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Effect of Feeding Soybeans or Formaldehyde-Treated Soybeans on Lipid Metabolism in Ruminants1
Effect of Feeding Soybeans or Formaldehyde-Treated Soybeans on Lipid Metabolism in Ruminants 1 Abstract
Three lactating fistulated goats were used in a 3 × 3 Latin Square design comparing control, formalin-treated, and untreated soybean rations. The concentrateto-roughage ratio was 2:1. Milk yield was depressed (P < .05) in the formalin-treated soybean group. Long chain unsaturated milk fat fatty acids increased in both soybean treatments compared to controls with no significant difference between treated and untreated beans. Rumen p i t and total protozoa counts were lower on the goats fed formaldehyde-treated beans. Total rumen lipids were elevated over controls in both treatments. Unsaturated 18 carbon f a t t y acids in the rumen lipids were higher with the treated soybeans compared to the untreated beans, suggesting some protection of the soybean lipids from hydrogenation. The inclusion of soybeans appeared to depress butyrate production and significantly increase propionate production in the rumen. Circulating blood acetate was depressed (P < .05) with the formaldehyde treatment. Plasma and fecal lipid levels and milk fatty acids suggested that the soybean lipids were being utilized in both treatments but with no distinct advantage for the treated soybeans. Introduction The major lipid fatty acids in the ruminant diet are unsaturated. During digestion unsaturated f a t t y acids are converted to more saturated forms by rumen organisms (5, 8). Because of this, the amount and proportion of unsaturated fatty acids reaching the lower tract are low. Feeding of polyunsaturated oils has led to nfilk fat depression and metabolic changes in the animal (7). Australian workers have attempted to increase polyunsaturation of milk fat by encapsulating linseed oil with sodium caseinate and spraying with fm~maldehyde (6). Formaldehyde binds to protein making it less soluble in the rumen and reducing protease activity ( p H above 6). In the abomasum ( p H below 3),
there is a reversal of the coating effect and utilization of the protected diet component (1). Since the soybean contains lipids with more than 80% unsaturated fatty acids and 38% total protein (4), it was reasoned that formaldehyde treatment might afford partial protection from microbial hydrogenation. I f the treatments were effective, it is conceivable that the technique may prove useful in altering the amounts and degree of unsaturated lipid presented to the ruminant animal for absorption. The purpose of the trial was to compare a ration containing formaldehyde-treated soybeans with one containing untreated beans as well as with a control ration based on soybean meal, measuring changes in rumen, blood, fecal, and milk components. Experimental Procedures
Three lactating fistulated goats were used in a 3 × 3 Latin square trial. Experimental periods were 3 weeks. Table 1 summarizes experimental concentrate rations. A control diet of corn and soybean meal was compared to diets containing ground soybeans with and without formaldehyde treatment. Alfalfa hay was the roughage source. Ground shelled corn was the main lipid source (2.7%) in the control diet. In Ration 2 soybean oil meal was replaced with raw soybeans resulting in 5.3% lipid in the concentrate ration. Ration 3 was identical to Ration 2 except soybeans were sprayed with a 3% solution (3 ml/100 g) of 40% formaldehyde. A f t e r spraying, the soybeans were sealed in a plastic bag allowing the formalin fumes to equilibrate with the ground soybeans for several days. Treated beans were exposed to the air for a day to allow excess fumes to evaporate to avoid palatability problems. The soybeans were then mixed with the remainder of the grain ration. The concentrate-to-roughage ratio was 2:1 on an as-fed basis. Experimental rations were fed twice daily at 8:00 A~ and 4:00 P•. Milk was analyzed once a week throughout the trial for fat content and fatty acid composition. The last week of each period two samples were taken, averaged, and reported. Once at the end of each period, at 8:30 A~, blood samples were taken from the jugular and subcutaneous abdominal vein. Blood lipids were analyzed by thin-layer chromatography, quantitated, and fatty acid composition was
1 Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. 1876
T E C H N I C A L NOTES
TABLE 1. Composition and analysis of experimental grain rations. Ration Analyses Composition ( % ) Ground shelled corn Soybean oil meal Soybeans Mineral and vitamin supplement Analysis (%) Crude protein Ether extract Crude fiber Lipid fatty acids (% of total) 16:0 18:0 18:1 18:2
1
2
3
84 ]5 ....
79 79 ........ 20 20
1877
acid composition were measured once at the end of each period at 9:00 A~, 12:00 A~, and 3:00 P~. Body weights were averaged for 3 consecutive days at the end of each period. Analysis of variance with a least-squares procedure and significance by Duncan's multiple range test were employed in statistical analysis. Results and Discussion
1
1
1
14.5 2.7 3.6
15.0 5.3 3.8
15.0 5.3 3.8
10.6 2.3 33.9 40.8
13.0 2.6 25.8 53.4
13.3 4.3 27.6 43.6
determined (2). Blood glucose, acetate, total ketones, and urea nitrogen were determined as described by ttutjens et al. (2). Once at the end of each period, fecal samples were collected for 6 hr (9 A~ to 3 e ~ ) , dried, and a representative sample was taken. Fecal and rumen lipids were isolated following a modified Folch procedure (2). Total lipids were determined gravimetrically. Methyl esters of total rumen and fecal lipids were prepared, separated from pigments and extraneous lipids by thinlayer chromatography (3), and analyzed by gas-liquid chromatography (2). Changes in total protozoa number, rumen volatile fatty acids, tureen pH, total rumen ]ipids, and f a t t y
Table 2 summarizes changes in milk, rumen, blood, and fecal components. Milk yield was significantly depressed in those goats receiving formalin-treated soybeans compared to controls (1.3 and 1.5 k g / d a y ) . Because of the decrease in milk yield, fat yield was depressed compared to controls even though the f a t percentage was higher during formalin treatment. Milk fat fatty acid composition was comparable when treated and untreated soybeans were fed. Medium chain saturated fatty acids were depressed while unsaturated long chain f a t t y acids tended to increase in both soybean treatments compared to controls. A decrease ( P < .05) in rumen p H occurred with the formalin-treated soybeans compared to the controls and untreated soybeans. The per cent of rmnen propionate was significantly increased, and rumen acetate and butyrate percentages decreased when either soybean ration was fed compared to controls. The change in volatile f a t t y acid pattern was similar to but of smaller magnitude than that seen in cows with milk fat depression due to feeding high grain (2). Circulating blood acetate was depressed (P < .05) in the formalin-treated group compared to control and untreated rations. There were no statistically significant differences in rumen protozoa counts or blood glucose, ketones, and urea nitrogen although alI tended to be lower with formalin treatment.
TABLE 2. Summary of milk, blood, rumen, and fecal analyses. Analyses Milk composition Milk yield (kg/day) F a t test ( % ) F a t yield (kg/day) Milk fatty acids (weight %) 10:0 12:0 14:0 16:0 18:0 18:1 18:2
(Continued)
Control
Soybeans
Soybeans and formaldehyde
1.5a 2.5 .04
1.4a 2.8 .04
1.3b 2.6 .03
12.8 7.3 14.3a 31.9a 7.1 23.6 3.0
10.8 5.4 12.1b 26.4b 10.6 29.9 4.6
15.5 5.5 10.7c 25.9b 7.2 29.2 5.9
J. DAIRY SCIENCE ~OL. 54, NO. 12
1878
J O U R N A L OF D A I R Y SCIENCE
TABLE 2. Summary of milk, blood, ramen, and fecal analyses. Analyses Rumen fermentation Total protozoa (106/ml) pH 9:00 ~-~ Lipids concentration (mg/ml) 9:00 AM 12:00 AM 3:00 P~ F a t t y acids (weight %) 18:0 9:00 AM 12:00 AM 3:00 P~ 18:1 9:00 A~ 12:0O AM 3:00 e ~ Acetate ( % ) Propionate ( % ) Butyrate ( % ) Blood components (rag/100 ml) Acetate Acetate J/iV[ diff. Glucose Total ketones Blood urea nitrogen Plasma components (rag/100 ml) Triglycerides Triglyceride J/qVI diff. Free fatty acids Free fatty acids J / T I diff. Free cholesterol Cholesterol esters Phospholipids Plasma lipid fatty acids (weight %) Triglyceride 18:0 18:1 18:2 Free fatty acids 18:0 18:1 18:2 18:3 Cholesterol esters 18:1 18:2 Phospholipids 18:0 ]8:1 18:2 Fecal lipids (mg/g) Fecal fatty acids (weight %) 18:0 18:1 18:2
(concluded)
Control
Soybeans
Soybeans and formaldehyde
2.9 6.1a
2.3 6.1a
2.0 5.9b
4.8 2.9 4.4
7.9 5.2 6.6
8.3 7.7 6.6
62 54 48 9 11 15 53.9a 19.1a 25.1
67 71 63 5 5 7 50.5ab 29.2b 18.4
49 66 67 18 7 8 49.2b 32.2b 18.0
6.6a -{- 2.6 47.6 2.2 21.5
6.9a + 3.1 47.4 1.9 23.2
3.8b ~- 1.7 43.9 1.6 19.9
12.9 + 4.2 3.6 -t- 1.9a 9.5a 58.9 91.2
12.1 + 2.9 1.3 -- 1.3b 14.6b 75.4 116.0
11.5 ~ 4.8 1.2 - - 1.0b 12.6b 70.0 99.7
39.4a 19.8 6.2
45.4b 22.6 7.4
47.6b 24.7 6.8
38.8 27.7 2.7 .8
33.9 21.3 5.0 1.3
22.0 17.4 5.7 2.1
31.0a 48.2
27.7b 52.8
22.4b 56.3
27.4 18.0 28.7 63.8
28.5 17.2 31.5 65.1
30.7 ]5.4 30.6 70.9
18.5 39.2 26.9
20.0 46.3 14.8
16.8 39.9 14.2
abe Values with different letters are significantly different (P < .05).
TECHNICAL NOTES Although certain observations suggested that formalin was having some effect on lipid metabolism in the rurnen, none of the measurements were significantly different. The main fatty acid in the Soybean is linoleic (4), but 1 hr after feeding C18:2, acid in tureen lipids was low on all rations (2.2, .9 and 3.8% in the control, untreated, and treated soybeans). However, at 1 hr after feeding, the ratio of ] 8 : 0 / ] 8 : 1 was considerably higher for the control and soybean rations than for the treateds o y b e a n r a t i o n , p o s s i b l y s u g g e s t i n g some protection or delay in hydrogenation. The difference tended to disappear in 3 hr. Differences in plasma lipids were small, appearing to reflect primarily differences between control and added lipid intake from the soybeans since there were no significant differences between the treated and untreated soybeans. The soybean groups had higher free fatty acids in the mammary than in the jugular vein, while the reverse was true for the controls. Free cholesterol was significantly higher for the soybean treatments. Plasma triglycerides had a higher proportion of C18:0 acid and cholesterol esters had a lower proportion of C18:1 acid when soybeans were being fed. No differences in total fecal lipid or feeaI fatty acids occurred between treatment groups. I f the goats: were not able to utilize the treated soybean lipid, higher total lipid in the feces would have been expected. Also C18:2 would be higher if lipids in formalin-treated beans had traversed the digestive tract unaltered or not absorbed. Summary The feeding of formaldehyde-treated soybeans to lactating goats reduced milk yield, rumen pH, and circulating blood acetate. Although there appeared to be small, temporary differences in rumen lipids due to the formaldehyde, none were statistically significant. The formaldehyde treatment did not increase the amount or degree of unsaturation in plasma or milk lipids compared to untreated soybeans.
1879
MICHAEL F. HUTJENS 2 a.d L. H. SCHULTZ, Department of Dairy Science, University of Wisconsin, Madison 53706 2 Current address: Department of Animal Science, University of Minnesota, St. Paul 55101. Acknowledgment The authors wish to express their appreciation to 1~. W. Schwarz for laboratory assistance and A. H. Quamme for management of experimenta] animals. References (1) Ferguson, K. A., J. A. Hemsley, and P. J. Reis. 1967. The effect of protecting dietary protei~t from microbial degradation in the rumen. Australian J. Sei., 30: 215. (2) ttutjens, M. F., and L. It. Schultz. 1971. Effects of addition of soybeans or methionine analog to high concentrate ration for dairy cows. J. Dairy Sei., 54: 1637. (3) Luddy, F. E., R. A. Barford, S. F. Herb, and P. Magodman. 1968. A rapid and quantitive procedure for the preparation of methyl esters of batteroil and other fats. J. Amer. Oil Chemists Soc., 45: 549. (4) Maynard, L. A., and J. K. Loosli. 1962. Animal Nutrition. p. 67. 5th ed. McGrawHill Book Co., Inc., New York City. (5) Moore, J. H., 1~. C. Noble, W. Steele, and J. W. Czerkawski. 1969. Differences in the metabolism of esterified and unesterified lino]eic acid by rumen microorganisms. British J. Nutrition, 28: 869. (6) Scott, T. W., L. J. Cook, K. A. Ferguson, I. W. McDonald, 1~. A. Buchanan, and G. L. Hills. 1969. Production of polyunsaturated milk fat in domestic ruminants. Australian J. Sci., 32: 291. (7) Shaw, J. C., and W. L. Ensor. 1959. Effect of feeding cod liver oil and unsaturated fatty acids on rumen volatile fatty acids and milk fat content, J. Dairy Sci., 42: 1238. (8) Storry, J. E. 1970. Review of the progress of dairy science. Section A. Physiology. l~uminant metabolism in relation to the synthesis and secretion of milk fat. J. Dairy Res., 37: 139:
J. DAVY SOImNCEYOL 54, NO. 12
Three lactating fistulated goats were used in a 3 × 3 Latin Square design comparing control, formalin-treated, and untreated soybean rations. The concentrateto-roughage ratio was 2:1. Milk yield was depressed (P < .05) in the formalin-treated soybean group. Long chain unsaturated milk fat fatty acids increased in both soybean treatments compared to controls with no significant difference between treated and untreated beans. Rumen p i t and total protozoa counts were lower on the goats fed formaldehyde-treated beans. Total rumen lipids were elevated over controls in both treatments. Unsaturated 18 carbon f a t t y acids in the rumen lipids were higher with the treated soybeans compared to the untreated beans, suggesting some protection of the soybean lipids from hydrogenation. The inclusion of soybeans appeared to depress butyrate production and significantly increase propionate production in the rumen. Circulating blood acetate was depressed (P < .05) with the formaldehyde treatment. Plasma and fecal lipid levels and milk fatty acids suggested that the soybean lipids were being utilized in both treatments but with no distinct advantage for the treated soybeans. Introduction The major lipid fatty acids in the ruminant diet are unsaturated. During digestion unsaturated f a t t y acids are converted to more saturated forms by rumen organisms (5, 8). Because of this, the amount and proportion of unsaturated fatty acids reaching the lower tract are low. Feeding of polyunsaturated oils has led to nfilk fat depression and metabolic changes in the animal (7). Australian workers have attempted to increase polyunsaturation of milk fat by encapsulating linseed oil with sodium caseinate and spraying with fm~maldehyde (6). Formaldehyde binds to protein making it less soluble in the rumen and reducing protease activity ( p H above 6). In the abomasum ( p H below 3),
there is a reversal of the coating effect and utilization of the protected diet component (1). Since the soybean contains lipids with more than 80% unsaturated fatty acids and 38% total protein (4), it was reasoned that formaldehyde treatment might afford partial protection from microbial hydrogenation. I f the treatments were effective, it is conceivable that the technique may prove useful in altering the amounts and degree of unsaturated lipid presented to the ruminant animal for absorption. The purpose of the trial was to compare a ration containing formaldehyde-treated soybeans with one containing untreated beans as well as with a control ration based on soybean meal, measuring changes in rumen, blood, fecal, and milk components. Experimental Procedures
Three lactating fistulated goats were used in a 3 × 3 Latin square trial. Experimental periods were 3 weeks. Table 1 summarizes experimental concentrate rations. A control diet of corn and soybean meal was compared to diets containing ground soybeans with and without formaldehyde treatment. Alfalfa hay was the roughage source. Ground shelled corn was the main lipid source (2.7%) in the control diet. In Ration 2 soybean oil meal was replaced with raw soybeans resulting in 5.3% lipid in the concentrate ration. Ration 3 was identical to Ration 2 except soybeans were sprayed with a 3% solution (3 ml/100 g) of 40% formaldehyde. A f t e r spraying, the soybeans were sealed in a plastic bag allowing the formalin fumes to equilibrate with the ground soybeans for several days. Treated beans were exposed to the air for a day to allow excess fumes to evaporate to avoid palatability problems. The soybeans were then mixed with the remainder of the grain ration. The concentrate-to-roughage ratio was 2:1 on an as-fed basis. Experimental rations were fed twice daily at 8:00 A~ and 4:00 P•. Milk was analyzed once a week throughout the trial for fat content and fatty acid composition. The last week of each period two samples were taken, averaged, and reported. Once at the end of each period, at 8:30 A~, blood samples were taken from the jugular and subcutaneous abdominal vein. Blood lipids were analyzed by thin-layer chromatography, quantitated, and fatty acid composition was
1 Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. 1876
T E C H N I C A L NOTES
TABLE 1. Composition and analysis of experimental grain rations. Ration Analyses Composition ( % ) Ground shelled corn Soybean oil meal Soybeans Mineral and vitamin supplement Analysis (%) Crude protein Ether extract Crude fiber Lipid fatty acids (% of total) 16:0 18:0 18:1 18:2
1
2
3
84 ]5 ....
79 79 ........ 20 20
1877
acid composition were measured once at the end of each period at 9:00 A~, 12:00 A~, and 3:00 P~. Body weights were averaged for 3 consecutive days at the end of each period. Analysis of variance with a least-squares procedure and significance by Duncan's multiple range test were employed in statistical analysis. Results and Discussion
1
1
1
14.5 2.7 3.6
15.0 5.3 3.8
15.0 5.3 3.8
10.6 2.3 33.9 40.8
13.0 2.6 25.8 53.4
13.3 4.3 27.6 43.6
determined (2). Blood glucose, acetate, total ketones, and urea nitrogen were determined as described by ttutjens et al. (2). Once at the end of each period, fecal samples were collected for 6 hr (9 A~ to 3 e ~ ) , dried, and a representative sample was taken. Fecal and rumen lipids were isolated following a modified Folch procedure (2). Total lipids were determined gravimetrically. Methyl esters of total rumen and fecal lipids were prepared, separated from pigments and extraneous lipids by thinlayer chromatography (3), and analyzed by gas-liquid chromatography (2). Changes in total protozoa number, rumen volatile fatty acids, tureen pH, total rumen ]ipids, and f a t t y
Table 2 summarizes changes in milk, rumen, blood, and fecal components. Milk yield was significantly depressed in those goats receiving formalin-treated soybeans compared to controls (1.3 and 1.5 k g / d a y ) . Because of the decrease in milk yield, fat yield was depressed compared to controls even though the f a t percentage was higher during formalin treatment. Milk fat fatty acid composition was comparable when treated and untreated soybeans were fed. Medium chain saturated fatty acids were depressed while unsaturated long chain f a t t y acids tended to increase in both soybean treatments compared to controls. A decrease ( P < .05) in rumen p H occurred with the formalin-treated soybeans compared to the controls and untreated soybeans. The per cent of rmnen propionate was significantly increased, and rumen acetate and butyrate percentages decreased when either soybean ration was fed compared to controls. The change in volatile f a t t y acid pattern was similar to but of smaller magnitude than that seen in cows with milk fat depression due to feeding high grain (2). Circulating blood acetate was depressed (P < .05) in the formalin-treated group compared to control and untreated rations. There were no statistically significant differences in rumen protozoa counts or blood glucose, ketones, and urea nitrogen although alI tended to be lower with formalin treatment.
TABLE 2. Summary of milk, blood, rumen, and fecal analyses. Analyses Milk composition Milk yield (kg/day) F a t test ( % ) F a t yield (kg/day) Milk fatty acids (weight %) 10:0 12:0 14:0 16:0 18:0 18:1 18:2
(Continued)
Control
Soybeans
Soybeans and formaldehyde
1.5a 2.5 .04
1.4a 2.8 .04
1.3b 2.6 .03
12.8 7.3 14.3a 31.9a 7.1 23.6 3.0
10.8 5.4 12.1b 26.4b 10.6 29.9 4.6
15.5 5.5 10.7c 25.9b 7.2 29.2 5.9
J. DAIRY SCIENCE ~OL. 54, NO. 12
1878
J O U R N A L OF D A I R Y SCIENCE
TABLE 2. Summary of milk, blood, ramen, and fecal analyses. Analyses Rumen fermentation Total protozoa (106/ml) pH 9:00 ~-~ Lipids concentration (mg/ml) 9:00 AM 12:00 AM 3:00 P~ F a t t y acids (weight %) 18:0 9:00 AM 12:00 AM 3:00 P~ 18:1 9:00 A~ 12:0O AM 3:00 e ~ Acetate ( % ) Propionate ( % ) Butyrate ( % ) Blood components (rag/100 ml) Acetate Acetate J/iV[ diff. Glucose Total ketones Blood urea nitrogen Plasma components (rag/100 ml) Triglycerides Triglyceride J/qVI diff. Free fatty acids Free fatty acids J / T I diff. Free cholesterol Cholesterol esters Phospholipids Plasma lipid fatty acids (weight %) Triglyceride 18:0 18:1 18:2 Free fatty acids 18:0 18:1 18:2 18:3 Cholesterol esters 18:1 18:2 Phospholipids 18:0 ]8:1 18:2 Fecal lipids (mg/g) Fecal fatty acids (weight %) 18:0 18:1 18:2
(concluded)
Control
Soybeans
Soybeans and formaldehyde
2.9 6.1a
2.3 6.1a
2.0 5.9b
4.8 2.9 4.4
7.9 5.2 6.6
8.3 7.7 6.6
62 54 48 9 11 15 53.9a 19.1a 25.1
67 71 63 5 5 7 50.5ab 29.2b 18.4
49 66 67 18 7 8 49.2b 32.2b 18.0
6.6a -{- 2.6 47.6 2.2 21.5
6.9a + 3.1 47.4 1.9 23.2
3.8b ~- 1.7 43.9 1.6 19.9
12.9 + 4.2 3.6 -t- 1.9a 9.5a 58.9 91.2
12.1 + 2.9 1.3 -- 1.3b 14.6b 75.4 116.0
11.5 ~ 4.8 1.2 - - 1.0b 12.6b 70.0 99.7
39.4a 19.8 6.2
45.4b 22.6 7.4
47.6b 24.7 6.8
38.8 27.7 2.7 .8
33.9 21.3 5.0 1.3
22.0 17.4 5.7 2.1
31.0a 48.2
27.7b 52.8
22.4b 56.3
27.4 18.0 28.7 63.8
28.5 17.2 31.5 65.1
30.7 ]5.4 30.6 70.9
18.5 39.2 26.9
20.0 46.3 14.8
16.8 39.9 14.2
abe Values with different letters are significantly different (P < .05).
TECHNICAL NOTES Although certain observations suggested that formalin was having some effect on lipid metabolism in the rurnen, none of the measurements were significantly different. The main fatty acid in the Soybean is linoleic (4), but 1 hr after feeding C18:2, acid in tureen lipids was low on all rations (2.2, .9 and 3.8% in the control, untreated, and treated soybeans). However, at 1 hr after feeding, the ratio of ] 8 : 0 / ] 8 : 1 was considerably higher for the control and soybean rations than for the treateds o y b e a n r a t i o n , p o s s i b l y s u g g e s t i n g some protection or delay in hydrogenation. The difference tended to disappear in 3 hr. Differences in plasma lipids were small, appearing to reflect primarily differences between control and added lipid intake from the soybeans since there were no significant differences between the treated and untreated soybeans. The soybean groups had higher free fatty acids in the mammary than in the jugular vein, while the reverse was true for the controls. Free cholesterol was significantly higher for the soybean treatments. Plasma triglycerides had a higher proportion of C18:0 acid and cholesterol esters had a lower proportion of C18:1 acid when soybeans were being fed. No differences in total fecal lipid or feeaI fatty acids occurred between treatment groups. I f the goats: were not able to utilize the treated soybean lipid, higher total lipid in the feces would have been expected. Also C18:2 would be higher if lipids in formalin-treated beans had traversed the digestive tract unaltered or not absorbed. Summary The feeding of formaldehyde-treated soybeans to lactating goats reduced milk yield, rumen pH, and circulating blood acetate. Although there appeared to be small, temporary differences in rumen lipids due to the formaldehyde, none were statistically significant. The formaldehyde treatment did not increase the amount or degree of unsaturation in plasma or milk lipids compared to untreated soybeans.
1879
MICHAEL F. HUTJENS 2 a.d L. H. SCHULTZ, Department of Dairy Science, University of Wisconsin, Madison 53706 2 Current address: Department of Animal Science, University of Minnesota, St. Paul 55101. Acknowledgment The authors wish to express their appreciation to 1~. W. Schwarz for laboratory assistance and A. H. Quamme for management of experimenta] animals. References (1) Ferguson, K. A., J. A. Hemsley, and P. J. Reis. 1967. The effect of protecting dietary protei~t from microbial degradation in the rumen. Australian J. Sei., 30: 215. (2) ttutjens, M. F., and L. It. Schultz. 1971. Effects of addition of soybeans or methionine analog to high concentrate ration for dairy cows. J. Dairy Sei., 54: 1637. (3) Luddy, F. E., R. A. Barford, S. F. Herb, and P. Magodman. 1968. A rapid and quantitive procedure for the preparation of methyl esters of batteroil and other fats. J. Amer. Oil Chemists Soc., 45: 549. (4) Maynard, L. A., and J. K. Loosli. 1962. Animal Nutrition. p. 67. 5th ed. McGrawHill Book Co., Inc., New York City. (5) Moore, J. H., 1~. C. Noble, W. Steele, and J. W. Czerkawski. 1969. Differences in the metabolism of esterified and unesterified lino]eic acid by rumen microorganisms. British J. Nutrition, 28: 869. (6) Scott, T. W., L. J. Cook, K. A. Ferguson, I. W. McDonald, 1~. A. Buchanan, and G. L. Hills. 1969. Production of polyunsaturated milk fat in domestic ruminants. Australian J. Sci., 32: 291. (7) Shaw, J. C., and W. L. Ensor. 1959. Effect of feeding cod liver oil and unsaturated fatty acids on rumen volatile fatty acids and milk fat content, J. Dairy Sci., 42: 1238. (8) Storry, J. E. 1970. Review of the progress of dairy science. Section A. Physiology. l~uminant metabolism in relation to the synthesis and secretion of milk fat. J. Dairy Res., 37: 139:
J. DAVY SOImNCEYOL 54, NO. 12