Pathways of the dominant follicle after exposure to sub-luteal circulating progesterone concentrations are different in lactating dairy cows versus non-lactating heifers

Ovarian luteal category at the time of exogenous progesterone treatment alters pre-ovulatory follicle size and pregnancy outcome but not initial GnRH treatment in repeat-breeder crossbred dairy heifers submitted to the 7-day fixed-time AI protocol

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Ovarian and fertility outcomes were similar for repeat-breeder crossbred dairy heifers with or without initial GnRH treatment.

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Presence of luteal tissue at the time of progesterone (P4) treatment in infertile heifers resulted in a 68.6% pregnancy rate (PR).

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The likelihood of PR was higher in infertile heifers bearing luteal tissue on the day of exogenous P4 trigger.

Repeat breeding is a substantial problem in heifer and cow breeding leading to greater infertility for female dairy herds. The aim of present study was to investigate the impact of corpus luteum (CL) presence and category and the first gonadotropin-releasing hormone (GnRH) administration concurrent with exogenous progesterone (P4) treatment on the largest follicle (LF) size and pregnancy rate (PR) in repeat-breeder crossbred dairy heifers submitted to the fixed-time artificial insemination (AI) protocol. Heifers (n= 243) were synchronised with (+GnRH) or without (–GnRH) first GnRH in the 7-day P4-GnRH-prostaglandin F2α-based programme. Each GnRH group was divided on presence of CL into two groups (+CL and –CL) in a 2 × 2 factorial arrangement. The PR was similar among –GnRH–CL (20.7%), –GnRH+CL (68.8%), +GnRH–CL (30.4%), and +GnRH+CL (68.3%) groups. However, presence of CL in heifers produced a 43.6% increase in PR compared to PR of heifers without CL (odds ratio = 6.550). Heifers bearing large-sized CL had greater large-sized LF on the day of fixed-time AI and PR. Plasma P4 concentration was positively related with CL diameter (r= 0.845; p < 0.001). The diameter of ovarian LF on the day of fixed-time AI was positively associated with P4 concentrations (r= 0.512; p < 0.001). We highlight that ovarian CL presence and category at the time of exogenous P4 treatment alters pre-ovulatory follicle size and PR but not initial GnRH treatment in repeat-breeder crossbred dairy heifers submitted to service with the 7-day fixed-time AI programme.

Circulating progesterone concentrations and preovulatory follicle diameters affecting ovulatory response in crossbred dairy heifers, following a 7-day progesterone-based synchronization protocol

The present study was aimed at evaluating the differences of ovarian follicular dynamics and circulating progesterone (P4) concentrations between crossbred Holstein heifers that ovulated and did not ovulate after a P4-based synchronization protocol. Twenty-one crossbred (Holstein × Thai native) heifers with random stages of the oestrous cycle were subjected to the ovulation synchronization protocol, using an intravaginal P4-releasing device (Eazi-Breed CIDR®) for 7 days. Out of 21 CIDR-treated heifers, 14 ovulating heifers were classified as the ovulatory group and 7 non-ovulating heifers were considered the anovulatory group. The heifers having new wave emergence in ovulatory and anovulatory groups were 11/14 (78.6%) and 4/7 (57.1%), respectively. In ovulating heifers, the mean (± SEM) diameter of preovulatory follicle (PF, mm) was significantly larger, compared to non-ovulating heifers (7.21 ± 0.32 versus 4.04 ± 0.44; P = 0.001), while the mean (± SEM) follicular growth rates (mm/d) in non-ovulating heifers tended to be lower, compared to ovulating heifers (0.73 ± 0.17 versus 1.06 ± 0.08; P = 0.07). The mean (± SEM) circulating P4 concentration (ng/ml) throughout the CIDR protocol (0-10 days) in non-ovulating heifers was significantly higher, in comparison with ovulating heifers (2.82 ± 0.27 versus 1.83 ± 0.16; P = 0.02). However, no significant difference in the mean corpus luteum volume between groups was observed. In conclusion, the present results suggested that elevated circulating P4 concentrations and smaller PF diameters could cause ovulation failure in crossbred Holstein heifers, following a 7-day CIDR-based synchronization protocol.

Design and evaluation of a recyclable intravaginal device made of ethylene vinyl acetate copolymer for bovine estrus synchronization

In bovine estrus synchronization, intravaginal devices made of silicone are used to administer exogenous progesterone with the aim of maintain plasmatic levels above 2 ng ml^-1 during the treatment. After their use, devices must be discarded. There is an important concern on the environmental impact of the disposal of these used products due mainly to the non-degradability of the silicone and to the residual content of the hormone. Different alternatives are being studied, and the use of ecological materials appears as the more important. The objective of the present contribution was to design and evaluate a recyclable intravaginal prototype using ethylene vinyl acetate copolymer (EVA). Devices were fabricated by an injection-molding technique and characterized in terms of dimensions, loading efficiency, release rate, and wing tension. An analysis was first conducted to compare three different matrices and two supports. Secondly, the best candidate prototype was assayed in both beef and dairy cattle. Finally, used matrices were recycled measuring the progesterone content in the resulting devices and testing them in vitro. According to release tests, no differences were observed between the three matrices both in vitro and in vivo. On the contrary, a better performance was achieved when a support with a more flexible Y shape was used in comparison with a rigid T geometry. Successful results were observed in non-lactating cows, with plasma concentrations above the threshold value defined for the synchronization therapy. However, lower progesterone levels resulted when devices were tested in animals with large milk production. By last, recycled matrices presented a similar initial content and in vitro release rate than original matrices. These findings could open the possibility to use recyclable EVA devices as an alternative to the non-degradable silicone intravaginal inserts. Future research must be carried out to optimize the performance of the recycled matrices in dairy cattle. Modifications of the release surface and/or the initial loading can give a solution to the lower values observed in these animals. Graphical abstract.

Role of certain growth factors and hormones in folliculogenesis

Folliculogenesis is an inextricable process associated with female fertility and infertility cases. This process involves many events at cellular and molecular level in a highly orchestrated fashion which culminates with ovulation. Various factors like hormonal factors, growth factors, role of ovarian micro environment, diseases of reproductive tract etc. influence the process of folliculogenesis in systematic manner. The function and mechano-biology of these growth factors and hormones have been studied by many researchers. This review discusses about those hormonal and growth factors which are involved in folliculogenesis process.