| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
,1
* Physiology Weihenstephan, Technical University Munich, Weihenstephaner Berg 3, D-85350 Freising-Weihenstephan, Germany;
and
Department of Animal Science, Group Animal Nutrition, Technical University Munich, Hochfeldweg 4–6, D-85350 Freising-Weihenstephan, Germany;
and
Institute of Animal Science, Physiology & Hygiene Group, University of Bonn, Katzenburgweg 7–9, D-53115 Bonn, Germany; and
Veterinary Physiology, Vetsuisse Faculty, University of Bern,Bremgartenstr 109a, CH-3001 Bern, Switzerland
 |
Abstract |
|---|
 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Key Words: body condition • dairy cow • energy supply • ketosis • metabolic profile
|
INTRODUCTION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). High-yielding cows are susceptible to metabolic diseases during the early postpartum period. A concomitant suppression of immune functions causes an increased risk for infectious deseases (Mallard et al., 1998). Moreover, metabolic disorders during early lactation are related to decreased fertility (Butler and Smith, 1989).
During early lactation, milk production increases more rapidly than DMI, and dietary intake lags behind the increase of nutrient needs (Bell, 1995). To meet the nutritional demands of milk synthesis, dairy cows need to mobilize body reserves causing negative energy balance (EB) until nutrient intake covers the demands (Nebel and McGilliard, 1993; Hattan et al., 2001). Circulating ketones [e.g., β-hydroxybutyrate (BHB)] increase during periparturient lipolysis and may result in metabolic disturbances (Herdt, 2000). For the identification of cows being at risk for subclinical disorders, various threshold values of BHB have been suggested, for example by Walsh et al. (2007).
If the metabolic adaptation around parturition is impaired by environmental influences or based on the animal genetics, cows develop periparturient illnesses (Drackley et al., 2005). We aimed to characterize the individual variation in this adaptive process by recording blood metabolite concentrations, liver enzymes, hormones, BCS, BW, and resumption of ovarian activity postpartum in individual cows fed to achieve similar EB under practical farming conditions. To test the hypothesis that the course of metabolite and hormone concentrations during the postpartum period differs among animals, cows were classified according to their BHB concentrations. Differences between the groups would support the notion that factors other than nutrition and housing, namely genetic or epigenetic differences, or both, affect the individual capacity to cope with metabolic stress.
|
MATERIALS AND METHODS |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Animals and Feeding Regimen
Red Holstein dairy cows (n = 45) were monitored from 2 wk antepartum (a.p.) to wk 14 postpartum (p.p.) during a period from September to May. The 305-d milk production in this herd was 7,909 ± 1,377 kg (mean ± SD) with 4.29% fat and 3.36% protein. The animals were housed in a free-stall barn, and individual feed intake was recorded electronically. A partially mixed ration consisting of roughage plus concentrate (relation 80:20 in DM) was fed ad libitum and was accessible 24 h per day. Troughs for roughage were connected to electronic balances; extra concentrate was provided by automatic feeders. Individual partially mixed ration and concentrate intake were continuously recorded in 24-h intervals during the entire study period. In addition, disease information was captured from daily animal inspections documented in on-farm data sheets and veterinary records.
During the dry period, cows were fed a ration that satisfied the demand for maintenance and the additional energetic needs of the conceptus and the mammary gland (i.e., 13 MJ of NE1/d from wk 6 to wk 4 a.p. and 18 MJ of NE1/d from wk 3 a.p. until calving, respectively), according to the recommendations of the German Society of Nutrition Physiology (GfE, 2001).
During lactation, the cows were fed ad libitum with a partially mixed ration (62% corn silage, 15% grass silage, 3% straw, and 20% concentrate) to provide approximately 6.7 MJ of NE1/kg of DM with 152 g of intestinally utilizable CP/kg of DM. The concentrate contained 8.1 MJ of NE1/kg of DM and 225 g of CP/kg of DM. Minerals and vitamins were fed according to the calculated needs. In addition, cows were fed concentrate in transponder feeding stations in increasing amounts up to 7 kg/d during the first 7 wk of lactation. Beginning with the eighth week of lactation, the amount of concentrate fed was adjusted to milk yield [i.e., if daily milk yield was above 18 kg, the cows received 0.5 kg (containing 88% DM) per kilogram of milk up to a maximum of 9 kg daily per cow].
Feed Samples and Analyses
Samples of corn and grass silage as well as of the concentrate were collected weekly; a sample of the mixed ration was obtained twice per week. Each feed sample was mixed to homogeneity, and aliquots of 800 g were stored at –20°C for further analyses. For the determination of DM, fresh feeds were weighed, dried for 24 h at 60°C, and were then reweighed. For the concentrate prepared weekly at the in-house mixing and milling facility at the farm, a 1-kg sample was hermetically sealed and stored cool and dry. For all further analyses, samples were milled (Brabender, Duisburg, Germany; filter width 1.1 mm) and combined afterwards into 2-wk sample pools.
Feed samples were analyzed for inorganic matter, crude fiber, crude fat, and nitrogen-free extracts according to the Weender protocol (Naumann et al., 2000). The Kjeldahl method was used to measure the CP content in the feed samples. Intestinally utilizable protein and NE1 of the feed samples were estimated according to the German Society of Nutrition Physiology (GfE, 2001). The nutrient contents of the individual components analyzed together with their respective digestibilities were used to calculate the EB.
BW, BCS, and Ultrasonographic Measurements
Body weights were recorded weekly on electronic scales after milking from wk 1 to 14 after calving. Body condition was scored according to Edmonson et al. (1989). The B-mode ultrasonographic measurements of LM diameter (MD) and backfat thickness (BFT) were performed as described earlier (Bruckmaier et al., 1998) at 1 to 2 wk a.p. and at wk 1, 3, 5, 7, 10, 12, and 14 p.p. Muscle diameter and BFT were measured on the right side at the fourth loin vertebra. The positions for the ultrasound measurements were clipped, fluid paraffin wax was applied, and the ultrasound probe transducer (SonoVet 2000, Kretztechnik, Zipf, Austria, 5-MHz linear array transducer) was held softly against the skin and rectangular to the interface to avoid compression of the fat layer. Body weight, BCS, and ultrasonic measurements were always performed by the same person.
Milk and Blood Samples
Milk yield was recorded routinely by an automatic device installed in the milking parlor. Milk samples were collected twice weekly on 2 consecutive days (2 complete days of milking: Monday p.m., Tuesday a.m., Thursday p.m., and Friday a.m.) for 100 d to determine the average fat, protein, urea, and lactose contents via an infrared analyzer (MilkoScan-FT-60000, Foss Analytical A/S, Hillerød, Denmark). Somatic cell counts were measured with a Fossomatic-5000 (Foss Analytical A/S). Once per week, milk acetone was measured using an autoanalyzer (DAM Method, Bran + Luebbe GmbH, Norderstedt, Germany).
Blood samples were taken weekly from 2 wk a.p. until wk 8 p.p. Thereafter, blood was sampled once every 2 wk until wk 14. Blood (20 mL) was collected via jugular puncture both in EDTA-coated vacuum tubes and in NaF vacuum tubes (Greiner, Frickenhausen, Germany); samples were cooled on ice, centrifuged at 1,600 x g at 4°C for 15 min, and the plasma was aliquoted and stored at –20°C.
Analysis of Metabolites, Hormones, and Hepatic Enzymes
Concentrations of BHB, NEFA, glucose, IGF-1, and leptin were assayed in blood plasma using enzymatic kit methods (BHB: No. 0907979, R-Biopharm, Darmstadt, Germany; glucose: No. 315-100, Sigma-Aldrich, Munich, Germany; NEFA: No. 994-75409, Wako, Neuss, Germany) and immunological assays (IGF-1: RIA, Daxenberger et al., 1998; leptin: enzyme immunoassay, Sauerwein et al., 2004), respectively. The activities of aspartate-aminotransferase (AST), glutamate-dehydrogenase (GLDH), and 
-glutamyl-transferase (GGT) were tested enzymatically; total bilirubin was measured colorimetrically using Modular Analytics (Hitachi/Roche, Mannheim, Germany).
Classification of Animals
To allocate the cows studied herein to groups in which adaptation to early lactation led to either hyper- or normoketonaemic conditions, we used the plasma concentrations of BHB with a threshold value of 1 mM as suggested by Huszenicza et al. (2006). Cows that had BHB values >1 mM at least once during the 16-wk observation period were considered as BHB positive (BHB+, n = 21), whereas those cows with BHB values <1 mM throughout the entire experiment were classified as BHB negative (BHB–, n = 24).
Reproductive Performance
Ovarian cyclic activity was evaluated by determining the progesterone concentrations (Prakash et al., 1988) in milk samples collected from each cow twice per week beginning wk 2 p.p. Progesterone concentrations exceeding 1.2 ng/mL for at least 1 wk and declining thereafter below 0.5 ng/mL were regarded as indicative of a corpus luteum developed in consequence of a preceding ovulation (Schopper et al., 1989).
Statistical Analyses
Data are presented as means ± SEM. The MIXED models procedure (SAS Inst. Inc., Cary, NC) program package used included animal, group, and time as class variables. Animal was the repeated subject. The compound symmetry matrix structure was used. Statistical significances (P < 0.05) between group and time and of interactions between both were tested by LSD. The 
2 test was used to analyze disease frequency and nominal reproduction data in BHB groups.
Incomplete test-day records and test-day records of cows under a medical or preventive treatment, which might have influenced metabolic or endocrine status, were omitted. In total, records of 45 cows from wk 2 a.p. to 14 p.p. were available for calculations.
|
RESULTS |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
The mean 100-d lactation milk yield recorded during the experimental period was 3,086 ± 78.0 kg; there was no difference between the BHB– and BHB+ groups. Milk production started with 28 kg/d and then increased (P < 0.05), reaching peak values of 35.3 ± 1.5 kg at wk 7 in the BHB– group and 33.7 ± 1.2 kg in wk 9 in the BHB+ group (Figure 1A). Thereafter, milk yield declined (P < 0.05) for both groups to about 31 kg/d until wk 13. For milk fat and protein content, the timely changes are shown in Figure 1B and C. Cows of the BHB+ group had greater (P < 0.05) milk fat contents than those of the BHB– group during lactation in wk 2, 3, 4, 5, 7, and 9 p.p. Mean milk protein percentage was greater (P < 0.05) in the BHB– group in wk 4, 6, and 9. All milk constituents were greatest (P < 0.05) in wk 1 p.p. and then decreased, reaching relatively constant values until wk 6 and 7 p.p. (fat), or slightly rein-creased thereafter (protein; P < 0.05). As presented in Figure 1D, the fat:protein ratio was greater (P < 0.05) in the BHB+ than in the BHB– group during the trial in wk 2 to 9, 12, and 14 p.p. (P < 0.05). The fat:protein ratio values peaked in wk 4 with 1.8 in BHB+ and in wk 2 with 1.4 in BHB–, respectively. No group differences were detected for lactose (4.7%) and urea concentrations (248.0 mg/L) in milk and for somatic cell counts (235 x 103 cells/mL).
|
Mean total DMI was least (P < 0.05) at about 13 kg/d during the first week p.p. and then increased (P < 0.05) steadily until wk 10 to 11 without detectable differences between the 2 BHB groups (Figure 2A). At the end of wk 14, DMI was about 19.5 kg/d in both groups. The intake of NE1 was also least (P < 0.05) in the first week postcalving with 92.9 MJ of NE1/d in BHB+ and 87.2 MJ of NE1/d in BHB–, increased (P < 0.05) rapidly within wk 4 p.p., and peaked at wk 11 p.p. at 133.4 MJ of NE1/d in BHB+ and in wk 10 at 134.1 MJ of NE1/d in BHB– cows. During the period after calving, NE1 intake was not different between BHB+ and BHB– cows from wk 3 to 11 of lactation. At the end of the experimental period, both groups had mean NE1 intakes of 132.9 ± 9.6 MJ/d. The calculated EB, presented in Figure 2B, started with a nadir at about –42 MJ/d in the first week after calving and increased (P < 0.05) thereafter. By wk 14, BHB– cows had reached positive EB values, whereas BHB+ cows still had an energy deficit of –4.8 NE1 (MJ/d). However, EB was not different between the 2 groups during the experimental period.
|
Body weight decreased (P < 0.05) rapidly after parturition up to wk 6 and 4 in BHB+ and BHB– cows, respectively. The cows lost BW (Figure 3A) to a nadir of 614 kg in wk 11, and to 656 kg in BHB+ and BHB– cows, respectively. Overall, BHB+ cows had greater (P < 0.05) reductions of BW after calving, with group differences in wk 6, 7, and 10. At the end of wk 14, the BW difference between the 2 groups was about 48 kg.
|
). Thereafter, the cows of the BHB+ group lost more (P < 0.05) condition than the BHB– animals, with differences established for wk 7 and 12. The ultrasound measurements of MD and BFT of BHB+ and BHB– cows from wk 2 a.p. until wk 14 p.p. are presented in Figure 3C and D. After calving, the cows lost (P < 0.05) subcutaneous fat rapidly until wk 10 in BHB+ and wk 7 in BHB–, respectively. Similarly, MD was greatest (P < 0.05) before calving and was then decreased, but again, no differences were seen between the 2 groups. Metabolites, Hormones, and Enzyme Activities
As expected, the cows grouped into BHB+ and BHB– were clearly distinguishable by the time course of the BHB concentrations in blood throughout the study (Figure 4A), but showed no differences with regard to EB (Figure 2B). In the BHB+ group, the concentrations were greater (P < 0.05) from 1 wk until wk 10 p.p. than in the BHB– animals. The timely changes were only marginal in the BHB– group, whereas in the BHB+ group, the concentrations increased (P < 0.05) after calving reaching peak values in wk 2 to 5 and decreased thereafter.
|
). In BHB+ cows, the concentrations were about 2-fold greater (P < 0.05) during wk 1 to 5 than in BHB– cows. Thereafter, the milk acetone concentrations from BHB+ animals decreased (P < 0.05) and reached similar concentrations as seen in the BHB– group by wk 10.
For NEFA, increasing values toward calving were observed in both groups (Figure 4C). At parturition, BHB+ animals had about 2-fold greater (P < 0.05) NEFA values than the BHB– cows and maintained these concentrations during the following 4 wk. In BHB– cows, maximal NEFA values were reached during the first week of lactation but decreased (P < 0.05) thereafter. At wk 12, both groups had reached almost equal concentrations that were falling below the a.p. values.
Glucose concentrations were greater (P < 0.05) in BHB– than in BHB+ cows at 2 wk a.p. (Figure 4D) and in wk 0, 2 to 5, and 7 p.p. The nadir of glucose concentrations was reached at wk 2 in BHB+ cows and 1 wk earlier in BHB– animals; the a.p. concentrations were again reached by wk 10 in both groups.
For IGF-1 (Figure 5A), there was a steep decrease (P < 0.05) of the concentrations until calving in both groups. In BHB– animals, the concentrations remained at this level and then increased (P < 0.05) slowly. In contrast, BHB+ cows had further decreasing concentrations until wk 2 and then increased (P < 0.05) again. Differences between groups were limited to wk 1 to 8 after calving. By the end of the study, both groups had reached about 50% of the IGF-1 concentrations recorded 2 wk a.p.
|
). When taking all measurements of both leptin and BFT into account, a correlation of r = 0.31 (P < 0.001) was observed; for individual time points considered as representative for the a.p. or p.p. situation (i.e., for wk –2 a.p. and wk 5), significant correlations were limited to the a.p. stage (r = 0.38, P = 0.03).
The activities of the enzymes AST, GGT, and GLDH were greater (P < 0.05) from wk 1 to 14 p.p. than before calving. Significant differences between the BHB+ and the BHB– group were established for AST and GGT; the time courses for these 2 enzymes are shown in Figure 6 and demonstrate greater (P < 0.05) activities in BHB+ cows in wk 2 and 4 (AST) and wk 3 to 8 (GGT), respectively. For GLDH, an analogous difference was limited to 1 time point only [i.e., to wk 4 p.p. (P < 0.05)]. Total bilirubin concentrations increased (P < 0.05) from parturition until wk 1, when maximal values were reached. In BHB– cows, the concentrations were greater (P < 0.05) than in BHB+ around parturition and in wk 4 (P < 0.05).
|
There was no difference between BHB groups for the occurrence of clinical cases of mastitis, endometritis, retained placenta, lameness, and metabolic diseases (taking hypocalcemia, ketosis, and acidosis together) based on 2 analysis. The variables recorded in the 2 BHB groups to evaluate reproductive performance are shown in Table 1. The interval from calving to the onset of ovarian activity was studied in 45 cows and was below 100 d in all cases. Five cows were not inseminated for reasons of lameness or elevated somatic cell count in milk in the previous lactation. Thus, 40 cows were included for the analysis of the interval from parturition to conception. Each of these 40 cows was inseminated at least once. There was no difference between groups for any reproductive endpoint.
|
|
DISCUSSION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). Overfeeding during the far-off period (drying-off to d 25 a.p.) has a more negative effect on a.p. metabolism than differences in nutrition 3 wk a.p. (Dann et al., 2006). The metabolic demands in this period require that the liver synthesizes more glucose from noncarbohydrate precursors. A reduction in the ruminal production of propionic acid, the main precursor of glucose in ruminants, will result in hypoglycaemia. This leads to a mobilization of free fatty acids and glycerol from the fat stores (Holtenius and Holtenius, 1996; Andrews, 1998). The level of increased serum concentrations of NEFA appears to be causally linked to these problems, and feeding strategies to decrease or avoid this dramatic increase are desirable for optimal health and performance in dairy cows (Gerloff, 2000). In case of excess NEFA associated with an elevated formation of acetyl-coenzyme A, fatty acids are used for ketogenesis. Extreme lipid mobilization from adipose tissue exceeds the metabolizing capacity of the liver, leading to an increased accumulation of triglycerides (Herdt, 1988). The affected cows display fat infiltration and degeneration of the liver (Moore and Ishler, 1997).
The adipose tissue thus has a critical role in the development of fatty liver and ketosis, because these changes in liver composition and metabolism arise both from excessive lipolysis in adipose tissue and altered secretion of adipose tissue-derived hormones, which modulate hepatic metabolism (Vernon, 2005). The postpartal mobilization of fat was associated with increasing milk fat and decreasing milk protein contents as a consequence of the energy deficit. The fat:protein ratio allowed for an identification of the cows with elevated ketone body concentrations. Cows with fat:protein ratios >1.3 in the first week of lactation are at risk for ketosis or are already affected with it (Heuer et al., 1999). Milk yields were similar in BHB- and BHB+ cows, although there were differences in milk composition associated with the metabolic profile.
Milk acetone concentrations represented in this paper were in agreement with Reist et al. (2000). The periodic sampling of milk for the determination of acetone is getting more common in herd-health monitoring programs and is most suitable for diagnosis of clinical and subclinical ketosis in the first 6 wk of lactation.
Both groups had decreased DMI in early lactation. The EB did not differ between the BHB+ and BHB- groups, and both groups failed to achieve a positive EB by wk 14 of lactation. Total DMI followed a curve similar to the reports of Ingvartsen and Andersen (2000). As a consequence of the overfeeding in the dry period, total DMI was low in both groups in the present study.
The consequences resulting from the decreased DMI are reflected by energy intake. The total intake of energy by cows after calving is usually below the energy requirements, even for healthy cows (Bell, 1995). The NE1 intake was fractionally less in BHB+ than BHB–. In agreement with Drackley et al. (2005), it appears that changes in DMI a.p., and not the absolute DMI per se, are more closely related to poor intake and fatty liver after calving. These data emphasize the importance of good management that keeps cows healthy and comfortable before calving. In this way, increased DMI indicates the overall comfort and well-being of the cows rather than revealing the underlying reasons.
The negative EB challenges the metabolic adaptation of the cow. The least values were observed between 2 and 12 d p.p. The balance between energy from feed intake and energy requirements is mostly attained at approximately 72 d p.p. (Jorritsma et al., 2003). If negative EB is prolonged beyond this time or has an extended magnitude, or both, successful metabolic adaptation is less likely.
The least BW and the greatest BCS losses p.p. were found in the BHB+ group. Thus, we assume that BHB+ cows mobilized a greater amount of body tissue as a support of lactation. This interpretation is based on differences in milk composition, which imply altered nutrient partitioning (Zulu et al., 2002). Our data on MD give some indication that mobilization of body tissue comprised not only fat but also muscle tissue. Muscle protein serves as a source for glucoplastic amino acids to supply the increased needs for glucose during early lactation. Body condition score losses were present in both groups, although the BCS loss in BHB+ was greater. In agreement with Kunz et al. (1985), Busato et al. (1998), and Heuer et al. (1999), cows with a high BCS a.p. were more likely to develop an elevated ketone body status p.p. than cows in moderate to low body condition. This might be due to a greater mobilization rate of NEFA from fat depots in overconditioned than in thin cows.
Generally, greater plasma NEFA and BHB and lesser plasma glucose concentrations are associated with decreased reproductive performance, indicating that the balance of lipogenic and glycogenic compounds is important for reproductive function (Knegsel et al., 2005). The increase observed in glucose concentrations was greater for BHB+ cows and remained elevated for a longer period. Nevertheless, BHB was the criterion used for classification; the values in both groups during the first 14 wk of lactation mirrored the detrimental situation of fresh cows and the measurable results of utilization of body fat as a source of energy for milk production (Dann et al., 2005).
In general, enzyme activities increased p.p. Significantly differing enzyme activities between both groups indicate differences in potential tissue damage and liver function, which are known to be impaired during energy deficits and ketosis (Mills et al., 1986).
Insulin-like growth factor-1 is known to be markedly influenced by energy intake in dairy cows (Ronge et al., 1988). A negative EB decreases IGF-I concentrations (Lucy et al., 1992) and may thus explain for the decrease in IGF-I concentration around parturition. Decreased IGF-1 concentrations are in turn related to impaired luteal activity, slower follicular growth, and altered production of sex steroids (Spicer et al., 1990; Lucy et al., 1992). Negative EB during the early weeks of lactation and a delayed EB nadir are associated with longer intervals to the first ovulation p.p. (Beam and Butler, 1998). In our study, the concentrations of IGF-1 were clearly distinguishable between the BHB groups, whereas no differences in EB could be established for these groups. Considering the other differences established between the 2 groups, BHB seems to be more sensitive and thus more suitable to characterize the metabolic situation relevant for reproduction. The fertility records of the cows studied herein were acceptable in general (Ruegg, 2001) but give some indication for problems resulting from lipid mobilization and ketone body formation in the BHB+ group.
Drackley et al. (1992) suggested that intrahepatic factors altered by early negative EB and extensive tissue mobilization act in support of mechanisms that increase ketogenesis. However, the fact that cows respond differently to the homeorhetic needs of early lactation even though their EB was not different emphasizes individual animal variation. The effect of other potential stressors was considered as being the same for all animals; nevertheless, it was not specifically addressed in this study. The variability observed within a given setup in feeding and management (Hachenberg et al., 2007) is thus likely to be attributable to genetic, epigenetic, or rumen bacterial metagenomic regulation or all three. As an example, heritability values have been reported for ketosis (Henricson et al., 1977). In addition, variations in rumen microbial populations and metabolism as recently reviewed by Firkins et al. (2007) might contribute to the range of responses observed for various metabolites, enzymes, and hormones.
In conclusion, the timely changes of the concentrations of metabolites and hormones during the p.p. period remarkably differ among animals kept under similar and highly standardized conditions on a research farm. This indicates that the ability to cope with metabolic stress varies between individual cows. When aiming to characterize the adaptive capability, the intricate estimation of EB will not provide the information required. Instead, blood analyses, in particular of BHB, seem more appropriate to reflect the individual situation. Considering these findings, the identification of cows with high or low adaptive capabilities seems promising to investigate the underlying causes.
1 Corresponding author: rupert.bruckmaier{at}physio.unibe.ch
Received for publication March 8, 2008. Accepted for publication June 26, 2008.
|
LITERATURE CITED |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
This article has been cited by other articles:
|
|
 |
|
  G. B. Penner and M. Oba Increasing dietary sugar concentration may improve dry matter intake, ruminal fermentation, and productivity of dairy cows in the postpartum phase of the transition period J Dairy Sci, July 1, 2009; 92(7): 3341 - 3353. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. A. van Dorland, S. Richter, I. Morel, M. G. Doherr, N. Castro, and R. M. Bruckmaier Variation in hepatic regulation of metabolism during the dry period and in early lactation in dairy cows J Dairy Sci, May 1, 2009; 92(5): 1924 - 1940. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
- = BHB+ group (BHB concentrations 
1 mM at least once during the study) and -•- = BHB– group (BHB values 
1 mM). Data are given as least squares means ± SEM. *Differences between the 2 BHB groups at a particular sampling week (P < 0.05).
- = BHB+ group (BHB concentrations 
