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Aureomycin1 Content, Bacterial Development, Starter Activity, and Cheese Quality of Milk From Cows Fed an Aureomycin Supplement2
A U R E O M Y C I N ~ C O N T E N T , B A C T E R I A L DEVELOP~IENT, S T A R T E ] ~ A C T I V I T Y , A N D C H E E ' S E Q U A L I T Y OF M I L K F R O M COWS FED AN AUREOMYCIN SUPPLEMENT 2 W. H. M A R T I N , T. J. CLAYDON, AND E. E. B A R T L E Y
Depart~ent of Dairy H~tsbandry, Kansas Agricultural Experiment Station, Manhattan
I t has been reported by H a q et al. (3) and Rusoff and H a q (6) t h a t the milk f r o m cows fed aureomycin in amounts of 130 rag. daily showed normal bacterial development during holding for 12 hours at 35 ° C. All such milk developed lactic acid and produced a normal acid curd. Presumably, the antibiotics either were not passed into the milk or were present in too low concentrations to affect bacterial development. Similar observations were made b y Loosli and W a r n e r (4), who found no aureomycin in milk of cows fed 700 rag. of the antibiotic daily for 10 days. Also, they f o u n d t h a t feeding 500 rag. per day for 6 days did not affect cheese starter activity in the milk. Bradfield et al. (2) f o u n d little inhibition of starter activity when aureomycin was added at less t h a n 0.25~ p e r milliliter of milk. Olson et al. (5) reported t h a t aureomycin added to pasteurized milk in a concentration of 0.2~ per milliliter had no preservative effect. Some types of bacteria were suppressed but were compensated for b y the growth of other types. A s t u d y on the feeding of aureomycin to d a i r y cows (1) provided an o p p o r t u n i t y to investigate f u r t h e r the possible elimination of the antibiotic into the milk. E x a m i n a t i o n s were made to determine if the milk had an inhibit o r y effect on bacterial development or if it affected cheese m a n u f a c t u r e and quality. Also, the milk was assayed for aureomycin content. METHODS
The conditions of feeding the aureomycin to the cows were described by Bartley et al. (1). Seven cows in Group A fed aureomycin during Period I received no aureomycin during Period I I and again received aureomycin d u r i n g Period I I I . Seven cows in Group B received no aureomycin during Period I, received aureomycin during Period I I , and received no aureomycin d u r i n g Period I I I . Six cows in Group C were not fed aureomycin d u r i n g a n y of the periods and served as controls. The experimental periods were 6 weeks. Lederle's A u r o f a c 2A was fed once a day in the grain in amounts calculated to s u p p l y 32 mg. of aureomycin for each 100 lb. body weight. The rate of feeding was equivalent to an average of 390 rag. per cow daily. Individual milk samples for this s t u d y were obtained during the fifth and sixth week of Period I I and during the second and t h i r d week of Period I I I . Received for publication August 4, 1954. The trademark of Lederle Laboratories Div., American Cyanamid Co., Pearl River, N. Y., for the antibiotic chlortetracyline. Contribution :No. 228, Dept. of Dairy Husbandry, Kansas Agricultural Experiment Station, Manhattan. 47
4~
~V. H. M A R T I N E T AL
Hence, in each period the cows involved were those c u r r e n t l y receiving aureomycin, those that had previously received the antibiotic, and those t h a t had never received aureomycin. Samples were obtained in milk bottles sanitized in the milk p l a n t bottlewasher, but not otherwise sterilized. The milk samples were iced and returned to the laboratory. Samples of milk for bacteriological studies were r e f r i g e r a t e d until making the initial bacterial counts and t h e n subsequently held at room t e m p e r a t u r e (70-80 ° F . ) . The first p l a t i n g was made within 20 hours of the time the samples were taken, and the second and t h i r d platings were made 18 and 24 hours later, respectively. S t a n d a r d Plate Count methods were employed with t r y p t o n e glucose extract agar. General observations were made for rate and t y p e of defect development in the samples. I n s t u d y i n g acid development, samples (140ml.) of milk f r o m each cow were laboratory pasteurized shortly a f t e r collection and' held r e f r i g e r a t e d over night. One per cent active cheese starter was then added to the samples, which were w a r m e d to 88 ° F. and incubated at t h a t t e m p e r a t u r e . Acid development in the milk was determined by t i t r a t i n g 9-ml. portions against 0.1 N N a O H at the s t a r t and a f t e r 4, 6, and 24 hours. I n the cheese studies each trial consisted of two vats of Cheddar cheese; one made f r o m milk of cows that had never received aureomycin and the other f r o m milk of cows c u r r e n t l y receiving the antibiotic. The initial acidity of each lot of milk and the acid in the curd at milling time were compared. The cheeses were held in storage for 3 months, then scored for flavor, body, and texture b y a panel of cheese judges. D u r i n g the f o u r t h week of the second period of the feeding trials, a composite sample of milk f r o m cows previously fed aureomycin and a composite f r o m those c u r r e n t l y receiving aureomycin were submitted to Lederle Laboratories for estimation of antibiotic content. RESULTS
Bacterial d e v e l o p m e n t iJt raw milk. The feeding of aureomycin to cows had no definite effect on the total numbers of bacteria that developed in the r a w milk as shown b y bacterial plate counts. Results f r o m the four trials, involving 216 counts on 72 samples, are summarized in Table 1. I n Trial 1, the average bacterial counts (antilog. of log. average) suggest a slight inhibition in samples f r o m the group of cows that were c u r r e n t l y receiving aureomycin and in the group t h a t had received aureomycin 5 weeks previously. Also, in Trial 4 some inhibiting effect on bacterial growth seemed evident in the milk f r o m the cows fed aureomycin, as indicated by average bacterial counts (antilog. of log. average). However, graphical analyses of the counts on the mill; f r o m individual cows during each of the four trials showed no clear:cut effect due to feeding aureomycin. There was considerable variability in counts f r o m cow to cow, with no a p p a r e n t significant difference in mean counts due to treatments. Also, there was no p a r t i c u l a r association between the initial counts and the 24-hour counts. In Trial l, the second series of counts was made a f t e r 6 hours instead of 18 hours,
EFFECT OF AUREOMYCIN FEEDING ON MILK
49
TABLE 1
Bacte~aldeveIopn~eati~raw milk (70-80°F.)from cowsfed an aureon~ycinsupplement
Period
Trial
Cow group
2
1
A B
2
C A B
3
3
C A B
4
C A B C
Treatment 5th wk. after start of aureomycin feeding 5th wk. after cessation of aureomycin feeding Never fed aureomycin 6th wk. after start of aureomycin feeding 6th wk. after cessation of aureomycin feeding Never fed aureomycin 2nd wk. after cessation of aureomycin feeding 2nd wk. after start of aureomycin feeding Never fed aureomycin 3rd wk. after cessation of aureomycin feeding 3rd wk. after start of aureomycin feeding Never fed aureomymin
Av. bacterial count (antilog. of log av.)/ml, milk ~ Initially After 18 hr. After 24 hr. 3,000
4,500 b
7,455,000
2,727 6,414
8,017 b 16,950 b
9,350,000 13,850,000
1,442
4,286,000
39,590,000
1,480 1,757
3,081,000 2,070,000
34,670,000 27,690,000
3,004
219,500
3,820,000
1,153 1,279
104,800 135,600
2,373,000 2,t47,000
2,454
132,200
1,999,000
2,977 3,909
58,770 184,600
867,500 2,033,000
a Average counts on individual samples from 6 cows, samp]ed once during each trial.. b Counts made 6 hr. after the initial count, instead of 18 hr. after. hence these c o u n t s were lower. A h i g h e r room t e m p e r a t u r e d u r i n g the h o l d i n g p e r i o d p r o b a b l y c o n t r i b u t e d to h i g h c o n n t s i n T r i a l 2 at the 18- a n d 24-hour periods. A c i d developnle~,t. The a v e r a g e increase i n t i t r a t a b l e a c i d i t y i n the s t a r t e r i n o c u l a t e d m i l k f r o m all cows c u r r e n t l y r e c e i v i n g a u r e o m y c i n was 0.626% comp a r e d w i t h 0.610 a n d 0.649%, respectively, i n the m i l k f r o m cows t h a t h a d received a u r e o m y c i n p r e v i o u s l y a n d i n the m i l k f r o m those t h a t h a d received n o a u r e o m y c i n ( T a b l e 2). T h e r e was c o n s i d e r a b l e v a r i a t i o n i n the r a t e of acid d e v e l o p m e n t a n d the final t i t r a t a b l e a c i d i t y of the m i l k f r o m i n d i v i d u a l cows i n all t h r e e groups. Cheese quality. The r e s u l t s on the acid d e v e l o p m e n t d u r i n g cheese m a k i n g a n d the score of the cheese m a d e f r o m f o u r lots of m i l k f r o m cows t h a t h a d received no a u r e o m y c i n a n d f r o m those c u r r e n t l y r e c e i v i n g a u r e o m y c i n are r e c o r d e d i n T a b l e 3. The r a t e of acid d e v e l o p m e n t i n the c u r d was a b o u t the same for m i l k f r o m the two g r o u p s of cows. The a v e r a g e a c i d i t y at m i l l i n g was 0.42% i n the c u r d f r o m m i l k f r o m the cows t h a t h a d received no a u r e o m y c i n a n d 0.44% i n the c u r d f r o m m i l k f r o m the cows r e c e i v i n g a u r e o m y c i n . The a v e r a g e flavor score for the f o u r cheeses m a d e f r o m the m i l k f r o m cows i n the c o n t r o l g r o u p was 38.9 points, the same as the a v e r a g e score for the cheese m a d e f r o m the m i l k f r o m cows r e c e i v i n g a u r e o m y c i n . There was o n l y 0.25 of a p o i n t difference i n the a v e r a g e b o d y a n d t e x t u r e score of all cheese m a d e f r o m the m i l k f r o m the two g r o u p s of cows.
W. H. MARTIN ET AL
50
TABLE 2 ]Effect of feeding cows aureomycin on acid developme~t in pasteurized milk inoculated with 1% starter and incubated at 88°~.
Period
Trial
Cow group
2
1
A B C
2
A B G
3
3
A B C
4
A B C
Average
Av. titratable acidity Treatment
Fresh
Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin
4 hr.
6 hr.
0.17
0.208
0.306
0.84
0.67
0.16
0.24
0.74
0.83
0.67
0.137
0.235
0.341
0.76
0.62
0.173
0.486
0.77
0.87
0.697
0.178
0.487
0.725
0.81
0.642
0.182
0.382
0.805
0.945
0.763
0.172
0.20
0.79
0.619
0.20
0.218
0.80
0.60
0.165
0.22
0.83
0.665
0.191
0.30
0.395
0.722
0.531
0.188
0.34
0.413
0.725
0.537
0.19
0.306
0.391
0.738
0.548
Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin
24hr.
Increase
0.626 0.610 0.649
Aureomycin content of milk. Aureomycin was not detected in the milk from cows previously fed aureomycin or those currently receiving the antibiotic. DISCUSSION
The examinations for bacterial development in the raw milk samples involved only total numbers, with no consideration given to possible selective effects on different bacterial types. However, examination of samples for rates and types of defects (data not shown) that occurred on holding showed the same general quality changes in each group. Presumably, if there was any selective effect on bacterial flora, it was not great enough to influence the types of defects or rates of their development. The differences in plate counts that might suggest an effect due to feeding aureomycin generally are within the usual range of variation that arises from normal differences in flora developing in milk held at room temperature. The differences in counts are of questionable significance in milk quality controi and do not justify the suggestion that aureomycin was eliminated in the milk.
EFFECT
OF AUREOMYCIN
FEEDING
ON MILK
51
TABLE 3 Effect of feeding cows a~reomycbJ on acid development of ~nilT~ d~ring cheese ~aalcing and on the score of the cheese
Titratable acidity Cow
Trial
group
Treatment
Milk
1
C A C A C A C A C A
Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin
0.16 0.15 0.17 0.17 0.18 0.18 0.20 0.19 0.177 0.172
2 3 4 Average
Score (3 too.)
Cheese at Bbdy and milling Flavor texture 0.41 0.35 0.45 0.44 0.44 0.50 0.39 0.47 0.42 0.44
39.0 . 38.5 38.5 40.0 39.5 39.0 38.5 38.0 38.9 38.9
27.5 29.5 29.5 28.0 28.0 29.0 28.0
27.5 28.25 28.50
A p p a r e n t l y , f e e d i n g a u r e o m y c i n to cows d i d n o t h a v e a n y effect on a n l o u n t of t i t r a t a b l e a c i d i t y d e v e l o p e d i n t h e s t a r t e r - i n o c u l a t e d m i l k f r o m these cows. N e i t h e r t h e r a t e n o r the final a m o u n t of a c i d was s i g n i f i c a n t l y d i f f e r e u t f o r t h e t h r e e g r o u p s . I t was possible to m a k e n o r m a l C h e d d a r cheese f r o m t h e m i l k p r o d u c e d b y t h e cows f e d the a n t i b i o t i c . The b e h a v i o r of t h e m i l k d u r i n g t h e cheese m a k i n g process was n o r m a l , a n d t h e cheeses m a d e f r o m t h e two t y p e s of m i l k w e r e a p p r o x i m a t e l y e q u a l in q u a l i t y . The f a c t t h a t no d e t e c t a b l e a m o u n t of a u r e o m y c i n was f o u n d in the m i l k samples previously submitted for analyses supports the results obtained. SUMMARY AND CONCLUSION The m i l k f r o m 20 cows, in t h r e e g r o u p s , was u s e d to d e t e r m i n e the effect of f e e d i n g a u r e o m y c i n on ( a ) b a c t e r i a l d e v e l o p m e n t i n t h e m i l k , ( b ) a m o u n t of a c i d d e v e l o p e d i n s t a r t e r - i n o c u l a t e d nfilk, a n d ( c ) cheese m a n u f a c t u r e a n d q u a l i t y . The r a t e of a u r e o m y c i n f e e d i n g was e q u i v a l e n t to a n a v e r a g e of 390 rag. p e r cow d a i l y . T h e d a t a show t h a t t h e r e were no s i g n i f i c a n t differences i n t o t a l p l a t e c o u n t s on t h e m i l k or i n t h e a m o u n t of a c i d d e v e l o p e d in the m i l k i n o c u l a t e d w i t h s t a r t e r f r o m t h e t h r e e lots of cows. C h e d d a r cheese was m a d e f r o m m i l k p r o d u c e d b y t h e cows f e d t h e a u r e o m y c i n a n d f r o m m i l k p r o d u c e d b y cows t h a t h a d r e c e i v e d no a u r e o m y c i n . The cheeses m a d e f r o m m i l k of b o t h g r o u p s of cows w e r e a b o u t e q u a l in q u a l i t y , a n d t h e r e was no m a r k e d difference i n t h e r a t e of a c i d developm e n t o r t h e a m o u n t of a c i d p r o d u c e d in t h e cheese. No d e t e c t a b l e a m o u n t of a u r e o m y c i n was f o u n d i n t h e m i l k f r o m cows p r e v i o u s l y f e d a u r e o m y c i n a n d those c u r r e n t l y r e c e i v i n g t h e a n t i b i o t i c . ACKNOWLEDGMENT The authors wish to thank Jack I. Northam of the Statistical Laboratory for analyses of the bacterial count data, and William L. Williams, Lederle Laboratories Division, American Cyanamid Co., for the aureomycin asssys of the milk. The Aurofac 2A was obtained through the. courtesy of Leder]e Laboratories.
52
W. H. MARTIN ET AL REFERENCES
(1) ]~ARTLEY, E. E., FOUhrTAINE, F. C., AND ATK]~SON, F. W. Antibiotics in Dairy Cattle Nutrition. II. Effects of Feeding an Aureomycin Product (Aurorae 2A) to Lactating Cows. J. Dairy Sci., 36: 402. 1953. (2) BKADFIELD,A., RESI, L. A., AND JOHNSTONE~ D. B. The Presence of Aureomycin in Milk and Its Effect on Cheese Making and Starter Activity. J. Dairy Sci., 35: 51. 195:~. (3) HAQ, M. O., RUSOFF, L. L., AND GELPI, A. J., JR. Antibiotic Feed and Vitamin B1.- Supplements for Lactating Dairy Cows. Science, 115: 215. 1952. (4) LoosLI, J. K., AND W,~-RNER, R. G. Antibiotics for Dairy Animals. F a r m Research. 1~. Y. State Agr. Expt. Sta., Quart. Bull. 18, 3: 3. 1952. (5) OLSON, J. C., JR., WILLOUGHBY, D. S., THOMAS, E. L., AND MORRIS, It. A. Observations on the Keeping Quality of Pasteurized Milk with and without Added Aureomycin, which Was Obtained from Various Sources and Stored at 45 ° F. J. Dairy Sci., 35: 485. 1952. (6) RUS0VF, L. L., AND HAQ, M. O. Studies on Aureomycin and Vitamin BI~ Supplements for Dairy Cows. II. Effect on Production, Composition, and Vitamin BI.- Content of the Milk. J. Dairy Svi., 37: 677. 1954.
Depart~ent of Dairy H~tsbandry, Kansas Agricultural Experiment Station, Manhattan
I t has been reported by H a q et al. (3) and Rusoff and H a q (6) t h a t the milk f r o m cows fed aureomycin in amounts of 130 rag. daily showed normal bacterial development during holding for 12 hours at 35 ° C. All such milk developed lactic acid and produced a normal acid curd. Presumably, the antibiotics either were not passed into the milk or were present in too low concentrations to affect bacterial development. Similar observations were made b y Loosli and W a r n e r (4), who found no aureomycin in milk of cows fed 700 rag. of the antibiotic daily for 10 days. Also, they f o u n d t h a t feeding 500 rag. per day for 6 days did not affect cheese starter activity in the milk. Bradfield et al. (2) f o u n d little inhibition of starter activity when aureomycin was added at less t h a n 0.25~ p e r milliliter of milk. Olson et al. (5) reported t h a t aureomycin added to pasteurized milk in a concentration of 0.2~ per milliliter had no preservative effect. Some types of bacteria were suppressed but were compensated for b y the growth of other types. A s t u d y on the feeding of aureomycin to d a i r y cows (1) provided an o p p o r t u n i t y to investigate f u r t h e r the possible elimination of the antibiotic into the milk. E x a m i n a t i o n s were made to determine if the milk had an inhibit o r y effect on bacterial development or if it affected cheese m a n u f a c t u r e and quality. Also, the milk was assayed for aureomycin content. METHODS
The conditions of feeding the aureomycin to the cows were described by Bartley et al. (1). Seven cows in Group A fed aureomycin during Period I received no aureomycin during Period I I and again received aureomycin d u r i n g Period I I I . Seven cows in Group B received no aureomycin during Period I, received aureomycin during Period I I , and received no aureomycin d u r i n g Period I I I . Six cows in Group C were not fed aureomycin d u r i n g a n y of the periods and served as controls. The experimental periods were 6 weeks. Lederle's A u r o f a c 2A was fed once a day in the grain in amounts calculated to s u p p l y 32 mg. of aureomycin for each 100 lb. body weight. The rate of feeding was equivalent to an average of 390 rag. per cow daily. Individual milk samples for this s t u d y were obtained during the fifth and sixth week of Period I I and during the second and t h i r d week of Period I I I . Received for publication August 4, 1954. The trademark of Lederle Laboratories Div., American Cyanamid Co., Pearl River, N. Y., for the antibiotic chlortetracyline. Contribution :No. 228, Dept. of Dairy Husbandry, Kansas Agricultural Experiment Station, Manhattan. 47
4~
~V. H. M A R T I N E T AL
Hence, in each period the cows involved were those c u r r e n t l y receiving aureomycin, those that had previously received the antibiotic, and those t h a t had never received aureomycin. Samples were obtained in milk bottles sanitized in the milk p l a n t bottlewasher, but not otherwise sterilized. The milk samples were iced and returned to the laboratory. Samples of milk for bacteriological studies were r e f r i g e r a t e d until making the initial bacterial counts and t h e n subsequently held at room t e m p e r a t u r e (70-80 ° F . ) . The first p l a t i n g was made within 20 hours of the time the samples were taken, and the second and t h i r d platings were made 18 and 24 hours later, respectively. S t a n d a r d Plate Count methods were employed with t r y p t o n e glucose extract agar. General observations were made for rate and t y p e of defect development in the samples. I n s t u d y i n g acid development, samples (140ml.) of milk f r o m each cow were laboratory pasteurized shortly a f t e r collection and' held r e f r i g e r a t e d over night. One per cent active cheese starter was then added to the samples, which were w a r m e d to 88 ° F. and incubated at t h a t t e m p e r a t u r e . Acid development in the milk was determined by t i t r a t i n g 9-ml. portions against 0.1 N N a O H at the s t a r t and a f t e r 4, 6, and 24 hours. I n the cheese studies each trial consisted of two vats of Cheddar cheese; one made f r o m milk of cows that had never received aureomycin and the other f r o m milk of cows c u r r e n t l y receiving the antibiotic. The initial acidity of each lot of milk and the acid in the curd at milling time were compared. The cheeses were held in storage for 3 months, then scored for flavor, body, and texture b y a panel of cheese judges. D u r i n g the f o u r t h week of the second period of the feeding trials, a composite sample of milk f r o m cows previously fed aureomycin and a composite f r o m those c u r r e n t l y receiving aureomycin were submitted to Lederle Laboratories for estimation of antibiotic content. RESULTS
Bacterial d e v e l o p m e n t iJt raw milk. The feeding of aureomycin to cows had no definite effect on the total numbers of bacteria that developed in the r a w milk as shown b y bacterial plate counts. Results f r o m the four trials, involving 216 counts on 72 samples, are summarized in Table 1. I n Trial 1, the average bacterial counts (antilog. of log. average) suggest a slight inhibition in samples f r o m the group of cows that were c u r r e n t l y receiving aureomycin and in the group t h a t had received aureomycin 5 weeks previously. Also, in Trial 4 some inhibiting effect on bacterial growth seemed evident in the milk f r o m the cows fed aureomycin, as indicated by average bacterial counts (antilog. of log. average). However, graphical analyses of the counts on the mill; f r o m individual cows during each of the four trials showed no clear:cut effect due to feeding aureomycin. There was considerable variability in counts f r o m cow to cow, with no a p p a r e n t significant difference in mean counts due to treatments. Also, there was no p a r t i c u l a r association between the initial counts and the 24-hour counts. In Trial l, the second series of counts was made a f t e r 6 hours instead of 18 hours,
EFFECT OF AUREOMYCIN FEEDING ON MILK
49
TABLE 1
Bacte~aldeveIopn~eati~raw milk (70-80°F.)from cowsfed an aureon~ycinsupplement
Period
Trial
Cow group
2
1
A B
2
C A B
3
3
C A B
4
C A B C
Treatment 5th wk. after start of aureomycin feeding 5th wk. after cessation of aureomycin feeding Never fed aureomycin 6th wk. after start of aureomycin feeding 6th wk. after cessation of aureomycin feeding Never fed aureomycin 2nd wk. after cessation of aureomycin feeding 2nd wk. after start of aureomycin feeding Never fed aureomycin 3rd wk. after cessation of aureomycin feeding 3rd wk. after start of aureomycin feeding Never fed aureomymin
Av. bacterial count (antilog. of log av.)/ml, milk ~ Initially After 18 hr. After 24 hr. 3,000
4,500 b
7,455,000
2,727 6,414
8,017 b 16,950 b
9,350,000 13,850,000
1,442
4,286,000
39,590,000
1,480 1,757
3,081,000 2,070,000
34,670,000 27,690,000
3,004
219,500
3,820,000
1,153 1,279
104,800 135,600
2,373,000 2,t47,000
2,454
132,200
1,999,000
2,977 3,909
58,770 184,600
867,500 2,033,000
a Average counts on individual samples from 6 cows, samp]ed once during each trial.. b Counts made 6 hr. after the initial count, instead of 18 hr. after. hence these c o u n t s were lower. A h i g h e r room t e m p e r a t u r e d u r i n g the h o l d i n g p e r i o d p r o b a b l y c o n t r i b u t e d to h i g h c o n n t s i n T r i a l 2 at the 18- a n d 24-hour periods. A c i d developnle~,t. The a v e r a g e increase i n t i t r a t a b l e a c i d i t y i n the s t a r t e r i n o c u l a t e d m i l k f r o m all cows c u r r e n t l y r e c e i v i n g a u r e o m y c i n was 0.626% comp a r e d w i t h 0.610 a n d 0.649%, respectively, i n the m i l k f r o m cows t h a t h a d received a u r e o m y c i n p r e v i o u s l y a n d i n the m i l k f r o m those t h a t h a d received n o a u r e o m y c i n ( T a b l e 2). T h e r e was c o n s i d e r a b l e v a r i a t i o n i n the r a t e of acid d e v e l o p m e n t a n d the final t i t r a t a b l e a c i d i t y of the m i l k f r o m i n d i v i d u a l cows i n all t h r e e groups. Cheese quality. The r e s u l t s on the acid d e v e l o p m e n t d u r i n g cheese m a k i n g a n d the score of the cheese m a d e f r o m f o u r lots of m i l k f r o m cows t h a t h a d received no a u r e o m y c i n a n d f r o m those c u r r e n t l y r e c e i v i n g a u r e o m y c i n are r e c o r d e d i n T a b l e 3. The r a t e of acid d e v e l o p m e n t i n the c u r d was a b o u t the same for m i l k f r o m the two g r o u p s of cows. The a v e r a g e a c i d i t y at m i l l i n g was 0.42% i n the c u r d f r o m m i l k f r o m the cows t h a t h a d received no a u r e o m y c i n a n d 0.44% i n the c u r d f r o m m i l k f r o m the cows r e c e i v i n g a u r e o m y c i n . The a v e r a g e flavor score for the f o u r cheeses m a d e f r o m the m i l k f r o m cows i n the c o n t r o l g r o u p was 38.9 points, the same as the a v e r a g e score for the cheese m a d e f r o m the m i l k f r o m cows r e c e i v i n g a u r e o m y c i n . There was o n l y 0.25 of a p o i n t difference i n the a v e r a g e b o d y a n d t e x t u r e score of all cheese m a d e f r o m the m i l k f r o m the two g r o u p s of cows.
W. H. MARTIN ET AL
50
TABLE 2 ]Effect of feeding cows aureomycin on acid developme~t in pasteurized milk inoculated with 1% starter and incubated at 88°~.
Period
Trial
Cow group
2
1
A B C
2
A B G
3
3
A B C
4
A B C
Average
Av. titratable acidity Treatment
Fresh
Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin
4 hr.
6 hr.
0.17
0.208
0.306
0.84
0.67
0.16
0.24
0.74
0.83
0.67
0.137
0.235
0.341
0.76
0.62
0.173
0.486
0.77
0.87
0.697
0.178
0.487
0.725
0.81
0.642
0.182
0.382
0.805
0.945
0.763
0.172
0.20
0.79
0.619
0.20
0.218
0.80
0.60
0.165
0.22
0.83
0.665
0.191
0.30
0.395
0.722
0.531
0.188
0.34
0.413
0.725
0.537
0.19
0.306
0.391
0.738
0.548
Currently receiving aureomycin Previously receiving aureomycin Never received aureomycin
24hr.
Increase
0.626 0.610 0.649
Aureomycin content of milk. Aureomycin was not detected in the milk from cows previously fed aureomycin or those currently receiving the antibiotic. DISCUSSION
The examinations for bacterial development in the raw milk samples involved only total numbers, with no consideration given to possible selective effects on different bacterial types. However, examination of samples for rates and types of defects (data not shown) that occurred on holding showed the same general quality changes in each group. Presumably, if there was any selective effect on bacterial flora, it was not great enough to influence the types of defects or rates of their development. The differences in plate counts that might suggest an effect due to feeding aureomycin generally are within the usual range of variation that arises from normal differences in flora developing in milk held at room temperature. The differences in counts are of questionable significance in milk quality controi and do not justify the suggestion that aureomycin was eliminated in the milk.
EFFECT
OF AUREOMYCIN
FEEDING
ON MILK
51
TABLE 3 Effect of feeding cows a~reomycbJ on acid development of ~nilT~ d~ring cheese ~aalcing and on the score of the cheese
Titratable acidity Cow
Trial
group
Treatment
Milk
1
C A C A C A C A C A
Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin Never received aureomycin Currently receiving aureomycin
0.16 0.15 0.17 0.17 0.18 0.18 0.20 0.19 0.177 0.172
2 3 4 Average
Score (3 too.)
Cheese at Bbdy and milling Flavor texture 0.41 0.35 0.45 0.44 0.44 0.50 0.39 0.47 0.42 0.44
39.0 . 38.5 38.5 40.0 39.5 39.0 38.5 38.0 38.9 38.9
27.5 29.5 29.5 28.0 28.0 29.0 28.0
27.5 28.25 28.50
A p p a r e n t l y , f e e d i n g a u r e o m y c i n to cows d i d n o t h a v e a n y effect on a n l o u n t of t i t r a t a b l e a c i d i t y d e v e l o p e d i n t h e s t a r t e r - i n o c u l a t e d m i l k f r o m these cows. N e i t h e r t h e r a t e n o r the final a m o u n t of a c i d was s i g n i f i c a n t l y d i f f e r e u t f o r t h e t h r e e g r o u p s . I t was possible to m a k e n o r m a l C h e d d a r cheese f r o m t h e m i l k p r o d u c e d b y t h e cows f e d the a n t i b i o t i c . The b e h a v i o r of t h e m i l k d u r i n g t h e cheese m a k i n g process was n o r m a l , a n d t h e cheeses m a d e f r o m t h e two t y p e s of m i l k w e r e a p p r o x i m a t e l y e q u a l in q u a l i t y . The f a c t t h a t no d e t e c t a b l e a m o u n t of a u r e o m y c i n was f o u n d in the m i l k samples previously submitted for analyses supports the results obtained. SUMMARY AND CONCLUSION The m i l k f r o m 20 cows, in t h r e e g r o u p s , was u s e d to d e t e r m i n e the effect of f e e d i n g a u r e o m y c i n on ( a ) b a c t e r i a l d e v e l o p m e n t i n t h e m i l k , ( b ) a m o u n t of a c i d d e v e l o p e d i n s t a r t e r - i n o c u l a t e d nfilk, a n d ( c ) cheese m a n u f a c t u r e a n d q u a l i t y . The r a t e of a u r e o m y c i n f e e d i n g was e q u i v a l e n t to a n a v e r a g e of 390 rag. p e r cow d a i l y . T h e d a t a show t h a t t h e r e were no s i g n i f i c a n t differences i n t o t a l p l a t e c o u n t s on t h e m i l k or i n t h e a m o u n t of a c i d d e v e l o p e d in the m i l k i n o c u l a t e d w i t h s t a r t e r f r o m t h e t h r e e lots of cows. C h e d d a r cheese was m a d e f r o m m i l k p r o d u c e d b y t h e cows f e d t h e a u r e o m y c i n a n d f r o m m i l k p r o d u c e d b y cows t h a t h a d r e c e i v e d no a u r e o m y c i n . The cheeses m a d e f r o m m i l k of b o t h g r o u p s of cows w e r e a b o u t e q u a l in q u a l i t y , a n d t h e r e was no m a r k e d difference i n t h e r a t e of a c i d developm e n t o r t h e a m o u n t of a c i d p r o d u c e d in t h e cheese. No d e t e c t a b l e a m o u n t of a u r e o m y c i n was f o u n d i n t h e m i l k f r o m cows p r e v i o u s l y f e d a u r e o m y c i n a n d those c u r r e n t l y r e c e i v i n g t h e a n t i b i o t i c . ACKNOWLEDGMENT The authors wish to thank Jack I. Northam of the Statistical Laboratory for analyses of the bacterial count data, and William L. Williams, Lederle Laboratories Division, American Cyanamid Co., for the aureomycin asssys of the milk. The Aurofac 2A was obtained through the. courtesy of Leder]e Laboratories.
52
W. H. MARTIN ET AL REFERENCES
(1) ]~ARTLEY, E. E., FOUhrTAINE, F. C., AND ATK]~SON, F. W. Antibiotics in Dairy Cattle Nutrition. II. Effects of Feeding an Aureomycin Product (Aurorae 2A) to Lactating Cows. J. Dairy Sci., 36: 402. 1953. (2) BKADFIELD,A., RESI, L. A., AND JOHNSTONE~ D. B. The Presence of Aureomycin in Milk and Its Effect on Cheese Making and Starter Activity. J. Dairy Sci., 35: 51. 195:~. (3) HAQ, M. O., RUSOFF, L. L., AND GELPI, A. J., JR. Antibiotic Feed and Vitamin B1.- Supplements for Lactating Dairy Cows. Science, 115: 215. 1952. (4) LoosLI, J. K., AND W,~-RNER, R. G. Antibiotics for Dairy Animals. F a r m Research. 1~. Y. State Agr. Expt. Sta., Quart. Bull. 18, 3: 3. 1952. (5) OLSON, J. C., JR., WILLOUGHBY, D. S., THOMAS, E. L., AND MORRIS, It. A. Observations on the Keeping Quality of Pasteurized Milk with and without Added Aureomycin, which Was Obtained from Various Sources and Stored at 45 ° F. J. Dairy Sci., 35: 485. 1952. (6) RUS0VF, L. L., AND HAQ, M. O. Studies on Aureomycin and Vitamin BI~ Supplements for Dairy Cows. II. Effect on Production, Composition, and Vitamin BI.- Content of the Milk. J. Dairy Svi., 37: 677. 1954.