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Milk yield response of dairy cows fed fat along with protein
Animal Feed Science and Technology 90 (2001) 169±184
Milk yield response of dairy cows fed fat along with protein$ T.R. Dhimana,*, I.S. MacQueena, N.D. Luchinib a
Animal, Dairy and Veterinary Sciences, Utah State University, 4815 Old Main Hill, Logan, UT 84322-4815, USA b Continental Grain Company, 222 South Riverside Plaza, Chicago, IL 60606, USA Received 22 August 2000; received in revised form 19 December 2000; accepted 2 January 2001
Abstract The in¯uence of a fat-coated protein on milk production of Holstein dairy cows was determined using a 4 4 Latin square experiment. Twelve cows were fed a control diet or test diets supplemented with fat, fat plus ruminally undegraded protein (RUP), or a fat-coated protein (DuetsTM). Cows fed test diets received 0.55 kg of more fat per day than cows in the control treatment. Daily intakes of feed, energy, and protein were the same in all treatments. Cows produced 36.5, 37.3, 37.9, and 39.3 kg of energy-corrected milk per day in control, fat, fat plus RUP, and fat-coated protein treatments, respectively. Cows fed fat-supplemented diets produced an average 1.7 kg more milk daily compared with cows in the control treatment. Feeding RUP along with fat or fat-coated protein provided no further improvement in milk yield compared with fat alone, but partially alleviated the depression in protein content caused by supplemental fat and increased the daily yield of milk protein. In the present experiment, cows fed fat-coated protein produced daily an average 60 g of milk protein more than cows fed fat alone. Since, there was no advantage in milk yield, the decision to include fat-coated protein in dairy rations should be based on its price compared to fat alone and the return in terms of milk protein yield. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Cow; Milk; Fat; Protein; Conjugated linoleic acid
1. Introduction Meeting the energy and protein needs of high-producing dairy cows is sometimes a challenge. Increasing grain relative to forage in dairy diets can increase energy density of $
Approved as journal paper number 7194 of the Utah Agricultural Experiment Station, Utah State University, Logan, UT, USA. * Corresponding author. Tel.: 1-435-797-2155; fax: 1-435-797-2118. E-mail address: [email protected] (T.R. Dhiman). 0377-8401/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 1 ) 0 0 2 0 9 - 7
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the diet and allow greater energy intake. However, excessive intake of starch can lead to acidosis (Erdman, 1988), milk fat depression (Sutton, 1989), and depressed feed intake (Holter et al., 1993). Fat has more than three times the net energy of lactation relative to protein and carbohydrate. Supplemental fat has been shown to increase milk yield in high-producing dairy cows (Coppock and Wilks, 1991). Replacing fermentable carbohydrate with fat in the diet of high-producing dairy cows may limit synthesis of microbial protein and will decrease the ¯ow of microbial protein to the small intestine (Palmquist et al., 1993). In some situations, supplementation with fat may limit the supply of amino acids to the mammary gland and reduce milk protein content (DePeters and Cant, 1992). A study by Dhiman et al. (1995) observed 1.0±1.5 g kg 1 decrease in protein content of milk from cows fed diets supplemented with fat. Wu and Huber (1994) summarized the results of 47 experiments from the literature and suggested that an increase in dietary fat from 25 to 80 g kg 1 would decrease milk protein by 3.8 g kg 1. Addition of rumen-protected amino acids to the fat-supplemented diet resulted in increases of 0.8±1.0 g kg 1 of milk protein output (Christensen et al., 1994). Increasing the energy content of the diet through supplemental fat also increases the protein requirements of a cow in order to maintain the ratio of protein to energy. Cows fed supplemental fat along with protein containing a higher proportion of ruminally undegraded protein (RUP) produced more milk compared with cows fed protein with low RUP content (Chan et al., 1997; Harouna and Schingoethe, 1997). These results suggest that the quality and quantity of protein supplied along with the fat in¯uences the performance of high-producing dairy cows. Since fat alone sometimes is not very palatable in the diet of high-producing dairy cows (Dhiman et al., 1995), our hypothesis was that feeding dairy cows a fat-coated protein would improve palatability of a diet containing fat, supply protein and energy simultaneously, and improve the performance of dairy cows. The objective of this research was to determine the milk yield and milk composition of high-producing dairy cows fed fat-coated protein (DuetsTM; Fig. 1). 2. Materials and methods 2.1. Animals and treatments Twelve multiparous Holstein dairy cows were strati®ed into three groups of four according to pre-treatment milk yield. Cows within each group were assigned randomly to four treatments over four periods in a 4 4 Latin square design. Each period was 21 days. The ®rst 14 days in each period were for adaptation to diets and the last 7 days for data collection. Cows were housed in tie stalls and fed individually. At the start of the experiment, cows were 38±93 days in lactation and were producing from 39.8 to 52.7 kg of milk per day. The study was conducted from December 1997 to March 1998 at the Caine Dairy Teaching and Research Center, Utah State University, Logan, UT, USA. Animal care and experimental procedures were approved and conducted under established standards of the Utah State University Institutional Animal Care and Use Committee (Approval # 900).
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Fig. 1. Fat-coated protein (DuetsTM). DuetsTM is the registered trademark of Continental Grain Company, Chicago, IL, USA, for fat-coated protein. Solvent-extracted soybean meal was used as a protein source in fatcoated protein. The fat-coated protein contained 43.6% fat and 29.8% protein, and fatty acid composition was 2.1% C14:0, 49.7% C16:0, 32.6% C18:0, 14.0% C18:1, and 1.6% C18:2 of total fatty acids.
The four treatment diets were control, supplemental fat (FAT), fat plus RUP (FATP), or fat-coated protein (FATPC). The source of fat in FAT and FATP treatments was Ener GIITM. Ener GIITM is the registered trademark of Bioproducts, Inc., Fairlawn, OH, USA, for calcium salts of palm oil fatty acids. The Ener GIITM contained 82.3% fat and 8.8% calcium. The fatty acid composition of Ener GIITM was 1.7% C14:0, 49.5% C16:0, 4.0% C18:0, 36.3% C18:1, and 8.5% C18:2 of total fatty acids. The source of RUP in the FATP diet was the Soybest1 (a registered trademark for soybean meal product of Grain States Soya, Inc., West Point, NE, USA). The source of fat-coated protein in FATPC treatment was DuetsTM. DuetsTM is the registered trademark of Continental Grain Company, Chicago, IL, USA, for fat-coated protein. Solvent-extracted soybean meal was used as a protein source in fat-coated protein. Fat-coated protein contained 43.6% fat and 29.8% protein. The fatty acid composition of fat-coated protein was 2.1% C14:0, 49.7% C16:0, 32.6% C18:0, 14.0% C18:1, and 1.6% C18:2 of total fatty acids.
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Table 1 Ingredient composition of the diets Ingredient
Lucerne hay Maize silage Maize steam rolled Soybean meal Soybest1a Ener GIITMb DuetsTMc Dehydrated beet pulp Molasses Dicalcium phosphated Trace-mineralized salte Vitamin ADE mixf
Treatment (g kg
1
dry matter)
Control
Fat
Fat RUP
Fat-coated protein
320 160 327 141 ± ± ± 22 13 7 5 5
320 160 294 148 ± 26 ± 22 13 7 5 5
320 160 289 126 27 26 ± 22 13 7 5 5
320 160 299 121 ± ± 48 22 13 7 5 5
a
A registered trademark for soybean meal product (Grain States Soya, Inc., West Point, NE, USA). A registered trademark for rumen-inert calcium-salts of long-chain fatty acids (Bioproducts, Inc., Fairlawn, OH, USA). c Fat-coated with protein (Continental Grain Company, Chicago, IL, USA). d Dicalcium phosphate contained; minimum 210 g P; 180 g Ca; ¯uorine maximum 2.1 g kg 1. e Trace-mineralized salt contained; NaCl, minimum 950 g kg 1; minimum 3.5 g Zn, 2 g Fe, 1.8 g Mn, 0.35 g Cu, 0.1 g I, 0.06 g Co kg 1 of mix. f Contained 1,102,317 IU of Vitamin A, 330,695 IU of Vitamin D, and 6614 IU of Vitamin E kg 1. b
Diets contained 480 g kg 1 forage DM (Table 1). The forage was comprised of 667 g kg 1 Lucerne hay and 333 g kg 1 maize silage on a DM basis. Fat and protein were added to the diet by partially replacing maize and soybean meal. The proportion of other ingredients remained the same across treatment diets. Diets were fed as a total mixed ration twice daily at 07.30 and 19.30 h. A common forage mix for the diets was prepared on alternate days and concentrates were mixed with forage daily before the morning feeding. Amounts of feed offered were adjusted daily to ensure feeding 50±100 g kg 1 in excess of ad libitum fresh feed intake. 2.2. Sampling and measurements Feed offered and refused for individual cows was measured daily. Feed refusals were removed every day. Daily samples of the total mixed ration offered and feed refused were collected from each cow during week 3 in each period. Feed refusals were mixed for each treatment and a representative sample was frozen. Weekly composite samples of total mixed ration and feed refusals were analyzed for DM. Samples of individual dietary ingredients were obtained weekly and used for DM determination. To determine DM, feed samples were dried at 608C for 48 h. Diet formulations were adjusted weekly, if necessary, to account for small changes in ingredient DM content. Dried samples were ground through a Wiley mill (Arthur H. Thomas, Philadelphia, PA, USA) using a 1 mm screen. Composite samples of feed ingredients for each period were
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analyzed for composition. Crude protein (CP) in the dietary ingredients and feed refusal samples were determined using a Protein Nitrogen Analyzer model 2100 (ThermoQuest Italia S.P.A., Strada Rivoltana, Milan, Italy). To calculate RUP in the diet, the Soybest1 and fat-coated protein were analyzed for RUP using the procedure described by Roe and Sniffen (1990), and RUP values from NRC (1989) were used for other dietary ingredients. The RUP values used in this study are a relative number due to lack of an accurate method for estimation. The forage samples were analyzed for neutral detergent ®ber (NDF) and acid detergent ®ber (ADF) using the ®lter bag technology of Ankom (Ankom Technology Corporation, Fairport, NY, USA). Dietary ingredients and feed refusal samples were analyzed for fatty acid content and composition using the procedure of Sukhija and Palmquist (1988). Ground samples of total mixed ration were hydrolyzed with sodium metabisul®te and analyzed for amino acids using an amino acid analyzer (Model 6300; Beckman Instrument Inc., Fullerton, CA, USA). During analysis, the samples were further dried at 1058C for 8 h to determine the absolute DM. Chemical analyses were expressed on this ®nal DM. Dry matter intake (DMI) was calculated by subtracting the weekly average feed refused from the total mixed ration offered. Chemical composition of the total mixed ration was calculated from chemical analyses of the individual ingredients. Net energy of lactation (NEL) content of the diets was calculated by using NEL values from NRC (1989) for individual dietary ingredients. The NEL and RUP intakes for each cow were calculated by multiplying NEL and RUP concentrations in the diet by the DMI of each cow. Daily protein and fatty acid intakes were calculated by subtracting protein and fatty acids in feed refusal from their respective values in the total mixed ration that was offered to cows. Milk weights were recorded daily. Milk samples were collected from two consecutive milkings (a.m. and p.m.) during the last week in each period. Milk samples were composited for each cow proportional to milk yield. Composite milk samples from individual cows were analyzed for fat, protein, and lactose by the Rocky Mountain Dairy Herd Improvement Association Laboratory (Logan, UT, USA) with near-infrared procedures using a Bentley 2000 (Bentley Instruments, Chaska, MN, USA). Gross feed ef®ciency was calculated as kilograms of energy-corrected milk (ECM; Tyrrell and Reid, 1965) produced per kg of feed intake on an individual cow basis. Average fat and protein yields were calculated by multiplying milk yield by fat and protein content on an individual cow basis. Weighted composite milk samples from each cow during the last week in each period were analyzed for fatty acid composition including conjugated linoleic acid (CLA). To determine fatty acid composition, fat was extracted by boiling in a detergent solution (Hurley et al., 1987) and derivatized to methyl esters by mixing 30 mg of fat with 5 ml of 4% HCl±methanol (Chin et al., 1992). Heptadecanoic acid was used as an internal standard. The methyl esters were extracted with 5 ml hexane and 1 ml of distilled water. The hexane extract was washed twice with distilled water and dried over anhydrous sodium sulfate. Fat samples were analyzed in a gas chromatograph (Model 6890, Hewlett-Packard Co., Wilmington, DE, USA) ®tted with a ¯ame ionization detector and 3397A integrator. Samples containing methyl esters in hexane (1±3 ml) were directly injected through the
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splitless injection port onto a Supelcowax 10, fused silica capillary column (100 m 0:32 mm i.d., 0.25 mm ®lm thickness; Supelco Inc., Bellefonte, PA, USA). Gas chromatography conditions were the same as described by Dhiman et al. (1999). The CLA standards used were synthesized as described by Chin et al. (1992). Fatty acids were identi®ed by comparing the retention times with the methylated fatty acid standards including CLA. The CLA reported is cis-9, trans-11 C18:2. Percentage of each fatty acid was calculated by dividing the area under the fatty acid peak by the sum of the areas under the total reported fatty acid peaks. The DM digestibility (DMD) was determined using ytterbium (Yb) as an external marker. A Yb solution was prepared by dissolving 1.15 g of 99% pure YbO3 (1 g of Yb) in 1.38 ml concentrated HCl and diluting with water to 25 ml. The Yb solution was sprayed onto 454 g of grain mix from the diet, which was pulse-fed daily from day 13 to day 21 in each period. The marked grain was fed before the regular feed was offered to ensure complete consumption of marked grain. Fecal grab samples were collected from individual cows at 06.00, 11.00, 17.00, and 23.00 h on day 8 and at 04.00, 09.00, 14.00, and 20.00 h on day 9 of marker feeding. Fecal samples were dried at 608C for 72 h and ground through a 2 mm Wiley mill screen. A composite fecal sample (1 g) for each period from individual cows was dry ashed in duplicate for 16 h at 5008C in a muf¯e furnace. Concentrations of Yb (parts per million) in marked feed, feed refusals, and fecal samples were determined by direct current plasma spectroscopy (Spectra Metrics, Inc., subsidiary of Beckman Instruments, Inc., Andover, MA, USA) using the procedure described by Combs and Satter (1992). The DM digestibility (%) for individual cows was calculated using the formula: ((1 concentration of Yb in DM consumed)/concentration of Yb in fecal samples 100. Apparent digestibility of fatty acids, expressed as a percentage, was computed as the difference between intake and amount excreted in feces divided by intake. Nutrient composition and fatty acid pro®le of the diets are in Table 2. Supplementation of fat in the test diets resulted in higher calculated energy (NEL) content compared with the control diet. The RUP as a proportion of total DM in FATP and FATPC treatments was an average 5 g kg 1 higher than RUP in control and FAT treatments (Table 2). Total fatty acids in fat-supplemented treatments contained an average 20 g more fatty acids per kg than control. Supplementation of fat to the diets reduced the proportions of C12:0, C14:0, and C15:0, and increased the proportions of C16:0 and C18:0 fatty acids compared with the control diet (Table 2). The proportions of fatty acids were the same in FAT and FATP treatments, because the same fat source was used in both treatments. The major difference between the two fat sources was that fat-coated protein had more C18:0 fatty acid and lower proportions of C18:1 than Ener GIITM. An advantage of using fat-coated protein was that it had higher content of saturated fatty acids, and saturated fatty acids are less toxic to the rumen microorganisms than unsaturated fatty acids (Jenkins, 1993). Additionally, fatcoated protein had lower proportions of C18:1 fatty acid, and a trans-isomer of C18:1 unsaturated fatty acid has been shown to reduce the fat content of milk (Romo et al., 1996). Since all diets had the same source of protein (soybean), the amino acid pro®le of total mixed rations was same in all diets (data not shown).
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Table 2 Nutrient composition of diets Treatment
1
DM (g kg of fresh feed) NEL (Mcal kg 1 DM)a CP (g kg 1 DM) RUP (g kg 1 DM)b Total fatty acids (g kg 1 DM)c
Control
Fat
Fat RUP
Fat-coated protein
586 1.642 160 59 28.3
583 1.719 161 59 48.3
585 1.719 163 63 49.6
578 1.688 164 64 47.2
0.4 6.6 16.6 23.5 6.2 317.7 34.3 279.1 275.5 40.1 38:62
0.4 6.4 16.2 23.2 6.1 312.1 34.6 277.1 282.4 41.5 38:62
0.3 6.6 16.0 24.0 6.7 317.3 160.7 180.9 248.2 39.3 51:49
Fatty acid (g kg 1 of total fatty acid reported) C10:0 0.4 C12:0 11.0 25.3 C14:0 C14:1 28.9 C15:0 10.4 C16:0 174.4 29.4 C18:0 C18:1 216.5 C18:2 437.5 C18:3 66.3 Saturated:unsaturated fatty acid 25:75 a
Calculated using NRC (1989) feed energy values. The RUP (as a percentage of total CP) values used for alfalfa hay, corn silage, steam rolled corn, soybean meal, and beet pulp were 28, 31, 58, 35, and 45, respectively (NRC, 1989). c Calculated by analyzing dietary ingredients for total fatty acids (C10:0 C18:3 ). b
2.3. Statistical data analysis Statistical analysis was performed by analysis of variance using the ANOVA procedures of SAS (1989). The experimental design was a replicated 4 4 Latin square and the statistical model used was: response overall mean group cow within group period period group treatment treatment group residual error. The single degree of freedom orthogonal comparisons were (1) control versus all other treatments, (2) fat versus fat and protein (FAT versus FATP and FATPC), (3) fat plus RUP versus fat-coated protein (FATP versus FATPC). Signi®cance was declared at P < 0:05 unless otherwise noted. 3. Results and discussion The effects of group and treatment by group interaction were not signi®cant for any of the variables reported. Daily DM, NEL, and CP intakes were the same in all treatments (Table 3). As expected, higher RUP content of diets in FATP and FATPC resulted in higher intake of RUP compared with the FAT treatment. However, as mentioned earlier, RUP values are relative and should be interpreted with caution due to lack of an accurate method for estimation. The RUP intakes between FATP and FATPC treatments or FAT
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Parameter
Feed intake NEL (Mcal per day) CP RUP Fatty acid a b
S.E.M.a
Treatment (kg per day) Control
Fat
Fat RUP
Fat-coated protein
26.4 43.3 4.30 1.59 0.78
25.9 44.4 4.25 1.55 1.33
25.4 43.6 4.29 1.66 1.36
25.8 43.5 4.34 1.70 1.31
0.4 0.6 0.06 0.02 0.02
Square root of the mean square error divided by number of observations in each treatment. Level of signi®cance P < 0:01 is shown as P 0:01.
Significance of differenceb Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
0.13 0.47 0.93 0.09 0.01
0.54 0.28 0.40 0.01 0.80
0.45 0.92 0.58 0.20 0.08
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Table 3 Dietary intake of feed, energy (NEL), protein, and fatty acid of cows fed fat, fat plus RUP, or fat-coated protein
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and control treatments were not different. Higher dietary fat in all fat-supplemented treatments resulted in higher intakes of fatty acids compared with the control. Cows in fat-supplemented treatments produced more milk compared with cows in the control treatment (Table 4). Milk yield often increases by 1.0±1.5 kg per day when dairy cow diets are supplemented with fat (Palmquist, 1984). Feeding RUP along with fat in the FATP and fat-coated protein in FATPC treatments showed no increase in milk yield compared with fat alone. Chan et al. (1997) reported improved milk yield by adding fat along with protein containing higher proportions of RUP versus protein with low RUP. Increasing RUP in the diet can increase milk yield of high-producing cows (Santos et al., 1998). In the present study, an average 0.130 kg per day increase in RUP intake in FATP and FATPC compared with FAT treatment did not result in a signi®cant change in milk yield. There was no difference in milk yields of cows in FATP and FATPC treatments. Fat content in the milk and daily yield of milk fat did not differ among treatments (Table 4). Feeding supplemental fat enriched in saturated fatty acids either maintains or increases milk fat content, whereas feeding fat enriched in unsaturated fatty acids reduces milk fat content (Griinari et al., 1998). In the present study, feeding fat-coated protein enriched with saturated fatty acids had no in¯uence on milk fat content. A milk fat depression was not observed in the present study, probably because of higher proportions of saturated fatty acids in the test diets compared with the control diet (Table 2). Addition of fat to the diet reduced the protein content of milk compared with the control treatment. Depression in milk protein content is often observed when dairy cows are fed supplemental fat (Dhiman et al., 1995; Wu and Huber, 1994). Supplying fat and RUP sources in FATP and FATPC treatments partially alleviated the depression in protein content of milk caused by supplemental fat (Table 4). Wu and Huber (1994) suggested that decreased milk protein content during fat supplementation relates to an inadequacy of critical amino acids available to the mammary gland for milk protein synthesis. Altering amino acid composition of the digesta entering the small intestine by manipulating the diet may improve milk protein content of cows supplemented with fat (Griinari et al., 1998). Results from the present study con®rm earlier ®ndings that the reduction in protein content of milk due to dietary fat can be partially eliminated by increasing the supply of RUP in the diet. Milk protein content of cows in FATP and FATPC treatments was not different, suggesting that feeding fat plus RUP or fat-coated protein alleviated the depression in milk protein content to the same extent. Because of slightly higher milk yield, cows in FATPC treatment produced 80 g more milk protein compared with cows in the FATP treatment. The lactose content did not differ among treatments. Higher milk yield and similar feed intakes improved the relative gross feed ef®ciencies (ECM produced per kg of feed intake) in fat-supplemented treatments compared with the control. Feeding fat plus RUP or fat-coated protein did not improve feed ef®ciency of cows compared with fat alone. However, it is dif®cult to evaluate feed ef®ciency in a short-term experiment. We recommend long-term studies to evaluate the feed ef®ciency of cows fed diets supplemented with fat-coated protein. Fatty acid composition of the milk fat is summarized in Table 5. The proportions of short- and medium-chain fatty acids (from C10:0 to C15:0) were reduced in fatsupplemented treatments compared with the control. The proportions of C16:0 and C16:1
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Parameter
Milk yield (kg per day) 3.5% Fat-corrected milkc (FCM) (kg per day) Energy-corrected milkc (ECM) (kg per day) Fat (g kg 1) Fat yield (kg per day) Protein (g kg 1) Protein yield (kg per day) Lactose (g kg 1) ECM (per kg of feed intake) a
S.E.M.a
Treatment Control
Fat
Fat RUP
Fat-coated protein
36.4 35.6 36.5 34.2 1.23 33.4 1.20 48.6 1.39
38.3 36.7 37.3 32.9 1.25 31.6 1.21 48.7 1.45
37.5 37.5 37.9 35.5 1.32 32.1 1.19 49.2 1.50
39.6 38.6 39.3 34.0 1.33 32.4 1.27 49.2 1.53
0.3 0.7 0.6 0.8 0.04 0.2 0.01 0.3 0.03
Significance of differenceb Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
0.01 0.05 0.05 0.98 0.17 0.01 0.08 0.21 0.04
0.61 0.18 0.14 0.13 0.15 0.02 0.03 0.23 0.15
0.01 0.32 0.15 0.24 0.81 0.20 0.01 0.90 0.54
Square root of the mean square error divided by number of observations in each treatment. Level of signi®cance P < 0:01 is shown as P 0:01. c Fat-corrected milk was computed as: 3.5% FCM 0:432 milk kg 16:23 fat (kg); energy-corrected milk was computed as: ECM 0:327 milk kg 12:95 fat kg 7:20 protein (kg); these equations were derived from Tyrrell and Reid (1965). b
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Table 4 Milk yield and milk composition of cows fed fat, fat RUP, or fat-coated protein
Table 5 Fatty acid composition of milk fat from cows fed fat, fat plus RUP, or fat-coated protein
C8:0 C10:0 C12:0 C14:0 C14:1 C15:0 C16:0 C16:1 C17:1 C18:0 Trans-9 C18:1 Trans-11 C18:1 Cis-9 C18:1 Cis-11 C18:1 C18:2 CLAd g-C18:3 C18:3 Cis-8, 11, 14 C20:3 Cis-11, 14, 17 C20:3 a
Treatment (g kg
1
weight of fatty acids reported)
Control
Fat
Fat RUP
Fat-coated protein
11.7 10.5 33.3 46.3 141.5 16.7 387 17.2 2.4 91 12.5 9.5 175.5 4.3 27.5 3.9 0.5 4.9 1.7 2.2
11.6 9.8 28.7 37.7 125.7 12.9 370 15.2 1.9 93 14.5 12.4 217.3 2.9 32.9 4.6 0.6 4.7 1.8 1.9
11.1 9.5 28.0 36.8 122.4 12.6 373 14.5 2.0 98 14.7 12.3 215.2 3.0 33.4 4.5 0.6 4.9 1.7 1.9
11.4 9.5 27.3 35.6 121.5 13.2 395 17.2 2.4 102 14.6 10.5 200.0 2.5 25.9 3.6 0.5 4.2 1.5 1.8
S.E.M.b
0.2 0.2 0.7 1.0 2.2 0.3 6.0 0.5 0.1 2.3 0.6 0.5 4.0 0.8 0.8 0.1 0.1 0.1 0.1 0.1
Number of carbons:number of double bonds. Square root of the mean square error divided by number of observations in each treatment. c Level of signi®cance P < 0:01 is shown as P 0:01. d Conjugated linoleic acid (cis-9, trans-11 C18:2).
Significance of differencec Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
0.12 0.01 0.01 0.01 0.01 0.01 0.10 0.12 0.01 0.05 0.01 0.01 0.01 0.18 0.02 0.05 0.20 0.01 0.47 0.01
0.10 0.02 0.01 0.03 0.02 0.92 0.02 0.53 0.01 0.05 0.59 0.01 0.01 0.92 0.03 0.01 0.48 0.18 0.01 0.84
0.30 0.80 0.01 0.11 0.48 0.24 0.01 0.05 0.01 0.22 0.74 0.01 0.01 0.73 0.01 0.01 0.24 0.01 0.03 0.24
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Fatty acida
b
179
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fatty acids in milk were higher in FATPC treatment compared to FATP. Higher proportions of C18:0, C18:1, and C18:2 fatty acids in milk of cows fed fat-supplemented diets probably re¯ects their supply in the diet. An increased supply of dietary long-chain fatty acids has been shown to increase their secretion in milk fat and inhibit de novo synthesis of short- and medium-chain fatty acids in the mammary gland (Grummer, 1991). The hypercholesterolaemic effect of saturated fats in human diets is largely due to C12:0, C14:0, and C16:0 fatty acids; C18:0 is as effective as C18:1 in lowering blood plasma cholesterol in humans (Bonanome and Grundy, 1988). Increases in the proportion of C18:0 and C18:1 in milk fat of cows fed fat-supplemented diets may have health bene®ts in humans by decreasing the cholesterolaemic effects of milk fat. Conjugated linoleic acid content in milk was higher in fat-supplemented treatments compared with the control treatment (Table 5). Increased supply of unsaturated fatty acids to the rumen microbes has been shown to increase CLA in milk due to incomplete biohydrogenation of unsaturated fatty acids in the rumen (Dhiman et al., 2000). The FATPC treatment had lower levels of CLA in milk compared with FATP due to higher proportions of saturated fatty acids in the diet (Table 2). Recently, CLA has received considerable attention as an anticarcinogen (Dhiman et al., 2000). Results from this study suggest that feeding fat-coated protein did not increase the CLA content of milk. Compared with FAT and FATP treatments, the control had lower CLA content despite having 75% unsaturated fat in total dietary fat. The fat should be accessible to the rumen microbes for biohydrogenation to convert it to CLA. The source of fat in the control diet was maize and soybean meal. Fat is less accessible to the rumen microbes when it is supplied through seeds compared with the free oil in FAT and FATP treatments (Dhiman et al., 2000). Additionally, the amount of fat intake was low in the control treatment compared with the others. Feed DM digestibility did not differ among treatments (Table 6), suggesting that addition of fat, fat plus protein, or fat-coated protein did not in¯uence the digestibility of DM in the present study. Dietary fat in excess of 70±80 g kg 1 of diet DM has been shown to inhibit microbial activity in the rumen and reduce feed digestibility (Palmquist, 1984). Total fatty acid content of the diets ranged between 28.3 and 49.6 g kg 1 of diet DM in the present experiment, and were within the presumed safe limits for inclusion of fat in dairy cow diets without decreasing nutrient utilization. Apparent digestibility of C12:0, C14:0, C14:1, and C15:0 fatty acids in the total gastrointestinal tract, as a percentage of intake, was not altered by supplemental fat, fat plus RUP, or fat-coated protein (Table 6). The average digestibilities were 97.6, 94.4, 80.8, and 48.8% of intake for the respective fatty acids. Compared with control, the apparent digestibility of C16:0 was increased in fat-supplemented treatments, probably due to its increased supply through the diet. The digestibility coef®cient for C18:0 was negative for all treatments. This was because dietary unsaturated 18-carbon fatty acids were biohydrogenated in the rumen, resulting in more C18:0 passing to the feces than was consumed by the cows (Klusmeyer and Clark, 1991). Ruminal biohydrogenation of dietary unsaturated fatty acids increases passage of certain fatty acids (saturated and unsaturated) to the small intestine which may be greater than their intake (Jenkins, 1993). The apparent digestibility of C18:0 was 3.2% of intake in FATPC treatment compared with 343.7% in the control treatment. Increased dietary supply of C18:0 in
Item
S.E.M.a
Treatment (%) Control
Fat
Fat RUP
Fat-coated protein
Significance of differenceb Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
Dry matter
63.2
62.0
61.3
62.1
1.4
0.41
0.86
0.68
Fatty acid C10:0 C12:0 C14:0 C14:1 C15:0 C16:0 C18:0 C18:1 C18:2 C18:3
100.0 97.8 94.7 80.0 48.1 59.9 343.7 82.7 97.3 97.8
85.8 97.9 94.3 81.0 49.1 69.2 205.0 88.8 97.4 98.0
93.7 96.9 94.0 81.8 48.0 71.8 198.6 89.7 97.7 98.2
96.6 97.8 94.6 80.2 49.8 68.2 3.2 86.5 97.2 98.0
6.7 0.4 0.3 0.6 2.6 2.1 31.8 0.4 0.1 0.1
0.34 0.61 0.19 0.17 0.78 0.01 0.01 0.01 0.09 0.01
0.29 0.30 0.96 1.0 0.95 0.78 0.04 0.21 0.51 0.07
0.77 0.13 0.20 0.10 0.66 0.28 0.01 0.01 0.01 0.06
a b
Square root of the mean square error divided by number of observations in each treatment. Level of signi®cance P < 0:01 is shown as P 0:01.
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Table 6 Digestibility of dry matter and fatty acids in cows fed fat, fat plus RUP, or fat-coated protein
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fat-supplemented treatments resulted in a less negative digestibility of C18:0 compared with the control treatment, probably because there were less 18-carbon unsaturated fatty acids available from the diet to convert to C18:0 through ruminal biohydrogenation. Klusmeyer and Clark (1991) reported similar fatty acid digestibility patterns. Average apparent digestibilities of C18:1, C18:2, and C18:3 were 86.9, 97.4, and 98.0% of intake, respectively. Apparent digestibility of unsaturated 18-carbon fatty acid averaged 96% of intake in sheep fed different sources of supplemental fat (Andrews and Lewis, 1970). Feeding fat sources enriched in C16:0 and C18:0 fatty acids altered the total tract apparent digestibility of these fatty acids and other unsaturated fatty acids, suggesting that there might be opportunities for optimizing fatty acid digestibility in the gastrointestinal tract by altering the fatty acid pro®le of dietary fat. Altering the supply of long-chain fatty acids can in¯uence the fatty acid composition of milk fat, because these fatty acids are directly incorporated into milk fat in the mammary gland (Palmquist, 1984; Grummer, 1991). Supplementing fat or fat-coated protein improved the milk yield of dairy cows compared with a control with no supplemental fat. Supplying RUP along with fat or fat-coated protein provided no further improvement in milk yield and relative gross feed ef®ciency (milk/feed intake) compared with fat alone. Feeding RUP along with fat or fat-coated protein partially alleviated the depression in milk protein content caused by supplemental fat and increased the daily yield of milk protein by 60±80 g per day. Inclusion of fat increased the proportions of longer-chain fatty acids in the milk and decreased the short- and medium-chain fatty acids. Further studies are recommended to evaluate the long-term bene®ts of including fat-coated protein in dairy diets. 4. Conclusions Cows fed diets containing fat-coated protein produced the same amount of milk as cows fed fat alone. Including fat-coated protein partially alleviated the depression in milk protein content caused by supplemental fat and increased protein yield by 60 g per day. Since there was no advantage in milk yield, the decision to include fat-coated protein in dairy rations should be based on its price compared to fat alone and the return in terms of milk protein yield. Acknowledgements The authors thank Donald V. Sisson, Department of Mathematics and Statistics, and Jeffrey L. Walters, Department of Animal, Dairy and Veterinary Sciences, Utah State University, for statistical analysis of the data. Research was partially supported by the Utah Agricultural Experiment Station, Utah State University, Logan, UT, USA. Continental Grain Company, Chicago, IL, USA, is gratefully acknowledged for the partial funding and supplying fat-coated protein (DuetsTM) for the research references.
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References Andrews, R.J., Lewis, D., 1970. The utilization of dietary fats by ruminants. 1. The digestibility of some commercially available fats. J. Agric. Sci. (Camb.) 75, 47±53. Bonanome, A., Grundy, S.M., 1988. Effect of dietary stearic acid on plasma cholesterol and lipoprotein levels. N. Engl. J. Med. 318, 1244±1248. Chan, S.C., Huber, J.T., Theurer, C.B., Wu, Z., Chen, K.H., Simas, J.M., 1997. Effects of supplemental fat and protein source on ruminal fermentation and nutrient ¯ow to the duodenum in dairy cows. J. Dairy Sci. 80, 152±159. Chin, S.F., Liu, W., Storkson, J.M., Ha, Y.L., Pariza, M.W., 1992. Dietary sources of conjugated dienoic isomers of linoleic acid, a newly recognized class of anticarcinogens. J. Food Compos. Anal. 5, 185±197. Christensen, R.A., Cameron, M.R., Clark, J.H., Drackley, J.K., Lynch, J.M., Barbano, D.M., 1994. Effects of amount of protein and ruminally protected amino acids in the diet of dairy cows fed supplemental fat. J. Dairy Sci. 77, 1618±1629. Combs, D.K., Satter, L.D., 1992. Determination of markers in digesta and feces by direct current plasma emission spectroscopy. J. Dairy Sci. 75, 2176±2183. Coppock, C.E., Wilks, D.L., 1991. Supplemental fat in high-energy rations for lactating cows: effects on intake, digestion, milk yield, and composition. J. Anim. Sci. 69, 3826±3837. DePeters, E.J., Cant, J.P., 1992. Nutritional factors in¯uencing the nitrogen composition of bovine milk: a review. J. Dairy Sci. 75, 2043±2070. Dhiman, T.R., Zanten, K.V., Satter, L.D., 1995. Effect of dietary fat source on fatty acid composition of cow's milk. J. Sci. Food Agric. 69, 101±107. Dhiman, T.R., Helmink, E.D., McMahon, D.J., Fife, R.L., Pariza, M.W., 1999. Conjugated linoleic acid content of milk and cheese from cows fed extruded oilseeds. J. Dairy Sci. 82, 412±419. Dhiman, T.R., Satter, L.D., Pariza, M.W., Gali, M.P., Albright, K., 2000. Conjugated linoleic acid (CLA) content of milk from cows offered diets rich in linoleic and linolenic acid. J. Dairy Sci. 83, 1016±1027. Erdman, R.A., 1988. Dietary buffering requirements of the lactating dairy cows: a review. J. Dairy Sci. 71, 3246±3266. Griinari, J.M., Dwyer, D.A., McGuire, M.A., Bauman, D.E., Palmquist, D.L., Nurmela, K.V.V., 1998. Trans-octadecenoic acids and milk fat depression in lactating dairy cows. J. Dairy Sci. 81, 1251±1261. Grummer, R.R., 1991. Effect of feed on the composition of milk fat. J. Dairy Sci. 74, 3244±3257. Harouna, A.M., Schingoethe, D.J., 1997. Optimizing the utilization of animal fat and ruminal bypass proteins in the diets of lactating dairy cows. J. Dairy Sci. 80, 343±352. Holter, J.B., Hayes, H.H., Kierstead, N., Whitehouse, J., 1993. Protein-fat bypass supplement for lactating dairy cows. J. Dairy Sci. 76, 1342±1352. Hurley, W.L., Warner, G.J., Grummer, R.R., 1987. Changes in triglyceride fatty acid composition of mammary secretions during involution. J. Dairy Sci. 70, 2406±2410. Jenkins, T.C., 1993. Lipid metabolism in the rumen. J. Dairy Sci. 76, 3851±3863. Klusmeyer, T.H., Clark, J.H., 1991. Effects of dietary fat and protein on fatty acid ¯ow to the duodenum and in milk produced by dairy cows. J. Dairy Sci. 74, 3055±3067. National Research Council (NRC), 1989. Nutrient Requirements of Dairy Cattle, 6th Edition. National Academy of Sciences, National Academy Press, Washington, DC, USA. Palmquist, D.L., 1984. The use of fats in diets for lactating dairy cows. In: Wiseman, J. (Ed.), Fats in Animal Nutrition. Butterworths, Boston, USA, pp. 357±381. Palmquist, D.L., Weisbjerg, M.R., Hvelplund, T., 1993. Ruminal, intestinal, and total digestabilities of nutrients in cows fed diets high in fat and undegradable protein. J. Dairy Sci. 76, 1353±1364. Roe, M.B., Sniffen, C.J., 1990. Techniques for measuring protein fractions in feedstuffs. In: Proceedings of the Cornell Nutrition Conference for Feed Manufacturer, Cornell University Ithaca, New York, USA, p. 81. Romo, G.A., Casper, D.P., Erdman, R.A., Teter, B.B., 1996. Abomasal infusion of cis- or trans-fatty acid isomers and energy metabolism of lactating dairy cows. J. Dairy Sci. 79, 2005±2015. Santos, F.A.P., Santos, J.E.P., Theurer, C.B., Huber, J.T., 1998. Effects of rumen-undegradable protein on dairy cow performance: a 12-year literature review. J. Dairy Sci. 81, 3182±3213.
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Statistical Analysis Systems Institute (SAS), 1989. SAS User's Guide: Statistic, Version 6, 4th Edition. SAS Institute, Inc., Cary, NC, USA. Sukhija, P.S., Palmquist, D.L., 1988. Rapid method for determination of total fatty acid content and composition of feedstuffs and feces. J. Agric. Food Chem. 36, 1202±1206. Sutton, J.D., 1989. Altering milk composition by feeding. J. Dairy Sci. 72, 2801±2814. Tyrrell, H.F., Reid, J.T., 1965. Prediction of the energy value of cow's milk. J. Dairy Sci. 48, 1215±1223. Wu, Z., Huber, J.T., 1994. Relationship between dietary fat supplementation and milk protein concentration in lactating cows: a review. Livestock Prod. Sci. 39, 141±155.
Milk yield response of dairy cows fed fat along with protein$ T.R. Dhimana,*, I.S. MacQueena, N.D. Luchinib a
Animal, Dairy and Veterinary Sciences, Utah State University, 4815 Old Main Hill, Logan, UT 84322-4815, USA b Continental Grain Company, 222 South Riverside Plaza, Chicago, IL 60606, USA Received 22 August 2000; received in revised form 19 December 2000; accepted 2 January 2001
Abstract The in¯uence of a fat-coated protein on milk production of Holstein dairy cows was determined using a 4 4 Latin square experiment. Twelve cows were fed a control diet or test diets supplemented with fat, fat plus ruminally undegraded protein (RUP), or a fat-coated protein (DuetsTM). Cows fed test diets received 0.55 kg of more fat per day than cows in the control treatment. Daily intakes of feed, energy, and protein were the same in all treatments. Cows produced 36.5, 37.3, 37.9, and 39.3 kg of energy-corrected milk per day in control, fat, fat plus RUP, and fat-coated protein treatments, respectively. Cows fed fat-supplemented diets produced an average 1.7 kg more milk daily compared with cows in the control treatment. Feeding RUP along with fat or fat-coated protein provided no further improvement in milk yield compared with fat alone, but partially alleviated the depression in protein content caused by supplemental fat and increased the daily yield of milk protein. In the present experiment, cows fed fat-coated protein produced daily an average 60 g of milk protein more than cows fed fat alone. Since, there was no advantage in milk yield, the decision to include fat-coated protein in dairy rations should be based on its price compared to fat alone and the return in terms of milk protein yield. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Cow; Milk; Fat; Protein; Conjugated linoleic acid
1. Introduction Meeting the energy and protein needs of high-producing dairy cows is sometimes a challenge. Increasing grain relative to forage in dairy diets can increase energy density of $
Approved as journal paper number 7194 of the Utah Agricultural Experiment Station, Utah State University, Logan, UT, USA. * Corresponding author. Tel.: 1-435-797-2155; fax: 1-435-797-2118. E-mail address: [email protected] (T.R. Dhiman). 0377-8401/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 1 ) 0 0 2 0 9 - 7
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the diet and allow greater energy intake. However, excessive intake of starch can lead to acidosis (Erdman, 1988), milk fat depression (Sutton, 1989), and depressed feed intake (Holter et al., 1993). Fat has more than three times the net energy of lactation relative to protein and carbohydrate. Supplemental fat has been shown to increase milk yield in high-producing dairy cows (Coppock and Wilks, 1991). Replacing fermentable carbohydrate with fat in the diet of high-producing dairy cows may limit synthesis of microbial protein and will decrease the ¯ow of microbial protein to the small intestine (Palmquist et al., 1993). In some situations, supplementation with fat may limit the supply of amino acids to the mammary gland and reduce milk protein content (DePeters and Cant, 1992). A study by Dhiman et al. (1995) observed 1.0±1.5 g kg 1 decrease in protein content of milk from cows fed diets supplemented with fat. Wu and Huber (1994) summarized the results of 47 experiments from the literature and suggested that an increase in dietary fat from 25 to 80 g kg 1 would decrease milk protein by 3.8 g kg 1. Addition of rumen-protected amino acids to the fat-supplemented diet resulted in increases of 0.8±1.0 g kg 1 of milk protein output (Christensen et al., 1994). Increasing the energy content of the diet through supplemental fat also increases the protein requirements of a cow in order to maintain the ratio of protein to energy. Cows fed supplemental fat along with protein containing a higher proportion of ruminally undegraded protein (RUP) produced more milk compared with cows fed protein with low RUP content (Chan et al., 1997; Harouna and Schingoethe, 1997). These results suggest that the quality and quantity of protein supplied along with the fat in¯uences the performance of high-producing dairy cows. Since fat alone sometimes is not very palatable in the diet of high-producing dairy cows (Dhiman et al., 1995), our hypothesis was that feeding dairy cows a fat-coated protein would improve palatability of a diet containing fat, supply protein and energy simultaneously, and improve the performance of dairy cows. The objective of this research was to determine the milk yield and milk composition of high-producing dairy cows fed fat-coated protein (DuetsTM; Fig. 1). 2. Materials and methods 2.1. Animals and treatments Twelve multiparous Holstein dairy cows were strati®ed into three groups of four according to pre-treatment milk yield. Cows within each group were assigned randomly to four treatments over four periods in a 4 4 Latin square design. Each period was 21 days. The ®rst 14 days in each period were for adaptation to diets and the last 7 days for data collection. Cows were housed in tie stalls and fed individually. At the start of the experiment, cows were 38±93 days in lactation and were producing from 39.8 to 52.7 kg of milk per day. The study was conducted from December 1997 to March 1998 at the Caine Dairy Teaching and Research Center, Utah State University, Logan, UT, USA. Animal care and experimental procedures were approved and conducted under established standards of the Utah State University Institutional Animal Care and Use Committee (Approval # 900).
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171
Fig. 1. Fat-coated protein (DuetsTM). DuetsTM is the registered trademark of Continental Grain Company, Chicago, IL, USA, for fat-coated protein. Solvent-extracted soybean meal was used as a protein source in fatcoated protein. The fat-coated protein contained 43.6% fat and 29.8% protein, and fatty acid composition was 2.1% C14:0, 49.7% C16:0, 32.6% C18:0, 14.0% C18:1, and 1.6% C18:2 of total fatty acids.
The four treatment diets were control, supplemental fat (FAT), fat plus RUP (FATP), or fat-coated protein (FATPC). The source of fat in FAT and FATP treatments was Ener GIITM. Ener GIITM is the registered trademark of Bioproducts, Inc., Fairlawn, OH, USA, for calcium salts of palm oil fatty acids. The Ener GIITM contained 82.3% fat and 8.8% calcium. The fatty acid composition of Ener GIITM was 1.7% C14:0, 49.5% C16:0, 4.0% C18:0, 36.3% C18:1, and 8.5% C18:2 of total fatty acids. The source of RUP in the FATP diet was the Soybest1 (a registered trademark for soybean meal product of Grain States Soya, Inc., West Point, NE, USA). The source of fat-coated protein in FATPC treatment was DuetsTM. DuetsTM is the registered trademark of Continental Grain Company, Chicago, IL, USA, for fat-coated protein. Solvent-extracted soybean meal was used as a protein source in fat-coated protein. Fat-coated protein contained 43.6% fat and 29.8% protein. The fatty acid composition of fat-coated protein was 2.1% C14:0, 49.7% C16:0, 32.6% C18:0, 14.0% C18:1, and 1.6% C18:2 of total fatty acids.
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Table 1 Ingredient composition of the diets Ingredient
Lucerne hay Maize silage Maize steam rolled Soybean meal Soybest1a Ener GIITMb DuetsTMc Dehydrated beet pulp Molasses Dicalcium phosphated Trace-mineralized salte Vitamin ADE mixf
Treatment (g kg
1
dry matter)
Control
Fat
Fat RUP
Fat-coated protein
320 160 327 141 ± ± ± 22 13 7 5 5
320 160 294 148 ± 26 ± 22 13 7 5 5
320 160 289 126 27 26 ± 22 13 7 5 5
320 160 299 121 ± ± 48 22 13 7 5 5
a
A registered trademark for soybean meal product (Grain States Soya, Inc., West Point, NE, USA). A registered trademark for rumen-inert calcium-salts of long-chain fatty acids (Bioproducts, Inc., Fairlawn, OH, USA). c Fat-coated with protein (Continental Grain Company, Chicago, IL, USA). d Dicalcium phosphate contained; minimum 210 g P; 180 g Ca; ¯uorine maximum 2.1 g kg 1. e Trace-mineralized salt contained; NaCl, minimum 950 g kg 1; minimum 3.5 g Zn, 2 g Fe, 1.8 g Mn, 0.35 g Cu, 0.1 g I, 0.06 g Co kg 1 of mix. f Contained 1,102,317 IU of Vitamin A, 330,695 IU of Vitamin D, and 6614 IU of Vitamin E kg 1. b
Diets contained 480 g kg 1 forage DM (Table 1). The forage was comprised of 667 g kg 1 Lucerne hay and 333 g kg 1 maize silage on a DM basis. Fat and protein were added to the diet by partially replacing maize and soybean meal. The proportion of other ingredients remained the same across treatment diets. Diets were fed as a total mixed ration twice daily at 07.30 and 19.30 h. A common forage mix for the diets was prepared on alternate days and concentrates were mixed with forage daily before the morning feeding. Amounts of feed offered were adjusted daily to ensure feeding 50±100 g kg 1 in excess of ad libitum fresh feed intake. 2.2. Sampling and measurements Feed offered and refused for individual cows was measured daily. Feed refusals were removed every day. Daily samples of the total mixed ration offered and feed refused were collected from each cow during week 3 in each period. Feed refusals were mixed for each treatment and a representative sample was frozen. Weekly composite samples of total mixed ration and feed refusals were analyzed for DM. Samples of individual dietary ingredients were obtained weekly and used for DM determination. To determine DM, feed samples were dried at 608C for 48 h. Diet formulations were adjusted weekly, if necessary, to account for small changes in ingredient DM content. Dried samples were ground through a Wiley mill (Arthur H. Thomas, Philadelphia, PA, USA) using a 1 mm screen. Composite samples of feed ingredients for each period were
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analyzed for composition. Crude protein (CP) in the dietary ingredients and feed refusal samples were determined using a Protein Nitrogen Analyzer model 2100 (ThermoQuest Italia S.P.A., Strada Rivoltana, Milan, Italy). To calculate RUP in the diet, the Soybest1 and fat-coated protein were analyzed for RUP using the procedure described by Roe and Sniffen (1990), and RUP values from NRC (1989) were used for other dietary ingredients. The RUP values used in this study are a relative number due to lack of an accurate method for estimation. The forage samples were analyzed for neutral detergent ®ber (NDF) and acid detergent ®ber (ADF) using the ®lter bag technology of Ankom (Ankom Technology Corporation, Fairport, NY, USA). Dietary ingredients and feed refusal samples were analyzed for fatty acid content and composition using the procedure of Sukhija and Palmquist (1988). Ground samples of total mixed ration were hydrolyzed with sodium metabisul®te and analyzed for amino acids using an amino acid analyzer (Model 6300; Beckman Instrument Inc., Fullerton, CA, USA). During analysis, the samples were further dried at 1058C for 8 h to determine the absolute DM. Chemical analyses were expressed on this ®nal DM. Dry matter intake (DMI) was calculated by subtracting the weekly average feed refused from the total mixed ration offered. Chemical composition of the total mixed ration was calculated from chemical analyses of the individual ingredients. Net energy of lactation (NEL) content of the diets was calculated by using NEL values from NRC (1989) for individual dietary ingredients. The NEL and RUP intakes for each cow were calculated by multiplying NEL and RUP concentrations in the diet by the DMI of each cow. Daily protein and fatty acid intakes were calculated by subtracting protein and fatty acids in feed refusal from their respective values in the total mixed ration that was offered to cows. Milk weights were recorded daily. Milk samples were collected from two consecutive milkings (a.m. and p.m.) during the last week in each period. Milk samples were composited for each cow proportional to milk yield. Composite milk samples from individual cows were analyzed for fat, protein, and lactose by the Rocky Mountain Dairy Herd Improvement Association Laboratory (Logan, UT, USA) with near-infrared procedures using a Bentley 2000 (Bentley Instruments, Chaska, MN, USA). Gross feed ef®ciency was calculated as kilograms of energy-corrected milk (ECM; Tyrrell and Reid, 1965) produced per kg of feed intake on an individual cow basis. Average fat and protein yields were calculated by multiplying milk yield by fat and protein content on an individual cow basis. Weighted composite milk samples from each cow during the last week in each period were analyzed for fatty acid composition including conjugated linoleic acid (CLA). To determine fatty acid composition, fat was extracted by boiling in a detergent solution (Hurley et al., 1987) and derivatized to methyl esters by mixing 30 mg of fat with 5 ml of 4% HCl±methanol (Chin et al., 1992). Heptadecanoic acid was used as an internal standard. The methyl esters were extracted with 5 ml hexane and 1 ml of distilled water. The hexane extract was washed twice with distilled water and dried over anhydrous sodium sulfate. Fat samples were analyzed in a gas chromatograph (Model 6890, Hewlett-Packard Co., Wilmington, DE, USA) ®tted with a ¯ame ionization detector and 3397A integrator. Samples containing methyl esters in hexane (1±3 ml) were directly injected through the
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splitless injection port onto a Supelcowax 10, fused silica capillary column (100 m 0:32 mm i.d., 0.25 mm ®lm thickness; Supelco Inc., Bellefonte, PA, USA). Gas chromatography conditions were the same as described by Dhiman et al. (1999). The CLA standards used were synthesized as described by Chin et al. (1992). Fatty acids were identi®ed by comparing the retention times with the methylated fatty acid standards including CLA. The CLA reported is cis-9, trans-11 C18:2. Percentage of each fatty acid was calculated by dividing the area under the fatty acid peak by the sum of the areas under the total reported fatty acid peaks. The DM digestibility (DMD) was determined using ytterbium (Yb) as an external marker. A Yb solution was prepared by dissolving 1.15 g of 99% pure YbO3 (1 g of Yb) in 1.38 ml concentrated HCl and diluting with water to 25 ml. The Yb solution was sprayed onto 454 g of grain mix from the diet, which was pulse-fed daily from day 13 to day 21 in each period. The marked grain was fed before the regular feed was offered to ensure complete consumption of marked grain. Fecal grab samples were collected from individual cows at 06.00, 11.00, 17.00, and 23.00 h on day 8 and at 04.00, 09.00, 14.00, and 20.00 h on day 9 of marker feeding. Fecal samples were dried at 608C for 72 h and ground through a 2 mm Wiley mill screen. A composite fecal sample (1 g) for each period from individual cows was dry ashed in duplicate for 16 h at 5008C in a muf¯e furnace. Concentrations of Yb (parts per million) in marked feed, feed refusals, and fecal samples were determined by direct current plasma spectroscopy (Spectra Metrics, Inc., subsidiary of Beckman Instruments, Inc., Andover, MA, USA) using the procedure described by Combs and Satter (1992). The DM digestibility (%) for individual cows was calculated using the formula: ((1 concentration of Yb in DM consumed)/concentration of Yb in fecal samples 100. Apparent digestibility of fatty acids, expressed as a percentage, was computed as the difference between intake and amount excreted in feces divided by intake. Nutrient composition and fatty acid pro®le of the diets are in Table 2. Supplementation of fat in the test diets resulted in higher calculated energy (NEL) content compared with the control diet. The RUP as a proportion of total DM in FATP and FATPC treatments was an average 5 g kg 1 higher than RUP in control and FAT treatments (Table 2). Total fatty acids in fat-supplemented treatments contained an average 20 g more fatty acids per kg than control. Supplementation of fat to the diets reduced the proportions of C12:0, C14:0, and C15:0, and increased the proportions of C16:0 and C18:0 fatty acids compared with the control diet (Table 2). The proportions of fatty acids were the same in FAT and FATP treatments, because the same fat source was used in both treatments. The major difference between the two fat sources was that fat-coated protein had more C18:0 fatty acid and lower proportions of C18:1 than Ener GIITM. An advantage of using fat-coated protein was that it had higher content of saturated fatty acids, and saturated fatty acids are less toxic to the rumen microorganisms than unsaturated fatty acids (Jenkins, 1993). Additionally, fatcoated protein had lower proportions of C18:1 fatty acid, and a trans-isomer of C18:1 unsaturated fatty acid has been shown to reduce the fat content of milk (Romo et al., 1996). Since all diets had the same source of protein (soybean), the amino acid pro®le of total mixed rations was same in all diets (data not shown).
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Table 2 Nutrient composition of diets Treatment
1
DM (g kg of fresh feed) NEL (Mcal kg 1 DM)a CP (g kg 1 DM) RUP (g kg 1 DM)b Total fatty acids (g kg 1 DM)c
Control
Fat
Fat RUP
Fat-coated protein
586 1.642 160 59 28.3
583 1.719 161 59 48.3
585 1.719 163 63 49.6
578 1.688 164 64 47.2
0.4 6.6 16.6 23.5 6.2 317.7 34.3 279.1 275.5 40.1 38:62
0.4 6.4 16.2 23.2 6.1 312.1 34.6 277.1 282.4 41.5 38:62
0.3 6.6 16.0 24.0 6.7 317.3 160.7 180.9 248.2 39.3 51:49
Fatty acid (g kg 1 of total fatty acid reported) C10:0 0.4 C12:0 11.0 25.3 C14:0 C14:1 28.9 C15:0 10.4 C16:0 174.4 29.4 C18:0 C18:1 216.5 C18:2 437.5 C18:3 66.3 Saturated:unsaturated fatty acid 25:75 a
Calculated using NRC (1989) feed energy values. The RUP (as a percentage of total CP) values used for alfalfa hay, corn silage, steam rolled corn, soybean meal, and beet pulp were 28, 31, 58, 35, and 45, respectively (NRC, 1989). c Calculated by analyzing dietary ingredients for total fatty acids (C10:0 C18:3 ). b
2.3. Statistical data analysis Statistical analysis was performed by analysis of variance using the ANOVA procedures of SAS (1989). The experimental design was a replicated 4 4 Latin square and the statistical model used was: response overall mean group cow within group period period group treatment treatment group residual error. The single degree of freedom orthogonal comparisons were (1) control versus all other treatments, (2) fat versus fat and protein (FAT versus FATP and FATPC), (3) fat plus RUP versus fat-coated protein (FATP versus FATPC). Signi®cance was declared at P < 0:05 unless otherwise noted. 3. Results and discussion The effects of group and treatment by group interaction were not signi®cant for any of the variables reported. Daily DM, NEL, and CP intakes were the same in all treatments (Table 3). As expected, higher RUP content of diets in FATP and FATPC resulted in higher intake of RUP compared with the FAT treatment. However, as mentioned earlier, RUP values are relative and should be interpreted with caution due to lack of an accurate method for estimation. The RUP intakes between FATP and FATPC treatments or FAT
176
Parameter
Feed intake NEL (Mcal per day) CP RUP Fatty acid a b
S.E.M.a
Treatment (kg per day) Control
Fat
Fat RUP
Fat-coated protein
26.4 43.3 4.30 1.59 0.78
25.9 44.4 4.25 1.55 1.33
25.4 43.6 4.29 1.66 1.36
25.8 43.5 4.34 1.70 1.31
0.4 0.6 0.06 0.02 0.02
Square root of the mean square error divided by number of observations in each treatment. Level of signi®cance P < 0:01 is shown as P 0:01.
Significance of differenceb Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
0.13 0.47 0.93 0.09 0.01
0.54 0.28 0.40 0.01 0.80
0.45 0.92 0.58 0.20 0.08
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Table 3 Dietary intake of feed, energy (NEL), protein, and fatty acid of cows fed fat, fat plus RUP, or fat-coated protein
T.R. Dhiman et al. / Animal Feed Science and Technology 90 (2001) 169±184
177
and control treatments were not different. Higher dietary fat in all fat-supplemented treatments resulted in higher intakes of fatty acids compared with the control. Cows in fat-supplemented treatments produced more milk compared with cows in the control treatment (Table 4). Milk yield often increases by 1.0±1.5 kg per day when dairy cow diets are supplemented with fat (Palmquist, 1984). Feeding RUP along with fat in the FATP and fat-coated protein in FATPC treatments showed no increase in milk yield compared with fat alone. Chan et al. (1997) reported improved milk yield by adding fat along with protein containing higher proportions of RUP versus protein with low RUP. Increasing RUP in the diet can increase milk yield of high-producing cows (Santos et al., 1998). In the present study, an average 0.130 kg per day increase in RUP intake in FATP and FATPC compared with FAT treatment did not result in a signi®cant change in milk yield. There was no difference in milk yields of cows in FATP and FATPC treatments. Fat content in the milk and daily yield of milk fat did not differ among treatments (Table 4). Feeding supplemental fat enriched in saturated fatty acids either maintains or increases milk fat content, whereas feeding fat enriched in unsaturated fatty acids reduces milk fat content (Griinari et al., 1998). In the present study, feeding fat-coated protein enriched with saturated fatty acids had no in¯uence on milk fat content. A milk fat depression was not observed in the present study, probably because of higher proportions of saturated fatty acids in the test diets compared with the control diet (Table 2). Addition of fat to the diet reduced the protein content of milk compared with the control treatment. Depression in milk protein content is often observed when dairy cows are fed supplemental fat (Dhiman et al., 1995; Wu and Huber, 1994). Supplying fat and RUP sources in FATP and FATPC treatments partially alleviated the depression in protein content of milk caused by supplemental fat (Table 4). Wu and Huber (1994) suggested that decreased milk protein content during fat supplementation relates to an inadequacy of critical amino acids available to the mammary gland for milk protein synthesis. Altering amino acid composition of the digesta entering the small intestine by manipulating the diet may improve milk protein content of cows supplemented with fat (Griinari et al., 1998). Results from the present study con®rm earlier ®ndings that the reduction in protein content of milk due to dietary fat can be partially eliminated by increasing the supply of RUP in the diet. Milk protein content of cows in FATP and FATPC treatments was not different, suggesting that feeding fat plus RUP or fat-coated protein alleviated the depression in milk protein content to the same extent. Because of slightly higher milk yield, cows in FATPC treatment produced 80 g more milk protein compared with cows in the FATP treatment. The lactose content did not differ among treatments. Higher milk yield and similar feed intakes improved the relative gross feed ef®ciencies (ECM produced per kg of feed intake) in fat-supplemented treatments compared with the control. Feeding fat plus RUP or fat-coated protein did not improve feed ef®ciency of cows compared with fat alone. However, it is dif®cult to evaluate feed ef®ciency in a short-term experiment. We recommend long-term studies to evaluate the feed ef®ciency of cows fed diets supplemented with fat-coated protein. Fatty acid composition of the milk fat is summarized in Table 5. The proportions of short- and medium-chain fatty acids (from C10:0 to C15:0) were reduced in fatsupplemented treatments compared with the control. The proportions of C16:0 and C16:1
178
Parameter
Milk yield (kg per day) 3.5% Fat-corrected milkc (FCM) (kg per day) Energy-corrected milkc (ECM) (kg per day) Fat (g kg 1) Fat yield (kg per day) Protein (g kg 1) Protein yield (kg per day) Lactose (g kg 1) ECM (per kg of feed intake) a
S.E.M.a
Treatment Control
Fat
Fat RUP
Fat-coated protein
36.4 35.6 36.5 34.2 1.23 33.4 1.20 48.6 1.39
38.3 36.7 37.3 32.9 1.25 31.6 1.21 48.7 1.45
37.5 37.5 37.9 35.5 1.32 32.1 1.19 49.2 1.50
39.6 38.6 39.3 34.0 1.33 32.4 1.27 49.2 1.53
0.3 0.7 0.6 0.8 0.04 0.2 0.01 0.3 0.03
Significance of differenceb Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
0.01 0.05 0.05 0.98 0.17 0.01 0.08 0.21 0.04
0.61 0.18 0.14 0.13 0.15 0.02 0.03 0.23 0.15
0.01 0.32 0.15 0.24 0.81 0.20 0.01 0.90 0.54
Square root of the mean square error divided by number of observations in each treatment. Level of signi®cance P < 0:01 is shown as P 0:01. c Fat-corrected milk was computed as: 3.5% FCM 0:432 milk kg 16:23 fat (kg); energy-corrected milk was computed as: ECM 0:327 milk kg 12:95 fat kg 7:20 protein (kg); these equations were derived from Tyrrell and Reid (1965). b
T.R. Dhiman et al. / Animal Feed Science and Technology 90 (2001) 169±184
Table 4 Milk yield and milk composition of cows fed fat, fat RUP, or fat-coated protein
Table 5 Fatty acid composition of milk fat from cows fed fat, fat plus RUP, or fat-coated protein
C8:0 C10:0 C12:0 C14:0 C14:1 C15:0 C16:0 C16:1 C17:1 C18:0 Trans-9 C18:1 Trans-11 C18:1 Cis-9 C18:1 Cis-11 C18:1 C18:2 CLAd g-C18:3 C18:3 Cis-8, 11, 14 C20:3 Cis-11, 14, 17 C20:3 a
Treatment (g kg
1
weight of fatty acids reported)
Control
Fat
Fat RUP
Fat-coated protein
11.7 10.5 33.3 46.3 141.5 16.7 387 17.2 2.4 91 12.5 9.5 175.5 4.3 27.5 3.9 0.5 4.9 1.7 2.2
11.6 9.8 28.7 37.7 125.7 12.9 370 15.2 1.9 93 14.5 12.4 217.3 2.9 32.9 4.6 0.6 4.7 1.8 1.9
11.1 9.5 28.0 36.8 122.4 12.6 373 14.5 2.0 98 14.7 12.3 215.2 3.0 33.4 4.5 0.6 4.9 1.7 1.9
11.4 9.5 27.3 35.6 121.5 13.2 395 17.2 2.4 102 14.6 10.5 200.0 2.5 25.9 3.6 0.5 4.2 1.5 1.8
S.E.M.b
0.2 0.2 0.7 1.0 2.2 0.3 6.0 0.5 0.1 2.3 0.6 0.5 4.0 0.8 0.8 0.1 0.1 0.1 0.1 0.1
Number of carbons:number of double bonds. Square root of the mean square error divided by number of observations in each treatment. c Level of signi®cance P < 0:01 is shown as P 0:01. d Conjugated linoleic acid (cis-9, trans-11 C18:2).
Significance of differencec Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
0.12 0.01 0.01 0.01 0.01 0.01 0.10 0.12 0.01 0.05 0.01 0.01 0.01 0.18 0.02 0.05 0.20 0.01 0.47 0.01
0.10 0.02 0.01 0.03 0.02 0.92 0.02 0.53 0.01 0.05 0.59 0.01 0.01 0.92 0.03 0.01 0.48 0.18 0.01 0.84
0.30 0.80 0.01 0.11 0.48 0.24 0.01 0.05 0.01 0.22 0.74 0.01 0.01 0.73 0.01 0.01 0.24 0.01 0.03 0.24
T.R. Dhiman et al. / Animal Feed Science and Technology 90 (2001) 169±184
Fatty acida
b
179
180
T.R. Dhiman et al. / Animal Feed Science and Technology 90 (2001) 169±184
fatty acids in milk were higher in FATPC treatment compared to FATP. Higher proportions of C18:0, C18:1, and C18:2 fatty acids in milk of cows fed fat-supplemented diets probably re¯ects their supply in the diet. An increased supply of dietary long-chain fatty acids has been shown to increase their secretion in milk fat and inhibit de novo synthesis of short- and medium-chain fatty acids in the mammary gland (Grummer, 1991). The hypercholesterolaemic effect of saturated fats in human diets is largely due to C12:0, C14:0, and C16:0 fatty acids; C18:0 is as effective as C18:1 in lowering blood plasma cholesterol in humans (Bonanome and Grundy, 1988). Increases in the proportion of C18:0 and C18:1 in milk fat of cows fed fat-supplemented diets may have health bene®ts in humans by decreasing the cholesterolaemic effects of milk fat. Conjugated linoleic acid content in milk was higher in fat-supplemented treatments compared with the control treatment (Table 5). Increased supply of unsaturated fatty acids to the rumen microbes has been shown to increase CLA in milk due to incomplete biohydrogenation of unsaturated fatty acids in the rumen (Dhiman et al., 2000). The FATPC treatment had lower levels of CLA in milk compared with FATP due to higher proportions of saturated fatty acids in the diet (Table 2). Recently, CLA has received considerable attention as an anticarcinogen (Dhiman et al., 2000). Results from this study suggest that feeding fat-coated protein did not increase the CLA content of milk. Compared with FAT and FATP treatments, the control had lower CLA content despite having 75% unsaturated fat in total dietary fat. The fat should be accessible to the rumen microbes for biohydrogenation to convert it to CLA. The source of fat in the control diet was maize and soybean meal. Fat is less accessible to the rumen microbes when it is supplied through seeds compared with the free oil in FAT and FATP treatments (Dhiman et al., 2000). Additionally, the amount of fat intake was low in the control treatment compared with the others. Feed DM digestibility did not differ among treatments (Table 6), suggesting that addition of fat, fat plus protein, or fat-coated protein did not in¯uence the digestibility of DM in the present study. Dietary fat in excess of 70±80 g kg 1 of diet DM has been shown to inhibit microbial activity in the rumen and reduce feed digestibility (Palmquist, 1984). Total fatty acid content of the diets ranged between 28.3 and 49.6 g kg 1 of diet DM in the present experiment, and were within the presumed safe limits for inclusion of fat in dairy cow diets without decreasing nutrient utilization. Apparent digestibility of C12:0, C14:0, C14:1, and C15:0 fatty acids in the total gastrointestinal tract, as a percentage of intake, was not altered by supplemental fat, fat plus RUP, or fat-coated protein (Table 6). The average digestibilities were 97.6, 94.4, 80.8, and 48.8% of intake for the respective fatty acids. Compared with control, the apparent digestibility of C16:0 was increased in fat-supplemented treatments, probably due to its increased supply through the diet. The digestibility coef®cient for C18:0 was negative for all treatments. This was because dietary unsaturated 18-carbon fatty acids were biohydrogenated in the rumen, resulting in more C18:0 passing to the feces than was consumed by the cows (Klusmeyer and Clark, 1991). Ruminal biohydrogenation of dietary unsaturated fatty acids increases passage of certain fatty acids (saturated and unsaturated) to the small intestine which may be greater than their intake (Jenkins, 1993). The apparent digestibility of C18:0 was 3.2% of intake in FATPC treatment compared with 343.7% in the control treatment. Increased dietary supply of C18:0 in
Item
S.E.M.a
Treatment (%) Control
Fat
Fat RUP
Fat-coated protein
Significance of differenceb Control vs. other treatments
Fat vs. fat and protein
Fat RUP vs. fat-coated protein
Dry matter
63.2
62.0
61.3
62.1
1.4
0.41
0.86
0.68
Fatty acid C10:0 C12:0 C14:0 C14:1 C15:0 C16:0 C18:0 C18:1 C18:2 C18:3
100.0 97.8 94.7 80.0 48.1 59.9 343.7 82.7 97.3 97.8
85.8 97.9 94.3 81.0 49.1 69.2 205.0 88.8 97.4 98.0
93.7 96.9 94.0 81.8 48.0 71.8 198.6 89.7 97.7 98.2
96.6 97.8 94.6 80.2 49.8 68.2 3.2 86.5 97.2 98.0
6.7 0.4 0.3 0.6 2.6 2.1 31.8 0.4 0.1 0.1
0.34 0.61 0.19 0.17 0.78 0.01 0.01 0.01 0.09 0.01
0.29 0.30 0.96 1.0 0.95 0.78 0.04 0.21 0.51 0.07
0.77 0.13 0.20 0.10 0.66 0.28 0.01 0.01 0.01 0.06
a b
Square root of the mean square error divided by number of observations in each treatment. Level of signi®cance P < 0:01 is shown as P 0:01.
T.R. Dhiman et al. / Animal Feed Science and Technology 90 (2001) 169±184
Table 6 Digestibility of dry matter and fatty acids in cows fed fat, fat plus RUP, or fat-coated protein
181
182
T.R. Dhiman et al. / Animal Feed Science and Technology 90 (2001) 169±184
fat-supplemented treatments resulted in a less negative digestibility of C18:0 compared with the control treatment, probably because there were less 18-carbon unsaturated fatty acids available from the diet to convert to C18:0 through ruminal biohydrogenation. Klusmeyer and Clark (1991) reported similar fatty acid digestibility patterns. Average apparent digestibilities of C18:1, C18:2, and C18:3 were 86.9, 97.4, and 98.0% of intake, respectively. Apparent digestibility of unsaturated 18-carbon fatty acid averaged 96% of intake in sheep fed different sources of supplemental fat (Andrews and Lewis, 1970). Feeding fat sources enriched in C16:0 and C18:0 fatty acids altered the total tract apparent digestibility of these fatty acids and other unsaturated fatty acids, suggesting that there might be opportunities for optimizing fatty acid digestibility in the gastrointestinal tract by altering the fatty acid pro®le of dietary fat. Altering the supply of long-chain fatty acids can in¯uence the fatty acid composition of milk fat, because these fatty acids are directly incorporated into milk fat in the mammary gland (Palmquist, 1984; Grummer, 1991). Supplementing fat or fat-coated protein improved the milk yield of dairy cows compared with a control with no supplemental fat. Supplying RUP along with fat or fat-coated protein provided no further improvement in milk yield and relative gross feed ef®ciency (milk/feed intake) compared with fat alone. Feeding RUP along with fat or fat-coated protein partially alleviated the depression in milk protein content caused by supplemental fat and increased the daily yield of milk protein by 60±80 g per day. Inclusion of fat increased the proportions of longer-chain fatty acids in the milk and decreased the short- and medium-chain fatty acids. Further studies are recommended to evaluate the long-term bene®ts of including fat-coated protein in dairy diets. 4. Conclusions Cows fed diets containing fat-coated protein produced the same amount of milk as cows fed fat alone. Including fat-coated protein partially alleviated the depression in milk protein content caused by supplemental fat and increased protein yield by 60 g per day. Since there was no advantage in milk yield, the decision to include fat-coated protein in dairy rations should be based on its price compared to fat alone and the return in terms of milk protein yield. Acknowledgements The authors thank Donald V. Sisson, Department of Mathematics and Statistics, and Jeffrey L. Walters, Department of Animal, Dairy and Veterinary Sciences, Utah State University, for statistical analysis of the data. Research was partially supported by the Utah Agricultural Experiment Station, Utah State University, Logan, UT, USA. Continental Grain Company, Chicago, IL, USA, is gratefully acknowledged for the partial funding and supplying fat-coated protein (DuetsTM) for the research references.
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