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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: VAIvaccinated with ND vaccines and intramuscularly inoculated with vNDV, VAUvaccinated uninfected, UNIunvaccinated infected and UNUunvaccinated 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.

This study investigated whether prior cyclophosphamide (CY) treatment influenced the susceptibility of young broiler chickens to velogenic Newcastle disease (vND) virus (vNDV) challenge. Broiler chickens treated with CY at 4 weeks of age showed a loss of weight, severe atrophy of the bursa and thymus and severe lymphocytic depletion in the bursa, spleen and thymus and lymphopaenia. On challenge at 6 weeks of age with vNDV, there were significant (p < .05) weight loss, severe depression, diarrhoea, coughing and sero-mucous nasal discharges and torticollis. Lesions included severe atrophy of the lymphoid organs and congested lungs. Proventricular, intestinal and caecal tonsil haemorrhages and ulcers were more severe in the CY-untreated than the treated broilers. Histopathology showed severe necrosis and depletion of the lymphocytes in the lymphoid organs, perivascular cuffin and endotheliosis in the brain. Total mortalities in the CY-treated and untreated broilers were 100% and 94.44%, respectively, by day 6 post-challenge. There was no statistical difference (p < .05) between the mortalities. These results show that CY treatment may not have an effect on the susceptibility of broilers to an acute disease like vND. ARTICLE HISTORY

This study investigated the immune responses to La Sota vaccination, used in protection of chickens against Newcastle disease, in light weight type breeds of chickens (pullets) and heavy weight type breeds of chickens (broilers) used in commercial poultry production. Seven‐week‐old 50 White Marshall broilers (Br) and 50 Isa Brown pullets (Pu) were randomly divided into four groups: vaccinated broilers chickens; (VBr), unvaccinated broiler chickens (UBr), and vaccinated pullet chickens (VPu) and unvaccinated pullet chickens (UPu). Chickens in groups VBr and VPu were vaccinated with La Sota vaccine, whereas groups UBr and UPu were not vaccinated. On day 0 post vaccination (PV), six chickens from group Br and Pu, and on day 4 PV, three chickens from each four groups were sacrificed and the bursa weight index (BWI), thymus weight index (TWI) and the splenic weight index (SWI) were obtained. The chickens were observed for clinical signs and lesions. Serum samples were collected from the chickens in all the groups on days 0, 7, 14, 21, 28 PV and assayed for haemagglutination inhibition (HI) antibodies. The BWI, TWI and SWI were 0.37 ± 0.05, 0.35 ± 0.17, 0.65 ± 0.26 for pullets and 0.11 ± 0.04, 0.13 ± 0.02, 0.36 ± 0.17 for broilers on day 0 PV. On day 4 PV there was no significant difference ( p < .05) between the indices of the vaccinated and unvaccinated chickens. The geometrical mean antibody titres (GMT) of the pullets were 2 to 3 times higher than those of the broilers on days 7 to 28 PV. Vaccination did not produce clinical signs or lesions. The above observations show that naturally pullets produce higher antibodies than broilers because of their higher BWI.

This study investigated the haematological changes in vaccinated and unvaccinated laying chickens experimentally infected with a velogenic Newcastle disease virus. Two hundred and forty laying chickens were randomly assigned into four groups of 60 each: vaccinated with Newcastle disease vaccines and infected with velogenic Newcastle disease virus (VI), vaccinated uninfected (VU), unvaccinated infected (UI), unvaccinated uninfected (UU). At peak production, 32-weeks-old, groups VI & UI were each inoculated intramuscularly with 0.2 ml of velogenic Newcastle disease virus. The changes in the blood cells were assayed in the groups on the specified days. The total red blood cell count (RBC) was significantly (P < 0.05) lower in UI group on days 6 & 15 post infection (PI). The packed cell volume (PCV) and haemoglobin concentration (HbC) were significantly (P<0.05) lower in UI group on day 15 PI. There were no significant (P > 0.05) differences between the PCV, RBC and HbC in VI & VU groups from day 0 to 21 PI. The leukogram showed significant (P < 0.05) differences in leukocytosis on days 3 & 6 PI followed by significant (P < 0.05) leukopenia on days 10, 15 & 21 PI in UI group. However, significant leukocytosis on day 10 PI followed by leukopenia on day 15 PI were recorded in VI group. These findings suggest that leukocytosis in UI & VI and decreased haemogram in UI are features of Newcastle disease in laying chickens.