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Department of Animal Sciences, University of Illinois, Urbana 61801
Department of Animal Science, Cornell University, Ithaca, NY 14853.
Department of Dairy Science, Louisiana State University, Baton Rouge, LA 70803.
Corresponding author: J. K. Drackley; e-mail: drackley{at}uiuc.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: dry period • energy • liver • supplemental fat
Abbreviation key: C = moderate-NFC control diet, CF = moderate-NFC, fat-supplemented diet, F = low-NFC, fat-supplemented diet, LCFA = long-chain fatty acids, TG = triglyceride.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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In previous research from our laboratory, feeding a diet supplemented with fat in an attempt to add BCS to thin cows during the dry period was associated with marked decreases in concentrations of total lipid and triglyceride (TG) in liver tissue obtained at d 1 postpartum (Grum et al., 1996b). At d 1 postpartum, rates of peroxisomal µ-oxidation of palmitate in homogenates of liver tissue were greater, and rates of palmitate esterification in liver slices were less, for cows fed the fat-supplemented diet compared with those fed an isocaloric low-fat diet or a lower energy control diet during the dry period (Grum et al., 1996b). Therefore, dietary fat might alter liver metabolism to contend with the marked peripartal increases in blood NEFA (Grum et al., 1996b; Drackley, 1999) that can lead to the development of fatty liver (Morrow, 1976). However, poor forage quality and high content of rumen-active fat (mainly choice white grease) in the fat-supplemented diet fed by Grum et al. (1996b) resulted in significantly lower DMI and BCS loss rather than gain during the dry period, leaving the effects of dietary fat throughout the dry period unresolved.
In contrast to results of Grum et al. (1996b), others have suggested that supplemental fat might increase the risk of peripartal lipid accumulation in the liver of dairy cows (Skaar et al., 1989; Vazquez-Añon et al., 1997). Some dietary long-chain fatty acids (LCFA) can enter the ruminant liver by specific pathways (Grum et al., 1996a; Drackley, 1999), although lymphatic transport of dietary lipids and low activity of hepatic lipase in ruminant liver (Emery et al., 1992) should limit the amount of dietary LCFA taken up by the liver and thereby minimize any significant contribution to the development of hepatic lipidosis.
Because of the confounding of diet composition and nutrient intakes in the study by Grum et al. (1996b), effects of supplemental rumen-active fat during the dry period remain uncertain and demand corroboration. The hypothesis tested in this experiment was that, if the additional fat per se was responsible for the prevention of total lipid and TG accumulation in the liver around parturition in the study by Grum et al. (1996b), then addition of the same fat to diets differing in ingredient composition and nutrient density should have repeatable and similar effects. Therefore, the objective of our study was to determine the effects of supplemental fat in dry cow diets with differing caloric densities on hepatic TG accumulation and other aspects of peripartal metabolism. Dietary treatments were designed in an effort to prevent the confounding effects of decreased DMI that occurred in the previous experiment (Grum et al., 1996b). Effects of diets on prepartum and postpartum DMI and performance also were determined.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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3.5 (1 to 5 scale; Wildman et al., 1982) so that addition of BCS before calving might be desirable (Grum et al., 1996b). Diets were fed throughout the dry period as in the study by Grum et al. (1996b) to allow BCS gain.
Diets were designed to test the same supplemental fat source as used in our previous study (Grum et al., 1996b), but in a lower amount and in diets of higher quality in an effort to minimize any fat-induced decreases in DMI as observed previously. Dry period diets (Table 1
) consisted of 1) a moderate-NFC control diet (C), 2) a low-NFC, fat-supplemented diet (F), and 3) a moderate-NFC, fat-supplemented (CF) diet. Diets were based on alfalfa silage and corn silage. The rumen-active fat source (Qual-Fat; National By-Products, Mason City, IL) consisted mainly of choice white grease. The LCFA composition as determined by GLC of methyl esters (Sukhija and Palmquist, 1988) was 3.1% C14:0, 0.9% C14:1, 24.2% C16:0, 4.9% C16:1, 0.3% C17:0, 13.8% C18:0, 46.2% cis-C18:1, 6.1% C18:2, and 0.4% C18:3. The fat had a calculated iodine value of 61 and a FFA content of 6.6%.
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Cows were housed in tie stalls throughout the experiment and were allowed to exercise daily in an outside lot from 0600 to 0930 h. Two weeks before expected parturition, cows were moved to maternity box stalls until parturition. During this time, a premix containing anionic salts from fermentation byproducts was added to each of the dry period diets at approximately 9% of total dietary DM. The resulting ingredient formulation is shown in Table 2. After parturition, all cows were offered a single lactation diet (Table 1
) that contained 2.0% supplemental fat, and postpartum production was measured for 105 d. Individual DMI was measured daily; BW and BCS were measured weekly. The BCS were assigned by 2 individuals independently. Health records were maintained for all cows, and calf birth weights were recorded.
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Sampling and Analysis of Feed and Milk
The TMR components were sampled weekly and dried at 105°C for determination of DM for ration adjustments. Samples of TMR components and complete TMR were obtained weekly and composited monthly. Composite samples were analyzed for contents of DM, CP, ADF, NDF, and minerals (Ca, P, Mg, and K) by a commercial laboratory (Dairy One, Ithaca, NY). The NEL of the dietary components was calculated using equations from the NRC (1989). Ether extract was analyzed according to standard procedures (AOAC, 1990).
Milk weights were recorded daily and samples were obtained once weekly from consecutive a.m. and p.m. milkings. Samples were composited in proportion to milk production at each sampling and were preserved with 2-bromo-2-nitropropane-1,3-diol. Composite samples were analyzed for fat and CP contents by infrared analysis (Dairy Laboratory Services, Dubuque, IA).
Sampling and Analysis of Liver and Blood
Puncture biopsy was performed under local anesthesia to obtain approximately 3 to 5 g of liver tissue (Drackley et al., 1991) at –65 and –21 d relative to expected parturition and at 1, 21, and 65 d after parturition. Aliquots of liver tissue were frozen immediately in liquid N2 until later analysis for contents of total lipid (Drackley et al., 1991), TG (Foster and Dunn, 1973), and glycogen (Lo et al., 1970).
Blood was sampled from the coccygeal vein or artery beginning at 0900 h; all sampling was completed before the morning dispensation of TMR. During the dry period, blood was sampled once weekly for 30 d after dry-off, twice weekly during wk –4 and –3, and 3 times weekly during wk –2 and –1 before expected parturition. After calving, blood was sampled 3 times weekly during wk 1 and 2 and twice weekly during wk 3 and 4, relative to parturition; thereafter, blood was sampled once weekly until 105 d postpartum.
Blood samples were collected in evacuated test tubes (Vacutainer; Becton Dickinson, Rutherford, NJ) containing sodium heparin. Plasma was obtained via centrifugation and aliquots were frozen at –20°C until later analysis for concentrations of NEFA (johnson and Peters, 1993), glucose (Trinder, 1969; kit number 315, Sigma Chemical Co., St. Louis, MO), and urea (Crocker, 1967; kit number 535, Sigma). Concentrations of BHBA (Williamson and Mellanby, 1974; kit number 310, Sigma) and total protein (Weichselbaum, 1945; total protein kit, Roche Diagnostics, Inc., Indianapolis, IN) in plasma were determined by enzymatic assays using an autoanalyzer (Hitachi 911; Roche Diagnostics). Cholesterol was determined using cholesterol esterase and cholesterol oxidase (Allain et al., 1974) coupled to the Trinder color development reaction (Trinder, 1969; cholesterol/HP kit, Roche Diagnostics) in an autoanalyzer. Concentrations of insulin in plasma were determined using a radioimmunoassay kit (Coat-a-Count Insulin kit; Diagnostic Products Inc., Los Angeles, CA) as modified by Studer et al. (1993).
Statistical Analysis
Data were subjected to ANOVA for a repeated measures design by using the MIXED procedure of SAS (SAS, 1998). The model contained the effects of dietary treatment (C, F, or CF), cow nested within dietary treatment, time (as a repeated factor), and the interaction of diet and time; cow nested within treatment was designated a random effect and was used as the error term to test the effect of dietary treatments. The covariance structure for the repeated effect of time (week or day) was modeled using the AR(1) option of SAS. The model for BCS analysis also contained the effects of scorer. Treatment effects were separated by use of nonorthogonal contrasts for 1) the effect of adding fat so that energy density was increased (C vs. CF), and 2) the effect of substituting fat for concentrate ingredients to maintain energy density (C vs. F).
Separate ANOVA were conducted for intakes of DM and NEL during the prepartum period (–60 d relative to expected calving to –1 d relative to actual calving), prepartum transition period (3 wk before expected calving to –1 d relative to actual calving), postpartum transition period (calving to 3 wk after calving), and postpartum period (calving to 105 d after calving). Separate ANOVA were conducted for BW and BCS data that were recorded during the prepartum and postpartum periods only. For concentrations of glucose, insulin, NEFA, cholesterol, BHBA, total protein, and urea in plasma, separate ANOVA were conducted for the entire prepartum period, the transition period (21 d before the expected calving date to 21 d after the actual calving), and the entire postpartum period. Concentrations of glucose, insulin, NEFA, cholesterol, BHBA, total protein, and urea in plasma were adjusted by analysis of covariance using the respective data obtained before dry-off at –65 d relative to expected parturition. The contents of total lipid, TG, and glycogen in liver during the prepartum and postpartum periods were combined for analysis; these data also were adjusted by analysis of covariance using the respective data obtained before dry-off at –65 d relative to expected parturition. The incidences of health problems recorded during the study, including displaced abomasum, ketosis, mastitis, metritis, milk fever, and retained placenta, were subjected to 
2 analysis to determine whether incidences differed among treatment groups.
Because one cow was determined not to be pregnant immediately before expected parturition, it was eliminated from the experiment; therefore, n = 11 for C, n = 12 for F, and n = 12 for CF. Least square means were computed (SAS, 1998) and are presented throughout. Significance was declared at P 0.05 and trends discussed when P > 0.05 but P < 0.15.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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and 4. Diets C and F were formulated to be isocaloric; calculated energy content based on actual chemical analyses averaged 1.45 and 1.47 Mcal of NEL per kg of DM (Table 3). Diet CF, formulated to represent a practical diet that was similar to C but with supplemental fat, had an increased NEL density (1.60 Mcal/ kg of DM; Table 3). However, intakes of DM and NEL were not statistically different among treatments during the dry period (Table 5). Dry cows fed C, F, and CF had mean DMI of 14.1, 15.2, and 13.9 kg/d, or 2.11, 2.36, and 2.10% of their BW at dry-off. Nonetheless, the slightly lower DMI for dry cows fed the more energy-dense dry diet (CF) resulted in similar intakes of NEL when compared with those for cows fed C and F.
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) and NEL (Figure 1B) steadily decreased, but no differences were noted among treatments for average intakes of DM and NEL during the prepartum transition period. Significant diet x day interactions were detected for intakes of DM (P < 0.01) and NEL (P < 0.01) during the prepartum transition period. To discern the nature of these interactions, we examined the simple linear regressions across days within treatments. Regression coefficients, representing average daily rate of DMI decline, were 53% greater for C (–0.35 kg/d) and 41% greater for F (–0.32 kg/d) than for CF (–0.23 kg/d). For NEL intake, regression coefficients were 38% greater for C (–0.50 Mcal/d) and 32% greater for F (–0.47 Mcal/ d) than for CF (–0.36 Mcal/d). We interpret these data to indicate that increasing dietary energy density with supplemental fat slowed the rate of prepartum decline in both DMI and NEL intake and therefore might facilitate maintenance of prepartal DMI and NEL intake.
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). Cows fed diet C seemed to decrease DMI beginning 3 d before parturition. Postpartum intakes of DM and NEL increased steadily during the first 10 wk of lactation (data not shown). No differences among diets and no diet by day interactions were observed for either variable during the postpartum transition period (Figure 1) or during the first 105 d of lactation (Table 5).
Diets C and F were formulated to allow gains of BCS (~0.6 BSC units; see Materials and Methods) during the dry period. Gains of BCS and BW (Figure 2) during the dry period were similar among treatments regardless of dietary energy densities, but average BCS gain for all treatments was less than expected. In contrast to our results, Grum et al. (1996b) reported that dry cows fed diets somewhat similar to F in the present study did not increase BCS; cows fed the high grain diet gained BCS, whereas those fed the fat-supplemented diet lost BCS. Decreases in BCS during the dry period in that study (Grum et al., 1996b) were attributed to decreased DMI of the fat-supplemented diet. In the present study, mean BCS began to decrease about 3 wk before parturition (Figure 2A) as observed by others (Domecq et al., 1997). Mean NEL intakes were substantially in excess of calculated NEL requirements until the last 1 to 3 d before parturition. Intakes of NEL were calculated using dietary NEL values estimated from NRC (1989) equations; subsequent recalculation of NEL using principles and equations in NRC (2001) resulted in slightly higher estimated values for dietary NEL content. Use of those higher values obtained from NRC (2001) would exaggerate the apparent discrepancy between adequacy of NEL intake and loss of BCS. Loss of BCS may have been attributable at least in part to precalving changes such as relaxation of pelvic ligaments that may have biased visual appraisal of BCS. However, others (VandeHaar et al., 1999; Keady et al., 2001) also have reported prepartum loss of BCS and backfat thickness despite apparently adequate NEL intakes. Based on those data, VandeHaar et al. (1999) suggested that prepartal energy requirements might be underestimated; our data would be consistent with that interpretation.
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) of 3.15, 3.25, and 3.32 on a 1 to 5 scale (Wildman et al., 1982).
Overfeeding during the dry period has been shown to increase the amount of BW loss around and after parturition (Morrow, 1976; Fronk et al., 1980; Reid et al., 1986; Rukkwamsuk et al., 1998), which in turn may increase the susceptibility of cows to peripartal health disorders (Fronk et al., 1980; Treacher et al., 1986; Cameron et al., 1998). Although cows fed CF had higher BCS (Figure 2A) and slightly greater (nonsignificant) mean BW (Figure 2B) during the first 105 d after calving, cows fed C tended to lose more BCS (Figure 2A) and BW (Figure 2B) during the peripartal period than did cows fed F or CF. Data for BCS and BW were not adjusted by analysis of covariance because of unreliable data that were collected before dry-off. Calf birth weights were similar among diets (Table 5).
Milk production (Table 5) did not differ among treatment groups during the first 105 d of lactation regardless of dry period diet. Milk production steadily increased for all cows (week, P < 0.0001) until wk 6 when it reached a plateau that was maintained through 15 wk of lactation (data not shown). Total solids content as well as contents and yields of fat and total protein in milk did not differ among treatments (Table 5).
The incidences of health problems that required treatment during the experiment are reported in Table 6. The results from 2 analyses indicated that the incidences of displaced abomasum, retained placenta, metritis, mastitis, ketosis, and milk fever were similar among treatments. The small number of cows per treatment and the large amount of variation that accompanies peripartal health data demand that these data be interpreted with caution. More extensive studies involving larger numbers of cows per treatment will be required to determine the expected responses to different dry cow feeding strategies on peripartal health in the field.
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), although insulin concentrations tended to be lower for cows fed C during the dry period (C vs. CF, P < 0.11) and during the transition period (C vs. CF, P < 0.08). Lack of differences in these metabolic variables likely is explained by the generally similar intakes of NEL among diets.
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). Postpartum cholesterol concentrations did not differ when all cows received the same diet, but increased from parturition to the end of the experiment (data not shown). Feeding diets containing supplemental fat (Palmquist and Conrad, 1978; Wrenn et al., 1978) or infusion of LCFA into the abomasum of lactating dairy cows (Drackley et al., 1992; Bremmer et al, 1998) has been shown to increase the concentrations of cholesterol in blood, which probably results from a greater demand for cholesterol in digestion, absorption, and transport of increased amounts of LCFA reaching the small intestine.
The concentration of total protein in plasma did not differ among dietary treatments, in agreement with Kunz et al. (1985), who reported no differences in total protein in plasma of cows that were fed to meet or exceed requirements during the dry period. Concentrations of urea in plasma from cows fed F were higher during the dry period than those for cows fed C (Table 7). Differences might reflect slightly decreased amounts of readily fermentable carbohydrate available for bacterial protein synthesis (Clark et al., 1992), which could allow more N to escape the rumen in the form of ammonia for conversion to urea in the liver, or alterations in microbial populations in response to supplemental fat, which might result in decreased ammonia incorporation. Of interest, but unexplained, is that the lower plasma urea concentration for cows fed C during the dry period persisted after parturition when all cows were switched to the same lactation diet (Table 7).
Although most of the TG that accumulates in liver during the periparturient period arises from hepatic uptake of NEFA mobilized from adipose tissue (Grummer, 1995; Drackley et al., 2001), some LCFA originating from the diet can enter the liver by specific pathways (Grum et al., 1996a; Drackley, 1999). Indeed, supplemental dietary fat during the mid and late stages of lactation has been associated with increases in the TG content of liver during the subsequent transition period (Vazquez-Añon et al., 1997). Skaar et al. (1989) reported that supplementing fat in the diet from 17 d before expected parturition through early lactation tended to increase concentrations of total lipid and TG in liver tissue at d 1 and wk 5 postpartum. In contrast, Grum et al. (1996b) demonstrated marked decreases in concentrations of total lipid and TG in liver tissue immediately postpartum after feeding supplemental fat throughout the dry period.
In contrast to these previous findings, concentrations of total lipid (Figure 3A) and TG (Figure 3B) in liver tissue at d 1 postpartum did not differ among treatments, and interactions of diet x day did not approach significance. Additionally, no difference among treatment groups was observed for concentrations of glycogen (Figure 3C) in liver tissue throughout the prepartum and postpartum periods. Concentrations of total lipid and TG increased (day; P < 0.0001), whereas concentrations of glycogen decreased (day; P < 0.0001) from d –21 to 1 relative to calving irrespective of diets fed throughout the dry period (Figure 3). Others have reported similar increases in liver lipid accumulation that accompanied peripartal increases in concentrations of NEFA in plasma (Skaar et al., 1989; Bertics et al., 1992; Vasquez-Añon et al., 1994). By d 65 postpartum, concentrations of total lipid, TG, and glycogen in liver had returned to those observed at –65 d relative to calving.
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Drackley (1999) and Rukkwamsuk et al. (1998) have proposed that alterations in liver metabolism might adapt the ruminant liver to contend with the large peripartal increases in blood NEFA and minimize the risk for the development of fatty liver. Indeed, Grum et al. (1996b) attributed distinct decreases in peripartal lipid accumulation in liver to the higher ratios of peroxisomal to total µ-oxidation and to lower in vitro rates of palmitate esterification in liver tissue after exposure to higher concentrations of NEFA in plasma throughout the dry period. Additionally, lower concentrations of insulin in plasma during the dry period might decrease the activities of pathways involved in the esterification and accumulation of LCFA in ruminant liver tissue. Grum et al. (1996b) reported that concentrations of insulin and glucose decreased while concentrations of NEFA increased in plasma obtained during the dry period from cows with lower lipid accumulation in liver tissue at calving. Rukkwamsuk et al. (1998) reported decreased peripartal accumulation of lipid in liver tissue from cows with decreased insulin concentrations in plasma because of restricted energy intake during the dry period. Although insulin is associated with increases in TG formation in rodent liver (Beyen et al., 1981; Cappello and Gnoni, 1994), the effects of insulin on the ability of ruminant liver to esterify LCFA are not fully understood (Drackley et al., 2001).
Alternatively, the decreased DMI, loss of BW, decreased insulin, and increased NEFA in plasma from pregnant nonlactating cows in the study of Grum et al. (1996b) indicate that those cows were in a state of negative energy balance throughout the dry period. The alterations in hepatic lipid metabolism may have resulted from a combination of physiological changes in response to the prolonged state of negative energy balance during the dry period. Indeed, results of a companion study conducted concurrently with the present study indicate that lower nutrient intake prepartum likely was the factor responsible for the prevention of lipid accumulation (Douglas, 2002). In the study reported here, similar intakes of DM and energy and similar concentrations of insulin in plasma among the treatment groups throughout the dry period could explain the lack of differences in peripartum lipid accumulation in liver. The exact mechanism(s) involved with the changes in peripartal liver lipid metabolism observed previously by Grum et al. (1996b) are not yet fully understood.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Regardless, based on our data, we suggest that there is little clear benefit (or detriment) to peripartal health and postpartum performance from adding fat to diets for dry cows. However, no control diet with caloric density meeting NRC specifications for dry cows (1.25 Mcal/ kg; NRC, 1989, 2001) was fed to allow a comparison with performance of cows fed above NRC standards as in this experiment (C and F, 1.46 Mcal/kg; CF, 1.60 Mcal/kg). Interactions of diet and day suggested that CF may have facilitated a slower decrease in DMI and maintenance of higher NEL intake during the last 3 wk before parturition, and tended to result in less loss of BCS and BW postpartum. Although intriguing, these results should be verified with larger numbers of cows. Our results were obtained with cows fed essentially the same diets throughout the entire dry period, rather than a 2-diet (i.e., far-off and close-up) approach. Responses to fat supplementation might be different if incorporated only for 2 to 3 wk preceding parturition. Moreover, caution should be exercised when increasing the caloric density of any diet fed for prolonged amounts of time during the dry period because overfeeding and overconditioning might increase the risk for peripartal health disorders, especially in cows with greater BCS than those in the present study.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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Current address: CPO 1862, Berea College, Berea, KY 40404.
Received for publication April 28, 2004. Accepted for publication August 11, 2004.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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), a low NFC diet supplemented with fat (F; 
), or a moderate NFC diet supplemented with fat (CF; •) during the dry period. A) Prepartum pooled SEM = 1.1 kg/d; postpartum pooled SEM = 1.6 kg/d. Effects in the prepartum model included C vs. CF (P = 0.99), C vs. F (P = 0.99), day (P < 0.0001), and the interaction of diet and day (P < 0.01). Effects in the postpartum model included C vs. CF (P = 0.29), C vs. F (P = 0.68), day (P < 0.0001), and the interaction of diet and day (P = 0.88). B) Prepartum pooled SEM = 1.7 Mcal/d; postpartum pooled SEM = 2.8 Mcal/d. Effects in the prepartum model included C vs. CF (P = 0.33), C vs. F (P = 0.42), day (P < 0.0001), and the interaction of diet and day (P < 0.01). Effects in the postpartum model included C vs. CF (P = 0.33), C vs. F (P = 0.65), day (P < 0.0001), and the interaction of diet and day (P = 0.87).
