Abstract
A. Twenty lactating Holstein cows were divided into
four comparable groups on the basis of lactation and
gestation. Each group consisted of 5 animals. They r
coived a 15.5% digestible protein basal retion. Group I
served as the control, group II recsived a supplement
containing 130 mg. of tyrothricin, group II received a
supplement containing 130 mg. of aureomycin, and group
IV received a supplament containing 0.83 mg. of vitanin
B12 per cow daily for a period of 60 days. All of the
animals had access to pasture during the experimental
period of 60 days. Daily milk production was recorded
for each animal. Milk samples were collected from each
animal prior to the experimental feeding and at intervals
of 15 days. These samples were analysed for butterfat,
total solids, solids-not-fat, protein, casein, titratable
acidity, pH, ash, caleiun, phosphorus, bacterial count
and vitanin B12 content.
No adverse effects were observed during the feeding
of antibiotics. The animals were in good appetite and
showed no evidence of diarrhea.
The milk records showed no difference in production
whether or not the animals received antibicties or vitamin B12. The anount of milk produced daily over that of
the initial period were 41.85, 40.02, 39.72, and 40.04
pounds 4% fat-corrected milk for the control, tyrothricin, aureomycin, and vitanin B12 groups, respectively.
The percentage of butterfat in the milk samples of
the different groups was very similar. The control group
averaged 3.36%, the tyrothricin group averaged 3.54%,
the aureomycin group averaged 3.28% and the vitamin B12
group averaged 3.24. These differences were not significant.
The total solids content of the samples of milk of
the different groups varied from 11.46 to 11.66%, and
the solids-not-fat from 8.16 to 9.25%. The tyrethricin
group had the highest value.
The protein content of the milk for the different
groups varied from 2.69 to 3.26%, and the cassin content
from 1.72 to 2.43%. The tyrothricin group averaged the
highest in protein and in casein contents.
The titratable acidity of the milk of the different groups varied from 0.130 to 0.175%, the averages
being 0.156, 0.158, 0.152, and 0.155% for the control,
tyrothricin, aureomycin, and vitanin B12 groups, respectively. The pH of the milk samples was similar. The
values were 6.61, 6.62, 6.60, and 6.60 for groups I, II,
III, and IV, respectively.
The ash content of the milk for the control group
averaged 0.6913%, the tyrothricin group, 0.7023%, the
aureomycin group, 0.6657%, and the vitamin B12 group,
0.6927%. These differences were not significant. The calcium and the phosphorus content of the milk
samples of the different groups were very similar. Calcium values ranged from 96.85 to 103.60 mg.%, and the
phosphorus values from 101,.65 to 10344 mg
The bacterial count of the milk samples showed no
significant difference anong the groups, the valuss being
9.400, 9,000, 12,200, and 12,700 per o.c. for the control,
tyrothricin, aureonycin, and vitamin B12 groups, respес
tively. The results show that the feeding of antibiotics
or vitanin Bi2 has no effect on the bacterial flora of
the milk. The samples produced normal acid curd on incubation at 35° C, indicating that the antibiotics were
not being secreted into the milk at the level fed.
The vitamin B12 content of the milk samples, assayed
microbiologically, averaged 1.777 mpg. per ml. for the
control group and 1.697 mµg. for the vitamin B12-fed
COWS.
Thus it is concluded that the feeding of aureomycin
or tyrothricin or vitamin B12 supplement at a 1% level
had no effect on the milk production, percentages of
fat, ash, titratable acidity, calcium, phosphorus, and
vitamin B12. The supplementation of tyrothricin at a
level of 1% did increase the total solids, solids-not
fat, protein and casein values of the milk. The vitamin
B12 content of cow's milk was not increased by feeding
vitamin B12 supplement at a 1% level. B. Experiment II involved supplementing the basal
ration with higher levels of vitamin B12 to determine
whether an increase in vitamin B12 value of the mil
would occur. Group I served as the control, groups II,
III, and IV received a 2, 3, or 4% vitamin Bia supplement, respectively, for a period of 15 days. This amounted
to 1.66, 2.49, or 3.32 mg. of vitamin B1z per cow daily.
All other treatments were similar to the previous trial.
The milk production for the different groups showed
no significant difference
Butterfat production was significantly depressed
when the higher levels of vitamin Biz supplement was fed.
The vitamin B12. content of the milk for the different groups was sinilar. The vitanin 22 content varied
from 3.90 to 4.12 mug per ml. of milk. The actual values
being 4.06, 4.10, 3.90 and 4.12 mug per al. for groups
I, II, III, and IV, respectively.
Thus it appears that the vitamin B2 content of
cow's milk can not be increased by feeding as much as
3.32 mg. of vitamin R12 daily. More than 0.03 mg. of vita
min B12 depressed the percentage of fat in the milk.