F. W.
PRIESTLEY
AND
D.
ARTIOLI
257
Association of mastitis with period of lactation
It has been suggested that the early stages of
lactation, constitute the period of greatest suscepti
bility to mastitis in cattle. Our results indicate a
similar finding in buffaloes, though our numbers
were too small to be statistically significant. It
may be briefly stated that at all ages up to 10 years
there was a greater incidence of mastitis during the
first hundred days of lactation than at later stages.
Summarizing the data it was found that of the 479
animals examined during the first hundred days of
lactation 161 per cent were infected, and of the
302 examined during the second hundred days
10.9 per cent were infected.
Milk yields of infected and non-infected buffaloes
It is accepted that cows give a reduced milk yield
when they become infected with mastitis strep
tococci but very few workers have actually demons
trated this with figures. Minett and Martin [1936]
studied by statistical methods the relationship of
milk yield to infection by Br. abortus and Str.
agalactice. In the case of the latter they found
that with Ayrshire cows in one herd the corrected
yield was reduced by 10.8 per cent, with Friesian
cows in two herds the percentage reductions in
corrected yields amounted to 16.5 and 19.5.
We obtained milk yield data for a small number
of buffaloes seven years old. and over. The animals
were examined for mastitis streptococci in October
1944, and again in January 1945. The yields for
October, November and December, 1944, were
tabulated according to the age of the animals and the
stage of lactation at the time of the first test. Only
animals which were negative at both tests or positive
at both tests were included. The results indicated
that the yield, as would be expected, increased as
lactation advanced, at any rate up to 200 days.
TABLE IV
Average milk yield (in lb.) over three months of infected
and non-infected 7-11 years old buffaloes
Buffaloes
Non infected . .
Infected . . .
Period of lactation (in days)
during which the first test was
carried out
1-50
1586
(89)
1151
(21)
51-100
2090
(58)
2059
(15)
101-150
2371
(51)
1197
(11)
151-200
2989
(30)
926
(4)
Figures in brackets represent numbers of animals from
which averages have been calculated.
In Table IV are summarized the results for 7 to
11 years old animals; figures for animals over 11
years old are not included since there were so few
of them available. From the table it may be seen
that among non-infected animals the average total
milk yield in lb. for the three months increased from
1,586 in early lactation to 2,989 later; among
infected animals, at least after they had been in
lactation over 100 days, there was a decrease in
milk yield, which might have been brought about by
progressive induration of the udder. Again, it is
to be noted that at all stages of lactation the infected
animals have given less milk than non-infected
animals. We think that these results, perhaps
inconclusive by themselves, lend support to the
general belief that mastitis infection leads to a
lowering of milk yield.
Vaccination
In September 1944, there was an opportunity to
carry out a controlled vaccination experiment.
While we did not expect vaccination to be beneficial,
the opportunity seemed too good to miss and experi
mental work was therefore commenced. Vaccine
was prepared from five strains of streptococci isolated
from buffaloes in the herd concerned. All strains
gave β-hæmolysis in deep horse-blood agar. Two
strains were long-chained, apparently typical Str.
agalactiæ, while two others formed relatively short
chains, fermenting lactose, trehalose and salicin
but not mannite or sorbite. The fifth strain was
short-chained and fermented all five sugars; this
strain in addition, contrary to the other four, reduced
1 in 5,000 methylene blue in milk. The organisms
were grown for 48 hours on Fildes' agar and then
washed off with sterile saline, the thick suspension
being heated at 56°C. for four hours. Subcultures
made after this time were always sterile. Enough
10 per cent phenol was then added to give a final
concentration of 0.5 per cent and the suspension
was stored in the ice-chest until required. A few
days before use, the suspension was diluted with
0.5 per cent carbol-saline to the required density.
Initial test of the vaccine.
Since a relatively large number of animals had
to be vaccinated, it was essential to be certain that
the vaccine had no marked deleterious effect on
milk yield. Ten buffaloes were therefore inoculated
subcutaneously with 5.0 c.c. suspension, standardized
to No. 2 of the Wellcome Opacity Tubes (approxi-
mately 600×10 6 organisms per c.c). Seven days
later these animals received a second dose of 5.0
c.c. ten times as strong (i.e. twice as dense as tube
10 of the standards). Milk yields were recorded
daily from seven days before the first inoculation
to seven days after the second inoculation.
B 2