288
ABSTRACTS
[Vol. XXVI, Part IV,
Studies on the productive value of roughages and concentrates for lactation. J. K.
LOOSLI, R. F. DAVIS and R. G. WARNER (1955). J. Dairy Sci. 38, 797-804.
T HE consistent increase in milk yield when concentrates were used to replace
part of the hay on an equal T. D. N. basis is to evidence that the T. D.N. system
does not accurately evaluate these two feed sources for milk production. This has
been interpreted by some workers as indication that concentrates contain a specific
unidentified factor(s) which stimulates lactation; while others have attributed the
observed increase in milk production to an increase in the estimated net energy
(ENE) intake on rations containing concentrates. To test the validity of the one or
the other of the two postulates above, the present authors undertook reversible type
experiments with 25 lactating cows; the basis of replacement was either equal TDN
or equal ENE. They found that when the replacement was made on the basis of
equal TDN (but more ENE) there was a considerably greater increase in milk pro-
duction than when the replacement was made on the basis of equal ENE (but less
TDN). Thus, cows, on an average, produced 2.5 lb. more FCN per head per day
when 10.2 lb. hay was replaced by 6.8 lb. concentrates containing almost equal TDN
(but more ENE). Replacing hay with concentrates according to the ENE system
resulted, in an average, increase of 0.8 lb. FCN per head per day on the same ENE
intake but less TDN. The significantly greater milk yield from the TDN above the
ENE feeding system, the authors state, shows rather conclusively that Morrison's
ENE values more accurately estimate the comparative productive usefulness of the
energy in the roughages and concentrates studied than do the TDN values. Even
ENE appeared to slightly overrate the value of roughages in comparison to concen-
trates for lactation, but to a much lesser degree than TDN. The data presented,
the authors conclude, disprove the lactation factor theory, which assumes the presence
in concentrates of some specific unidentified factor(s) stimulating lactation.
(B. N. M.).
Beta-propiolactone as virus altering agent for New Castle Disease vaccine. WALTER
N. MACH and ACHIT CHOTISEN, (1955). Poultry Sci. 34, 1010-1013.
T HE authors describe a Newcastle disease (Ranikhet disease) vaccine produced
through chemical alternation of its pathogenecity.
The virus was isolated from a recent clinical case, and propagated in the allantoic
fluid of embryonating chicken eggs. It was then treated with 0.025 per cent beta-
propiolactone and incubated for two hours at 37ºC. The vaccine so produced was
injected intra-muscularly in doses varying from 0.5 ml. to 2 ml. into 43 ten-month
old white Leghorn chickens of a disease-free flock. On the 16th day heart-blood from
the vaccinated birds was collected to determine antibody titres, and all the vaccinated
birds and controls were challenged with 0.2 ml. of virulent virus. Vaccinated birds
did not show any disease symptoms, but 97.4 per cent of the controls got the infec-
tion and 84.6 per cent died. The agglutination inhibition titre in the pre-vaccination
serum was 1:10 while it rose to 1:320 or higher in the post-vaccination samples.
Further trials with this method of preparing a vaccine are considered advisable
as the risk of introducing the infection which accompanies the use of attenuated virus
vaccine is avoided here.
MGIPC—M—31 AR/56—9-3-57—1,000.