- Email: [email protected]
Studies of the Fungistatic Activity of Antifungal Compounds in Mash and Pelleted Feeds1
Studies of the Fungistatic Activity of Antifungal Compounds in Mash and Pelleted Feeds1 N. PASTER2 and I. BARTOV 3 Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel A. PERELMAN Agrozan Co., 14 Renanim St., Ramat Gan, Israel (Received for publication December 13, 1984)
1985 Poultry Science 64:1673-1677 INTRODUCTION Fungi growing o n grains and feeds can cause severe damage and result in quality r e d u c t i o n and e c o n o m i c losses. T h e ability of storage fungi, especially species in t h e genera Aspergillus and Penicillium, to p r o d u c e m y c o t o x i n s requires careful consideration of fungal spoilage, especially as m y c o t o x i c o s i s has been recognized t h r o u g h o u t t h e world as a major p r o b l e m in t h e animal i n d u s t r y (Mirocha and Christensen, 1 9 7 4 ) . Pelleting p o u l t r y feed can partially eradicate t h e feed microflora and reduced bacterial and mold counts ( S t o t t et al, 1 9 7 5 ; T a b i b et ai, 1 9 8 4 ) . However, although t h e n u m b e r of microorganisms is m a r k e d l y reduced during this process, t h e pellets remain susceptible t o
1
Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 1245-E, 1984 Series. 2 Department of Stored Products. 3 Department of Poultry Science. 4 A mixture of 25% ammonium propionate, 25% propionic acid, and 50% inert materials. Produced by Agrozan Co., Ltd., Israel.
reinfestation t h a t m a y b e delayed b y t h e addition of fungistats t o t h e pelleted feed (Tabib etal, 1984). A large n u m b e r of generally regarded as safe ( G R A S ) materials have been tested for their ability t o inhibit fungal growth in feedstuffs. Short-chain fatty acids and their salts w e r e m o s t efficient (Christensen, 1 9 7 3 ; Sauer and Burroughs, 1 9 7 4 ; Paster, 1 9 7 9 ) , and of these, p r o p i o n i c acid is t h e m o s t c o m m o n l y used (Christensen and Sauer, 1 9 8 2 ) . However, p r o p i o n i c acid is corrosive to m e t a l bins and requires care in handling. Efforts have b e e n m a d e t o f o r m u l a t e new fungistats containing p r o p i o n i c acid t h a t are less corrosive b u t as efficient as t h e acid. A g r o u p of such materials are those in which p r o p i o n i c acid is absorbed a l o n e , or in c o m b i n a t i o n w i t h s o m e o t h e r acids, o n an inert carrier. O n e such material is MoldX, w h i c h c o n t a i n s four organic acids ( p r o p i o n i c , acetic, sorbic, and benzoic) distributed o n a finely divided calcium silicate carrier ( D i x o n and H a m i l t o n , 1 9 8 1 ) . Agrosil ( A G ) 4 is a new fungistat based o n p r o p i o n i c acid recently i n t r o d u c e d in Israel. This material (given at .6%) was as effective as propionic and sorbic acids ( b o t h at .3%) in
1673
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
ABSTRACT The effect of calcium propionate (CP) and Agrosil (AG) as mold inhibitors in wetted mash and pelleted feed was studied using both commercial cattle and poultry rations. Number of fungal colonies isolated after pelleting was markedly reduced; however, wetting the pellets accelerated the build-up of inoculum and resulted in spoilage. The addition of CP (.3%) to the cattle ration before pelleting prevented mold proliferation during one month of storage while the number of fungal colonies counted in pellets treated with AG (.15%) markedly increased over that period. However, AG had a longer fungistatic effect than CP in preserving the mash diet. Both materials, applied at .2%, were ineffective in preserving wet pelleted poultry feed. After 17 days of storage, feed treated with either of the agents was visibly moldy. In all cases, an increase in mold population was concomitant with elevated carbon dioxide concentrations, which indicated the sensitivity of this parameter for measuring fungal activity. Fat content of the diets remained unchanged during the storage period in spite of increased fungal activity. (Key words: mold inhibitors, pelleting, mash, mold count carbon dioxide production)
1674
PASTER ET AL.
preventing the decrease in fat and the increase in moisture of diets containing moldy corn and in affecting performance of chicks (Bartov, 1985). However, the fungistatic properties of AG have not been studied previously. The purpose of the present investigation was to evaluate AG as a mold inhibitor in mash and pelleted feed. MATERIALS AND METHODS
RESULTS
Experiment 1. The number of visible colonies detected in pellets after 6 days of storage was about 10 times less than that recorded in the mash (Table 1). However, wetting the pellets resulted in an increase in the number of visible colonies after 6 days storage, and after an additional 24 days, a further increase was observed. Calcium propionate prevented mold proliferation in the wet pellets, and the mold count in this feed did not markedly increase even after 30 days of storage. Agrosil was less effective in preventing an increase in mold in the wet pellets, and the number of colonies counted in that feed after 30 days of storage
TABLE 1. Effect of calcium propionate (CP) and Agrosil (AG) on changes in mold counts, fat, and moisture content of wetted mash and pelleted cattle feed during storage (Experiment 1) Storage period 30 days
6 days Type of feed
Additional water
Antifungal compound 1
Mold count
Dietary fat
(colonies/ g feed) Mash Pellet Mash Pellet Mash Pellet Mash Pellet 1
— -
+ + + + + +
— -
CP CP AG AG
1170 110 1775 25 3 1030 170 820 200
Moisture content
Dietary fat
(colonies/ g feed)
V'O)
2.6 2.9 1.9 2.4 2.0 2.5 2.4 2.6
Mold count
13.7 12.8 17.5 16.0 18.3 16.4 16.4 16.1
1,360 400 10,000 4,500 10,000 200 5,600 4,600
Moisture content \h>)
3.3 3.3 1.8 2.8 2.1 2.9 2.5 2.8
The CP and AG were added at .3 and .15%, respectively.
*'Significantly (P<.01) different from the corresponding value observed after 6 days of storage.
14.2 13.7 19.3** 16.1 19.2** 17.0 17.0 16.2
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
Diet and Experimental Procedure. The first experiment was conducted with a commercial cattle feed containing 16% crude protein and with metabolizable energy of 2893 kcal/kg. The diet used in the second experiment was a commercial chick starter containing 18.2% crude protein and 4.5% crude fat with 3001 kcal/kg metabolizable energy. Moisture content of the feeds (mash or pellets) was raised to 16% by the addition of water in a vertical mixer tumbling for approximately 2 hr. In the first experiment, feeds (mash or pellets) were treated with calcium propionate (CP) .3% or AG .15%; in the second experiment each material was applied at .2% concentration. The fungistats were added prior to the pelleting process; after mixing the fungistat with the feed, each treatment was divided into three plastic bins of 15 kg each. The bins were closed (not hermetically) and kept at a temperature ranging from 23 to 25 C.
Examination of Feed Condition. Moisture in the diet was determined after drying in a forced air oven (105) for 18 hr. Fat content was determined gravimetrically after extraction of the dried sample with a mixture of chloroform and methanol (2:1, v/v). Total counts of fungal colonies were carried out using the method described previously (Paster, 1979). Determination of Carbon Dioxide. Carbon Dioxide in the bins was measured with the aid of an Orsat apparatus to which a hollow bar was connected. The bar was inserted separately into the bottom of each bin and air samples were withdrawn directly into the Orsat using a hand pump.
ANTIFUNGAL COMPOUNDS IN FEEDS
X 10 4 , 5.7 X 10 4 , and 15 X 10 4 , respectively, and the pellets of all treatments were caked and visibly molded. The results of C 0 2 measurements (Figure 3) showed a marked increase from the 10th day, reaching 12.5, 14, and 14.5% at 17 days for the CP-treated, AGtreated, and untreated feeds respectively. Neither moisture nor fat level were markedly affected in the various diets under the experimental storage conditions (data not detailed for brevity).
A — 6 CONTROL (MEAL) CONTROL (PELLETS)
18 1 -
O—0 MEAL* Co* PROPIONATE
16
-
14
—
12
"
• - - •
PELLETS'Ca* PROPIONATE
D—O
MEAL* AGROSIL
m--m
PELLETS* AGROSIL
•
,- s —
n
y y
Calcium
/ / p /// /
10
1675
8 6
"
4
;/ 0
4
g--j=r^_^.
1__ 8
12
16
20 TIME
-*?=,^^ 24
28
, , . ,
32
36
40
44
(days)
FIG. 1. Carbon dioxide production during storage in wetted mash and pellets treated with calcium propionate and Agrosil. Each is the mean of three replicates (Experiment 1).
was almost identical to that of the control. The number of colonies counted in untreated wet mash as well as in that treated with CP rose during 24 days of storage from 1,775 and 1,030 colonies/g feed, respectively, to 10,000 colonies/g of feed (Table 1). Moisture content in these two diets was also significantly increased during that period. Agrosil added to wet mash inhibited mold proliferation, and the number of colonies in this feed after one month of storage was 5,600/g feed. Fat contents in each treatment, was not markedly changed during the storage period. The levels of carbon dioxide ( C 0 2 ) measured are given in Figure 1. The data show that the increase in CO2 started in the untreated mash and in that treated with CP after 5 days of storage, whereas in the AG-treated mash it started after 19 days. In the pellets, an increase in CO2 was recorded in the untreated and the AG-treated feed after 29 days of storage, while in the CP-treated pellets CO2 started to accumulate after 36 days. Experiment 2. Increases in mold counts were recorded after 10 days of storage in the untreated, CP-treated, and AG-treated pellets (Figure 2). Numbers of colonies counted at that time were 2,200, 2,000, and 1,500/g feed, respectively, as compared with 1,500, 1,100, and 1,000 colonies/g feed at the beginning of the experiment. After 17 days of storage the numbers of colonies (per gram feed) were 90
Carbon dioxide has been used by several workers as a criterion of fungal activity. Inter alia it served as a parameter to evaluate mold inhibitors in silage (Daniel et al, 1970) and in studying the efficiency of fungistats in poultry feed (Paster, 1979). Recently, Dixon and Hamilton (1981) evaluated some organic acids as mold inhibitors by measuring CO2 production from feed and its ingredients. They pointed out a possible weakness of this method
Log
Scale
CONTROL
10001—
Co* PROPIONATE O-O
500 ~
*
AGROSIL Calcium
•o 0)
m O CO
O O
TIME
(days)
FIG. 2. Effect of calcium propionate and Agrosil on mold counts in wetted pellets during storage. Each is the mean of three replicates (Experiment 2).
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
A
DISCUSSION
/
2
1676
PASTER ET AL.
1 0
14
1
-
~~
'J 5?
12 -
O
10 -
« O
4-
• — •
CONTROL
• — •
Co* PROPIONATE
O—O
AGROSIL
* Calcium
^ ^ ^ 0 /
^Wj^^^-^-—i " i 1 1 1 I 1 I 1 I 1 2 4 6 8 10 12 14 16 TIME
(days)
FIG. 3. Carbon dioxide production during storage in wetted pellets treated with calcium propionate and Agrosil. Each is the mean of three replicates (Experiment 2).
— it does not discriminate between CO2 production by fungi and C 0 2 produced by bacteria and yeasts — yet noted this method seemed desirable from many aspects. The increase in CQ~ served also in our studies as a parameter for fungal activity and the accumulation of the gas was concomitant with the increase in mold counts, again indicating the sensitivity of this parameter. Effect of pelleting on the reduction of bacteria in feed has been reported previously (Stott et al, 1975). The pelleting process can also markedly reduce the mold count, as reported recently by Tabib et al. (1984), who found that pelleting reduced the mold counts by a factor of approximately 100 to 10,000, depending upon the sample. Similar data were obtained in our studies, although reduction was less. However, in both of our experiments fungi were not eradicated, and wetting the pellets accelerated mold proliferation and resulted in spoilage of the feed, which appeared caked and moldy. It seems, therefore, that when there is a risk of feed being exposed to high humidity (which is the situation in this country), the addition of fungistats to the pellets is of importance. Moreover, the heat treatment destroys the natural microflora, thus exposing the feed to reinfestation by the fungi common in silos or
ACKNOWLEDGMENT We thank Mazal Menasherov for technical assistance. REFERENCES Bartov, I., 1985. Comparative effects of antifungal compounds on the nutritional value of diets containing moldy corn for broiler chicks. Poultry Sci. 64:1236-1238. Bartov, I., N. Paster, and N. Lisker, 1982. The nutritional value of moldy grains for broiler chicks. Poultry Sci. 61:2247-2254.
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
2-
// / J/ /
the farm environment. The addition of fungistats to the pellets may prevent or limit this phenomenon. Calcium propionate prevented fungal activity in the wetted pellets in the first experiment, while such an effect was not observed in the second experiment. This discrepency might be due to the different concentration of CP used (.3 vs .2% in Experiments 1 and 2, respectively). The possibility that the type of the diets used in the two experiments also affected the efficiency of CP can not be ruled out. The diet for chicks, used in Experiment 2, had a higher nutritional value. Such a diet was found to be, under certain climatic conditions, more sensitive to fungal spoilage (unpublished data). Agrosil was less effective than CP in preventing fungal activity in wet pellets in both experiments. However, it was more effective than CP when the diet was in mash form. It seems, therefore, that the pelleting process depressed the antifungal properties of AG, presumably due to the effect of the steam treatment on volatile propionic acid. Although amounts of C 0 2 and mold counts were high at the end of each experiment, no reduction in fat content was noticed. These data seem to be in disagreement with Bartov et al. (1982) who observed that fungal activity in diets is followed by a marked decrease in fat content. However, it should be emphasized that the mentioned phenomenon was observed when grains that were heavily infested with fungi were included in the diet. It seems therefore, that CO2 accumulation and direct fungal counts can serve as early parameters for identification of fungal activity, while a decrease in fat content could be detected in latter stages. As these parameters have not yet been compared in one experiment this assumption needs further clarification.
ANTIFUNGAL COMPOUNDS IN FEEDS Christensen, C. M., 1973. Tests with propionic and acetic acids as grain preservatives. Feedstuffs 45:37. Christensen, C. M., and D. B. Sauer, 1982. Microflora. Pages 219—238 in Storage of Cereal Grains and their Products. C. M. Christensen, ed. Am. Assoc. Cereal Chem., St. Paul, MN. Daniel, P., H. Horring, F. Weise, and E. Zimmer, 1970. Wirking von Propionsause bei der Grunfutter — Silierung. Wirtschaftseigene Futter 3:239—249. Dixon, R. C , and P. B. Hamilton, 1981. Evaluation of some organic acids as mold inhibitors by measuring CO 2 production from feed and ingredients. Poultry Sci. 60:2182-2188. Mirocha, C. J., and C. M. Christensen, 1974. Fungus metabolites toxic to animals. Annu. Rev. Phy-
1677
topathol. 12:303-330. Paster, N, 1979. A commercial scale study of the efficiency of propionic acid and calcium propionate as fungistats in poultry feed. Poultry Sci. 58:572-576. Sauer, D. B., and R. Burroughs, 1974. Efficiency of various chemicals as grain mould inhibitors. Trans. Am. Soc. Agric. Eng. 17:557-559. Stott, J. A., J. E. Hodgeson, and J. C. Chaney, 1975. Incidence of Salmonellae in animal feed and the effect of pelleting on content of Enterobacteriaceae J. Appl. Bacteriol. 39:41—46. Tabib, Z., F. T. Jones, and P. B. Hamilton, 1984. Effect of pelleting of poultry feed on the activity of molds and mold inhibitors. Poultry Sci. 63:70-75. Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
1985 Poultry Science 64:1673-1677 INTRODUCTION Fungi growing o n grains and feeds can cause severe damage and result in quality r e d u c t i o n and e c o n o m i c losses. T h e ability of storage fungi, especially species in t h e genera Aspergillus and Penicillium, to p r o d u c e m y c o t o x i n s requires careful consideration of fungal spoilage, especially as m y c o t o x i c o s i s has been recognized t h r o u g h o u t t h e world as a major p r o b l e m in t h e animal i n d u s t r y (Mirocha and Christensen, 1 9 7 4 ) . Pelleting p o u l t r y feed can partially eradicate t h e feed microflora and reduced bacterial and mold counts ( S t o t t et al, 1 9 7 5 ; T a b i b et ai, 1 9 8 4 ) . However, although t h e n u m b e r of microorganisms is m a r k e d l y reduced during this process, t h e pellets remain susceptible t o
1
Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 1245-E, 1984 Series. 2 Department of Stored Products. 3 Department of Poultry Science. 4 A mixture of 25% ammonium propionate, 25% propionic acid, and 50% inert materials. Produced by Agrozan Co., Ltd., Israel.
reinfestation t h a t m a y b e delayed b y t h e addition of fungistats t o t h e pelleted feed (Tabib etal, 1984). A large n u m b e r of generally regarded as safe ( G R A S ) materials have been tested for their ability t o inhibit fungal growth in feedstuffs. Short-chain fatty acids and their salts w e r e m o s t efficient (Christensen, 1 9 7 3 ; Sauer and Burroughs, 1 9 7 4 ; Paster, 1 9 7 9 ) , and of these, p r o p i o n i c acid is t h e m o s t c o m m o n l y used (Christensen and Sauer, 1 9 8 2 ) . However, p r o p i o n i c acid is corrosive to m e t a l bins and requires care in handling. Efforts have b e e n m a d e t o f o r m u l a t e new fungistats containing p r o p i o n i c acid t h a t are less corrosive b u t as efficient as t h e acid. A g r o u p of such materials are those in which p r o p i o n i c acid is absorbed a l o n e , or in c o m b i n a t i o n w i t h s o m e o t h e r acids, o n an inert carrier. O n e such material is MoldX, w h i c h c o n t a i n s four organic acids ( p r o p i o n i c , acetic, sorbic, and benzoic) distributed o n a finely divided calcium silicate carrier ( D i x o n and H a m i l t o n , 1 9 8 1 ) . Agrosil ( A G ) 4 is a new fungistat based o n p r o p i o n i c acid recently i n t r o d u c e d in Israel. This material (given at .6%) was as effective as propionic and sorbic acids ( b o t h at .3%) in
1673
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
ABSTRACT The effect of calcium propionate (CP) and Agrosil (AG) as mold inhibitors in wetted mash and pelleted feed was studied using both commercial cattle and poultry rations. Number of fungal colonies isolated after pelleting was markedly reduced; however, wetting the pellets accelerated the build-up of inoculum and resulted in spoilage. The addition of CP (.3%) to the cattle ration before pelleting prevented mold proliferation during one month of storage while the number of fungal colonies counted in pellets treated with AG (.15%) markedly increased over that period. However, AG had a longer fungistatic effect than CP in preserving the mash diet. Both materials, applied at .2%, were ineffective in preserving wet pelleted poultry feed. After 17 days of storage, feed treated with either of the agents was visibly moldy. In all cases, an increase in mold population was concomitant with elevated carbon dioxide concentrations, which indicated the sensitivity of this parameter for measuring fungal activity. Fat content of the diets remained unchanged during the storage period in spite of increased fungal activity. (Key words: mold inhibitors, pelleting, mash, mold count carbon dioxide production)
1674
PASTER ET AL.
preventing the decrease in fat and the increase in moisture of diets containing moldy corn and in affecting performance of chicks (Bartov, 1985). However, the fungistatic properties of AG have not been studied previously. The purpose of the present investigation was to evaluate AG as a mold inhibitor in mash and pelleted feed. MATERIALS AND METHODS
RESULTS
Experiment 1. The number of visible colonies detected in pellets after 6 days of storage was about 10 times less than that recorded in the mash (Table 1). However, wetting the pellets resulted in an increase in the number of visible colonies after 6 days storage, and after an additional 24 days, a further increase was observed. Calcium propionate prevented mold proliferation in the wet pellets, and the mold count in this feed did not markedly increase even after 30 days of storage. Agrosil was less effective in preventing an increase in mold in the wet pellets, and the number of colonies counted in that feed after 30 days of storage
TABLE 1. Effect of calcium propionate (CP) and Agrosil (AG) on changes in mold counts, fat, and moisture content of wetted mash and pelleted cattle feed during storage (Experiment 1) Storage period 30 days
6 days Type of feed
Additional water
Antifungal compound 1
Mold count
Dietary fat
(colonies/ g feed) Mash Pellet Mash Pellet Mash Pellet Mash Pellet 1
— -
+ + + + + +
— -
CP CP AG AG
1170 110 1775 25 3 1030 170 820 200
Moisture content
Dietary fat
(colonies/ g feed)
V'O)
2.6 2.9 1.9 2.4 2.0 2.5 2.4 2.6
Mold count
13.7 12.8 17.5 16.0 18.3 16.4 16.4 16.1
1,360 400 10,000 4,500 10,000 200 5,600 4,600
Moisture content \h>)
3.3 3.3 1.8 2.8 2.1 2.9 2.5 2.8
The CP and AG were added at .3 and .15%, respectively.
*'Significantly (P<.01) different from the corresponding value observed after 6 days of storage.
14.2 13.7 19.3** 16.1 19.2** 17.0 17.0 16.2
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
Diet and Experimental Procedure. The first experiment was conducted with a commercial cattle feed containing 16% crude protein and with metabolizable energy of 2893 kcal/kg. The diet used in the second experiment was a commercial chick starter containing 18.2% crude protein and 4.5% crude fat with 3001 kcal/kg metabolizable energy. Moisture content of the feeds (mash or pellets) was raised to 16% by the addition of water in a vertical mixer tumbling for approximately 2 hr. In the first experiment, feeds (mash or pellets) were treated with calcium propionate (CP) .3% or AG .15%; in the second experiment each material was applied at .2% concentration. The fungistats were added prior to the pelleting process; after mixing the fungistat with the feed, each treatment was divided into three plastic bins of 15 kg each. The bins were closed (not hermetically) and kept at a temperature ranging from 23 to 25 C.
Examination of Feed Condition. Moisture in the diet was determined after drying in a forced air oven (105) for 18 hr. Fat content was determined gravimetrically after extraction of the dried sample with a mixture of chloroform and methanol (2:1, v/v). Total counts of fungal colonies were carried out using the method described previously (Paster, 1979). Determination of Carbon Dioxide. Carbon Dioxide in the bins was measured with the aid of an Orsat apparatus to which a hollow bar was connected. The bar was inserted separately into the bottom of each bin and air samples were withdrawn directly into the Orsat using a hand pump.
ANTIFUNGAL COMPOUNDS IN FEEDS
X 10 4 , 5.7 X 10 4 , and 15 X 10 4 , respectively, and the pellets of all treatments were caked and visibly molded. The results of C 0 2 measurements (Figure 3) showed a marked increase from the 10th day, reaching 12.5, 14, and 14.5% at 17 days for the CP-treated, AGtreated, and untreated feeds respectively. Neither moisture nor fat level were markedly affected in the various diets under the experimental storage conditions (data not detailed for brevity).
A — 6 CONTROL (MEAL) CONTROL (PELLETS)
18 1 -
O—0 MEAL* Co* PROPIONATE
16
-
14
—
12
"
• - - •
PELLETS'Ca* PROPIONATE
D—O
MEAL* AGROSIL
m--m
PELLETS* AGROSIL
•
,- s —
n
y y
Calcium
/ / p /// /
10
1675
8 6
"
4
;/ 0
4
g--j=r^_^.
1__ 8
12
16
20 TIME
-*?=,^^ 24
28
, , . ,
32
36
40
44
(days)
FIG. 1. Carbon dioxide production during storage in wetted mash and pellets treated with calcium propionate and Agrosil. Each is the mean of three replicates (Experiment 1).
was almost identical to that of the control. The number of colonies counted in untreated wet mash as well as in that treated with CP rose during 24 days of storage from 1,775 and 1,030 colonies/g feed, respectively, to 10,000 colonies/g of feed (Table 1). Moisture content in these two diets was also significantly increased during that period. Agrosil added to wet mash inhibited mold proliferation, and the number of colonies in this feed after one month of storage was 5,600/g feed. Fat contents in each treatment, was not markedly changed during the storage period. The levels of carbon dioxide ( C 0 2 ) measured are given in Figure 1. The data show that the increase in CO2 started in the untreated mash and in that treated with CP after 5 days of storage, whereas in the AG-treated mash it started after 19 days. In the pellets, an increase in CO2 was recorded in the untreated and the AG-treated feed after 29 days of storage, while in the CP-treated pellets CO2 started to accumulate after 36 days. Experiment 2. Increases in mold counts were recorded after 10 days of storage in the untreated, CP-treated, and AG-treated pellets (Figure 2). Numbers of colonies counted at that time were 2,200, 2,000, and 1,500/g feed, respectively, as compared with 1,500, 1,100, and 1,000 colonies/g feed at the beginning of the experiment. After 17 days of storage the numbers of colonies (per gram feed) were 90
Carbon dioxide has been used by several workers as a criterion of fungal activity. Inter alia it served as a parameter to evaluate mold inhibitors in silage (Daniel et al, 1970) and in studying the efficiency of fungistats in poultry feed (Paster, 1979). Recently, Dixon and Hamilton (1981) evaluated some organic acids as mold inhibitors by measuring CO2 production from feed and its ingredients. They pointed out a possible weakness of this method
Log
Scale
CONTROL
10001—
Co* PROPIONATE O-O
500 ~
*
AGROSIL Calcium
•o 0)
m O CO
O O
TIME
(days)
FIG. 2. Effect of calcium propionate and Agrosil on mold counts in wetted pellets during storage. Each is the mean of three replicates (Experiment 2).
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
A
DISCUSSION
/
2
1676
PASTER ET AL.
1 0
14
1
-
~~
'J 5?
12 -
O
10 -
« O
4-
• — •
CONTROL
• — •
Co* PROPIONATE
O—O
AGROSIL
* Calcium
^ ^ ^ 0 /
^Wj^^^-^-—i " i 1 1 1 I 1 I 1 I 1 2 4 6 8 10 12 14 16 TIME
(days)
FIG. 3. Carbon dioxide production during storage in wetted pellets treated with calcium propionate and Agrosil. Each is the mean of three replicates (Experiment 2).
— it does not discriminate between CO2 production by fungi and C 0 2 produced by bacteria and yeasts — yet noted this method seemed desirable from many aspects. The increase in CQ~ served also in our studies as a parameter for fungal activity and the accumulation of the gas was concomitant with the increase in mold counts, again indicating the sensitivity of this parameter. Effect of pelleting on the reduction of bacteria in feed has been reported previously (Stott et al, 1975). The pelleting process can also markedly reduce the mold count, as reported recently by Tabib et al. (1984), who found that pelleting reduced the mold counts by a factor of approximately 100 to 10,000, depending upon the sample. Similar data were obtained in our studies, although reduction was less. However, in both of our experiments fungi were not eradicated, and wetting the pellets accelerated mold proliferation and resulted in spoilage of the feed, which appeared caked and moldy. It seems, therefore, that when there is a risk of feed being exposed to high humidity (which is the situation in this country), the addition of fungistats to the pellets is of importance. Moreover, the heat treatment destroys the natural microflora, thus exposing the feed to reinfestation by the fungi common in silos or
ACKNOWLEDGMENT We thank Mazal Menasherov for technical assistance. REFERENCES Bartov, I., 1985. Comparative effects of antifungal compounds on the nutritional value of diets containing moldy corn for broiler chicks. Poultry Sci. 64:1236-1238. Bartov, I., N. Paster, and N. Lisker, 1982. The nutritional value of moldy grains for broiler chicks. Poultry Sci. 61:2247-2254.
Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015
2-
// / J/ /
the farm environment. The addition of fungistats to the pellets may prevent or limit this phenomenon. Calcium propionate prevented fungal activity in the wetted pellets in the first experiment, while such an effect was not observed in the second experiment. This discrepency might be due to the different concentration of CP used (.3 vs .2% in Experiments 1 and 2, respectively). The possibility that the type of the diets used in the two experiments also affected the efficiency of CP can not be ruled out. The diet for chicks, used in Experiment 2, had a higher nutritional value. Such a diet was found to be, under certain climatic conditions, more sensitive to fungal spoilage (unpublished data). Agrosil was less effective than CP in preventing fungal activity in wet pellets in both experiments. However, it was more effective than CP when the diet was in mash form. It seems, therefore, that the pelleting process depressed the antifungal properties of AG, presumably due to the effect of the steam treatment on volatile propionic acid. Although amounts of C 0 2 and mold counts were high at the end of each experiment, no reduction in fat content was noticed. These data seem to be in disagreement with Bartov et al. (1982) who observed that fungal activity in diets is followed by a marked decrease in fat content. However, it should be emphasized that the mentioned phenomenon was observed when grains that were heavily infested with fungi were included in the diet. It seems therefore, that CO2 accumulation and direct fungal counts can serve as early parameters for identification of fungal activity, while a decrease in fat content could be detected in latter stages. As these parameters have not yet been compared in one experiment this assumption needs further clarification.
ANTIFUNGAL COMPOUNDS IN FEEDS Christensen, C. M., 1973. Tests with propionic and acetic acids as grain preservatives. Feedstuffs 45:37. Christensen, C. M., and D. B. Sauer, 1982. Microflora. Pages 219—238 in Storage of Cereal Grains and their Products. C. M. Christensen, ed. Am. Assoc. Cereal Chem., St. Paul, MN. Daniel, P., H. Horring, F. Weise, and E. Zimmer, 1970. Wirking von Propionsause bei der Grunfutter — Silierung. Wirtschaftseigene Futter 3:239—249. Dixon, R. C , and P. B. Hamilton, 1981. Evaluation of some organic acids as mold inhibitors by measuring CO 2 production from feed and ingredients. Poultry Sci. 60:2182-2188. Mirocha, C. J., and C. M. Christensen, 1974. Fungus metabolites toxic to animals. Annu. Rev. Phy-
1677
topathol. 12:303-330. Paster, N, 1979. A commercial scale study of the efficiency of propionic acid and calcium propionate as fungistats in poultry feed. Poultry Sci. 58:572-576. Sauer, D. B., and R. Burroughs, 1974. Efficiency of various chemicals as grain mould inhibitors. Trans. Am. Soc. Agric. Eng. 17:557-559. Stott, J. A., J. E. Hodgeson, and J. C. Chaney, 1975. Incidence of Salmonellae in animal feed and the effect of pelleting on content of Enterobacteriaceae J. Appl. Bacteriol. 39:41—46. Tabib, Z., F. T. Jones, and P. B. Hamilton, 1984. Effect of pelleting of poultry feed on the activity of molds and mold inhibitors. Poultry Sci. 63:70-75. Downloaded from http://ps.oxfordjournals.org/ at Kainan University on May 6, 2015