Relationship Between Ovarian Activity and Energy Status During the Early Postpartum Period of High...

Relationship Between Ovarian Activity and Energy Status Duringthe Early Postpartum Period of High Producing Dairy CoWS1,2

c. R. STAPL~ and W. W. THATCHERDairy Science Department

Institute of Food and Agricultural SciencesUniversity of Florida

Gainesville 32611

J. H. CLARKDepartment of Animal Sciences

University 01 IllinoisUrbana 61801

ABSTRACT

The effect of energy status upon ovarian activity during early lactation wasassessed in 54 multiparous Holsteincows. Dry matter intake and milk yieldwere measured daily from parturitionthrough 9 wk of lactation. Milk composition and body weight were measuredweekly during this time. Energy balancecorrected for body weight loss was calculated weekly. Blood was collected via tailvein three times weekly and plasma analyzed for progesterone and nonesterifiedfatty acids. Fifteen cows were anestrusfor the 9 wk based on their plasma progesterone «1 nglml). These cows werecompared with two cycling groups, onegroup of 25 cows showing corpus luteurnactivity within 40 d after parturition and asecond group of 14 cows showing corpusluteum activity between 40 and 60 d postpartum. Anestrus cows ate less feed, produced less milk, and lost more bodyweight, resulting in a more negative energy status than cycling cows. Differences in energy balance among cowgroups were greatest the first 3 wk postpartum. Anestrus cows and cows showingcorpus luteum activity between d 40 and60 obtained more energy from body re-

Received JWle 9. 1989.Accepted September 25. 1989.. .lAorida Agricultural Experiment StaUon Jownal Senes

Number 9554.2supported in part by the Illinois Agricultural Experiment

Station.3To whom reprint requests should be made.

serves for milk production the first 2 wkof lactation, than cows cycling prior to d40.(Key words: energy balance, lactation,estrus)

INTRODUCTION

Homeorhesis, defined as the orchestrated orcoordinated changes in metabolism of bodytissues necessary to support a physiologicalstate (l), may be applied to the interrelationshipof lactation and ovarian activity of the earlypostpartum cow. A prioritized physiologicalstate, lactation for the survival of the newborn,may be allowed to proceed at the temporaryexpense of the procreation of a future calf. Thisordering of events, when taken beyond the accepted "temporary" time frame, results in aninefficiency of the production system (moredays open) that is considered unacceptable.

The physiological mechanism(s) associatedwith this cause and effect relationship have notbeen elucidated clearly. Two gross factors havebeen linked to the number of days betweencalving and normal ovarian activity of healthycows: amount of nutrients delivered for thecows' metabolism [body tissue mobilizationand DM intake; (30)] and quantity of milkproduced (16, 31). Estimating energy balancecombines these two factors into a possible assessment of the homeorhetic state of the animal. Using 13 cows, Butler et al. (3) found thatenergy balance during the first 20 d of lactationwas related inversely (-.60) to days to normalovulation. The purpose of this study was toexamine the relationship of energy balance andovarian activity of early postpartum dairy cowsexperiencing homeorhesis.

1990 J Dairy Sci 73:938-947 938

ENERGY BALANCE AND RElURN TO OVARlAN AcrIVITY 939

TABLE 1. Ingredient and chemical composition of experi·mental diet.

Net energy intake (NEI Mcal/wk) = NE, ofdiet (McalIkg) (21) x DM intake (kg/wk).

P4 concentrations greater than 1 nglm] for morethan 2 consecutive sample days (short cycle)and followed by subsequent sustained rises inP4 concentrations, or 2) sustained rises in P4

concentrations without a prior short cycle.Cows were grouped into three preplanned reproductive statuses from which potential differences in energy balance were tested. It washypothesized that cows with distinctive differences in timing of postpartum ovarian recrudescence would have marked differences in energybalance. Cows were classified according totheir time of return to normal ovarian activity(Table 2). Early responders (ER; n =25 or 46%of cows), Group I, showed corpus luteum activity within 40 d after parturition. Group 2contained cows showing corpus luteum activitybetween 40 and 60 d postpartum and classifiedas late responders (LR, n = 14 or 26%). Group3 was composed of anestrus cows or nonresponders (NR, n = 15 or 28%) during the first63 d postpanum.

Energy status of cows was determined usingthe following assumptions and equations:

MATERIALS AND METHODS

Multiparous Holstein cows at the Universityof lllinois were housed in a maternity barn 10to 14 d prior to expected calving date. Cowswere weighed the initial day in the barn. Theperformance of 54 cows was monitored fromparturition through wk 9 of lactation. Cows thatexperienced debilitating illness or injury wereremoved from the trial. While housed in thematernity barn, cows were fed rolled highmoisture corn supplemented with protein, minerals, and vitamins at 1% of body weight, cornsilage for ad libitum access, and 4.5 kg of longalfalfa hay.

Within 24 h after calving, cows received adlibitum a diet of 55% com silage and 45%concentrate consisting of ground com, soybeanmeal, minerals, and vitamins (Table 1). Thediet was fed twice daily as a totally mixedration. Dry matter intakes were recorded daily.Feeds were sampled weekly, and OM (55·C for48 h) was determined to maintain the properforage to concentrate ratio. Feeds collectedweekly were composited at 4-wk intervals andassayed for CP (Kjeldahl) and ADF (9). Cowswere milked twice daily and milk weights recorded. Each week, milk samples were collected from two consecutive milkings (a.m. andp.m.) and composited according to milk yield.Samples were analyzed for fat (Dairy Lab Services, Inc., Dubuque, IA; Multispec A, infraredmilk analysis) and SNF (10). Cows wereweighed weekly prior to the a.m. feeding.

Ten milliliters of blood were collected viatail vein at approximately 1400 h each Monday,Wednesday, and Friday after parturition untilapproximately 63 d postpartum. Samples werecentrifuged at 5000 x g for 10 min. Plasma wasremoved via micropipette and frozen until analyzed for nonesterified fatty acids (NEFA;Wako Chemical, Dallas, TX) and progesterone(P4)' Progesterone concentrations in heparinized plasma samples were measured with anassay system described by Knickerbocker et al.(14). An antiserum dilution of 1:40000 wasused, and sensitivity of the assay was 31.2 pgper tube. Assays were conducted with 100 or200 J.Ll of sample. Intraassay and interassaycoefficients of variation were 8.2 and 12.5%,respectively. Plasma P4 concentrations wereused to indicate when the cow had returned tonormal estrous cycles. Evidence of corpus luteum activity was defined as either: 1) plasma

Item

IngredientCom silageGround sbelled comSoybean mealUmestoneOicalcium phosphateSodium sulfateTrace mineralized saltMagnesium oxideVitamins A and D

O1emicalCrude protein. % OMUndegradable intakeprotein, % OM

Net energy of lactationMcaVkg

Acid detergent fiber.% DM

Calcium, % DMPhosphorus. % OMMagnesium, % OMPotassium, % DMSulfur, % DM

% of DM

SS.OO23.2319.42

1.17.38.23.45.10.02

16.3

S.9

1.68

19.6.70.40.25

1.05.22

Joumal of Daily Science Vol. 73, No.4, 1990

940 STAPLES ET AL.

TABLE 2. Age and incidence of health disorders of dairycows differing in ovarian activity during the fIrSt 9 wkpostpanum.

Classificationof ovarian activity I

ovarian activity (NR), and 2) cows returning tononnal ovarian activity within 40 d postpartum(ER) versus cows returning to normal ovarianactivity between d 40 and 60 (LR).

IER =Early responder. LR = late responder. NR =nonresponder.

EB (Mcal/wk) = NE[ - NEro - NEI +NEBWL

Net energy of maintenance (NEro; Meal) =BW75 x (.073 Mca1/k.g BW required for

maintenance plus 10% for activity) (17, 21).

Energy in milk (NEI; Mcal/wk) = milkyield (pounds) x ([41.84 x % of milk fat]

+ [22.29 x % SNF] - [25.58]) (28).

RESULTS AND DISCUSSION

Weekly least squares means of plasma P4for the three classification groups are depictedin Figure 1. The average plasma P4 values for63 d were 2.59, 1.39, and .52 ng/ml for ER,LR, and NR groups, respectively. Average dayof first ovulation for ER was 21.9 ± 7.7. This iscomparable to values in previous reports: 17.6(25), 19.5 (13), 20.8 (7), and 23.9 (29) d.Duration of first postpartum estrous cycleranged from 6 to 22 d. which is similar to the 9to 28 d range of cycles observed by Fonesca etal. (7). Fifty-four percent of ovulating cows (n= 21 of 39) showed a short estrous cycle lastingan average of 10 d. The percentage of cowsexhibiting a short estrous cycle was substantially greater than the 33% observed by Stevenson and Britt (25) involving 28 Holstein cowssampled twice weekly to detennine P4 concentration of plasma. Forty percent of ER cowsshowed no short estrous cycle but immediatelystarted a normal cycle (defined as at least 17 din length). Whitmore et al. (31) studied 396ovulations of which 43% occurred without adetected estrus.

Mean peak P4 concentration in blood plasmaduring first estrous cycle was reported to beless than that of second estrous cycle [3.7 vs.4.7 ng/ml; (25)]. A similar pattern was observed for those ER cows that had two diestrous phases or two plasma P4 peaks within 63d postpartum. Average plasma P4 peak for firstestrous cycle was 5.95 ± 3.44 ng/ml, butplasma P4 peak for the second cycle was 8.79 ±3.30 ng/ml. Thus, corpus luteum function wasnot maximal during the first estrous cycle.

The percentage of anestrus cows observed inthis study (28%) was more than the previouslyreported 10% (7 of 69) determined by King etal. (13) but similar to the 25.9% reported byThatcher and Wilcox (26) who examined 1398cows for 60 d postcalving.

Because health disorders at the time of calving or during early lactation have negative effects on reproductive (4, 7) and lactational performance (27), incidence of health disorders issummarized in Table 2 for the three groups ofcows classified according to ovarian activity.

NR

:>60154.6

40--60143.9

LRERItem

Energy in body weight loss (NEBWL; Meal)= body weight loss (kg/wk) x 6 Meal ofbody tissue energy/kg of empty BWL (16)x 18% (estimate of inefficiency of convert

ing 1 kg of body tissue reserves to I kg of4% FCM) (19).

All data except P4 and NEFA concentrationsin plasma were analyzed as a completely randomized design with sources of variation beinggroup classification according to ovarian activity, cow (group classification), week, and weekby group classification interaction. Single degree of freedom contrasts for treatment were I)cows returning to normal ovarian activity (ERand LR) versus cows not returning to normal

Return to ovarian activity.d postpanwn <40

No. of cows 25Age. yr 4.6

Incidence of health disordersMetritis 3 2 3Pnewnonia 0 0 3Retained placenta 3 4 3Udder edema 1 0 1Displaced abomasum 1 0 1Milk fever I 1 1

Energy balance (EB) was calculated by thefollowing equation for each cow on a weeklybasis because cows were weighed weekly, andmilk samples were taken and analyzed weekly.

Journal of Dairy Science Vol. 73. No.4, 1990

ENERGY BALANCE AND RETURN TO OVARIAN ACfIVITY 941

Pneumonia was the only health disorder thatwas a greater problem among NR than ER andLR groups. Pneumonia always occurred withanother health disorder: milk fever once andmetritis twice. To determine whether the inclusion in the data analysis of cows experiencinghealth problems may have biased the results insome manner, an analysis with only healthycows (n = 46) was done. Results were notdifferent between the two data sets; thereforeall cows were included. Thus, it does not appear that the lack of normal ovarian activityexperienced by cows in this study was due to ahigher incidence of health problems during theearly postpartum period.

Another factor shown to influence reproductive performance is age. Cows that had completed four or more lactations had more days tofirst service than younger cows (12). Averageage of each group of cows is listed in Table 2.The average age of the ER and NR groups was4.6 yr, but the LR group was only slightlyyounger, averaging 3.9 yr. Therefore, age probably did not account for differences in ovarianactivity.

During wk 1, all cows consumed feed at lessthan 2% of body weight with the NR groupconsuming the least (Figure 2). Thereafter, ERand LR cows, having normal ovarian activity.increased their feed intake more rapidly thanNR cows with abnormal ovarian activity. By d25, cows with cycling ovaries were consumingOM at a rate of 3% of their body weight, but

anestrus cows did not consume that quantity ofOM until approximately 2 wk later. The NRgroup continued to lag behind other cows forthe entire experiment and never reached theOM intake of 3.5% of body weight achieved byER and LR groups. A slow increase in OMintake postpartum is commonly observed forcows that have poor milk production and reproduction. Coppock et aI. (5) reported that OMintake progressively increased for the first 16wk of lactation before starting to decline. Because of the long time required by cows toreach peak feed intakes, Reid et aI. (23) concluded that appetite was the greatest limitationto large milk yields.

The ER and LR groups consumed more(P<.05) feed (kg/d and % of body weight) thanthe NR group (Table 3). Large cows arethought to be slower to return to estrus thansmall cows, but in our experiment, the NRgroup of cows that had the lowest body weightfailed to return to normal corpus luteum activity within the first 9 wk after calving, probablybecause of the lowered intake of OM (Table 3).Our data agree with previous data obtainedfrom cows fed at 66, 100, or 133% of recommended NRC (21) guidelines. Cows fed 66%of their requirements took 17 d to form afollicle of at least 10 mm in diameter; cowsoffered diets formulated to provide 100 or133% of NRC guidelines required only 10 and11 d, respectively (22).

5·--- ------~~._~~-

orj :::1 .~-------------.~- l

3-

6 104 6

Week of Lactation

-----1- Nonr•• ponde,.

-+- Elrly r••ponden

-&- Lat. ,upond.,.

P4

PIa• 4ma

ng 1ImI IO'----~-~

o

Figure I. Average weekly plasma progesterone (P4)concenlrations of dairy cows differing in ovarian activityduring the first 9 wk postpartum.

Figure 2. Average weekly dry matter intake as a percentage of body weight of dairy cows differing in ovarianactivity during the first 9 wk postpartum.


942 STAPLES ET AL.

TABLE 3. Mean body weight and dry matter intake of dairy cows during first 9 wk postpartum.

Qassification I

Measurement

DM intake kg/da

DM intake. %~ weighta

Body weight, krb

ER

18.83JJ7

617

LR

17.73.11

576

NR

15.22.73

560

SEM

.7

.1113.8

aNR vs. ER + LR (P<.05).

~R vs. LR (P<.05).

IER = Early responders; LR = late responders; NR = nonresponders.

Groups ER and LR produced more milkthan the NR group (fable 4). Daily milk yieldby the NR group was 6.1 kg less than for ERcows. All groups appeared to have a normallactation curve with peak milk occurring between 3 to 6 wk postpartum (Figure 3). For thefirst 7 d postpartum and throughout the9-wk experiment, NR cows produced the smallest quantity of milk and ER cows the largest.High milk production by dairy cows is associated normally with poor reproductive performance. Higher producing cows have a greaternumber of days to first ovulation and estrus(16, 31) and first breeding (12, IS, 24), lowerconception rates (7, II, 24), and more daysopen (11, 15). Our data do not support thisconcept but they agree with data of Fonesca etal. (7) and Stevenson and Britt (25), who reported that daily milk yields were positivelycorrelated with day of first ovulation. Dachir etal. (6) also found no relationship between postpartum intervals to each of the first three ovulations and yield of 4% FCM of 35 Holstein and17 Jersey cows. If energy status of the cow is

more important than yield of milk in determining return to estrus, then milk yield alone maybe either positively or negatively correlatedwith days to first breeding.

Production of 4% FCM showed the sametrends as uncorrected milk production, becausethere were no differences in milk fat percentages among groups of cows (averaging 3.50%)(Table 4). The ER and LR groups produced 4.0kg more milk/d than the NR group (P<.05;Table 4). In contrast, Villa-Godoy (29) reportedthat the correlation between yield of 4% FCMand duration of postpartum anovulation was notdifferent. However. their 32 cows did not differwidely in duration of anovulation (23.9 ± 2.2d). Cows showing ovarian activity demonstrated a typical curve for production of 4%FCM (Figure 4). The ER group exhibited aplateau for 4% FCM production that lastedfrom wk 2 through 5 before declining, and theLR group peaked lower and started their decline 2 wk earlier. Anestrus cows showed avery atypical curve. peaking quickly at wk 2and declining rapidly.

TABLE 4. Yield and composition of milk from dairy cows differing in ovarian activity during the flfSt 9 wk postpartum.

Classification1

Measurement ER LR NR SEM

Milk, kg/da 36.6 35.2 30.5 1.3Milk fat. % 3.51 3.46 3.53 .08Milk fat, kg/da 1.25 1.17 1.07 .05Milk SNF. % 8.83 8.72 8.74 .06Milk SNF. kg/da 3.23 3.05 2.70 114% FCM, kg/da 33.4 31.7 28.5 1.2Somatic cell counts (x 103) 382 655 559 105

aNR vs. ER + LR (P<.05).



ENERGY BALANCE AND RETIJRN TO OVARIAN ACfIVITY 943

42

40M 38;I 38k

Y 34; 32•I

3() :-d

28 i26 r24 r-

22f

20r-

180

-+- -;:~~=~~~~d.r~"""*"" Early r••ponder.

-B- Late r••ponde,.

4 8 9

Week of Lactation

10

FCM

YI.Id

28 -

::l' I :.. ::,cl~e..,:..o.:::~:" ·.l,22 L-B-.Lete 'e.pond", J20 -+---+- ----+----+__+_ -+-- .------j

12345678

Week of lactation

Figure 3. Average weekly milk production of dairycows differing in ovarian activity dwing the fIrSt 9 wkpostpartum.

Gross efficiency of milk production (4%FCM/DM intake) was most efficient for the NRgroup of cows during the first 4 wk of lactation, but after wk 4 postpartum all groups wereproducing milk with the same gross efficiency(Figure 5). Efficiency of milk production corrected for energy derived from body tissue lossis in Table 5. Although the NR group producedmilk with an improved gross efficiency of energy utilization compared to ER and LR groupsof cows (1.88 vs. 1.78 kg milklkg OM intake),

Figure 4. Average weekly 4% FCM production by dairycows differing in ovarian activity during the first 9 wkpostpartum.

they also lost about 50% more body weightthan cows with ovarian activity (1.22 vs..81kg/d). When efficiency of milk yield was corrected for energy derived from loss of bodytissue, the NR group of cows was less efficientin producing milk than cows showing estrousactivity (1.35 vs. 1.49 kg FCM/kg DM intake).Therefore, much of the milk produced by theNR group of cows was derived from bodyreserves. About 28% ([(28.5 - 20.5)/28.5] x100%) of milk produced by cows in NR group

TABLE 5. Efficiency of conversion of dry feed to 4% FCM by cows differing in ovarian activity during the first 9 wkpostpartum.

Classification1

Item ER LR NR

28.1

33.418.8

1.78-.813.995.33

4% FCM Yield. kg/dDry matter intake (DMI). kgldEfficiency of production kg FCM/kg DMIAverage change in body weight, kgldNet energy for milk from body tissue loss, McaVd2

Estimated yield of 4% FCM from body tissue loss. kg3Corrected yield of 4% FCM derived solely from

feed consumed, kgldCorrected efficiency of FCM production.

kg 4% FCM/kg DMI 1.49

31.717.7

1.79-.813.995.33

26.4

1.49

28.515.2

1.88-1.22

6.008.02

20.5

1.35


2Assumes that loss in body weight represents 6 McalJkg (18) and that the energy was used with an efficiency of 82%(19).

3A kilogram of 4% FCM contains .748 Meal (21).

Joumal of Dairy Science Vol. 73. No.4. 1990

944 STAPLES ET AL.

r----- .....----... ------.

30t - Nonre.ponda,a I- --iII'i- earlV re.ponden ,

~ Late r••ponder~

-40 ·-+----+----+---+---I-----II--__+_I----+13 4 5 8 7 8 9

Week of Lactation

Ch -20

•ng

•

Body

W

•i~ -10

I

8

-+- Nonr••pond.r.

--.- early rupond.r.

-S- late r••pofldar.

2.2 i

F 2.81'

C 2.8M i

r 2.4

•IdIot.lI

2 1

J ~ I

1::f ,_, ---,---+---f----+-I_+--_~4 8

Week of Lactation

Figure 5. Average weekly gross efficiency of 4% FCMproduction by dairy cows differing in ovarian activityduring the first 9 wk postpanwn.

Figure 6. Weekly changes in body weight of dairy cowsdiffering in ovarian activity during the f1fSt 9 wk postpartwn.

came from body tissue reserves, but only 15.9and 16.7% came from body tissue reserves ofgroups ER and LR, respectively.

An increased loss of body weight during thefirst 2 wk of lactation coincided with decreasedovarian activity: ER cows losing the leastweight and NR cows losing the most weight(Figure 6). From wk 3 to 9, all groups lostabout the same amount of body weight. It wasnot until the 8th wk of lactation that all cowsgained body weight, which agrees with data ofCoppock et al. (5). The relationship betweenbody weight change and interval to first ovulation was not significant in a previous report(25).

Mean energy balance for the 9 wk of theexperiment was lower for the NR group ofcows than for the ER or LR groups of cows(-5.6 vs. -4.4 and -4.1 Meal/cow per d). Themore negative energy balance for the NR groupof cows compared with the ER and LR groupscan be attributed to differences that occurredduring the first 3 wk of lactation (Figure 7) asdetennined by homogeneity of regression(P<.05). The increasing negative energy balance for the LR and NR groups at wk 2 resulted because output of energy in milk wasaccelerating much more quickly than intake ofenergy from feed. The differences in NEI andNEL for the ER, LR, and NR groups of cowsbetween wk 1 and wk 2 were -49 and -52Meal, -33 and -45 Meal, and -33 and -32Meal, respectively. The acceleration of energy

output in milk was about equal to the acceleration of energy intake in feed by the ER and NRgroups during wk 1 to 2. In contrast, energyintake from feed by cows in the LR grouplagged behind energy output in milk from wk 1to 2. Although all cows were mobilizing bodyreserves for milk production, the NR group ofcows was mobilizing the largest amount ofbody reserves (Figure 6) and were in the greatest energy deficit (Figure 7). Magnitude ofnegative energy balance of all cows during thefirst 28 d of lactation (-9.6 Meal/cow per d)was greater than that of Israeli cows (~.9

Mca1/cow/d; (20)]. Most cows were in positiveenergy balance by wk 8, which agrees with the53 ± 4 d observed by Berghorn et al. (2) but isquicker than the 7Q-d average recorded byVilla-Godoy (29). First ovulation occurred 25 ±4 d before zero energy balance was attained in58 Holstein cows (2); therefore, cows do nothave to be in positive energy balance to ovulate. However, in this experiment cows thatwere in the more positive energy balance werethe first cows to show ovarian activity.

The impact of severe negative energy balance in early lactation potentially can influenceovarian activity later in lactation. Cows in mostnegative energy balance during their first 9 d oflactation «~ Meal/d) had secreted less progesterone in milk during their second and thirdestrous cycles than cows in zero or slightlynegative energy balance (-.1 to 3.0 Meal/d)(29). However, no correlation between energybalance and amount of progesterone secreted inmilk was observed during the first estrous cycle

lownal of Dairy Science Vol. 73. No.4, 1990

ENERGY BALANCE AND RETURN TO OVARIAN ACTIVITY 945

TABLE 6. Reproductive performance of dairy cows differing in ovarian activity during the first 9 wk postpartwn.

Classification1

Measurement ER LR NR SEM

Number of cows 25 14 15Day of ovulationa 21.9 43.1 1.3Days to first estrus2,a,b 47 73 110 11.4Days to first service2 96 94 112 7.6Number of cows conceivingC 21 13 5Services per conception 2.38 1.77 2.80 .47Days opena•b 133 88 200 18

aNR vs. ER + LR (P<.OS).

~ vs. LR (P<.05).

cChi-square = 15.98, P<.ool.

tER = Early responder; LR = later responder; NR = nonrespondcr.

2Five cows belonging to group NR were not detected in estrus and were not serviced.

postpartum. Therefore, evidence of negative energy balance on luteal function was not demonstrated until 40 to 70 d postpartum (29). Thelarge negative energy balance during their frrst2 to 3 wk postpartum may be the reason for thelack of ovarian activity for the frrst 63 d in 28%of our cows.

Concentrations of NEFA in plasma decreased each week (P<.05) and decreased from612 !J.e<l/L at wk I to 237 tJ.eq/L at wk 9(Figure 8). Treatment by week interaction wasnot significant. Average NEFA concentrationswere 348, 351, and 346 tJ.eq/L for groups ER,LR. and NR, respectively. Despite the greater

loss of BW during early lactation, the NRgroup had plasma concentrations of NEFA similar to the ER and LR groups. Plasma NEFAconcentration was not a good indicator of energy status of the cows in this study. Plasmaconcentrations of NEFA were important indicators of energy status for cows with a body scoreof around 3.0 at parturition but not for thincows [score of 2.2; (20)] or heavy cows [scoreof 3.8; (8»). Cows in our study were not scoredfor body condition.

Days to first ovulation, estrus, and servicewere longest for the NR group (Table 6). Estruswas detected approximately 25 and 30 d afterovulation for groups ER and LR. respectively.

~ -12

•I -14Id -'5

-+- Nonr••pcnd.,.

"""'*"" Early r••ponder•

-e- Late rellponden

P 700~~-~ 550

•m 600a

~ :1"o 400nc

~ :::l---+-+ --~--~--- --+-~;~, 2 3 4 5 5 7 5 9

Week of lactation

l

i'-+- Nonr••~cnd."---i+l'- Early r••ponder.

~ Lat. ,upond.,.

455

Week of lactation

_:~.---

-4

-5

-8 !

•n•rgy

b

•I•nC

•

N•t

Figure 7. Weekly net energy balances (McaVcow/d) ofdairy cows differing in ovarian activity during the 9 wkpostpartum.

Figure 8. Average weekly concentrations of plasmanonesterified fatly acids (NEFA) of dairy cows differing inovarian activity during the first 9 wk postpartum.

Journal of Dairy Science Vol. 73, No.4, 1990

946 STAPLES ET AL.

Consequently, first postpartum ovulations wereassociated with a high frequency of silent estruses, or a diminished ability to detect estrus atthe first ovulation. Services per conceptionwere not different (P>.05) for cows that conceived. From the interrelationships between energy balance (Figure 7) and plasma P4 concentrations (Figure 1), the marked deficit in earlyenergy balance exerted a marked carryover effect on ovarian activity in the NR group. Thesecows failed to cycle until after 9 wk of lactationeven though the energy balance of the threegroups was the same by 5 wk postpartum. Thisprolonged carryover effect on reproduction isfurther substantiated by the observation thatonly 33.3% (5 of 15) of NR cows eventuallyconceived compared with 84 and 93% for ERand LR groups, respectively.

The homeorhetic drive for milk productionin dairy cows immediately after calving putscows into negative energy balance. The partitioning of energy from the diet and from mobilization of body reserves for milk productionand ovarian activity is highly regulated andappears to be influenced by energy status oflactating cows. The ER and LR groups of cowsin a less negative energy balance than the NRgroup were able to restore ovarian activity during the first 63 d postpartum. In contrast. theNR group of cows, which were in a morenegative energy balance, did not have the capability to consume as much dietary energy, produced less milk, and were more dependent onenergy from body reserves to produce milk. Asa consequence, their metabolic status inhibitedrecrudescence of postpartum ovarian activitywithin 63 d postpartum.

Additional research is warranted to examinewhether postpartum negative energy balancecompromises ovarian follicular development orovulation and subsequent corpus luteum development. The decline in plasma concentrationsof NEFA were rather dynamic in the postpartum period but appeared to be unrelated toovarian function in the present study. Feedingsystems to minimize postpartum deficits in energy balance (e.g., increase in caloric density ofthe diet) and whether such management strategies alter ovarian follicular and corpus luteumdynamics need to be examined.

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Journal of Dairy Science Vol. 73, No.4. 1990

Relationship Between Ovarian Activity and Energy Status During the Early Postpartum Period of High...

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