Studies of bone marrow and leucocyte counts in peripheral blood in fetal and newborn foals

Clinical and pathological records of 124 foals were studied. The foals were assigned to six groups; normal, premature, dysmature, bacterially infected, neonatal maladjustment syndrome and Equid herpesvirus type 1 (EHV-1) infected. Also, 6 pony fetuses were sampled via catheters in the umbilical vein and artery between 280 and 310 days gestation. Bone marrow aspiration was performed on a further 14 foals. Premature foals had significantly lower neutrophil counts than normal foals up to 5 h. Foals with bacterial infections had significantly lower neutrophil counts up to age 12 h. EHV-1 infected foals had significantly lower neutrophil counts up to age 24 h and significantly lower lymphocyte counts than all other groups up to age 12 h. Premature foals showed a higher neutrophil count and neutrophil/lymphocyte (N:L) ratio in survivors compared with non-survivors when all ages were considered, although the differences were not significant before 35 h. Discriminant analysis showed a 99% chance that the EHV-1 group could be identified from all other groups except dysmature foals, where discrimination between the two groups was about 90%. In catheterized fetuses, age-related increases in neutrophil counts and the N:L ratio occur from 280 to 310 days of gestation. In one preparation available for study leading up to parturition, the N:L ratio widened during the 3 days pre-partum. The bone marrow aspirates showed no significant changes in the myeloid:erythroid (M:E) ratio during the first 4 days post partum. The left shift (LS) index was significantly higher in foals suffering bacterial infection compared with normal or dysmature foals.(ABSTRACT TRUNCATED AT 250 WORDS)