Abstract
In this study, the second use of an intravaginal progesterone-releasing device or controlled intravaginal drug release device (CIDR) was evaluated. After a first use of 11 days, the CIDR was again used for either nine or 12 days with 200 or 300 IU equine chorionic gonadotrophin (eCG) being injected on its removal. Sixty-four ewes were randomly distributed to four treatments (n=16/group): CIDR9+eCG200, CIDR9+eCG300, CIDR12+eCG200, and CIDR12+eCG300. The eCG was administered intramuscularly on withdrawal of the device. Thus, the experiment was a completely randomized design with a 2×2 factorial arrangement of treatments. Oestrus presentation did not differ between treatments (P =0.29). However, with the dose of 200 IU of eCG, oestrus presentation tended to increase (P =0.08). The onset and duration of oestrus, percentage of gestation, and return to oestrus did not differ between treatments (P >0.05). Progesterone concentration in serum was greater (P < 0.05) in ewes treated with CIDR12+eCG300. Prolificacy was greatest (1.44) with the CIDR12+eCG300 treatment and was different (P = 0.001) from the treatments CIDR9+eCG200 (1.21) and CIDR9+eCG300 (1.20), but not from the CIDR12+eCG200 treated ewes (1.31). The CIDR12+eCG300 treatement produced the highest percentage of twin births (45.8%) (P =0.001). Leaving the device in place for 12 days increased (P =0.001) the incidence of twin births. Use of the CIDR for a second time synchronized oestrus in ewes successfully with better fertility being obtained when the device was left in place for 12 days, and 300 IU of eCG was injected on its removal.
 Key words: gonadotropin, progesterone device, synchronization
Highlights
Oestrous synchronization has been used for a long time
The high percentage of ewes that showed oestrus behaviour (95.31%) in response to the reused controlled intravaginal drug release device (CIDR) suggests that in the second use CIDRs still contain enough P4 to cause LH blockage and allow the brain to respond to concentrations of circulating oestradiol, so that oestrous behaviour can be induced in the female (Swelum et al, 2018b)
Previous studies have shown that when associated with equine chorionic gonadotrophin (eCG) and a luteolytic agent, use for the third time in short protocols is viable for the synchronization and induction of oestrus and ovulation in ewes without affecting the percentages of oestrus presentation (Pinna et al, 2012; Bazzan et al, 2013; Vilariño et al, 2013; Da Silva et al, 2014) since the eCG favours follicular growth and the consequent production of oestradiol (Murphy, 2012)
Summary
Oestrous synchronization has been used for a long time. with the increase in knowledge of the dynamics of follicular development (Ginther et al, 1995), experiments have been focused on concentrating the oestrus period to a shorter time if artificial insemination is desired. Reproductive seasonality in sheep is a limiting factor to achieving the goal of three parturitions in two years (Rosa et al, 2003) To overcome this limitation various reproductive strategies have been studied. These include treatments with exogenous hormones and their synthetic analogues, melatonin implants either separately or in combination (Abecia et al, 2011). These treatments induce and synchronize ovulation and oestrus in the reproductive period or during the periods of reproductive transition and anoestrus with varying degrees of success (Abecia et al, 2012; Laven, 2019)
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