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      New treatments associated with timed artificial insemination in small ruminants

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      Reproduction, Fertility and Development
      CSIRO Publishing

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          Abstract

          Timed artificial insemination (TAI) is a very important tool in production systems, as it has a direct impact on cost-efficiency by reducing labour resulting from oestrus detection. However, to make TAI commercially feasible, hormonal treatments need to assure acceptable pregnancy rates and be economically viable. Recent advances in the knowledge of ovarian physiology (e.g. determination of follicular waves, sensitivity of the early corpus luteum) in small ruminants allowed the development of new treatments focused on an efficient estimation and synchronisation of the time of ovulation of the females of a treated flock/herd. In this review we summarise new information and concepts in the hormonal control of the life span of the corpus luteum, as well as methods to manipulate follicular growth in small ruminants. Additionally, we elaborate on recent studies concerning the use of TAI associated with short progestogen treatment in goats and the newly developed Synchrovine™ protocol (two doses of prostaglandin F2α given seven days apart) in sheep.

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          Most cited references59

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          Effects of induction of low plasma progesterone concentrations with a progesterone-releasing intravaginal device on follicular turnover and fertility in cattle.

          The effects of concentration of progesterone in plasma on development and fertility of the first wave dominant follicle were studied in cattle. To identify a source of exogenous progesterone that would permit extension of the first wave dominant follicle, nonlactating Holstein cows (n = 6) received on day 8 of two successive oestrous cycles an injection of PGF2 alpha (25 mg) and a new (1.9 g of progesterone (Period 1)) or used (approximately 1.2 g of progesterone (Period 2)) CIDR-B device that was removed on day 17. Control cows (n = 6) received a new CIDR-B device on day 8 that was removed on day 17 and a PGF2 alpha injection (25 mg) on day 17. Ultrasonography and collection of blood samples were performed on alternate days throughout the experiment. Plasma concentrations of progesterone and oestradiol were different between treatments (P < 0.0001 and P < 0.05, respectively). The dominant follicle was maintained until day 17 and ovulated upon removal of the intravaginal device in 1 of 6, 6 of 6 and 0 of 6 in new CIDR-B, used CIDR-B and control groups, respectively (P < 0.01). The preovulatory dominant follicles were 14.2 +/- 1.6 mm, 20 +/- 1.3 mm and 10 +/- 1.3 mm, respectively (P < 0.001) on day 17. There were fewer 5-9 mm follicles in cows having a persistent dominant follicle (P < 0.01). The interval to onset of oestrus was negatively correlated with size of the dominant follicle on day 17 (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
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            Pulsatile secretion of luteinizing hormone: differential suppression by ovarian steroids.

            In sheep, physiological levels of estradiol and progesterone each suppress the pulses of LH characteristics of tonic LH secretion, but do so by completely different mechanisms. Estradiol treatment decreases LH pulse amplitude but not frequency and also inhibits the height of the LH peak resulting from the administration of gonadotropin-releasing hormone (GnRH). In contrast, progesterone decreases the frequency of LH pulses without reducing their amplitude or the response to exogenous GnRH. This suggests that progesterone suppresses tonic LH secretion by acting in the brain to decrease the frequency of GnRH pulses, while estradiol may suppress the response of the pituitary to GnRH and thereby decrease LH pulse amplitude.
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              Ovarian follicular dominance in cattle: relationship between prolonged growth of the ovulatory follicle and endocrine parameters.

              In cattle, the development of ovarian follicles 5 mm or larger occurs in either two or three consecutive follicular waves per estrous cycle. When the luteal phase is artificially lengthened with an intravaginal progesterone-releasing device (CIDR) that maintains subluteal levels (i.e. levels of progesterone that are below normal luteal levels, but higher than basal follicular phase levels), prolonged development of the ovulatory follicle is observed. To study the endocrinological correlates of prolonged follicular dominance and to test the hypothesis that it is mediated by effects of plasma progesterone on LH pulse frequency, heifers (n = 6/group) were treated with blank CIDRs (no progesterone, control group), with one CIDR for 14 days from day 14 of the cycle (1 CIDR group), or with one CIDR for 14 days from day 14 plus a second CIDR during days 24-28 (2 CIDR group). Cycle length was significantly longer in the 1 and 2 CIDR groups than in the controls (30.2 +/- 0.2 and 31.8 +/- 0.5 vs. 21.6 +/- 0.4 days, respectively; P < 0.0001). Follicular dynamics were normal in the control heifers. In the 1 CIDR group, the ovulatory follicle grew larger than in control or 2 CIDR animals, was maintained as the largest follicle on the ovaries for a much longer time, and ovulated after CIDR removal. In the 2 CIDR group, a similar growth pattern was observed until day 24; after insertion of a second CIDR, however, prolonged dominance was reversed, a new wave was recruited, and the dominant follicle of this wave ovulated after CIDR removal. The size of the ovulatory follicle and the length of the dominance phase in the 2 CIDR group were similar to those in control animals. Reversal of prolonged dominance in the 2 CIDR group was associated with changes in progesterone. Progesterone remained at subluteal levels (1.5-2.3 ng/ml) in both CIDR groups until day 24, when insertion of the second CIDR in the 2 CIDR group restored progesterone concentrations to normal luteal levels (3.5-6 ng/ml). Pulsatile LH secretion was assessed by frequent blood sampling every 12 min for 6 h (0800-1400 h) on selected days of the treatment cycle. LH pulse frequency was not different among groups before treatment started (days 12 and 13). However, LH pulse frequency was significantly higher in the 1 CIDR than in the 2 CIDR group on both day 26 (P < 0.03) and day 28 (P < 0.05), i.e. during the reversal of prolonged dominance in the 2 CIDR group.(ABSTRACT TRUNCATED AT 400 WORDS)
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                Author and article information

                Journal
                Reproduction, Fertility and Development
                Reprod. Fertil. Dev.
                CSIRO Publishing
                1031-3613
                2004
                2004
                : 16
                : 4
                : 403
                Article
                10.1071/RD04037
                15315739
                3be8a086-6fb4-46de-a636-e73341761889
                © 2004
                History

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