Changes in serum calcium and phosphorus levels and their relationship to egg production in laying hens infected with velogenic Newcastle disease virus

This study evaluated the changes that occurred in the serum levels of calcium and phosphorus in laying hens infected with velogenic Newcastle disease (ND) virus (vNDV), and their relationship to the decrease in egg production usually associated with ND. Two hundred and forty laying hens (32 weeks old) were randomly assigned into four groups of 60 each viz: VAI - vaccinated with ND vaccines and intramuscularly inoculated with vNDV, VAU - vaccinated uninfected, UNI - unvaccinated infected and UNU - unvaccinated uninfected. At weekly intervals blood was collected from six randomly selected hens in each group for serum calcium and phosphorus assays. Groups VAI and UNI showed a significant (p < .05) drop in egg production. Serum phosphorus levels of groups VAI and UNI were significantly (p < .05) lower than those of groups VAU and UNU. There was a highly positive correlation between serum phosphorus levels and egg production which was highly significant (r = .74; p < .01). The changes in serum calcium levels of infected groups were only slight, and the relationship between serum calcium levels and egg production was low, positive and not significant (r = .26; p > .05). Drop in egg production that occurred in the ND-infected laying hens was positively strongly correlated with the drop in serum phosphorus levels.