Detection of oestrus by milk progesterone assay, visual conservation and cervical mucus conductivity in oestrus - synchronised dairy cows.

Abstract

Proc. Aust. Soc. Anim, Prod. Vol. 18 DETECTION OF OESTRUS BY MILK PROGESTERONE ASSAY, VISUAL OBSERVATION AND CERVICAL MUCUS CONDUCTIVITY IN OESTRUS - SYNCHRONISED DAIRY COWS G.J. SAWYER*, P.E. WILLIAMSON*, Adji DRADGET* and G. HOWELL* Sixty cows were treated with Syncro-Mate B or prostaglandin and cyclical by frequent sampling for milk progesterone and activity was monitored Visual the electrical resistance of cervical mucus. measurement of was practised four times daily. Oestrus and observation of oestrus of Syncro-Mate B and 87% of prostaglandin occurred in 80% ovulation treated cows. The proportion of cows which could be inseminated at the based on milk progesterone profiles, then correct time was highest if finally on measurement of the observation of oestrus, and visual electrical resistance of cervical mucus. The large individual variation in resistance readings, labour requirement and irritation to the vagina caused by the probe lead us to conclude that this technique is not suitable for oestrus detection or the timing of insemination on commercial dairy farms. INTRODUCTION Strategic use of hormone treatments can reduce calving to conception intervals, concentrate calving patterns, reduce herd empty rates, and lactation length and the period of peak potentially increase the average (Macmillan 1985). There have been numerous milk production in dairy herds studies on synchronisation methods which either shorten the life span of the corpus luteum (prostaglandins), or which lengthen the cycle using progesterone treatments in intravaginal devices (PRID or CIDR) or subcutaneous implants with progestagen (Syncro-Mate B). In all cases conception rates are higher when insemination is based on detected oestrus rather than at a fixed postSome encouraging results were obtained with fixed time treatment interval. insemination in programs using Syncro-Mate B (Pelot et al. 1984) but few experiments have been conducted in Australia with this product. factors influencing More information is required on ovarian response to synchronising treatments, including stage of the oestrous cycle, follicular development endogenous hormones and the level of such as progesterone. Measurement of milk progesterone provides a useful aid in monitoring response to synchronising treatments and oestrous cycle activity. It may usefully be applied in evaluating methods of oestrus detection such as observation by the herdsman and measurement of the electrical resistance of cervical mucus by electronic probe (Foote et al. 1979; Cavestany and Foote 1985). The present study compared two treatments to synchronise oestrus and ovulation in dairy cattle, using milk progesterone levels to evaluate the response to treatment and the accuracy of oestrus detection based on visual observation and changes in electrical conductivity of cervical mucus. HATERIALSAND XKTHODS Sixty cows were paired at least 60 days after calving according to calving date and parity, and alternately allocated to one of two groups. Group 1 (n = 30) - injected with 5 mg oestradiol valerate, and 3 mg norgestomet on day 0 and given a norgestomet ear implant for 10 days (Syncro-Mate B treatment, Intervet, Sydney, Australia Pty Ltd); Group 2 (n = 30) - injected twice with prostaglandin (cloprostenol 0.5 mg, Estrumate, ICI Australia Ltd)-11 days * Department of Agriculture, PO Box 1231, Bunbury, W.A. 6230. 352 Proc. Aust. Soc. Anim. Prod. Vol. 18 apart. Fig. 1. Milk samples were collected according to the protocol illustrated in Fig. 1. Milk sampling, timing of treatments and vaginal probe measurements concentration of progesterone in duplicate 10 ul milk samples was The a solid phase, microtitre plate progesterone enzymedetermined using The sensitivity of the EIA standard immunoassay (Munro and Stabenfeldt 1984). progesterone pools (4.9, 14.3 and 25.6 . and with three curve was 0.4 ug/l to 16.7%, the inter-assay C.V. measured ug/l) the intraplate C.V. was 4.8% 7.3% to 17.4% and the intra-assay C.V. was 3.9% to 8.2% Three days after allocation to treatments the electrical resistance of cervical mucus was measured in 18 cows chosen at random from each group using inserted into the anterior vagina the Animark Ovascan probe, sanitized and until the displayed resistance units stabilised (30-40 against the cervix, Cows were observed for oestrus set). The protocol is described in Fig. 1. artificially four times daily at 0600, 1000, 1600 and 2200 h and were inseminated using thawed frozen semen 12 h after first observed in oestrus. Continuous data relating milk progesterone levels, the electrical resistance mucus and the timing of the onset of oestrus were analysed by of cervical analysis of variance and Student's 't' test. Discrete data including synchrony response and detection of oestrus were analysed by Chi-square tests. RESULTS Control of oestrus and ovulation was similar in both treatment groups at but 80% within three days for Group 1 and 87% within five days for Group 2, fewer cows treated with Syncro-Mate B were detected in oestrus (n-s., Table Cows injected with prostaglandin displayed oestrus 27.7 hours later, on 1). average, than 'those treated with Syncro-Mate B (P <O.OOl, Table 1). Examination of progesterone profiles showed that six cows in Group 1 and four in Group 2 were not synchronised, Half of these Group 1 cows had low concentrations of progesterone (<2 ug/l) at implant insertion, which stayed low for 3-5 days then gradually increased, signifying the presence of a new, active corpus luteum. Progesterone did not decline at implant removal. The other cows not synchronised had luteal concentrations of progesterone which declined, then a new ovulation occurred. Four cows did not respond to prostaglandin. One had uniformly low (<l ug/l) progesterone and was judged to be not cycling, and in the progesterone concentrations fell in others response to prostaglandin, but a new corpus luteum was not initiated and hence, cows could not respond to the second of injection proscaglandin.. Based on milk progesterone profiles all cows which were not detected in oestrus were apparently synchronised. Undetected oestrus could not be related to the progesterone concentration or stage of the oestrous cycle when treatment commenced. Only 37.5% (g/24) cows of Group 1 and 50% (13/26) cows of Group 2 conceived to AI at the synchronised oestrus, 353 Proc. Aust, Soc. Anim. Prod, Vol. 18 All inseminations were made when milk progesterone was below 0.5 ug/l. Table 1 Cows responding to synchronising treatments assessed by milk progesterone profiles, visual detection of oestrus and vaginal probe readings * XX Within 3 days. ** Within 5 days. #Significantly different, P<O.OOl. Cows not included because they were not synchronised or a lack of readings due to irritation of vaginal mucosa. Successful detection of oestrus based on retrospective analysis of vaginal Average probe data was worse than that using visual detection (Table 1). electrical resistance readings are presented in Fig. 2 and show that the lowest resistance values are generally associated with the peri-oestrus period (2 2 errors (Table 1) indicate that this days ) I but the large standard The measurement is much less reliable than visual observation of oestrus. drop in electrical resistance from luteal t o oestral phases ranged between 20-30% for individual cows (Fig. 2) whereas cyclical differences in profiles of milk progesterone at similar stages of the oestrous cycle range between 8 and 15 fold. Fig. 2. electrical resistance of cervical mucus in dairy Mean (+ 8-e.) cows during and after Syncro-Mate B and prostaglandin treatments. DISCUSSION Concentrations of milk progesterone proved useful in interpreting the response to both synchronising regimes used in this experiment. The work highlights the value of this technology when studying reproductive activity in dairy cattle. the Profiles during and after Syncro-Mate B treatment generally confirmed luteolytic action of oestradiol valerate on corpora lutea at least six old, When treatment began just after oestrus and ovulation the days secretory activity of the corpus luteum was sometimes modified and cows showed but in three cases oestrus and subsequent ovulation a synchronised oestrus, 354 Proc. Aust. Soc. Anim. Prod. Vol. 18 luteum established in the functional corpus was delayed due to a et al. similar to observations by Thimonier presence of Syncro-Mate B, biological variation in response to inherent This may be (1975). and precludes the oestradiol valerate early in the oestrous cycle, possiblity of good results to fixed time insemination with this treatment. In those animals which responded to treatment with Syncro-Mate B the time until was and was one day shorter than the response to prostaglandin oestrus published treatment from the timing of oestrus after within five hours Failure to synchronise oestrus and ovulation in by Whittier et al. (1986). was due to the lack of establishment of a new prostaglandin response to corpus luteum ready for a second luteolytic dose of prostaglandin. In this experiment- concentrations of milk progesterone served as a yardstick Though a against which other methods of oestrus detection were measured. useful research tool, successive measurement of milk progesterone to form a and ovulation, profile for each cow and establish the timing of oestrus is neither practical nor economic on commercial farms. The next most reliable The proportions of cows detected method was visual observation of oestrus. were similar to other work where oestrus was looked for frequently (Foote Measurement of the electrical resistance of cervical mucus by vaginal 1975). probe proved the least reliable method for detection of oestrus. The large individual variation and sometimes erratic readings meant that although the to follow cyclical patterns, results were too resistance measured tended insemination appropriately. variable to accurately predict oestrus or time agreement with other studies (Gartland et al. This result is in general and at variance with other work by Foote et 1976; Cavestany and Foote 1985) We took care al. (1979) who inseminated cows on the basis of probe readings. not to let air in the vagina influence probe readings, which increased the time taken to perform the task. This time requirement, and the fact that frequent use of the probe around the expected time of oestrus led to irritation of the vulvo-vestibular mucosa and some discomfort to cows on a few occasions, mitigates against widespread use on commercial dairy farms. Though not evaluated here, oestrogen-treated steers or heifers (Sawyer et al. 1986) or tailpaint (Macmillan and Curnow 1977) would appear to offer practical alternatives to aid oestrus detection in commercial dairy herds run at pasture. ACKNOWLEDGEMENTS Our thanks to the staff of Wokalup Research Station for care of the animals, and to MS J. Speijers and Mr R. Morris for assistance with analysis of the data, REFEIRENCES CAVESTANY, D. and FOOTE, R-H. (1985). Cornell. Vet. 75:441. FOOTE, R.H. (1975). J. Dairy Sci, 58:248. FOOTE, R-H., OLTENACU, E.A.B., MELLINGER, J,, SCOTT. N-R. and MARSHALL, R-A. (1979). J. Dairy Sci. 62:69. GARTLAND, P., SCHIAVO, J., HALL, C-E., FOOTE, R.H. and SCOTT, N.R. (1976). J. Dairy Sci, 59:982. 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