Plasma and milk progesterone and plasma LH in ovariectomized lactating cows treated with new or used controlled internal drug release devices

Animal Reproduction Ekevier

Science,

27 ( 1992)

91-106

91

Science Publishers B.V.. Amsterdam

Plasma and milk progesterone and pl ovariectomized lactating cows treated used controlled internal drug release devices’

J. van Cleeff, M.C. Lu#, C.J. Wilcox and W.W. Thatcher’ DairyScienceDepartmen:. UniversiryoJF/orida, Gainesville, FL 32411. USA

(Accepted13September1991)

ABSTRACT

Van Cleeff,J., Lucy, MC.. Wilcox,C.J. and Thatcher.W.W.. 1992.Plasma and milk progesterone and plnma LH in ovariectomized lactating cows treated with new or used controlled internal drug nleardevimdnim.

Reprod Sri., 27: 91-106.

Lacutin& ovarimomized Holsteincowsweretreated with mw (NC, 1.9g progesterone,P,; n=4)

n=4) mntmlled internaldrug release(CIDR) devices for 9 days. .&her a 3 day clcamnce.CIDR typeswerereversedfor a second9 day period. Blood was collected lwice daily

or wed (UC; used 9 days;

for Days - I.5 to +5 and then once daily until Day + I I. Milk slmples and milk yield data were

mllec~edtwiced&Ivfor Davs - 1.5to + 11.5. Intensiveblood samnlinE(cverv IOmin for 8 h) was performedon Days -2, +2. +5 and +c)ofPeriod 1.PlasmaP, (Pi’,)r&lk P; (MP,) andlutiinizing bomwne (LH) were analyzed by validated radioimmunoassays.During CIDR exposure,PP, (2.4f0.14~1.5+0.14ngm1-‘)andMP,(7.0f0.37>5.2+0.37ngml-‘)werc~~crwithanew CIDR (PcO.001). MaximumPP. (armI-* kSE(mnge)) duringClDRcaposweoccunedon Day +2 and.wcn$sd3.4+0.23 (2.&4.i)for NC and. l.P%b.lS (L&2.6) for bZ. Maximum MP, for

NC occurred on Day +2 2nd avcqcd 8.8+0.98 (5.2-14.2). and for UC occurred on Day +4 and avenged 6.7f0.62 (5.1-9.7). Minimum PP. (ng ml-‘*SE (range)) during CiDR exposureoc-

curredonDw +Sforho~l~~neollnadaver~sed 1.7+0.24 (1.1-3.2) forNCand 1.1+0.07 (0.91.4) forUC.Minimum MP,cccurrcdon Day +%for both trc&wds&~davemp,ed 5.0+0.83 (2.810.0) for NCand 3.4f0.35 (2.0-4.7) for UC. lntmclass correlationsof PP, and MF’,for cows wem hi& ( ~0.6). implyinginherentdifferencesamongcowsin P, metabolism.LuIcbGng hormonepulse frqoency (l+O.l pulsch-‘), LH mean (1.78+0.20 ngmi-‘),bascline (0.98+0.10ngml-‘),and pulse amplilude (2.7820.48 ng ml-‘) did not differ belwcea CIDR type or among days. Device wnovalduriy LHsamplingoo Day +P increazd (PcO.09) LHbssclinewitbinanhour (0.73kO.26 naml-‘vs. 1.30+0.16 ngml-‘; beforevs. aflerdevice removal).New CIDR incnaxd PP. and MP. morr rhan UC, but neither af&ctedthe dynamicsof plasmaLH secretionin ovaricctomizedcows. ‘Florida Agricuhural Experiment Station, Journal Series No. R-01402. *Present addrew Monsanto Co., Mail Zone AA3C, 700 ChesterfieldViiage Pkwy, Chesterfield

MO 63 198, USA. ‘Author to whom reprint requests sboold be addused.

@ 1992 Else&r SciencePublishers B.V. AU ripbts reserved 0378-4320/92/SO5.00

92

J. “AN CLEEFFET AL.

INTRODUCTION

Intravaginal progesterone releasing devices are used frequently for estrous synchronization of cattle, and can be used for resynchrooization of cows failing to conceive to synchronized insemination if no luteolytic agent is used (Folman et al., 19sb). Previous experiments imrestigating the use of eontrolled internal drug release (CIDR ) devices after insemination have indicated that CIDR devices used for 9 days can be reinserted in dairy heifers to resvnchronize a maiority of nonpregnant heifers effectively (Van Cl&f et al., 1989). Such treatment &en toWlactatingdairy cows resulted in an unaeeeptable resynchronization rate of return services, but results improved when new CIDR devices were utilized (J. van Cleeff and W.W. Thatcher, unpublished observations). The reduced response in lactating cows compared with heifers may be related to lower progesterone concentrations in peripheral plasma.

Subnormal concentrations of progesterone result in increased luteinizing hormone (LH) pulse frequency due to reduced negative feedback on gonadotropin secretion (Roberson et al., 1989). Although normally low frequency luteal phase LH pulsatility permits follicular turnover, increased gonadotropin support appears to cause kxtension of follicular dominance andmaintenance of an aned follicle (Savio et al.. 1990: Sirois cad Fortune. 1990). The following experiment was conducted ;o de&mine the concen&tions bf plasma and milk progesterone delivered by new and used ClDR devices, and the effects of plasma progesterone concentrations on LH secretion dynamics, using the ovariectomized lactating cow model. MATERIALS

AND METHODS

Nine cows in mid to late lactation were ovariectomized and allowed IO days to recover from surgery. The experiment was conducted as a single reversal, with two periods of 14 days each (Day - 2 to Day + I I ) . On Day 0 of

Period 1, new ClDR devices ( 1.9 g progesterone; Carter Holt-Harvey, Hamilton, New Zealand) were inserted into the vaginas of five cows (new CIDR). Four cows (used CIDR) received CIDR devices which had been used previously in lactating cows for 9 days for an unrelated experiment and cleaned with a dilute iodine solution. Any experimental difference between new and used CIDR devices includes the cleans@ process that the used CIDR was subjected to before reinsertion. Evaluation of progesterone content of used CIDR devices was derived from analysis of the five new CIDR devices aft-i use for 9 days in Period I ofthis experiment. Briefly, the progesterone residue from the hormone-impregnated skin of each device was subjected to Soxhlet extraction, and the residue was quantified by measurinp, UV absorption at

HOPMONESIN COWS WITH NEW OR USED DRUG RELEASEDEVICES

93

240 nm. This procedure was accomplished in cooperation with A.J. Peterson and JCL. Macmillan at the Ministry of Agriculture and Fisheries, Ruakura Animal Research Station, New Zealand. Treatment with ClDR devices lasted for 9 days in both groups, and devices were removed from all cows on Day + 9. Period 2 began 3 days after tbe completion of Period I, on Day - 2. On Day 0 of Period 2, CIDR devices were inserted again, but treatments were reversed. Cows which were in the new CIDR group in Period 1 received used CIDRs in Period 2, and vice versa. One cow which had received a new CIDR

in Period 1 was removed from the experiment when she ceased lactating. Milk and blood collection From Day -2 to Day + 11 of both periods, composite milk samples were collected at morning and evening milkings. Samples were frozen (-20°C) until determination of progesterone concentration via a validated radioimmunoassay. From Day -2 to Day +5 of each period, blood samples were collected twice daily at 12-h intervals; from Day +6 to Day + I I of each period, blood samples were collected once daily. Samples were collected via coccygeal venipuncture into heparinized evacuated tubes (Vacutainer, Becton Dickinson, Rutherford, NJ), and were placed on ice until centrifugation (3000xg at 4°C for I5 min) within 20 min. Plasma was harvested and frozen (-20°C) until determination of progesterone concentration via a validated radioimmunoassay. In order to determine the effect of CIDR treatment on LH secretion dynamics, on Days - 2, + 2, + 5 and + 9 of Period I three cows fmm each group were selected at random for intensive periods of serial blood sampling. Each sampling period lasted for 8 h, and lo-ml samples were collected at 10 min

intervals via a jugular cannula ( 16 gauge, 13.3 cm Angiocath, Becton Dickinson. Rutherford. NJ ). Samules were ulaced into tubes containina 50 United States Pharmacopia (USP) units sodium heparin (Sigma ChemGal Co., St. Louis, MO) and kept on ice until centrifuged (3OOOxnat 4°C for 15 min). Plasma was harvested and stored as described above until radioimmunoassay for LH concentration. Hormone measurements in milk

andplasma

For determination of progesterone concentration, plasma was ahquoted in 200-d duplicates, extracted with 2 ml benzene/hexane (I :2 vol/vol), and assayed using the procedures of Knickerbocker et al. ( 1986 ) . Intra- and interassay coefftcients of variation were 8.4% aud l5.2%, respectively. Milk progesterone was measured by radioimmunoassay after extraction of whole milk using the following procedure. Individual samples (200 ~1) in

-I of iso-octane for 5 min on a multivorduplicate were extracted with 3.5 i-l texer. Samples were frozen ( -20°C for 1h) and the iso-octane fraction de-

J. “AN CLEEFFET *L.

94

canted into I2 mm x 75 mm borosilicate glass tubes and dried under air. Extracted aqueous phases were then thawed and re-extracted using the same procedure. The &-octane fraction resulting from the second extraction was combined with the previously extracted material in 12 mmx75 mm tubes. After completely drying under air, 1 ml of ethanol was added to all tubes and samples were stored overnight at. -20°C. The next day, a 500 JLIaliquot of the ethanol solution was removed. Three milliliters of iso-octane and 500 ul of distilled water were added to all tubes and samples were vortexed for 5 mia using the multivortexer. After samples had settled, the iso-octane fraction (top) was removed from each tube using a Pasteur pipet. and placed in new I2 mm x 75 mm tubes. The iso-octane fraction was then dried down under air, and the extracted residue was assayed for progesterone using procedures described by Knickerbocker et al. ( 1986). Extraction recovery efficiency of progesterone was 97 2 l%, calculated from four recovery tubes per assay. The milk progesterone assay was validated by the followingmethods. Assay of different dilutions of milk ( 1:4, I :2, 1: 1.5, and I : 1 milk volume:buffer volume) resulted in a displacement curve which was similar to the standard curve (tested for homogeneity of regression, P> 0.10 ). Addition of progesterone (5, lo,20 and 30 ng ml-‘) to two different milk pools resulted in a recovery of mass described by two equations (Pool I, j=2.943+ 1.383k, Pool 2, $= 2.270+ 1,0534x, where y is the amount of mass measured per milliliter of milk. and x is mass of progesteroneper milliliter added to milk samples). High ( 8.8 ng ml- ’ ) and low (5.0 ng ml-’ ) reference pools were included in each assay (n = 8) in order to determine assay variation. Intra-and interassay coeffbzientsof variation for the milk progesterone assay were 10.3%and 9.3%. respectively. Sensitivity of the milk progesterone assay was 0.3 1 ng ml-‘. Plasma LH was measured by radioimmunoassay using the procedures of Lucy et al. ( I99 I ). Intra- and interassay coefficients of variation were 1 I .9% and 7.496,respectively. After analysis of samples, one cow was found to have no detectable concentrations of LH on any sampling day. This was the same cow which was dropped after the first period because of low milk yield, and data from this cow were excluded. Statistical

analysis

Differences in progesterone concentrations between treatments with new and used CIDR devices were compared using General Linear Models procedures of the Statistical Analysis Systems institute GAS, 1987). Mathematical models for analyses of milkand plasma progesterone concentrations on days of CIDR treatment (Days + I to +9) included effects of cow, period, treatment (CIDR type) and day, and interactions (see Tables 2 and 4). Day trends were evident for both plasma and milk progesterone, and polynomial regrcssion equations were fitted for each response and treatment. Dynamics of LH

secretion were analyzed using the PULSAR algorithm for peak identification (Meriam and Wachter, 1982). Peak frequency, and LH mean, mean amplitude and smoothed baseline concentrations were subjected to General Linear

Models procedures using models which included the main effects of CIDR type(newvs.used)andday(-2,+2,+5and+9). RESULTS

Plasma and milk progesterone concentrations were positively correlated (r=0.63, P~0.01; Table 1). The mathematical model of cow, period, CIDR and Error I explained 32.0% (R’) of the variation in milk progesterone

(MP.+). When plasma progesterone (PP,) was added to the model as a continuous independent variable, RZ was equal to 48.0%; PP., accounted for 16% of the variation in the total model. The equation best describing the relationship between PP., and MP, was Jo= 3.3097 + I .3641x, where y is MP4 (ng ml-’ ), and x is PP4 (ng ml- ’ ). Correlation between MP, and PP., was somewhat higher for new (r=0.64) than for used CIDR (rc0.43; Table I ). After laboratory analysis, CIDR devices used in lactating cows for 9 days were found to contain I. 14 5 0.017 g progesterone, and approximately

6.1% of the total

skin weight was accounted for by the progesterone content. Used CIDR devices employed in the present experiment were assumed to contain this amount of hormone at the initiation of treatment. Plasma progesterone In both Periods I and 2, PP4 concentrations before CIDR insertion (Days - 1.5 to -0.5)

were near the detectable limits of the assay (0.31 ng ml-‘)

for all cows, and returned to near undetectable concentrations by Day + IO, 24 h after device removal. Therefore, the source of measutable concentrations of PP. was the CIDR device. No significant differences in mean daily TABLE I Correlations between plasma and milk progesterone treavxl with new or used CIDR devices

mncentrations

source

n

Correlation

CIDR type New Uxd Pooled within CIDR Pooled within cow and CIDR GIMS

IO1 102 203 203 203

0.640.430.59” 0.560.63”

“P
in ovariectomized

lactating cows

96 TABLE

J.“ANcLEEFFErAL.

2

Least squares analysis of variance for -,!asma prqestemne concentrations dunng iectomized lactatingcowstreated with new or used CIDR devices for 9 days SOUPX

cow Period (Per) Treatment (TR)

ErrorI

Day CowxDav TlWDay. Per x Day Error 2

treetment

of war-

d.f.

Mean square

Error term

7 1 1 6 8 56 8 a 48

3.16 1.05 29.671 1.38 1.34” 0.13 0.12 0.21 0.15

En-w I En-or I Error

I

Error 2 Error 2 Error2 Error 2

“PCO.01.

PP4 concentrations or pattern of change in concentrations over the course of both treatments were detected between periods (P> 0.40), so these data were combined. Treatment of ovariectomized cows with both new and used CIDR devices resulted in an abrupt increase in circulating PP, within 12 h of insertion, maintenance of elevated PP, throughout treatment, and an abrupt decrease in circulating PP, within 24 h of device removal to basal concentrations. Within 12 h of device insertion (Day +O.S), PP. was elevated to a mean concentrationof 2.4kO.20 ngml-’ (new CIDR) and 1.8k0.27 ngml-’ (used CIDR). Analysis of variation associated with differences bctwcen morning and evening PP4 concentrations, on days in which two samples were collected (Days - 1 to +5.5), excluding the day ofClDR insertion (Days 0 and +0.5),

ticant (PcO.01) effect of rime of day on PP4 (morning, -I vs. evening, 1.6+0.06 ng ml-‘). This difference, though consistent, was less than 0.3 ng ml-‘. Therefore, data for each half day were combined kto daily means. Least squares analysis of variance for plasma progesterone concentrations is presented in Table 2. On all days of CIDR exposure, new CIDR PP., excecdcd used CIDR PP, (PeO.01). and for both treatments PP4 cha during treatment (effect of day, PeO.01). The following fifth-order ssion curves best describe changes in PP., over the experimental period (Days - 1.5 to + I I .5) PP,(newCIDR:ngml-‘)=0.168+3.6725~&-1.6477 xd2+0.3058xd’-0.0252xd4+0.000754xd5

PP4 (used CIDR; ng ml-‘)=0.675+

1.7689x&0.8648

xd2+0.17t2xd’+0.01487xd~+0.000465xds

where d is day.

The wrves described by these equations, with daily !east squares means of PP4 vahtes superimposed to show the tit, appear in Fig. I. The complete model (cow, period, treatment, and day to the fifth orderxtreatment) accounted for 82% of the variation in PP+ The two fifth-order regressions accounted for

33% of the variation in the complete model. For the period of CIDR treatment (Days + 1 to +9), mean PP4 was 2.4?0.l4ngml-‘(newCIDR)and 1.5+0.14ngml-‘(usedCIDR).Peak PP, concentrations obtained during CIDR treatment were reached on Day + 2 for both treatments. On this day, PP., averaged 3.0 20.22 ng ml- * (new CIDR, range, 2.5-4.4 ng ml- ’ ) and 1.8 + 0.17 ng ml-’ (used CIDR, range, I. l-2.6 rg ml-‘). Minimum PP4 concentrations during CIDR exposure occurred on Day +8 in both treatments, with I .950.27 ng ml-’ (new CIDR; range, 1.1-3.6 ng ml-‘) and 1.2ZO.07 ng ml-’ (used CIDR, range, 1.0-1.6

ngml-‘). The variation among animals in PP4 was high in cows treated with new and used CIDR devices. Daily mean PP, values for individual cows are shown in Figs. 2(A) (new CIDR) and 2(B) (used CIDR). Estimate of among-cow repeatability of PP., (Table 3) for new CIDR (n.66), was somewhat higher than for a used ClDR (0.45). Cows treated with used CIDR devices were much more similar to each other in the concentrations of PP* found in the blood (Fig. 2 (B) ) I Most likely, the smaller amount of progesterone available to the cow tiom the used CIDR device was not sufficient to reveal maximum differences in metabolism of PPr which probably account for the higher variation among cows treated with the new CIDR.

0

New CIDR

0

“aed

6

9

ClOR

1

-2

-1

.S

1

2

3

4

6

6

7

10

11

Day Fii. 1. Regression lines and least squares means for daily plasma progesterone concentrations (ng ml-‘) in ovariectomized lactating cows treatedwith newor used CIDR devices (Days -2 to +

1I, PeriodsI and

2 combined).

98 TABLE 3 Estimationof repelability’ for plasma and milk progesteroneconcentrationsin cows treated with new or used CiDR devices for 9 days Pa SLwrce

CIDR

Plasma

NW

0.44

0.23

0.66

Plasma Milk Milk

Used New used

0.04 3.78 0.59

0.05 2.02 1.51

0.45 0.65 0.28

‘Conelalion of repeatedmeasures within cow-periods, tijustcd for day effects.

” [ A:

New CIDR

- [ 8: Used

CID

Fig. 2. Ditily plasma pm&%xme concentrations (ng ml-‘) in individual ovariectomized lactating cows treated with (A) new or (B) used CIDR devices (Days -2 to + I I, Periods I and 2 combined 1

HORMONES IN COWSWITH NEW OR USED DRUO RELEASEDEVICES

99

Milk progesterone A regular and predictab!e change in mean milk progesterone concentrations occurred diurnally, with samples collected at the evening milking having consistently higher concentrations of progesterone (mean evening value for days of CIDR treatment, 6.5 ? 0.17 ng ml- ’ ) compared with samples collected at the morning milking (mean morning value, 5720.17 ng ml-‘; P~0.02, Table 4). As PP4 and MP4 were significantly correlated (Table I ), someof the variation in MP., probably was a consequence of variation in PP4 available to the mammary gland, and this in turn was likely owing to diurnal variations in metabolic rates. The diurnal pattern seen in MP4 was opposite to the pattern of milk yield, which was higher at the morning milking (moming. 7.420.2 kg vs. evening, 5.1 TO.2 kg, PcO.01). When analysis of MP4 included milk yield as a continuous independent variable, the model containing cow, period, CIDR, day, time of day and yield explained 62% of the variation in MP,. Each source, except cow and time of day, was significant (Pt0.04). Yield accounted for only I .2% of the variation. Therefore, adjusting for milk production eliminated the time of day effect on milk progesterone concentrations (E’S 0.50). The line best describing the influence of yield on MP, was: 9=7.8718-0.2831x, where y is MF’I (ng ml-‘) and x is milk yield (kg). Thus, the diurnalchanges in MP, appeared to be a function of the amount of milk produced. No treatment differences in milk yield were detected. There did not appear to be the same relationship between milk yield and MP, from day to day as there was between morning and evening samples. Daily means of both MP, (Pt0.01) and milk yield (Pt0.07) were slightly higher in Period 2 (7.120.4 ng ml-’ and 12.7 2 0.4 kg day-‘) than in Period t (5.1 kO.4 ng ml-’ and 11.7ZO.4 kg da-‘). For the purposes of overall TABLE 4 Least squares analysis of variance for milk progesterone concentrations during treatment of ovarieccorn treated with new or used CIDR devices for 9 days ~-

tomizcdlactating source CUW FtriGd (Per) Treatment (Tn) Error I Day CowxDsy TnxDay FWxDPy Time ofday Milk yield Error2

‘PCO.10. ‘P<0.OS;*‘P<0.01.

d.f. 7

I I 6 8 56 8 8 i I 189

Mean square

Error term

source

77.50’ 287.08** 242.13’ 24.71 11.7r. 2.49 3.84 4.31 0.12 36. IS” 4.07

Error

COW Per Trl Error I Day CowxDav Trtx DayPer x Dav Error2 -

t

Error I Error I Error 2 Error 2

d.f. 7 I :, 8 56 8 8 191

Mean square 103.339 249.79217.73’ 19.52 1 I .70” 2.50 3.35 3.36 4.48

100

3. “ANCl.EEFFETAL.

data analysis, morning and evening data were combined into daily MPs means. Least sauares analysis of variance for MP, concentrations on days of CIDR treatmentis presented in Table 4. There were significant differences between oeriods (PcO.01) for MP, (Period 1.4.6 na ml-‘: Period 2.6.5 ng ml-‘). Although mean MP, was higher in new than-in used CIDR for bc O.40). Relative patterns of change in MP., due to CIDR treatments did not differ between periods. Mean MP., concentrations before CIDR insertion (Days - 1.5to - I ) were 3.620.25 ng ml-‘. Within 12 h of device insertion (Day +0.5), MP, was elevated to a mean concentration of 8.020.74 ng ml-’ (new CIDR) and 6.2kO.37 ng ml-’ (used CIDR). Mean milk MP, concentrations obtained during CIDR treatment (Days + 1 to +9) were 7.020.36 ng ml-’ (new CIDR) and 5.2kO.36 ng ml-’ (used CIDR) for both periods combined (P
ml-‘)=

6.934+0.2246xd-0.0196xd2-0.00216xd3 MP.,(used CIDR, ng ml-’ ) = The regression lines described by these equations, with daily means superimposed to show the fit, are presented in Fig. 3. The complete model (cow, period, treatment, and ay to the third orderx treatment ) accounted for 8 I% of the variation in PP.,. The two third-order regressions accounted for 14% of the variation in the complete model.

Milk progesierone profiles for cows treated with new CIDR (Fig. 4(A) ) showed high variation among cows. Repeatability for PPJ among cows within period, adjusted for day etfects, when treated with a new CIDR was 0.65. Relatability for used CIDR cows was only 0.28. Among cows treated with

101

J -2

-1

.5

1

2

3

4

5

6

7

6

9

10

11

Day Fig. 3. Regression lines and least sqoarcs means ml-‘) in ovariectomized lactating cows treated + Periods and 2 combined).

I I,

for daily milk progesterone concentrations with new or used CIDR devices (Days

-2

(ng to

I

used ClDR (Fig. 4 (B) ), distinct cow differenceswere much less obvious (see Table 3). Dynamics of I.H secretion In three cows per treatment, intensive sampling at IO-mm intervals for 8 h was conducted 2 days before CIDR insertion, and during CIDR exposure on Days + 2, + 5 and + 9 of Period I _After radioimmunoassay, one new CIDR cow, which was dropped before the second period after ceasing to lactate, proved to have undetectable concentrations of LH. With dria from two new CIDR and three used CIDR cows and the high variation among cows, it was not possible to detect any effect of CIDR type (new vs. used) on LH secretion ( Ps- 0. IO). Data then were combined to assess the effect of CIDR treatment (Day - 2 vs. Days +2, + 5 and + 9) on LH secretion. Mean LH concentration, peak amplitude and smoothed mean, peak frequency per 8 h, and the mean PPa concentration for each day are presented in Table 5, and profiles of serial samples from two representative cows are depicted in Fig. 5. No effect of day was detected (P> 0.10). indicating that progesterone delivery from either new or used CIDR devices was not sufftcient to alter any characteristic of LH secretion from the basal state of the ovariectomized cow. Basal secretion of LH in the ovariectomized cow was characterized by high basal concentrations ( 1.29ng ml-’ ) and a high puIse frequency ( 7.8 pulses per 8 h; see Day -2, Table 5). The CIDR device was removed from the cows approximately 3 h after the initiation of serial sampling on Day +9. Within an hour, LH smoothed mean concentration increased (PcO.07) from 0.7 ng ml-’ before

J. VAN

A:

New

Cl,“R.-..-

._,,,,

I--..._,_

CLEEFFETAL.

\

~~

Fig. 4. Daily milk progesterone concentrations (ng ml-‘) in individual ovariectomizcd Iactating cows trcntcd with (A) new or (B) used ClDR devices (Days + 2 to + II, Periods 1 and 2 combined).

TABLE 5 Luteinizing hormone scccretiondynamics before and duringtreatment with new or used CIDR devices Pulsarility

Day

Plnsmu Pa’ (ngml-‘*SE)

Lilrespow(ngml-‘?SE) ~Mean Amplitude

Smarrthed mean

(peaksper8h)

-2

0.3Sf0.09 2.45+o.s3 1.6710.51 1.69+0.42

1.291t0.21. 2.01 f0.35b 2.0810.63b l.76f0.27b

@.78+0.16c I.lIfO.?O’ I.lo*o.25’ 0.9‘i+o.ls

7.8+0.8 7.8+ 1.5 8.0f0.9 7.6+ 1.2

+2 CT +9

I.so+o.57~ 2.99+ 1.01” 3.37f I.450 2.9510.726

‘Mean concentration for al! wws in Period I. Valueswith diffcerentsuPaxaipts dit% for cantnut. pre-treatment YE.treatment: LbP~0.02;‘“P~0.0S; “‘kO.10.

HORMONES IN COWSWITH NEW OR USED DRUG RELEASEDEVICES

103

Fig. 5. Pleame LH concentrations (ng ml-‘) in two representative cows on Days -2, + 2, +5 and +9ofPeriod 1.

removal to I .3 og ml- ’ after removal, and this change was seen in four out of five cows. DISCUSSION

Treatment of ovariectomized cows with CIDR devices significantly eievated milk and plasma progesterone over pre- and post-treatment coocentratioos. New CXDRtreatment elevated plasma and milk proge&erone to a greater extent than used CIDR treatment. Mean differences between CIDR types during CIDR exposure were 0.92 ng ml-’ for PP4 and 1.75 ng ml-’ for MP4. Concentrations of MP., were highly correlated with PP., concentrations (see

104

J.VANCLEEFFETAL

Table 1), and correlation between PP, and MP., seemed higher for new than for used CIDR devices. Higher progesterone concentrations in milk than plasma is well documented and associated with the high amount of progesterone in milk fat (Foote, 1979). The milk progesterone concentration of 3.6 ng ml-‘, in ovariectomized cows before CIDR insertion, approximated the values found in cows withcut a corpus luteum (Foote, 1979) and considerably lower than the 5 ng ml-’ concentmtion reported by Dobson and Fitzpatrick (1976). Variation among cows may reflect either differences in the progesterone concentration delivered by the CIDR device, or differences in the metabolism of progesterone among cows. Analysis of the CIDR devices after 9 days of use in Period 1 showed little variation in the amount of progesterone left in the device, suggesting that the rate and degree of depletion of hormone

from the device was consistent for all cows. However, consistent differences in PP4 existed among the cows treated with uew CIDR devices. This likely reflects ditTerences in metabolism among the cows exposed to the higher dose of progesterone delivered by the new CIDR device, Among-cow variation in PP, was diminished in cows treated with the used CIDR. Dosage of progesterone delivered by the used CIDR was probably well below the capacity of the cows to metabolize progesterone,and thus inherent differencesin metabolizing capacity were not reflected in progesterone concentrations. inherent differences among cows, with CIDR devices, in plasma progesterone also were reported by Peterson and Henderson ( 199 1) and were attributed to variation in metabolism of progesterone among cows. Am6ng-cow differences in MP, were generally less than those seen in plasma (see Table 3). However, the repeatability again seemed greater with a new CIDR than with a used CIDR. As milk is a potential excretory route for the clearance of progesterone, the lower variation in MP4 among cows may reflect the low milk production in these cows (approximately 12 kgday-‘). Results 6f analysis of LH dynamics demonstrated that CIDR devices released quantities of progesterone which, in ovariectomized cows, were insufficient to effect a negative progesterone feedback on LH secretion. These data agree with the findings of Roberson et al. (1989). In their experiment, normal P4 and subnormal P4 profiles were induced in mature beef cows by regressing corpoia lutea using prostaglandins and treating cows with two progesterone releasing intravaginal devices (PRID) or 0.5 PRID devices. Mean PP, in the subnormal P4 group (0.5 PRID) of that experiment was 2.14 ng ml- ’ ( n = 6)) significantly lower than the normal P4 group (2 PRID, 6.19 ng ml- ‘: n = 7 ), but similar to the concentration in cows of the present experiment on Day +2 (2.4550.83 ng ml-t). Luteinizing hormone peak frequency in subnormal P4 (0.5 PRID) cows was approximately 9 peaks per 8 h, whereas normal P4 (2 PRID) cows had approximately 5 peaks in 8 h. Average LH pulsatility found in the ovarlectomized CIDR-treated cows at Day

HORMONES x.4 CoWSWtTH

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was 8 TO.9 peaks per 8 h. This did not differ from Day -2 pulsatility (7.82 0.8 peaks per 8 h), which is representative of the high LH pulse frequency typical of ovatiectomized cows prior to progesterone exposure. Concentration and amplitude of LH were not comparable between the Roberson et ai. ( 1989) study and the present experiment in which detected values were higher, probably because the cows in the present experiment were ovariectomized. It is clear that a PP, concentration of approximately 2.5 ng ml-’ seen in an ovariectomized cow treated with a new CIDR device is far helow a normal luteal concentration of approximately 6 ng ml- I. At the concent:ation of PP4 induced by the CIDR in the ovariectomized cow, the negative feedback of PPa would be less effective than normal iuteal concentrations would hc. In fact, LH concentrations tended to increase gradually during CIDR treatment (see Table 5. Fia. 5 ). A weak neaative feedback may have occurred with CIDR treatment, as d;mdnstrated bythe slight increase-in LH smoothed mean, or baseline, concentration after CIDR removal on Day +9. Foiiicular deveiopment is dependent on a specific basal concentration of gonadotropins, e.g. LH. However, the normal turnover of follicles is affected by both LH concentration and peak pattern (Savio et al., 1990). Normal iuteai phase LH peak pattern, with only one peak approximately every 3 h (Rabe et al., 1980), allows normal turnover of follicles (Savio et ai., 1988). If CIDR treatment is insufficient to substantially affect LH secretion in ovariectomized cows, this may have an impact on follicular development in intact cows which have undergone htteolysis early during CIDR treatment. In summary, t:eatment with new or used CIDR devices resulted in eievation of plasma and milk progesterone concentrations in ovatiectomized iactating cows, and treatment with new CIDR device caused a greater increase compared with treatment with used CIDR device. Neither CIDR type deiivered sufftcient concentrations of progesterone during treatment to significantly alter the high frequency puisatile secretion of LH in ovariectomized cows. +5

ACKNOWLEDGMENTS

Research was supported by the Rorida Dairy Checkoff Program. CIDR devices were supplied by Carter Hoit-Har-sy Plastic Products Group, Ltd., Hamilton, New Zealand.

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