S. MONDAL* AND B. S. PRAKASH
National Dairy Research Institute,
Karnal - 132 001
(Received on November 5, 2001)

 

 
Key words : progesterone, overt, estrus, estrus, expression, silent, estrus, cow

INTRODUCTION

Poor expression of estrus is one of the major factors that hamper efficient utilization of tropical Sahiwal cows.  Estrus is traditionally observed by behavioural symptoms which, however, are practically impossible to observe or monitor in situations where herd size is large and animals are stallfed.  Heat detection is also very difficult due to lack of expert personnel, variation of duration of estrus and reluctance of some teaser bulls to mate.  Progesterone serves as a marker for determination of functional status of corpus luteum and as a diagnostic tool for identifying ovarian condition such as estrus confirmation, silent estrus and lack of cyclicity (3, 5, 8).  Progesterone at appropriate level is essential for expression of estrus, preparing the uterus for implantation and maintenance of pregnancy (12).  There is no information available on peripheral plasma progesterone concentration in relation to expression of behavioural estrus symptoms in Sahiwal cows.  The present study was, therefore, undertaken to measure peripheral progesterone concentrations during estrous cycle and to relate them to occurrence of overt or silent estrus in Sahiwal cows.

METHODS

Experimental animals and blood sampling
Three healthy Sahiwal cows were selected from the animal herd of National Dairy Research Institute and maintained under standard feeding and management schedule as practised in the herd.  Blood samples were collected daily through jugular venepuncture for 32 consecutive days during the winter months of January and February.  Blood samples were centrifuged at 3000 rpm for 30 min.  Plasma was harvested and stored in deep freeze at -20°C for analysis of progesterone.  The animals were kept in loose housing system and checked for manifestation of estrus twice daily (8A.M. and 6P.M.) by using vasectomized bull, palpation of reproductive organs per rectum and confirmed by plasma progesterone estimation.

Hormonal assay
Progesterone was estimated by a simple, direct radio-immunoassay developed in our laboratory (9).  The sensitivity of the assay was 8 pg/tube.  The intra- and inter-assay coefficients of variation were 13.4 and 16.9%, respectively (n = 6).  The progesterone antiserum (anti-progesterone- 11 alpha-hemisuccinate- BSA) crossreacted 4 pregnane-3, 20 diene, 11 alpha-hydroxyprogesterone and corticosterone to the extent of 100, 110 and 0.2%, respectively The crossreactivity of the antiserum with cortisone, hydrocortisone was less than 0.01% and with b-estradiol, estriol and testosterone was less than 0.001%.

Statistical analysis
For statistical analysis, the estrous cycle was divided into 4 phases namely late luteal (day - 4 to day - 2, day 0 = day of estrus), periestrus phase (day - 1 to day 1), early luteal phase (day 2 to day 5) and midluteal phase (day 6 to day 14).  The changes in peripheral plasma progesterone concentrations during different phases of the cycle in cows that exhibited both overt and silent estrus were analysed by Analysis of Variance (16).

 

RESULTS AND DISCUSSION

Out of a total of five estrus, three were accompanied by overt signs whereas the remaining two were silent estrus.  The plasma progesterone concentrations in cows that exhibited overt estrus behaviour and those that showed silent estrus during different days of cycle are depicted in Fig. 1. The mean (±S.E.M.) plasma progesterone concentrations were 0.40 ± 0.02 and 0.40±0.03 ng/ml on the day of estrus and rose to a peak level of 3.03 ± 0.91 and1.75              ± 0.35 ng/ml on day 10 and day 8 which then declined gradually to the basal level on the day of next estrus in cows that exhibited overt signs and silent estrus, respectively.  These results are in agreement with earlier reports in cows (6, 14) and buffaloes (1, 2, 13) in terms of minimum level on the day of estrus with gradual rise to the higher levels during luteal phase and then declining to basal level at subsequent estrus.  Stabenfeldt et al. (17) reported that progesterone levels ranged from less than 0.5 ng/ml during follicular phase to 6.6 ng/ml at peak luteal phase in cows.  Progesterone levels increased rapidly from day 3 to day 8 with much slower rate of increase from day 8 to 17 indicating a cyclic pattern of progesterone concentration in plasma of cows.  A cyclic pattern of progesterone in nonpregnant cows with 7.5-10 ng/ml during luteal phase and 1-2 ng/ml for 4 to 6 day period around the time of ovulation was reported by Gupta and Pope (6).  In another study a cyclic pattern of progesterone in ovarian venous blood of cows was found with peak concentration on about day 16 followed by a decline on day 17 till ovulation (4).

Fig. 1

Fig. 1: Peripheral plasma progesterone concentration during overt and silent estrus in Sahiwal Cows.

The cyclic pattern of progesterone concentrations in jugular plasma is in agreement with known changes in corpus luteum function in cow during estrous cycle.  The decline of progesterone in plasma of cows towards the end of the cycle as well as a marked rise during the time of corpus luteum development suggests that corpus luteum functioning can be monitored in plasma by progesterone determination.  The functional activity of bovine corpus luteum was reported to be increased by about day 15 and then declined as reflected from decrease in corpus luteum weight and progesterone concentration in cows (10).  It has been reported that the net progesterone content increased progressively from day 2 (17 mg/gm) to day 11 (136 mg/gm) and remained relatively constant (150 mg/gm) upto day 20 and thereafter fell (46 mg/gm) at day 0 (7).  Corpus luteum weight increased from early to midluteal phase corpus luteum and declined in the late luteal phase in Surti buffaloes as is shown in previous study (15).  Corpus luteum extract progesterone was significantly (P<0.01) higher in midluteal corpus luteum compared to other luteal phases.  A previous study has shown that corpus luteum weight rose progressively from 605 mg on day 3 to 1885 mg on day 13 followed by a decline to 1292 mg on day 18 in Surti buffaloes.  The progresterone concentration was 34.5 mg/gm on day 3 rising to 62 mg/gm on day 13 and lowest concentration of 32.3 mg/gm on day 18 (11).  The mean (±S.E.M.) progesterone levels in cows that exhibited overt estrus and those in silent estrus during different phases of cycle are shown in Table 1. Plasma progesterone concentrations increased from 0.40 ± 0.02 ng/ml during periestrus phase to 0.74       ± 0.10 ng/ml during early luteal phase and then further (P<0.05) to 1.94 ± 0.22 ng/ ml during midluteal phase following which declined (P<0.05) to 0.63 ± 0.16 ng/ml during late luteal phase in cows exhibited overt estrus.  In cows that exhibited silent estrus plasma progesterone concentrations increased from 0.47 ± 0.03 ng/ml during periestrus phase to 0.94 ± 0.08 ng/ml during early luteal phase and then further (P<0.05) to 1.39 ± 0.13 ng/ml during midluteal phase following which declined to 0.95 ± 0.19 ng/ ml during lateluteal phase.  The overall mean (±S.E.M.) plasma progesterone levels in cows that exhibited overt estrus was 1.23 ± 0.99 ng/ml as against 1.08 ± 0.09 ng/ ml in silent estrus.  It was concluded that plasma progesterone levels were lower (P>0.05) in cows that exhibited silent estrus compared to overt estrus and might be responsible for poor expression of estrus.

Table I

Table I: Plasma progesterone concentration (ng/ml) during different phases of cycle in cows exhibited overt and silent estrus.

ACKNOWLEDGEMENTS

We thank Director, NIANP for providing the facility for preparing the manuscript.  S. Mondal was supported by Junior NDRI fellowship.  Technical assistance rendered by Mr. P. C. Singh and Mrs. A. Ladkhani is acknowledged.

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