six pregnant animals with neutralising antibodies, one was aged 1–5 years (17%, 95% CI 9–31), four were aged 6–10 years (67%, 95% CI 12–76), and one was aged over 10 years (17%, 95% CI 13–47) (Table 2). The correlation between the presence of SARS-CoV-2-neutralising antibodies and the age of the cows was analysed using Fisher’s exact test, which showed a significant relationship (P < 0.05). Comparison of the 1–5-year-old group to the >10-year-old group yielded a statistically significant two-sided p value (p = 0.041). However, no statistically significant difference was observed when comparing the other groups. In addition, no correlation with pregnancy status was detected.
Furthermore, evaluating the analysed antibodies and age of the cows via Pearson correlation analysis showed a significant relationship (P < 0.05) between anti-S and neutralising antibodies against SARS-CoV-2 with age (Table 3) and interestingly, Pearson correlation analysis showed a strongly significant correlation (P < 0.01) between anti-S and anti-N antibodies (Table 3).
None of the cows with neutralising antibodies displayed fever, diarrhoea, and/or respiratory signs at sampling.