Abstract:
A cohort study was conducted in order to measure the effect of the
chronic indurative lymphocytic mastitis caused by the South African
strain of maedi visna virus (MVV) on the pre-weaning growth of lambs
born either of naturally infected or uninfected ewes kept under
similar conditions. Fifty naturally infected ewes as well as another 40
from a maedi-visna-free source to be used as control animals, were
purchased and kept in separate flocks which were managed in a similar
way. All the ewes were of the same breed and 3-4 years old. During the
adaptation period, and through the mating, pregnancy and lactation
periods they were periodically monitored for the presence of MVV serum
antibodies. The lambs were weighed at birth and thereafter every 2 weeks
until the age of 90 days, when they were weaned. The ewes were then
slaughtered, and their udders examined histologically and the number of
lymphocytic follicles were counted and assessed. Although the calculated
values indicated a correlation between the number of follicles in the
udder and the reduction in the growth rate of the lambs, this was not
statistically significant. Similarly, despite higher counts of lymphoid
follicles in the udders of sero-positive ewes as compared to those that
were sero-negative and the lower ewe productivity indexes in infected
ewes, no statistically significant differences were found in the indexes
of ewes in different follicle categories.
