Marys Medicine


The effect of subclinical ketosis in early lactation on reproductive performance of postpartum dairy cows

J. Dairy Sci. 90:2788–2796
American Dairy Science Association, 2007.
The Effect of Subclinical Ketosis in Early Lactation on Reproductive
Performance of Postpartum Dairy Cows

R. B. Walsh,*1 J. S. Walton,† D. F. Kelton,* S. J. LeBlanc,* K. E. Leslie,* and T. F. Duffield*
*Department of Population Medicine, and
†Department of Animal and Poultry Science, University of Guelph, Ontario, Canada, N1G 2W1
d). To further investigate this, the effect of elevatedcirculating BHBA was permitted to vary with time. The Data generated from 796 Holstein cows enrolled in effect decreased with time, such that the daily probabil- a clinical trial to investigate the health effect of a mo- ity of pregnancy increased similar to nonsubclinically nensin controlled release capsule were analyzed to in- ketotic cows by approximately 160 d in milk. From this vestigate the association between circulating serum analysis, both the relative circulating concentration of β-hydroxybutyrate (BHBA) concentration in the peri- BHBA and the duration of elevated circulating BHBA parturient period and subsequent reproductive perfor- were negatively associated with the probability of preg- mance. Overall, accounting for both repeated measures nancy at first service.
within cow and clustering at the herd level, non-preg- Key words: subclinical ketosis, β-hydroxybutyrate,
nant cows after first insemination tended to have in- time to pregnancy creased circulating BHBA concentrations from 3 wkbefore calving to 9 wk after calving relative to pregnantcows. Including the interaction between the week of sample collection and pregnancy outcome, non-preg- The concept of homeorhesis or prioritization of energy nant cows had higher circulating BHBA concentrations distribution to meet specific physiological demands was in the second week after calving than cows diagnosed refined in 1980 (Bauman and Currie, 1980). Parti- pregnant after first artificial insemination. Within indi- tioning of available energy to milk production early in vidual weeks, cows with circulating BHBA concentra- lactation, at the expense of reproduction, has formed a tions ≥1,000 ␮mol/L in the first week postpartum were conceptual framework to address the effect of negative less likely to be diagnosed pregnant after first insemina- energy balance on future reproductive performance, as tion. In the second week postpartum, the cows with measured by the time to establishment of luteal activ- circulating BHBA concentrations ≥1,400 ␮mol/L were ity, probability of pregnancy after first AI [pregnancy significantly less likely to be pregnant after first artifi- risk (PR)/AI], and time to conception.
cial insemination. A dose response relationship was Cows experiencing delayed onset of luteal activity found when a comparison of the probability of preg- postpartum typically have lower DMI, produce less nancy after first insemination and duration of elevated milk, and subsequently lose more body condition early circulating ketone bodies was investigated. The proba- in lactation (Staples et al., 1990). At the whole-animal bility of pregnancy was reduced by 20% in cows diag- level, the magnitude and duration of negative energy nosed subclinically ketotic in either the first or second balance are influenced by feed intake and milk produc- week postpartum. Nevertheless, cows above the sub- tion. At the organ and molecular level, variation in clinical ketosis threshold in both the first and second energy utilization efficiency, ranging from rumen func- week postpartum were 50% less likely to be pregnant tion to the ability of the liver to repartition mobilized after first insemination. Similarly, the median time to fat, affect energy balance status.
pregnancy increased in cows experiencing elevated Previous research has reported an association be- BHBA concentrations in either (124 d) or both (130 d) tween calculated negative energy balance and repro- the first and second week postpartum relative to cows ductive traits, including days to first luteal activity, never experiencing elevated BHBA concentrations (108 first service conception risk, days from calving to AI,and days from calving to conception (Villa-Godoy etal., 1988; Staples et al., 1990; Reist et al., 2003b). Thephysiological state of energy deficiency impairs hypo- Received August 28, 2006.
Accepted January 31, 2007.
thalamic responsiveness to circulating estradiol-17β, 1Corresponding author: [email protected] resulting in reduced GnRH pulse frequency and con- EFFECT OF SUBCLINICAL KETOSIS ON REPRODUCTION comitant reduction in LH required for follicular devia- collected from a coccygeal blood vessel into a 10-mL tion and eventual ovulation (Jolly et al., 1995; Dawuda vacuum tube (Monoject red stopper blood collection et al., 2002; Butler, 2003).
tubes; Sherwood Medical, St. Louis, MO). Blood was Energy balance is dependent on many factors. Vari- collected at the time of monensin CRC or placebo oral ous metabolic and endocrine blood and milk measures administration 3 wk before calving and at wk 1, 2, 3, such as NEFA, ketone bodies, glucose, insulin, milk 6, and 9 postpartum. Blood samples were stored, on fat, or fat:protein ratio are indirect measures of energy ice, in an insulated cooler from time of collection until balance. Circulating ketones increase when the maxi- sample processing occurred. Within 5 h postcollection, mal ability of the liver to oxidize NEFA and store triac- blood samples were centrifuged at 733 × g for 10 min.
ylglycerol is exceeded. Associations between elevated The samples of serum were submitted to the Clinical circulating ketone concentration and periparturient Pathology Laboratory (Department of Pathobiology, uterine disease were described by Reist et al. (2003a); Ontario Veterinary College) for the measurement of Ca, however, investigation of thresholds was based on the P, total protein, urea, glucose, and BHBA concentra- distribution of circulating ketone concentrations or an- tions and determination of aspartate aminotransferase ecdotal experience rather than the associated change activity using an automated analyzer (Dacos 2 ana- in the risk of disease (Duffield et al., 1998). Similarly, lyzer; Coulter Electronics, Hialeah, FL).
the effect of postpartum circulating ketone concentra- Peripartum disease information including dystocia tion on PR/AI, time to commencement of luteal activity, (veterinary-assisted parturition), retained placenta and time to pregnancy has been described later in lacta- (failure to pass the fetal membranes within 24 h), milk tion with variable results (Andersson and Emanuelson, fever (veterinary diagnosed), metritis (inflammation of 1984; Cook et al., 2001). A circulating BHBA concentra- the uterus <15 DIM), clinical ketosis, displaced aboma- tion threshold immediately postpartum, defined by de- sum (left or right displacement diagnosed by a veteri- monstrable reduction in the PR/AI, has not been val- narian), respiratory illness, and lameness was captured in on-farm data sheets, veterinary records, and on-farm The objectives of this retrospective analysis were to computer record systems (Duffield et al., 1999). Repro- investigate relationships between the magnitude and ductive data, including DIM at first insemination, con- duration of increased serum BHBA measured at −3 wk ception date, number of inseminations, herd removal and in each of the first, second, third, sixth, and ninth date, and pregnancy status at removal, were recorded weeks postpartum and the PR/AI, the time from calving using the same methods. There was minimal use of to first AI, and time from calving to pregnancy.
ovulation synchronization protocols. Pregnancy diagno-sis was performed at least 40 d after insemination by MATERIALS AND METHODS
rectal palpation. Five herds had first lactation animalsexcluded, because they had been exposed to a monensin Data were collected as part of a clinical trial to deter- premix within 4 wk of parturition.
mine the effect of prepartum administration of monen-
sin as a controlled release capsule (CRC) on postpartum
Data Management and Statistical Analysis
health, energy balance, and reproductive performance(Duffield et al., 1998, 1999). Briefly, 25 Holstein herds Statistical analysis was performed using Intercooled around Guelph, Ontario, Canada, that were enrolled in Stata 9.1 (StataCorp LP, College Station, TX) and SAS milk recording through Ontario DHI were studied from (SAS Inst. Inc., Cary, NC). Descriptive statistics were March 1995 to December 1995. Herd size ranged from used to characterize animals diagnosed pregnant after 25 to 160 lactating animals, with 305-d rolling herd first insemination, relative to animals diagnosed not average for milk production from 7,000 to 10,000 kg.
pregnant. Data were collected as part of a clinical trial; Five herds were fed a TMR, and the remaining herds therefore, treatment remained in all analyses.
had a component feeding system. A technician visited The shape of the BHBA curve between weeks was each farm weekly at a consistent time of day. At each assessed using PROC MIXED in SAS (SAS Institute, weekly visit, the technician administered the randomly 2004), accounting for the random effect of herd and assigned treatment (monensin CRC or placebo); re- repeated measures of cows within herd. After trans- corded animal data including lactation, season of calv- forming the BHBA data into the natural logarithm ing (winter: December through February; spring: scale, variables offered to the model included treat- March through May; summer: June through August; ment, parity, periparturient disease, the pregnancy sta- fall: September through November), and BCS (Fergu- tus diagnosed after first AI, and all 2-way interactions.
son et al., 1994; ≤2.5 thin; ≥2.75 to ≤3.5 fair; ≥3.75 fat); Residual analysis was performed at the cow level. The and collected blood samples. Each blood sample was distribution of residuals was symmetrical with long Journal of Dairy Science Vol. 90 No. 6, 2007 WALSH ET AL.
tails, thus violating the normality of residual assump- Table 1. Characterization of 796 Holstein dairy cattle from 25 On-
tario herds diagnosed pregnant or non-pregnant after first insemina-
tion. To investigate the effect of influential observations (extreme values in the independent or dependent vari-ables), they were removed from the analysis. Removal of influential observations improved the normality of residual assumption without affecting the direction of Days to first insemination1 80.4 (77.3 to 83.5) 79.4 (77.1 to 81.8) the reported coefficients indicating that the observed 3.44 (3.35 to 3.43) 3.39 (3.43 to 3.5) effect was not solely due to the effect of extreme observa- tions. Final models included all observations. Least Periparturient disease3 Retained placenta squares means of weekly BHBA concentration were estimated for pregnant and non-pregnant cows at each weekly measurement. To appropriately account for the Displaced abomasum repeated measures within cow, a postestimation adjust- ment was performed on the reported probability value using the Bonferroni-Sidak adjustment to account for Cystic ovarian disease correlation between sampling intervals.
The effect of BHBA concentration at each week on Mean (95% confidence interval).
probability of pregnancy at first insemination was as- Proportion of randomly assigned treatments with the monensin controlled release capsule (CRC).
sessed using multivariable logistic regression account- 3Proportion (n).
ing for correlation of cows within herd using a general-ized estimating equation with an exchangeable correla-tion structure. Cow level variables offered to the model to modified Cox-Snell residuals assessed goodness of included parity, season of calving, initial BCS, BCS at fit. Animals with survival times less than 30 DIM were 60 DIM, change in BCS, season of calving, and peripar- excluded from this analysis, because they were not at tum disease information. Herd level variables included risk for pregnancy, and they did not complete the sam- farm type (free stall vs. tie stall) and herd size. Treat- pling protocol. The proportionality assumption was as- ment with monensin was retained in all models, be- sessed graphically by plotting the logarithm of the haz- cause the data were generated as part of a monensin ard function against the logarithm of time. The Akaike clinical trial. Initial screening of variables was per- information criterion was used to assess the overall fit formed using a manual backward stepwise procedure of the final model. Delta-beta-like residuals were used with significant variables (P < 0.1) remaining in the to identify points of leverage, whereas deviance residu- model. This procedure was repeated for each week post- als were calculated and sorted to identify possible partum in which serum BHBA measurements were available. Initially, serum BHBA was offered as a con-tinuous variable. Subsequently, based on the appear- ance of a smoothed scatterplot of serum BHBA andprobability of pregnancy at first AI, realistic thresholds The prevalence of dystocia, twins, peripartum dis- were created at 200 ␮mol/L increments from 1,000 to ease, reproductive abnormalities, and other health 1,600 ␮mol/L. Ultimately, sequential multivariable lo- events in the present data were reported previously gistic regression, accounting for the effect of clustering (Duffield et al., 1999). Briefly, treatment with a monen- at the herd level, was applied based on the predicted sin CRC reduced the risk of displacement of the aboma- thresholds to evaluate their potential significance.
sum by 40% [odds ratio (OR) = 0.59; P = 0.004] and the
The effect of prolonged exposure to elevated ketone risk of multiple illnesses by 40% (OR = 0.6; P = 0.01).
bodies on PR at first insemination was investigated The data and outcome of first insemination were re- by generating a composite variable representing the corded for 796 cows. The PR/AI at first insemination additive effect of the number of weeks with serum was 34.8%. Further characterizations of animals based BHBA ≥1,000 ␮mol/L in the first week and ≥1,400 ␮mol/ on pregnancy result to first AI are presented in Table L in the second week.
1. Median time from calving to first insemination was Finally, time from calving to first insemination and 74 d, ranging from 31 to 243 d. Days in milk at first time to pregnancy were modeled using semiparametric AI, parity, season of calving, and periparturient disease survival analysis. This method accounted for animals were significant in a model to determine risk factors that did not become pregnant. Robust standard errors for PR/AI. A BCS of 3.25 to 3.75 was assigned to 86% were generated to account for clustering of animals of animals independent of treatment. Treatment did within herds. Plotting the cumulative hazard relative not affect the probability of pregnancy at first AI (mo- Journal of Dairy Science Vol. 90 No. 6, 2007

EFFECT OF SUBCLINICAL KETOSIS ON REPRODUCTION Figure 1. Least squares mean serum BHBA concentrations and
standard error accounting for the random effect of herd and repeated Figure 2. Predicted probability of pregnancy generated through
measures with unequal spacing and adjusting for treatment and multivariable logisitic regression accounting for the correlation of parity in Holstein cows that were subsequently diagnosed pregnant cows within herds relative to serum BHBA concentration determined or non-pregnant after first insemination. Each cow was sampled once in the second week postpartum in 796 Holstein dairy cows.
in the third week before calving, in each of the first 3 wk, and againin the sixth and ninth weeks after calving. *P < 0.05.
1,064.0 ± 30.1, 66 to 8,976, respectively). The predicted nensin-treated group, 35.2%; placebo group 34.5%; probability of pregnancy, relative to circulating BHBA OR = 1.03; P = 0.84).
concentration for the second week postpartum is pre- Cows diagnosed non-pregnant after first AI tended to sented in Figure 2. Serum BHBA in wk 3, 6, and 9 were have increased circulating BHBA concentrations from 3 not significantly associated with PR.
wk before calving to 9 wk after calving relative to cows The proportion of animals classified as subclinically diagnosed pregnant after first AI (P = 0.09) accounting ketotic (SCK) at the predetermined thresholds by first
for monensin treatment and parity. A tendency for an service conception is presented in Table 2. From these interaction between the week of sample and pregnancy models, cows with serum BHBA ≥1,000 ␮mol/L in wk status after first AI was identified (P = 0.1). This inter- 1 or ≥1,400 ␮mol/L in wk 2 were significantly less likely action term was significant at wk 2. Least squares to be diagnosed pregnant after first insemination. There means were calculated at each sampling period for preg- were a total of 288 animals with serum BHBA ≥1,000 nant and non-pregnant cows and compared adjusting ␮mol/L in wk 1, and 150 cows were ≥1,400 ␮mol/L in for repeated measures within cow. Nonpregnant cows wk 2. A total of 104 cows were classified as SCK in both had increased circulating BHBA concentrations rela- tive to pregnant cows in the second week after calving Given the available data, evaluation of the effect of (P = 0.03; Figure 1). Treatment with the monensin CRC prolonged exposure to elevated ketones was limited to reduced the BHBA estimate at each sampling point (P analysis of the number of weeks above a series of thresh- < 0.001). Periparturient disease did not significantly olds. A dose response curve was identified when model-alter the shape of the BHBA curve. Neither initial BCS, ing the number of weeks positive without specifying final BCS (thin, fair, fat), nor BCS change (≥1 unit) was the order of weeks positive and using a 1,000 ␮mol/L significant in a model of factors affecting the probability threshold in wk 1 and the 1,400 ␮mol/L threshold in of pregnancy at first AI.
wk 2 (Table 3).
Within individual weeks after calving, an association Survival analysis was used to measure the time from between serum BHBA concentration and the PR/AI was calving to first insemination and from calving to preg- identified, accounting for the effect of correlation of cows nancy. The daily probability of AI was reduced in cows within a herd. The PR/AI was reduced by 2% (OR = classified as SCK in either wk 1 or 2 relative to cows 0.98, P = 0.06) in wk 1 and 3% (OR = 0.97, P = 0.01) never classified as SCK (P = 0.04; Table 4). Further, in wk 2 for each 100 ␮mol of BHBA/L increase. Although median time to first AI was delayed (P < 0.01) for cows the reported OR appears exceedingly small, the range calving in the spring relative to cows calving in the fall of serum BHBA reported is wide in both wk 1 and wk [median, 95% confidence interval (CI) spring = 81 d
2 (mean ± SE; range: 1,032.4 ± 27.6, 101 to 9,382 vs.
(95% CI = 78 to 85 d; fall 70 d, 68 to 72 d)].
Journal of Dairy Science Vol. 90 No. 6, 2007 WALSH ET AL.
Table 2. Investigation of the effect of serum BHBA threshold on the probability of pregnancy after first
insemination in 796 lactating Holstein dairy cows from 25 Ontario herds
1Odds ratio (OR) determined by logistic regression controlling for the effect of treatment with monensin controlled release capsule and clustering at the herd level. Each week modeled individually.
Median time to pregnancy for animals never classi- probability of pregnancy, measured using the adjusted fied as SCK was 108 d (95% CI = 102 to 112) relative hazard ratio (HR), between SCK and non-SCK cows
to 124 d (95% CI = 116 to 132 d) for animals above the was equivalent (Table 6; Figure 3).
threshold in either wk 1 or 2 and 130 d (95% CI = 115to 136 d) for animals greater than the BHBA threshold in both wk 1 and 2. The proportional hazard assumptionwas violated in this data set. Therefore, the effect of Postpartum hyperketonemia has repeatedly been as- exceeding the BHBA threshold was permitted to vary sociated with reduced reproductive performance in lac- over time. This correction significantly improved the tating cows. The current analysis offers several unique fit to the model. Controlling for season of calving and opportunities. First, the large number of individual monensin treatment, the daily probability of pregnancy cows that were followed continuously from before calv- was reduced in cows classified as SCK in either or both ing, weekly for the first 3 wk after calving, and again wk 1 or 2 relative to cows never classified as SCK (Table in the sixth and ninth weeks allows investigation of 5). The effect of elevated BHBA concentration remained the differences in energy status between cows over the until approximately 140 DIM, after which the daily transition period and within individual weeks. A com-prehensive investigation of the effect of magnitude andduration of hyperketonemia on reproductive perfor- Table 3. Effect of prolonged elevation of serum BHBA concentration
mance would best be calculated using the cumulative on the probability of pregnancy after first insemination in 796 lactat- exposure to elevated circulating BHBA concentrations.
ing Holstein dairy cattle from 25 Ontario herds Unfortunately, the sampling frequency combined with a lack of information on the typical duration of ketosis prevented this calculation in this data. Second, this > Threshold either week2 data set predates ovulation synchronization protocols > Threshold both weeks3 and as such offers a unique opportunity to investigate Never subclinically ketotic the association between SCK and time to insemination 1Odds ratio (OR) adjusting for the effect of clustering at the herd and other reproductive performance traits. Third, the large number of herds enrolled permits description of 2≥1,000 ␮mol of BHBA/L in wk 1 or ≥1,400 ␮mol of BHBA/L in wk the average effect of SCK in lactating dairy cows on 3≥1,000 ␮mol of BHBA/L in wk 1 and ≥1,400 ␮mol of BHBA/L in reproductive performance controlling for differences in Journal of Dairy Science Vol. 90 No. 6, 2007 EFFECT OF SUBCLINICAL KETOSIS ON REPRODUCTION Table 4. Final Cox proportional hazard model of the effect of the number of weeks cows were classified as
subclinically ketotic (SCK) based on circulating serum BHBA concentration on days from calving to first
insemination in 796 Holstein dairy cows from 25 herds in Ontario, Canada
Numbers of weeks above SCK threshold Season of calving 1HR = hazard ratio.
2≥1,000 ␮mol of BHBA/L in wk 1 or ≥1,400 ␮mol of BHBA/L in wk 2.
3≥1,000 ␮mol of BHBA/L in wk 1 and ≥1,400 ␮mol of BHBA/L in wk 2.
4Relative to cows randomly assigned to receive the placebo device.
There was a tendency for increased circulating BHBA physiologic lesion associated with negative energy bal- concentrations in non-pregnant cows after first AI from ance and leads to delayed resumption of luteal activity 3 wk before calving to 9 wk after calving relative to (Reist et al., 2000; Butler, 2003).
cows diagnosed pregnant. The delayed effect of negative Within individual weeks, the probability of preg- energy balance or hyperketonemia on reproductive per- nancy after first AI decreased linearly with increasing formance is well documented. Both the duration and circulating BHBA concentration in both wk 1 and 2. A magnitude of negative energy balance are associated 3% reduction in probability of pregnancy for each 100 with reduced hypothalamic GnRH pulse frequency and ␮mol of BHBA/L increase was significant in wk 2 (Fig- perpetuation of an inappropriate negative feedback ure 2). This difference is relatively small; however, the loop between estradiol concentration and the required range of values observed in the second week makes LH release necessary to support follicular deviation and this finding very large at BHBA concentrations >1,400 ovulation. This failure of communication along the hy- ␮mol/L. Pregnancy risk at first insemination was not pothalamic-pituitary-ovarian axis is the most common significantly affected by BHBA concentrations in wk Table 5. Final Cox proportional hazard model of the effect of number of weeks cows were classified as
subclinically ketotic (SCK) based on circulating serum BHBA concentrations on days from calving to concep-
tion in 796 Holstein dairy cows from 25 herds in Ontario, Canada
Number of weeks above SCK threshold Season of calving 1HR = hazard ratio.
2TVC = time varying covariate estimate varying with the natural logarithm of time.
3≥1,000 ␮mol of BHBA/L in wk 1 or ≥1,400 ␮mol of BHBA/L in wk 2.
4≥1,000 ␮mol of BHBA/L in wk 1 and ≥1,400 ␮mol of BHBA/L in wk 2.
5Relative to cows randomly assigned to receive the placebo device.
Journal of Dairy Science Vol. 90 No. 6, 2007

Table 6. Adjusted hazard ratio (AHR) representing the relative effect
predicted independent of threshold used. This associa- of classification as subclinically ketotic (SCK; serum BHBA concen-tration ≥1,000 ␮mol/L in wk 1 or ≥1,400 ␮mol/L in wk 2) in either tion was significant at ≥1,000 ␮mol/L of BHBA. The or both of the first 2 wk postpartum on the daily probability of preg- low number of cows above the higher threshold in- nancy at selected time intervals after calving creases the likelihood of a type II error in this analysis.
In the second week after calving, the probability of preg-nancy decreased with increasing BHBA concentration > SCK threshold > SCK threshold thresholds, with a 40 to 50% reduction at thresholds≥1,400 ␮mol/L.
The duration of exposure to elevated circulating BHBA affects the PR/AI. Cows identified as SCK in either of the first 2 wk were 17% less likely to be preg- nant after first AI, whereas cows that remained above 1Hazard ratio × time varying covariateln(time).
the SCK thresholds in both weeks were 53% less likelyto be pregnant. The probability of pregnancy after firstinsemination in cows classified as SCK in either week −3, 3, 6, or 9. A strong association between elevated was not different (P = 0.28) from cows never classifiedcirculating ketone concentration in the first week post- as SCK but was greater than cows classified as SCK in partum and risk of uterine disease was reported (Reist both weeks (P = 0.02; Table 3). There are few other et al., 2003a). Significant associations between propor- studies with which to compare these findings. The mag- tion of lactating cows cycling by 30 DIM, PR/AI, and nitude of and the rate of recovery from negative energy proportion pregnant by 80 DIM have been reported with balance were associated with time to pregnancy (Reist hyperketonemia from the second to fifth week after et al., 2003a). Similarly, most of the variation in onset calving (Plym Forshell et al., 1991; Reist et al., 2000; of ovarian activity and time to pregnancy was attrib- Koller et al., 2003).
uted to the maximum ketone concentration recorded, Within individual weeks and using thresholds, cows independent of the week postpartum when it occurred with circulating BHBA concentrations ≥1,000 ␮mol/L (Reist et al., 2000; Koller et al., 2003).
(40% of cows) in the first week and ≥1,400 ␮mol/L (19% Time from calving to first insemination is a reflection of cows) in the second week were at significantly in- of management practice regarding the voluntary wait- creased risk of non-pregnancy after first insemination ing period and estrus detection efficiency and accuracy.
(Table 2). In the first week after calving, a 25% reduc- Subclinically ketotic cows in either of the first 2 wk tion in the probability of pregnancy was consistently were inseminated 8 d later than animals that werenever SCK. Delayed insemination between cows classi-fied as SCK in either week relative to those classifiedas SCK in both weeks was not anticipated. This outcomemay reflect a differential effect on reproductive effi-ciency for cows that experience a first elevation in circu-lating ketone concentrations in the first week (in-creased risk of uterine disease; Reist et al., 2003a) andsecond week (increased risk of delayed ovulation; Reistet al., 2000) relative to cows that recover from hyperke-tonemia before the second week of lactation (Table 3).
There was a significant effect of SCK on time from calving to pregnancy. Concentrations of BHBA thatwere ≥1,000 ␮mol/L in wk 1 and ≥1,400 ␮mol/L in wk2 were associated with increased time to pregnancy.
This effect was not consistent over time. Animals thatwere SCK in either week had an adjusted HR of 0.55at 60 DIM and 0.75 at 120 DIM. Animals SCK in bothweeks had an associated HR of 0.52 at 60 DIM and 0.84 Figure 3. Survival curves of time to pregnancy for 796 lactating
at 120 DIM. In other words, the negative effect of SCK Holstein cows classified as subclinically ketotic (SCK) based on serum early in lactation appears to diminish as cows progress BHBA concentration determined in either the first week (>1,000 through lactation. Moreover, it is important to note that ␮mol/L) or the second week postpartum (≥1,400 ␮mol/L) or both ofthe first 2 wk postpartum relative to cows not SCK in either of the there was no significant difference in time to pregnancy first 2 wk.
between cows classified as SCK in either week relative Journal of Dairy Science Vol. 90 No. 6, 2007 EFFECT OF SUBCLINICAL KETOSIS ON REPRODUCTION to those classified as SCK in both weeks (P = 0.28; effect is unknown. Monensin (22 mg/kg of DM) de- creases days to first ovulation and decreases the num- Despite reports on the association between energy ber of large follicles before 30 DIM with no change in balance and commencement of luteal activity, PR/AI, first service conception risk (Tallam et al., 2003). Both and time to first insemination and to pregnancy, the clinical and subclinical endometritis increases time to underlying mechanisms are still not fully clear. The pregnancy (LeBlanc et al., 2002). This association may results of the current analysis provide further evidence represent the link between monensin treatment and a of residual effects of health problems in the transition reduced daily probability of pregnancy (HR).
period on subsequent reproductive performance. Spe-cifically, SCK in early lactation is associated with im- paired reproductive performance 50 to 100 d later. Thisdelayed effect on reproductive traits has been attrib- Cows diagnosed as SCK in either of the first 2 wk uted to increased risk of delayed commencement of ovu- postpartum, using a threshold of serum BHBA concen- lation (Butler, 2003). More recently, Leroy et al. (2006) tration ≥1,000 ␮mol/L in the first week postpartum or found that in vitro maturation of follicles in media con- ≥1,400 ␮mol/L in the second week postpartum, were ditions analogous to those follicular fluid concentra- 20% less likely to be pregnant at first insemination.
tions of glucose and BHBA experienced during SCK The probability of pregnancy was reduced by 50% in significantly reduced the ability of fertilized ova to be- cows experiencing SCK in both of the first 2 wk. Using come morula and hatched blastocysts, indicating a di- time to pregnancy as the outcome, SCK in either the rect toxic effect of BHBA and NEFA on maturing ova.
first 2 wk postpartum decreased the daily probability of The peak herd level prevalence of SCK has been re- pregnancy (HR) until approximately 165 d postpartum.
ported from the second to fifth week postpartum (An-dersson and Emanuelson, 1984). Attempts have been made to understand factors that influence when the Financial support was provided by Elanco Animal peak level of SCK occurs within individual herds. One Health, the University of Guelph Doctor of Veterinary such study by Heuer et al. (2001) reported that season Science program, and Ve´toquinol. The technical assis- of calving and pen number (specifically management tance provided by Eleanor Robinson is greatly ap- practices such as time away from feed) explained 17% of the variation in milk acetone concentrations. Thus,application of this data would best identify herds at risk for reproductive failure rather than cows.
Similar to the present study, others reported no asso- Abe, N., I. J. Lean, A. Rabiee, J. Porter, and C. Graham. 1994. Effects of sodium monensin on reproductive performance of dairy cattle.
ciation of BCS at calving, or change in BCS early in II. Effects on metabolites in plasma, resumption of ovarian cy- lactation, with any reproductive parameters (Ruegg clicity and oestrus in lactating cows. Aust. Vet. J. 71:277–282.
and Milton, 1995). The distribution of BCS and BCS Andersson, L., and U. Emanuelson. 1984. An epidemiological study of hyperketonemia in Swedish dairy cows: Determinants and the loss in this data set was similar between animals that relation to fertility. Prev. Vet. Med. 3:449–462.
were pregnant to first insemination and those that were Bauman, D. E., and W. B. Currie. 1980. Partitioning of nutrients not pregnant. Insufficient variation in body condition during pregnancy and lactation: A review of mechanisms involv-ing homeostasis and homeorhesis. J. Dairy Sci. 63:1514–1529.
data has been previously cited as a partial explanation Butler, W. R. 2003. Energy balance relationship with follicular devel- for the inconsistent association between BCS and en- opment, ovulation and fertility in postpartum dairy cows. Livest.
ergy balance (Heuer et al., 2000).
Prod. Sci. 83:211–218.
Cook, N. B., W. R. Ward, and H. Dobson. 2001. Concentrations of A treatment effect of Na monensin on time to preg- ketones in milk in early lactation, and reproductive performance nancy has not been reported. Further, the CRC formu- of dairy cows. Vet. Rec. 148:769–772.
lation was not associated with alterations in commence- Dawuda, P. M., J. R. Scaife, J. S. Hutchinson, and K. D. Sinclair.
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THE EFFECTS OF ADVERTISING USING GLOBAL APPEAL VS CHINA- SPECIFIC APPEALS: A STUDY OF CHINESE CONSUMERS IN HONG KONG AND CHINA Fung Sze Man A Project Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Arts in Communication Supervisor: Dr. Vivian Sheer

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Curriculum PERSONAL INFORMATION: Name: Lynn B. Gerald, PhD, MSPH RANK/TITLE: Canyon Ranch Endowed Chair/Professor Health Promotion Sciences Business Address: University of Arizona Mel and Enid Zuckerman College of Public Health 1295 N. Martin Ave. Tucson, Arizona 85724 HOSPITAL AND OTHER (NON ACADEMIC) APPOINTMENTS: