J. Dairy Sci. 89:1081-1091
© American Dairy Science Association, 2006.
Effects of Fatty Acid Supplements on Milk Yield and Energy Balance of Lactating Dairy Cows
K. J. Harvatine1 and
M. S. Allen2
Department of Animal Science, Michigan State University, East Lansing 48824-1225
2 Corresponding author: allenm{at}msu.edu
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ABSTRACT
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Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on yield of milk and milk components, concentration of milk components including milk fatty acid profile, and energy balance. Eight ruminally and duodenally cannulated cows and 8 noncannulated cows were used in a replicated 4 x 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). The SAT treatment did not change milk fat concentration, but UNS linearly decreased milk fat in cannulated cows and tended to decrease milk fat in noncannulated cows compared with control. Milk fat depression with UNS corresponded to increased concentrations of trans-10, cis-12 conjugated linoleic acid and trans C18:1 fatty acids in milk. Milk fat profile was similar for SAT and control, but UNS decreased concentration of short- and medium-chain FA. Digestible energy intake tended to decrease linearly with increasing unsaturated FS in cannulated and noncannulated cows. Increasing unsaturated FS linearly increased empty body weight and net energy gain in cannulated cows, whereas increasing saturated FS linearly increased plasma insulin. Efficiency of conversion of digestible energy to milk tended to decrease linearly with increasing unsaturated FS for cannulated cows only. Addition of SAT provided little benefit to production and energy balance, whereas UNS decreased energy intake and milk energy yield.
Key Words: fatty acid • saturation • milk yield • energy partitioning
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INTRODUCTION
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High-producing dairy cows have large energy requirements that may exceed their ability to consume dietary energy, resulting in less than maximum milk yield. Addition of fat to the diet increases energy density without increasing rumen acid production, or maintains energy density while increasing fiber for stabilization of rumen fermentation (Allen, 1997). However, fatty acids available in the rumen may have associative effects on nutrient digestion (Wu et al., 1991). Prilled saturated free fatty acids (FA) and calcium salts of FA are two manufactured products marketed to minimize effects of fat on ruminal fermentation. However, calcium salts of FA are not entirely protected in the rumen and dissociation of the calcium ion allows ruminal biohydrogenation of unsaturated FA (Wu et al., 1991).
Traditionally, FA are considered a source of energy, but are now appreciated as biological modifiers of physiology and metabolism. Incomplete biohydrogenation of polyunsaturated fatty acids (PUFA) increases duodenal flow of trans-C18:1 and conjugated linoleic acids (CLA), which have been implicated in milk fat depression through decreased lipogenic gene expression (Bauman and Griinari, 2003; Peterson et al., 2003). Milk fat depression normally occurs with little effect on DM intake, which is expected to increase BW gain (Baumgard et al., 2002b). Increased BW gain in response to trans-10, cis-12 CLA in lactating cows is contrary to decreased body fat gain observed in growing nonruminant animals (Mersmann, 2001) although the levels of CLA supplementation are quite different between ruminant and nonruminant experiments (Bauman and Griinari, 2003).
The profile of FA absorbed in the duodenum can alter the FA profile of animal products, especially modifying FA saturation and CLA concentration (Grummer, 1991; Mansbridge and Blake, 1997). Consumers are increasingly concerned about FA intake; decreasing saturated FA intake may decrease heart disease and diabetes (Mansbridge and Blake, 1997), and increasing CLA intake may decrease the incidence of cancer and obesity (Kelly, 2001). Strategies for dietary FA supplementation can be developed to alter the FA profile of meat and milk products to meet consumer demands.
The objective of this experiment was to determine effects of FA supplements differing in FA saturation on milk and milk component yield, milk fatty acid profile, and energy partitioning. Prilled and hydrogenated free FA and calcium soaps of long-chain FA were selected to provide the largest expected difference in unsaturated FA, especially PUFA, flow to the duodenum with commonly available feed ingredients.
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MATERIALS AND METHODS
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This article is the first of 3 papers in a series from one experiment that evaluated effects of FA supplements (FS) differing in FA saturation. This paper discusses treatment effects on milk yield, milk FA profile, and energy balance; the companion papers discuss ruminal digestion kinetics and site of digestion (Harvatine and Allen, 2006a), and DMI and feeding and chewing behavior (Harvatine and Allen, 2006b). Experimental procedures were approved by the All University Committee on Animal Use and Care at Michigan State University.
Cows and Treatments
Eight ruminally and duodenally cannulated (77 ± 8.7 DIM; mean ± SD) and 8 noncannulated (106 ± 15 DIM; mean ± SD) multiparous Holstein cows from the Michigan State University Dairy Cattle Teaching and Research Center were blocked by cannulation and assigned randomly to replicated 4 x 4 Latin squares in a linear substitution arrangement of treatments plus a control (Table 1
). Noncannulated cows were included in the experiment to increase the number of observations for intake and milk yield. Cows were blocked by cannulation because they were selected at different times and differed in DIM, BCS, and surgical preparation. Treatments were a control diet containing no added FS or FS containing 2.5% added FA as saturated (SAT; prilled, hydrogenated FA, Energy Booster 100, MS Specialty Nutrition, Dundee, IL), an intermediate mixture of saturated and unsaturated (INT), or partially unsaturated (UNS) FA (Ca Soaps of LCFA, Megalac-R, Church and Dwight Company, Inc., Princeton, NJ). Treatment periods were 21 d with the final 11 d used for sample and data collection. Surgery was performed at the Department of Large Animal Clinical Science, College of Veterinary Medicine, Michigan State University. Immediately before initiation of the experiment, mean empty BW (ruminal digesta removed) of cannulated cows was 516 ± 33 kg (mean ± SD) and mean BW of noncannulated cows was 638 ± 51 kg (mean ± SD).
Treatment mix composition is shown in Table 2. Treatment mixes included limestone and rice hulls to balance for calcium and FA concentration and 50% ground corn as a carrier. The base ration was formulated to provide 2.5% rumen-available FA from cottonseed to represent low-cost, commonly used FA from oilseeds; treatments were formulated to provide 2.5% added FA from FS. Experimental diets contained 40% forage (66:33 corn silage:alfalfa silage), 13.5% whole cottonseed, dry ground corn, premixed protein supplement (soybean meal, corn gluten meal, and blood meal), a mineral and vitamin mix, and ~5.7% control mix, saturated FS (SAT) mix, 50:50 mix of saturated and unsaturated FS (INT) mixes, or unsaturated FA (UNS) mix (Table 3). All diets were fed as a TMR once a day at 0900 h. Final diet FA concentration and composition is shown in Table 3.
Data and Sample Collection
Throughout the experiment, cows were housed in tie-stalls and fed once daily (0900 h) at 115% of expected intake. Amounts of feed offered and orts were weighed for each cow daily. Samples of all diet ingredients (0.5 kg) and orts from each cow (12.5%) were collected daily on d 11 to 14 and combined into one sample to represent 4 d for digestibility determination (d 11 to 14). Cows were milked twice daily in their stalls during the feeding behavior monitoring phase (d 16 to 19) and in a milking parlor during the remainder of each period. Milk yield was measured at each milking on d 11 to 19, and milk was sampled at each milking on d 16 to 19.
Methods for determining fecal output and digestibility for cannulated cows are described in Harvatine and Allen (2006a). Indigestible NDF was used as a marker to calculate total tract fecal flow for noncannulated cows. Fecal samples (1,000 g) were collected every 9 h from d 12 to 14 yielding 8 samples representing every 3 h of a 24-h period to account for diurnal variation.
Sample and Statistical Analysis
Feed and fecal samples were processed and analyzed as described in Harvatine and Allen (2006a). Milk samples were composited based on milk fat yield and centrifuged at 17,800 x g for 30 min at 8° C. Fat cake (300 to 400 mg) was extracted according to Hara and Radin (1978) and methyl esters were formed according to Christie (1982) as modified by Chouinard et al. (1999). Fatty acids were quantified by gas chromatography (model 8500, Perkin-Elmer Corp., Norwalk, CT), using an SP-2560 capillary column (100 m x 0.20 mm i.d. with 0.02-µm film thickness; Supelco, Bellefonte, PA). Oven temperature was 140° C for 5 min, then increased 4° C/min to 240° C, and held for 15 min. Helium flow was 20 cm/s. Milk samples were analyzed for fat, true protein, and lactose by midinfrared spectroscopy (AOAC, 1990) by Michigan DHIA (East Lansing, MI). Commercial radioimmunoassay kits were used to determine plasma concentration of insulin (Coat-A-Count, Diagnostic Products Corporation, Los Angeles, CA; intraassay CV 6.8, interassay CV 9.0), and glucagon (Hammon and Blum, 1998; glucagon kit GL-32K, Linco Research Inc., St. Charles, MO; intraassay CV 0.96). Commercial enzyme kits were used for analysis of glucose (Raabo and Terkildsen, 1960; glucose kit #510; Sigma Chemical Co., St. Louis, MO; intraassay CV 2.0, interassay CV 2.4), NEFA (Johnson and Peters, 1993; NEFA C-kit; Wako Chemicals USA, Richmond, VA; intraassay CV 4.4, interassay CV 4.7), and BHBA (Williamson et al., 1962; kit #310-A; Sigma Chemical Co.; intraassay CV 2.7, interassay CV 2.8).
Energy values were calculated as follows: Digestible energy (DE) intake = gross energy (GE) intake x GE digestibility (GE digestibility as reported in Harvatine and Allen, 2006a); NEL intake was calculated from DE through ME according to NRC (2001). Milk NEL (Mcal/d) = milk yield (kg) x [0.0929 x (Fat %) + 0.0563 x (True Protein %) + 0.0395 x (Lactose %)] (NRC, 2001); NEL body weight gain was calculated according to NRC (2001); and NEL available for Maintenance = NEL intake – NEL milk –NEL body weight gain.
All data were analyzed using the fit model procedure of JMP (Version 5, SAS Institute, Cary, NC) according to the following model:
where Yijk = dependent variable, µ = overall mean, Ci = random effect of cow (i = 1 to 8), Pj = fixed effect of period (j = 1 to 4), Tk = fixed effect of treatment (k = 1 to 4), and eijk = residual error.
The fixed effect of block was tested. There was a significant block by treatment effect for milk production and other variables of primary interest (P < 0.10) so cannulated and noncannulated cow data were separated for presentation. Period by treatment interaction was evaluated, but was removed from the statistical model when not significant (P > 0.10). Period by treatment interaction was not significant for any variable of primary interest; variables with significant interactions are noted in the tables. Data points with Studentized Residuals greater than 3 were considered outliers and excluded from analysis. Few points were excluded in analysis and rarely more than one per response variable. Preplanned contrasts included the effect of addition of FS (control vs. SAT, INT, and UNS), linear effect of substituting unsaturated FA for saturated FA (SAT vs. UNS), and quadratic effect of substituting unsaturated FA for saturated FA (INT vs. SAT and UNS). The preplanned contrasts do not allow individual comparison of each fat treatment to the control. Protected LSD was used for mean separation for parameters of main interest in the discussion when there was a significant effect of FS addition and a significant effect of FA saturation. Pearson correlation coefficients were determined between cow-period observations for some parameters. Average parameters for each block presented in Table 1
were determined by including block in the above model. Treatment effects, linear and quadratic responses, and correlations were declared significant at P < 0.05, and tendencies were declared at P < 0.10.
Data from two cow-periods were excluded from statistical analysis. One cannulated cow developed clinical mastitis on d 19 of period 3; rumen samples, BW, and BCS were not collected for this period. Data collected before this health incident were included in our analysis. The cow did not fully recover and data from period 4 were not used.
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RESULTS AND DISCUSSION
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Characteristics of cows within each block are presented in Table 1. Cannulated cows were 30 d earlier in lactation at the start of the experiment, with lower BW and greater milk yield than noncannulated cows, and were selected from a different herd group. Blocks were similar for DIM but there was a large difference in BCS indicating differences in metabolic state.
Diets contained a common base mix and differed only in FS mix (Table 2). The CP concentration of the diets averaged 16.1%, which was lower than the target of 17.8% CP formulated because a number of dietary ingredients contained lower concentrations of CP during the experiment than measured before the experiment. Treatments were formulated to contain the same calcium concentrations using limestone, and rice hulls were used to take the place of FA in the control diet to maintain approximately the same fermentable and digestible carbohydrate concentration (Table 2). Treatments differed in FA concentration and profile. The control diet contained 5.5% FA and FS diets contained 8.3, 8.1, and 7.8% FA for SAT, INT, and UNS, respectively. Treatment mixes (Table 2) were formulated based on manufacturer’s product specifications. Calcium salts of long-chain FA contained much lower FA than expected. To compensate for the lower FA concentration of UNS, a greater concentration of UNS mix was included in UNS and INT diets; and control mix (rice hulls) was used to compensate for the increased inclusion rate in the control diet, SAT, and INT. The small FA concentration differences among the final FS diets are attributed to variation during the experiment. Dietary unsaturated FA density increased from SAT to UNS (3.9, 4.4, and 4.9% for SAT, INT, and UNS, respectively). Increased unsaturated FA from SAT to UNS included increased C18:1, C18:2, and C18:3, and decreased C18:0 (Harvatine and Allen, 2006c). Addition of FS increased the C16:C18 ratio, but the ratio was not changed within FS treatments.
Milk and Milk Component Yield
Fatty acid supplement did not affect milk yield of cannulated (Table 4) or noncannulated cows (Table 5). However, within FS, milk yield was linearly decreased with increasing unsaturated FS for cannulated cows only. Increasing unsaturated FS linearly decreased milk fat concentration and yield of cannulated cows and tended to decrease milk fat concentration of non-cannulated cows. Milk fat synthesis is inhibited by FA intermediates formed in the rumen during biohydrogenation of unsaturated FA and milk fat depression is associated with diets containing higher concentrations of PUFA (Bauman and Griinari, 2003). Differences in ruminal FA passage and biohydrogenation rates between blocks is expected to have resulted in different duodenal flow of biohydrogenation intermediates resulting in different extents of milk fat depression. Yields of milk and fat-corrected milk as well as concentrations of milk fat and lactose were not different for SAT compared with control for either block of cows. Yield and concentration of milk protein was not affected by treatment of cannulated or noncannulated cows and MUN was linearly decreased with increasing unsaturated FS for cannulated cows only.
Milk FA Profile
Milk FA profile of cannulated and noncannulated cows was consistent with previous reports during milk fat depression (Baumgard et al., 2002a; Peterson et al., 2003) including increased concentration of biohydrogenation intermediates. Saturated FS did not increase cis-9, trans-11 CLA or trans-C18:1 FA concentration, but UNS increased their concentration in cannulated and noncannulated cows (Tables 6 and 7). In the cannulated cows, trans-10, cis-12 CLA was increased by SAT and linearly increased with increasing unsaturated FS. Noncannulated cows did not increase trans-10, cis-12 CLA with SAT, but UNS increased the trans-10, cis-12 CLA compared with control. Milk fat concentration had a strong quadratic relationship with trans-10, cis-12 CLA, and trans-C18:1 in agreement with others (Bauman and Griinari, 2003; Peterson et al., 2003). Saturated FS had very little effect on milk FA profile, but increasing unsaturated FS decreased concentration of short- and medium-chain FA and increased concentration of some long-chain FA. Milk fat depression, induced by increased duodenal flow of trans-10, cis-12 CLA, is mediated through decreased gene expression of lipogenic enzymes, leading to decreased mammary FA and triglyceride synthesis (Baumgard et al., 2002a; Peterson et al., 2003). The observed FA profile changes are consistent with decreased FA synthesis causing a decrease in concentration of short- and medium-chain FA. Increasing unsaturated FS increased the proportion of unsaturated C18 FA, but also increased trans-C18:1 concentration. We recognize the importance of separation of trans-C18:1 isomers but they could not be separated with the FA analysis procedure used.
Energy Intake and Balance
Cannulated Cows.
Fatty acid supplement decreased DE intake and unsaturated FS tended (P = 0.06) to linearly decrease DE intake. However, calculated NEL intake accounts for increased efficiency of converting DE from FA to NEL (NRC, 2001) and was not affected by treatment (Table 8). Milk NEL yield was not affected by SAT but decreased linearly with increasing unsaturated FS. Empty BW gain and calculated net energy of tissue gain (NRC, 2001) increased linearly with increasing unsaturated FS but BCS was not affected by treatment. Composition of BW gain was not observed and it is possible that calculated net energy of tissue gain might overestimate energy retained. However, energy balance can be verified by calculation of energy conservation and treatments did not differ in energy available for maintenance calculated by the difference of NEL intake and NEL for milk production and BW gain (Table 8). This approach was selected over the more common calculation of energy balance to remove the bias of increased BW gain overestimating increases in maintenance energy requirement on some treatments. Metabolic BW may be used to predict the maintenance energy requirement between animals differing in BW, but does not predict changes in maintenance energy requirement with weight gain within animals because of changes in body composition. Simple efficiency calculated as NEL milk as a fraction of DE intake tended to decrease with increasing unsaturated FS (P = 0.10). But NEL for production (tissue gain plus milk) as a fraction of DE intake was not changed by treatment. Decreased energetic efficiency for milk production but no difference in efficiency of total production provides further support for increased body weight gain with increasing unsaturated FS.
Fatty acids may change energy balance through changes in DMI, nutrient digestibility, and milk and tissue synthesis. Treatment changed nutrient partitioning; UNS decreased milk and milk fat yield compared with control and SAT, and increasing unsaturated FS linearly increased BW gain resulting in no difference in energy output (NEL milk plus NEL BW gain). Other experiments have observed no change in intake or BW gain during milk fat depression in short-(Baumgard et al., 2002b) and long-term lactation experiments (Perfield et al., 2002), although these previous experiments may have lacked sufficient power or responsive measures of BW gain. Tyrrell and Moe (1972) observed decreased efficiency of ME use for milk synthesis during milk fat depression, consistent with the tendency for decreased efficiency of converting DE to NEL milk, because of increased energy use for tissue gain. Milk production and BW gain are both homeorhetically controlled. Feed intake is normally expected to decrease with increasing BW gain during midlactation through chemostatic regulation. Directed growth or compensatory gain may not account for the increased BW gain because DMI for SAT and INT was not likely limited by distension from physical fill and would be expected to have increased intake to meet directed BW gain (Harvatine and Allen, 2006b). Milk fat depression induced by biohydrogenation intermediates normally does not result in decreased intake (Baumgard et al., 2002a). Increased tissue energy gain instead of decreased energy intake as a result of decreased milk energy output is unexpected because it demonstrates a disconnect of production and intake leading to an imbalance in energy homeostasis (Harvatine and Allen, 2006b). Increased fat deposition in response to biohydrogenation intermediates that also induce milk fat depression is opposite of the effect of CLA in monogastrics (Mersmann, 2001). Milk fat depression increases availability of acetate that may be either directed or demanded by tissue to increase gain. Increased BW gain may represent directed lipid deposition or it may represent disposal of fuels to correct a metabolite imbalance (Harvatine and Allen, 2006b). Energy spared during milk fat depression is not a balance of metabolites and the spared metabolites lack potency in feedback on intake regulation (Harvatine and Allen, 2006b). The rate of BW gain observed is not expected to be sustainable over a long period. The effect of CLA on BW gain should be experimentally tested with cows differing in production level over longer experimental periods to verify the rate and composition of energy gain. Cannulated cows in the current experiment had high milk yields and low BCS that may uniquely allow increased BW gain during milk fat depression.
Metabolic control during milk fat depression is not well understood. Milk fat depression of 25 to 50% resulted in no change in plasma glucose, insulin, and leptin concentration or insulin-stimulated glucose clearance, but did result in 24 to 33% reduced lipolytic response to an epinephrine challenge (Baumgard et al., 2002a). Abomasal infusion of cis or trans-C18:1 had no effect on disappearance rates of glucose, insulin secretion following a glucose challenge, or appearance rates of NEFA and triglycerides after a norepinephrine challenge (Gaynor et al., 1996). In the current experiment, SAT increased plasma insulin concentration compared with control (cannulated cows only), but UNS had no effect (Table 11). Furthermore, within FS, increasing saturated FS linearly increased insulin concentration for cannulated cows. In a previous experiment we reported increased plasma insulin with saturated FA compared with calcium salts of palm FA (Harvatine and Allen, 2005), consistent with in vitro insulinotropic effects of saturated FA in other animal models (Stein et al., 1997). There was no difference among treatments for plasma glucagon, and BHBA decreased linearly with increasing unsaturated FS. A period by treatment interaction was observed for plasma glucose and NEFA concentration so treatment effects cannot be determined. Increased BW gain and little change in intake during milk fat depression represents a failure in energy balance regulation that cannot be attributed to homeostatic signaling or regulation of lipid and glucose metabolism.
Noncannulated Cows.
Observation of nutrient intake, ruminal digestion kinetics, and site of digestion of cannulated cows is presented in the companion papers (Harvatine and Allen, 2006a,b). Noncannulated cow DM and OM intakes were not affected by treatment. Intakes of NDF and starch were decreased and intake of total FA was increased by addition of FS. Greater NDF and lower FA intake for control compared with FS was because rice hulls were included in place of FA for the control diet. Addition of FS increased total tract digestibility of NDF and potentially digestible NDF, and tended to increase OM digestibility (Table 9). Increasing unsaturated FS tended to quadratically increase total tract NDF digestibility and tended to quadratically decrease total tract starch digestibility. Changes in nutrient digestibility with increasing unsaturated FS tended to increase the amount of NDF and potentially digestible NDF digested in the total tract with a quadratic response across FS.
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Table 9. Effects of dietary fatty acid (FA) supplements on intake and total tract digestion for noncannulated cows
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Addition of FA did not increase DE or NE intake in noncannulated cows, but increasing unsaturated FS tended to linearly decrease DE and NEL intake (Table 10). There were no effects of treatment on NEL milk production or BW gain, although FS tended to increase BCS. Observing BW rather than rumen empty BW increases error and bias because of variation and treatment effect on rumen digesta weight and explains the larger standard error and inability to distinguish treatment effects in the noncannulated block. Treatment did not change efficiency of milk production or energy use. Large differences in energy balance are not expected because plasma insulin, glucagon, glucose, and BHBA were not affected by treatment.
Cannulated and noncannulated cows responded differently to treatment. Milk fat concentration was significantly decreased with increasing unsaturated FS for cannulated cows but only tended to be decreased with increasing unsaturated FS for noncannulated cows. Differences in milk fat depression and milk CLA concentration indicate less duodenal flow of biohydrogenation intermediates in the noncannulated block. Duodenal trans-FA flow may be decreased by more effective protection of PUFA or more complete biohydrogenation of trans-FA. Fatty acid protection and bio-hydrogenation may differ between the blocks because of differences in intake or passage rate. Noncannulated cows had much more adipose tissue (BCS was 1.2 units higher) and lower milk yield (5.7 kg/d) and were expected to be in a different metabolic state. Metabolic state may interact with metabolic and physiologic response to FA biohydrogenation intermediates.
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CONCLUSIONS
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Increasing unsaturated fat supplement decreased milk fat yield and tended to decrease intake of digestible energy. Milk fat depression was consistent with the biohydrogenation theory of milk fat depression with decreased milk fat yield associated with increased concentrations of trans-10, cis-12 CLA and total trans C18:1 FA. Cows experiencing milk fat depression increased BW gain. Increased BW gain may be because of the type of fuels available and incomplete intake compensation to maintain energy homeostasis.
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ACKNOWLEDGEMENTS
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We wish to acknowledge MS Specialty Nutrition (Dundee, IL) for partial financial support of this research. We also thank N. K. Ames for performing duodenal and ruminal cannulations, and D. G. Main, R. A. Longuski, Y. Ying, M. Oba, C. S. Mooney, J. A. Voelker, C. C. Taylor, R. E. Kreft, and the staff of the Michigan State University Dairy Cattle Teaching and Research Center for their assistance in this experiment.
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FOOTNOTES
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1 Current address: Department of Animal Science, Cornell University, Ithaca, NY 14853. 
Received for publication January 13, 2005.
Accepted for publication September 14, 2005.
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B. J. Bradford and M. S. Allen
Depression in Feed Intake by a Highly Fermentable Diet Is Related to Plasma Insulin Concentration and Insulin Response to Glucose Infusion
J Dairy Sci,
August 1, 2007;
90(8):
3838 - 3845.
[Abstract]
[Full Text]
[PDF]
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K. J. Harvatine and M. S. Allen
Effects of Fatty Acid supplements on ruminal and total tract nutrient digestion in lactating dairy cows.
J Dairy Sci,
March 1, 2006;
89(3):
1092 - 1103.
[Abstract]
[Full Text]
[PDF]
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K. J. Harvatine and M. S. Allen
Effects of Fatty Acid supplements on feed intake, and feeding and chewing behavior of lactating dairy cows.
J Dairy Sci,
March 1, 2006;
89(3):
1104 - 1112.
[Abstract]
[Full Text]
[PDF]
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TOP
ABSTRACT
INTRODUCTION
