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Metabolic Predictors of Displaced Abomasum in Dairy Cattle

Department of Population Medicine, University of Guelph, Ontario, Canada N1G 2W1

Corresponding author: S. J. LeBlanc; e-mail: sleblanc{at}ovc.uoguelph.ca.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The objective of this field study was to identify metabolic tests available in clinical practice that identified cows at increased risk of left displaced abomasum (LDA). A technician visited 1044 cows in 20 herds weekly from 1 wk before expected calving until 1 wk postpartum. Cows were assigned a body condition score and samples were collected at each visit for measurement of serum nonesterified fatty acids (NEFA), cholesterol, ß-hydroxybutyrate (BHBA), glucose, urea, calcium, and phosphorus, and a milk sample was collected postpartum for measurement of BHBA. The probability of LDA was modeled with multivariable logistic regression accounting for clustering. There were 53 cases of LDA (incidence risk = 5.1%) and the median time of diagnosis was 11 d in milk. In cows with LDA, mean NEFA concentrations began to diverge from the mean in cows without LDA 14 d before calving, whereas mean serum BHBA concentrations did not diverge until the day of calving. Prepartum, only NEFA concentration was associated with risk of subsequent LDA. Between 0 and 6 d before calving, cows with NEFA concentration 0.5 mEq/L were 3.6 times more likely to develop LDA after calving. For prospective application, among samples taken 4 to 10 d before expected calving, the optimum NEFA cut-point remained 0.5 mEq/L. The sensitivity, specificity, and likelihood ratio (LR) were 46%, 82%, and 2.6, respectively. Between 1 and 7 d postpartum, retained placenta, metritis, and increasing serum concentrations of BHBA and NEFA were associated with increased risk of subsequent LDA. However, considered separately, postpartum serum BHBA was a more sensitive and specific test than NEFA concentration. The odds of LDA were 8 times greater in cows with serum BHBA 1200 µmol/L (LR = 3.5). Cows with milk BHBA concentration 200 µmol/L were 3.4 times more likely to develop LDA. Serum calcium concentration was not associated with LDA. Strategic use of metabolic tests to monitor transition dairy cows should focus on NEFA in the last week prepartum and BHBA in the first week postpartum.

Key Words: peripartum • health • energy • transition

Abbreviation key: CI = confidence interval, LDA = left displaced abomasum, LR = likelihood ratio, OR = odds ratio, ROC = receiver operator characteristic

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Displacement of the abomasum is a common and economically important problem of dairy cattle in early lactation. In addition to the direct costs of treatment, affected cows produce less milk at least in the short term (Detilleux et al., 1997; Raizman and Santos, 2002) and have a higher culling rate (Geishauser et al., 1998; Gröhn et al., 1998; Raizman and Santos, 2002). The median incidence of LDA was 1.7% in 22 studies published between 1982 and 1995 (Kelton et al., 1998). Considering published reports from data from the US and Canada, it appears that the incidence of LDA is increasing in the last decade, from between 1 and 2% lactational incidence risk (Dohoo et al., 1983; Lissemore et al., 1992; Correa et al., 1993) to 5 to 7% (Cameron et al., 1998; Gröhn et al., 1998; Gröhn, 2000; LeBlanc et al., 2002). Risk factors for left displaced abomasum (LDA) have been reviewed (Geishauser, 1995; Shaver, 1997), but significant gaps remain in understanding its pathogenesis. Numerous studies have identified twins, dystocia, milk fever, retained placenta, metritis, and ketosis as risk factors for LDA (Gröhn et al., 1989; Correa et al., 1990; Rohrbach et al., 1999; Gröhn, 2000). Herd level risk factors related to nutrition and feeding management in the transition period have also been identified (Correa et al., 1990; Cameron et al., 1998). Most published evidence points to a lack of association between individual cows’ milk production and risk of LDA (Erb and Gröhn 1988; Cameron et al., 1998; Gröhn, 2000).

Geishauser et al. (2000a) summarized research on the association of various metabolites with the risk of subsequent LDA. Subclinical ketosis (serum BHBA 1400 µmol/L) and serum aspartate aminotransferase activity in the first 2 wk postpartum were associated with increased risk of LDA. Experimentally induced severe hypocalcemia (serum total calcium of approximately 1.2 mmol/L) has been associated with decreased abomasal motility (Daniel, 1983; Madison and Trout, 1988), but it is not clear whether this can be generalized to clinical milk fever or subclinical hypocalcemia. There is a report from one herd that subclinical hypocalcemia at calving was a risk factor for LDA (Massey et al., 1993), but there are conflicting data from field studies on the effect of oral supplementation of calcium around calving on the incidence of LDA (Oetzel, 1996; Melendez et al., 2003). Evidence for the mechanism of displacement of the abomasum is lacking. Constable et al. (1992) suggest that lack of rumen fill (to create a physical barrier to movement of the abomasum) and abomasal atony are key elements in the pathogenesis of LDA. Although inadequate feed intake (that might lead to lack of rumen fill, among other effects) and hypocalcemia (that might lead to lack of abomasal motility) seem logical as risk factors for LDA, there is little direct evidence to support these hypotheses.

The study reported here is derived retrospectively from samples collected during a previously reported clinical trial to determine the effect of one injection of vitamin E 1 wk before expected calving on the incidence of retained placenta (LeBlanc et al., 2002). Samples and data collected during that trial provided an opportunity to study the associations between serum measures of key aspects of peripartum metabolism and the occurrence of LDA. The objective of this study was to identify metabolites and potential cut-points associated with increased risk of subsequent LDA for practical application in monitoring transition cows.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Details of the clinical trial, data collection, laboratory and statistical analyses, and overall disease incidences were reported in LeBlanc et al. (2002). Briefly, from September 1998 through October 1999, a technician visited each of 20 farms weekly on the same day, at approximately the same time, within 2 h of the morning feeding. All cows were randomly assigned to receive either 3000 IU of RRR--tocopheryl acetate (label dose of Vital-E 300, Schering-Plough, Union, NJ) or placebo (propylene glycol), s.c. 1 wk before expected calving. There was no effect of treatment on the incidence of LDA (LeBlanc et al., 2002). Cows’ body condition was scored at enrolment (Ferguson et al., 1994). Immediately before treatment (4 to 10 d before expected calving based on a 280-d gestation length) and at each weekly visit up to and including the first week postpartum, 10 mL of blood was collected from the coccygeal vein into an evacuated sterile tube without anticoagulant (Vacutainer, Becton-Dickinson, Franklin Lakes, NJ). Samples were allowed to clot and kept chilled until serum was harvested and an aliquot stored at –20°C within 5 h of collection. Serum biochemistry analyses (concentrations of BHBA, NEFA, cholesterol, glucose, urea, calcium, and phosphorus) were conducted at the Animal Health Laboratory, University of Guelph, with a Hitachi 911 auto-analyzer. Prepartum, the technician attempted to induce cows to urinate by stroking the escutcheon. If successful, a free-flow urine sample was collected and a drop was applied to a ketone (acetone and acetoacetate) test tablet (Acetest, Bayer, Etobicoke, ON, Canada), which was scored as positive or negative based on observation of a color change from white to purple after 30 s. A sample of milk was collected at the postpartum visit (between 1 and 7 DIM) for measurement of BHBA using a validated (Geishauser et al., 2000b) semiquan-titative test strip (Keto-Test, Elanco Animal Health, Guelph, ON, Canada). Diaries were provided to producers to record all disease events. Additionally, at each weekly visit, the technician questioned producers about the occurrence of disease in the trial animals. Finally, medical records for the study herds were collected. The case definition for LDA was diagnosis by a veterinarian of a left side displacement of the abomasum within 30 DIM based on auscultation of a characteristic tympanic resonance ("ping") during percussion on the left side, which was generally confirmed during subsequent surgical correction. The case definitions for covariates were retained placenta (failure to pass the fetal membranes within 24 h after calving), milk fever (paresis with hypocalcemia within 2 d after calving), dystocia (veterinary-assisted delivery), and metritis (systemic illness including fever >39.5°C with fetid discharge from the vulva).

All statistical analyses were performed with SAS version 8.0 (SAS Institute, Inc., Cary, NC). Determinants of risk of LDA before 30 DIM was modeled with multivariable logistic regression, accounting for clustering of cows within herds with generalized estimating equations (Proc GENMOD, with binary distribution, logit link function, and compound symmetry correlation structure; Shoukri and Pause, 1999). Initially, metabolite concentrations as model inputs were treated as continuous variables. In addition to accounting for the random effect of herd, covariates included parity group (1, 2, or 3), season of calving (Fall: September–November; Winter: December–February; Spring: March–May; Summer: June–August), and BCS at enrolment. Cows that calved more than 16 d after enrolment in the study were excluded from the analysis. Within each of the 3 periods modeled (enrolment (4 to 10 d before expected calving, based on a 280-d gestation), n = 1132; wk –1 (d –6 to the day of calving, but before parturition), n = 1044; wk 1 (1 to 7 DIM), n = 1063), each cow was sampled only once. Because serum NEFA concentration normally begins to rise in the last few days before calving, it has been suggested to exclude samples taken in the last 2 d before calving from investigations of NEFA concentrations to monitor close-up dry cows (Oetzel, 2003). A model examined the association of samples taken 1 wk (4 to 10 d, inclusive) before the expected calving date, excluding samples drawn within 2 d of actual calving, on the risk of LDA. For the postpartum models, cows with LDA whose samples were taken on or after the date of diagnosis of LDA (n = 3) were excluded. Also for the postpartum models, the occurrence of twins, dystocia, and any disease events (milk fever, retained placenta, clinical mastitis, metritis) that occurred before diagnosis of LDA were offered to the models. Variables that were not significant at P < 0.05 were removed by manual backward stepwise elimination. For metabolites that remained in the final models, a range of cutpoints of the test result was tested for association with subsequent LDA, and their epidemiologic test characteristics were calculated. Sensitivity was the proportion of animals diagnosed with LDA that were at or above a given metabolite cutpoint, while specificity was the proportion of animals that did not have LDA that were below a given cutpoint (Dohoo et al., 2003). The likelihood ratio [(LR) = sensitivity/(1 – specificity)] describes the probability of an animal subsequently diagnosed with LDA having a test result at or above a given cutpoint compared with a similar result in an unaffected animal (Dohoo et al., 2003). Receiver operator characteristic (ROC) curves [sensitivity vs. (1 – specificity)] were constructed to identify the optimum threshold among the significant cutpoints (Dohoo et al., 2003). The point on an ROC curve that is closest to the upper left corner has the highest combined sensitivity and specificity.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
There was at least one prepartum and one postpartum serum sample, as well as data on the occurrence of LDA, from 1044 cows, of which 53 were diagnosed with LDA within 30 d after calving (lactational incidence risk = 5.1%). The median time of diagnosis of LDA was 11 DIM (range of 3 to 30 DIM). There was a tendency for cows starting their second lactation to have a lower risk of LDA [risks of LDA in first (29% of animals in the study), second (25% of animals), and third and greater parity (46% of animals) were 4.3, 2.9, and 6.1%, respectively, P = 0.11]. The median (minimum – maximum) BCS was: first parity, 3.75 (2.5 to 5.0); second parity, 3.5 (1.75 to 4.25); third and greater parity, 3.5 (2.0 to 4.5). There was no association of BCS category (3.0, 3.25 to 3.75, or 4.0) with the probability of LDA (², P = 0.78). The incidence of LDA was not affected by the vitamin E treatment in the underlying clinical trial (5.0 vs. 4.6%, P = 0.73, in cows that received vitamin E and placebo, respectively), and treatment was not a significant effect in any of the present models.

Descriptive data on serum concentrations of NEFA, BHBA, and calcium in the study period in cows that did and did not have LDA are presented in Figures 1 to 3. Serum NEFA concentrations in cows that went on to have LDA began to increase sooner and to a greater magnitude than in unaffected cows, beginning to diverge approximately 2 wk before calving, or an average of 3 to 4 wk before diagnosis of LDA. Serum BHBA concentrations also diverged in cows with subsequent LDA, but only from approximately the day of calving onward. In contrast, there were no differences in serum calcium concentration before diagnosis between cows with and without LDA. There was no association of clinical milk fever with LDA (59 cases of milk fever, of which 2 had subsequent LDA, P = 0.62). In the subset of cows sampled on the day of calving (n = 146, including 7 cows with subsequent LDA) or cows sampled on d –1, 0, or 1 relative to calving (n = 465, including 25 cows with subsequent LDA), there was no association of subclinical hypocalcemia (serum total calcium < 1.8, 1.9, or 2.0 mmol/L) with subsequent LDA (P > 0.3 for all tests).

View larger version (21K): [in this window] [in a new window]   Figure 1. Serum nonesterified fatty acids (NEFA) concentrations (mean and SE) in Holstein dairy cattle that were and were not subsequently diagnosed with left displaced abomasum (DA) within 30 d after calving. Each cow was sampled once weekly from 1 wk before expected calving until the first week postpartum. The data are pooled into 2-d increments relative to the actual day of calving.

View larger version (19K): [in this window] [in a new window]   Figure 2. Serum ß-hydroxybutyrate (BHBA) concentrations (mean and SE) in Holstein dairy cattle that were and were not subsequently diagnosed with left displaced abomasum (DA) within 30 d after calving. Each cow was sampled once weekly from 1 wk before expected calving until the first week postpartum. The data are pooled into 2-d increments relative to the actual day of calving.

View larger version (20K): [in this window] [in a new window]   Figure 3. Serum total calcium concentrations (mean and SE) in Holstein dairy cattle that were and were not subsequently diagnosed with left displaced abomasum (DA) within 30 d after calving. Each cow was sampled once weekly from 1 wk before expected calving until the first week postpartum. The data are pooled into 2-d increments relative to the actual day of calving.

Samples based on expected calving date.
When prospectively monitoring cows before calving, the actual interval between sampling and calving is unknown. A model examined the association of all samples (n = 1131) taken 1 wk (4 to 10 d, inclusive) before the expected calving date on the risk of LDA. The mean and median actual time to calving in these data was 7 ± 4 d (no difference in mean sample to calving interval between cows with and without LDA, P = 0.40) with a range of 0 to 16 d. Again, the only variable that remained in the final model was serum NEFA concentration. The optimum cutpoint for prediction of risk of subsequent LDA remained NEFA 0.5 mEq/L (Figure 4). Cows above this threshold were 4 times more likely to be diagnosed later with LDA (Table 1; OR = 4.1, 95% CI = 2.5 to 6.9, P < 0.0001). A NEFA test result 0.5 mEq/L in this time frame was 2.6 times more likely to come from a cow subsequently diagnosed with LDA.

View larger version (10K): [in this window] [in a new window]   Figure 4. Receiver operator characteristic (ROC) curve for cutpoints of prepartum serum nonesterified fatty acids (NEFA) concentration measured 4 to 10 d before expected calving (all samples included; from Table 1) for prediction of the risk of subsequent left displaced abomasum.

In the last week before calving, urine samples were obtained from 502 cows (48%), of which 18 were eventually diagnosed with LDA. There were 32 samples (6%) positive for ketones, of which 7 came from cows with subsequent LDA. Cows with a positive urine ketone test prepartum were almost 12 times more likely to later have LDA (OR = 11.7, P < 0.0001). The sensitivity of this test was 39% and the specificity was 95% for a LR of 7.8.

Postpartum Predictors of LDA
In the first week after calving (n = 1063; mean ± SD = 3.9 ± 1.9 DIM; no difference in mean sample to calving interval between cows with and without LDA, P = 0.26), given data on the serum metabolites analyzed in this study, retained placenta, metritis, and increasing serum concentrations of both NEFA and BHBA were significantly associated with increased risk of subsequent LDA (Table 2). During the same period (1 to 7 DIM), given the result of one milk ketone test (but not the serum metabolites), twins, metritis, and increasing milk BHBA concentration were associated with increased risk of subsequent diagnosis of LDA (Table 3). For field application, the univariate associations of cutpoints of each of serum NEFA, serum BHBA, and milk BHBA concentrations were analyzed (Table 4). Essentially all cutpoints within the range of observed values for each analyte were significantly associated with increased risk of LDA. Receiver operator characteristic curves identified serum BHBA 1200 µmol/L, serum NEFA 1.0 mEq/L (Figure 5), and milk BHBA 200 µmol/L (not shown), each considered alone, as the optimum cutpoints for classifying cows at high risk of LDA. Comparing the significant serum metabolites at their optimum cutpoints, BHBA (OR = 8.0) was more strongly associated with risk of LDA than NEFA (OR = 4.8) and had slightly higher sensitivity and specificity, resulting in a higher LR.

View larger version (17K): [in this window] [in a new window]   Figure 5. Receiver operator characteristic (ROC) curves for cutpoints of postpartum (1 to 7 DIM) serum ß-hydroxybutyrate (BHBA) and nonesterified fatty acids (NEFA) concentrations (from Table 2) for prediction of the risk of subsequent left displaced abomasum. The point on each line closest to the upper left corner (BHBA 1200 µmol/L or NEFA 1.0 mEq/L) is the optimum observed combination of true positive and true negative predictions.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

The results of this study are generally in agreement with other reports on the predictive association of prepartum NEFA and postpartum BHBA concentrations with LDA. The present results can be applied to inform strategic monitoring of the management of transition cows or the investigation of herd problems of high incidence of LDA. Cameron et al. (1998) found that cows with plasma NEFA > 0.3 mEq/L between 3 and 35 d before calving were twice as likely to subsequently have a displaced abomasum. The present results agree with this finding and further strengthen and refine the application of prepartum NEFA measurement for assessment of the risk of LDA. Geishauser et al. (1997a) found that in cows with serum BHBA 1200 or 1400 µmol/L in the first week postpartum the odds of LDA were 3 and 4 times greater, respectively, than in cows with BHBA below the cutpoints. In the present study the association was even stronger (OR = 8.0) at the same cutpoints. Similar to the present results, Geishauser et al. (1997a) found that the optimum BHBA threshold in the first week postpartum for prediction of LDA was between 1200 and 1400 µmol/L. However, the sensitivity and specificity of both cut-points were higher in the present data. The association of the milk BHBA test results with the probability of subsequent LDA was similar in the present study to that observed by Geishauser et al. (1997b) using the same test strip, with the odds of LDA in cows with milk BHBA 200 µmol/L 3 and 5 times greater, respectively. At the same cutpoint, sensitivity was higher (48% vs. 35%), specificity was lower (80 vs. 91%), and LR was similar (2.4 vs. 2.7) in the present study and that of Geishauser et al. (1997b), respectively.

The present results confirm the association of RP, twins, and metritis with increased risk of LDA. The multivariable models indicate the associations of NEFA and BHB with LDA, accounting for the effects of the disease covariates. Twins, RP, and metritis are associated with each other, which explains the slightly different disease covariates in the final postpartum models (Tables 2 and 3) depending on the metabolic information in the model (serum or milk). Elevated NEFA concentration prepartum is a risk factor for RP (LeBlanc et al., 2004), suggesting that RP and LDA have some causal factors in common. In turn, once RP and/or metritis occur, these conditions may cause cows to eat less, increasing their risk of LDA. On the other hand, the association of RP, twins, or metritis with LDA may be less direct. Maladaptive response to peripartum negative energy balance and other stressors may contribute to impaired immune function, resulting in RP or metritis (Kehrli et al., 1999), or may be manifest by the separate but related pathology of LDA. The lack of association of milk fever or serum calcium concentration prepartum or postpartum with the risk of LDA argues against hypocalcemia as a direct factor in the causal pathways to LDA. These results are in contrast to Massey et al. (1993). In that study, no data on other metabolites were considered. We hypothesize that the reported associations between clinical milk fever (Gröhn et al., 1989; Correa et al., 1993; Rohrbach et al., 1999) or subclinical hypocalcemia (Massey et al., 1993) are not directly causal. Rather, hypocalcemia may be symptomatic of inadequate prepartum feed intake, which leads to other direct risks for LDA such as elevated NEFA concentration and subclinical ketosis.

Although there was a strong association prepartum between detection of ketones in urine and risk of LDA, this technique was applicable to less than half of the cows (from which urine could be obtained). Additionally, the sensitivity of this test was lower than that of serum NEFA concentration in the same time frame. Although the cost per sample is greater for measurement of serum NEFA than for the urine tablet, blood samples can be obtained reliably, and for prepartum classification of cows as to risk of LDA, serum NEFA 0.5 mEq/L identified more cows that were at elevated risk of LDA.

Prepartum and postpartum, the metabolites that were significantly predictive of LDA (NEFA and BHBA) were both indirect measures of the magnitude of negative energy balance and the success of the cow’s adaptation to it (Herdt, 2000). Interestingly, prepartum BCS was not associated with the risk of LDA. These findings do not refute the importance of body condition, but indicate that NEFA and BHB provide better insight into metabolic function, at least with respect to development of LDA. The present results confirm a previous large field study (Cameron et al., 1998) showing that the severity of peripartum negative energy balance, reflected by NEFA concentration, is a key element in the etiology of LDA. Although DMI was not measured in this study, it is likely that a considerable proportion of the variability in these metabolites was attributable to differences in DMI, which in turn has many sources of variability (Hayirli et al., 2002). Prepartum DMI has been shown to be associated with the risk of postpartum subclinical ketosis (Osborne, 2003). While the present data do not explain the mechanism of development of LDA, peripartum NEFA and BHBA concentrations offer a meaningful summary "snapshot" of energy metabolism, which is a significant component in the causal web of LDA.

The selection of tests, their timing, and cutpoints will depend on the objective of the sampling. Generally, programs to monitor transition cows may have the objective of either group-level monitoring of the adequacy of the design and delivery of a nutritional and management program, or individual-level early detection of metabolic problems with the goal of intervention to mitigate the problem or lower the risk of subsequent disease. Although there is overlap between these 2 objectives, the present results were analyzed and should be interpreted at the individual-cow level. Different strategies or cutpoints that emphasize test sensitivity or specificity may be appropriate, depending on the logistics of sample collection in a herd, the prevalence of LDA, and the expected costs and benefits of intervention in animals on the basis of test results. A major challenge for implementation of prepartum metabolic testing is the inability to know precisely when cows will calve. Although significant associations of NEFA were found in each of the time periods examined in this study, practically, collection of samples weekly from cows that are 4 to 10 d before expected calving is likely an achievable program. For samples taken approximately 1 wk before expected calving, the present results indicate that it is not necessary to wait to submit samples for analysis to exclude those from cows within 2 d before calving. The present data were relatively sparse more than 10 d before calving, and in any case it would be very difficult to accurately select those cows that are exactly in their last or second-to-last week prepartum. The variability of NEFA prepartum evident in Figure 1 reflects the relatively small numbers of animals with LDA (approximately 15 cows) at any one data point on the graph. The associations of NEFA concentration with LDA within the periods and at the cutpoints described are valid, but must be viewed as probabilities, not absolute indications of outcomes. The data should be interpreted at the individual-cow level, but within the weekly periods described, not at specific days when variability may be excessive.

Unfortunately, there is presently little evidence to inform choices of intervention in response to elevated NEFA or BHBA as metaphylactic or early therapeutic treatment. In cows identified as being at high risk of LDA on the basis of a NEFA or BHBA test result as described in the present study, administration of propylene glycol might be beneficial (Grummer et al., 1994; Pickett et al., 2003). However, further research is needed on the timing and duration of administration of propylene glycol that might be effective at reducing the risk of LDA. Likewise, further investigation is needed to determine the efficacy of other possible treatments such as dextrose, propionate salts, corticosteroids, or insulin.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The response to peripartum negative energy balance is one key aspect in the pathogenesis of LDA. The timing and magnitude of peripartum increases in circulating concentrations of NEFA and BHBA are associated with the risk of eventual abomasal displacement. Programs to monitor management of the transition period in general and risk of LDA in particular should focus on NEFA concentrations in the week before expected calving and on BHBA concentration in the first week after calving.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Dairy Farmers of Ontario and the Ontario Ministry of Agriculture and Food provided funding for this study. We are grateful to Jeromy Ten Hag and Jodi Wallace for sample and data collection and entry.

Received for publication May 4, 2004. Accepted for publication September 3, 2004.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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