Animal Reproduction Science 80 (2004) 353361

Ovarian follicular wave characteristics in alpacasJ.L. Vaughan a,, K.L. Macmillan b, M.J. DOcchio c

a Animal Sciences and Production Group, Central Queensland University, Rockhampton, Qld, Australiab Veterinary Clinical Centre, Department of Veterinary Science, University of Melbourne,

Werribee, Vic., Australiac School of Animal Studies, Faculty of Natural Resources, Agricultural and Veterinary Science,

University of Queensland, Gatton, Qld, AustraliaReceived 30 December 2002; received in revised form 15 August 2003; accepted 15 August 2003

Abstract

The objectives were to describe in detail ovarian follicular growth characteristics and to es-tablish the interval between successive large follicles in unmated alpacas. The ovarian follicularstatus of 16 non-pregnant, non-lactating mature alpacas was recorded using ultrasound every sec-ond day for between 46 and 100 days. An inverse relationship was observed between the diameterof the largest follicle and the total number of follicles indicating that follicular growth in alpacasoccurs in waves. There were 15/38 (39%) inter-wave intervals of 12 days and 12/38 (32%) in-tervals of 16 days. The maximum follicular diameter in each follicular wave was 8.8 0.3 mm(n = 38). Inter-wave intervals of longer duration were associated with a larger maximum folliclediameter (P < 0.001). However, the growth rate of dominant follicles was consistent over the first10 days after emergence. They reached a diameter capable of ovulation by this time, regardlessof subsequent inter-wave interval. The latter observation suggested that the optimal time of mat-ing might be predicted in alpacas, provided that the emergence of ovarian follicular waves wascontrolled. 2003 Elsevier B.V. All rights reserved.

Keywords: Alpaca; Ovarian follicular waves; Inter-wave interval

1. Introduction

Camelids are an important group of animals for basic studies on the reproductive biol-ogy of induced ovulators and they are emerging as significant production and recreational

Corresponding author. Present address: P.O. Box 406, Ocean Grove, Vic., Australia. Tel.: +61-3-5254-3365;fax: +61-3-5254-3365.E-mail address: vaughan@ava.com.au (J.L. Vaughan).

0378-4320/$ see front matter 2003 Elsevier B.V. All rights reserved.doi:10.1016/j.anireprosci.2003.08.002

354 J.L. Vaughan et al. / Animal Reproduction Science 80 (2004) 353361

animals (Mason, 1979; Sumar, 1983). Future genetic improvement and genetic dispersal incamelids will require the refinement of assisted reproductive technologies such as oestroussynchronisation, ovarian follicular superstimulation, MOET, and oocyte pickup combinedwith IVF. The application of these technologies has been variously attempted in camelids(Bourke et al., 1995; Brogliatti et al., 1996; Chaves et al., 2002; Miragaya et al., 2002).However, success has been limited, due primarily to a lack of understanding of ovarianfollicular wave dynamics in the females. Female camelids are all assumed to undergo re-peated cycles of follicular growth and regression with lack of ovulation, until an appropriatestimulus induces ovulation (Adams et al., 1990; Skidmore et al., 1995). The occurrence ofovarian follicular waves has been confirmed in llamas (Adams et al., 1990) and camels(Skidmore et al., 1995) but not in other camelids. The interval between the emergence ofsuccessive dominant follicles (inter-wave interval) in llamas was reported to be around 20days (Adams et al., 1990) or 1112 days (Bravo and Sumar, 1989; Bravo et al., 1990).These studies demonstrated the lack of consistency in information on ovarian follicularwave dynamics in camelids and highlighted the need for further research.

Alpacas have been recognised for the high quality of their fibre with international inter-est in the development of a fibre industry. Breeding in alpacas relies exclusively on naturalmating being dictated by the behavioural response of a female (Bravo and Sumar, 1989).Sexual receptivity in the female is not always indicative of the presence of an ovulatoryfollicle containing an oocyte with high fertilisation potential and normal embryo devel-opmental competency (Bravo et al., 1991a,b). The ability to predict the period of optimalfertility in female alpacas would improve the efficiency of natural mating and would alsoprovide a basis for the application of assisted reproductive technologies. The main aimin the present study was to provide a detailed characterisation of the features of ovarianfollicular waves in alpacas, with particular attention to the inter-wave interval and growthrate of dominant follicles. This information could be used to predict the time of matingfor optimal fertility and to develop protocols to control the ovarian follicular status ofalpacas.

2. Materials and methods

2.1. Animals

Sixteen non-pregnant, non-lactating mixed-age Huacaya alpacas (71.6 1.9 kg) wereused to characterise ovarian follicular dynamics. They were isolated from male alpacas andgrazed phalaris-based pastures.

2.2. Ovarian ultrasonography

Ovarian follicular growth and regression were monitored by trans-rectal ultrasonographyby a single operator (JV) using an Aloka SSD-500 ultrasound machine (Aloka Co., Japan)equipped with a 7.5 MHz linear array transducer. This procedure was conducted everysecond day for at least 46 days (n = 8) and up to 100 days (n = 8) from spring 1999 toautumn 2000. The smallest detectable follicle size was 3 mm.

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2.3. Statistical analyses

Descriptive statistics were derived using Minitab for Windows Release 12.1 1998 andMicrosoft Excel 97 SR-1.

Pearsons correlation was used to examine the relationship between follicular diameterand number of follicles. The day that the second successive large follicle to exhibit an entiregrowth and regression profile first reached maximum diameter was used as a commonreference point (Day 0). The sum of the number of follicles detected in both ovaries wastabulated in relation to the diameter of the largest follicle from 12 before to 12 days afterthe common reference point.

Linear regressions were performed on (a) inter-wave interval (y-axis) versus maximumfollicle diameter (x-axis); and, (b) inter-wave interval versus live weight.

Day of emergence (the day of first detection) of the dominant follicle was used as areference point to study profiles of follicular waves. Repeated measures ANOVA was im-plemented using the MIXED procedure of SAS (SAS Institute Inc., 1997) on diameters offollicles exhibiting different inter-wave intervals in relation to days after emergence.

Results were analysed only from data obtained from follicles derived when was no corpusluteum was visible on either ovary. Statistical significance was set at P < 0.05 and resultsare presented as means standard error of the mean (SEM).

3. Results

3.1. Relationship between diameter of the largest follicle and numberof follicles detected

There was an inverse relationship between the diameter of the largest follicle and the num-ber of follicles detected in both ovaries on a single day (Pearsons correlation = 0.369,P < 0.001, n = 10; Fig. 1). The total number of follicles decreased as the diameter of thelargest follicle increased.

3.2. Ovarian follicular waves in individual alpacas

Four examples of growth and regression profiles of ovarian follicles observed in the eightfemales that were monitored for 100 days are shown in Fig. 2(a)(d). New wave emergencewas characterised by the appearance of numerous (810) follicles less than 3 mm followedby continued growth of usually one, but sometimes two or three follicles up to 35 mm.The follicle destined to become the dominant one continued its growth while the others inthe cohort regressed.

Emergence of the next successive dominant follicle occurred in the ipsilateral ovary on26 occasions (60%), and in the contralateral ovary on 17 occasions (40%). A dominantfollicle appeared in the left ovary on 34 occasions (52%) and on the right ovary on 27occasions (42%). There were four occasions (6%) when there was a follicle considereddominant in both ovaries of an individual. Ten follicles developed echogenicity with only

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Fig. 1. Inverse relationship between the diameter of the largest ovarian follicle (mm, mean S.E.M.;) and thenumber of follicles detected in both ovaries (mean S.E.M.; ; r = 0.369, P < 0.001, n = 10). Day 0 isthe day that the second successive large follicle to exhibit an entire growth and regression profile first reachedmaximum diameter.

4 cases of spontaneous ovulation. The simultaneous presence of more than one follicle of7 mm diameter was observed 5 times.

3.3. Mean inter-wave interval and follicular diameter

The inter-wave interval over the total of non-ovulatory follicular waves (n = 38) was15.4 0.5 days. The inter-wave interval had a distribution of 15/38 (39%) follicular wavesexhibiting an interval of 12 days and 12/38 (32%) follicular waves with an interval of 16days. There were also five waves with an 18-day interval, 4 waves with a 20-day intervaland two waves with a 22-day interval. Individual animals exhibited relatively short as wellas longer inter-wave intervals.

The average maximum follicular diameter was 8.8 0.3 mm (n = 38). Inter-waveintervals of longer duration were associated with a larger maximum follicle diameter (P 6 mm from 3 to 4 days afterovulation in association with a shorter interval from wave emergence to peak concentrationsand higher peak concentrations of inhibin A during the first wave compared with cows with3 follicular waves per oestrous cycle. Differences in peak FSH concentrations were lesssignificant (Parker et al., 2003). The reasons for variation in inter-wave interval in alpacasremain to be resolved.

There was no regularly alternating pattern of dominant follicle emergence between the leftand right ovaries in the present study. This was consistent with previous findings in alpacasand llamas (San-Martin et al., 1968; Fernandez-Baca et al., 1970; Adams et al., 1990;Bourke et al., 1992). In contrast, Bravo et al. (1989, 1990 and 1991b) reported regularlyalternating follicular activity between the left and right ovaries in 8085% of alpacas andllamas.

The present study has shown that the rate of follicular growth for the first 10 days afterthe emergence of a new follicular wave in alpacas is constant, irrespective of the subsequentinter-wave interval. Optimum time of mating was predicted to be 68 days after new waveemergence. The development of a treatment protocol that controlled new follicular waveemergence should allow fixed-time mating in alpacas and also facilitate the greater use ofartificial insemination.

Acknowledgements

This research was supported by funding from the Rural Industries Research and De-velopment Corporation and Research Services Office of Central Queensland University.The authors thank the Bellarine Veterinary Practice and the Australian Alpaca Associationfor provision of alpacas, and Mr Garry Anderson (University of Melbourne) for statisticaladvice.

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Ovarian follicular wave characteristics in alpacasIntroductionMaterials and methodsAnimalsOvarian ultrasonographyStatistical analyses

ResultsRelationship between diameter of the largest follicle and number of follicles detectedOvarian follicular waves in individual alpacasMean inter-wave interval and follicular diameterPrediction of optimum mating time

DiscussionAcknowledgementsReferences