Fecal progestin concentrations as an indicator of reproductive success in American Mink

Effects of dietary vitamin E supplementation on the reproductive performance of yearling female mink (Neovison vison) fed wet fish-based feed

This study was conducted to investigate the effects of dietary vitamin E (VE) supplementation on the reproductive performance of female mink, preweaning growth performance of their kits, and antioxidative status and immune functions of dams and kits. Yearling mink dams (n = 180) were randomly assigned to five treatment groups (n = 36). The dietary treatments included a basal diet supplemented with VE at 0 (control), 80, 160, 320, or 640 mg/kg DM. Compared with the control, the addition of 160-320 mg/kg VE decreased (P = 0.0362) the percentage of pre-weaning mortality of mink kits. At weaning, the average body weight was greater (P = 0.0408) in kits fed 320 mg/kg supplemental VE. In mink dams, the addition of 80-320 mg/kg VE increased (P = 0.0125) serum SOD. Supplementation of 320 or 640 mg/kg VE decreased (P = 0.0260) serum reactive oxygen species (ROS). Furthermore, feeding a large dose of VE (640 mg/kg diet) resulted in increased (P = 0.0245) serum α-tocopherol. In mink kits, the addition of 320 or 640 mg/kg VE increased serum α-tocopherol (P = 0.0207) and IgG (P = 0.0464). Supplementation of 640 mg/kg VE decreased (P = 0.0471) serum ROS. The present results indicate that VE supplementation improved the antioxidative status of mink dams and enhanced the immune functions, decreased pre-weaning mortality and enhanced weaning weight of their kits. Taken together, the effective VE supplementation was 320 mg/kg of diet for yearling female mink.

The Reproductive Success of Farmed American Mink (Neovison Vison) – A Review

The aim of this review was to define the most important factors that affect the reproductive success of farmed mink. The biology of mink reproduction is unique when comparing it with other farmed fur animals. The article emphasizes the importance of optimal environmental conditions in prevention of reproductive disorders. The novel attempts to the mating schedule, optimal diet and body condition of dams, kits transfer between dams, these are only examples of advantageous procedures used in mink farming to increase the effectiveness of reproduction.

Glycogen metabolism in mink uterine epithelial cells and its regulation by estradiol, progesterone and insulin

Glycogen content in mink uterine glandular and luminal epithelia (GE and LE) is maximal during estrus and is depleted before implantation while embryos are in diapause. Uterine glycogen synthesis in vivo is stimulated by estradiol (E₂) while its mobilization is induced by progesterone (P₄). Nevertheless, treatment of an immortalized mink uterine epithelial cell line (GMMe) with E₂ did not affect glycogen production. Interestingly, insulin alone significantly increased synthesis of the nutrient and glycogen content in response to insulin + E₂ was greater than for insulin alone. Our objectives were to determine: 1) If insulin receptor protein (INSR) is expressed by mink uterine GE and LE in vivo and if the amount differs between estrus, diapause and pregnancy; 2) if E₂, P₄ or insulin regulate insulin receptor gene (Insr) expression by GMMe cells, and 3) if E₂ and P₄ act independently to regulate glycogen metabolism by GMMe cells and/or if their effects are mediated in part through the actions of insulin. The mean (±S.E.) percent INSR content of uterine epithelia was greatest during diapause (GE: 15.65 ± 0.06, LE:16.56 ± 1.25), much less during pregnancy (GE: 2.53 ± 0.60, LE:2.25 ± 0.32) and barely detectable in estrus (GE: 0.03 ± 0.01, LE:0.02 ± 0.01). Glycogen concentrations in GMMe cells increased 10-fold in response to insulin and 20-fold with insulin + E₂ when compared to controls. Expression of Insr was increased 2-fold by insulin and insulin + E₂ when compared to controls and there was no difference between the two hormone treatments, indicating that E₂ does not increase Insr expression in insulin-treated cells. To simulate E₂-priming, cells were treated with Insulin + E₂ for 24 h, followed by the same hormones + P₄ for the second 24 h (Insulin + E₂ → P₄) which resulted in Insr and glycogen levels not different from controls. Similarly, cells treated with Insulin + P₄ resulted in glycogen concentrations not different from controls. We conclude that the glycogenic actions of E₂ on GMMe cells are due to increased responsiveness of the cells to insulin, but not as a result of up-regulation of the insulin receptor. Glycogen mobilization in response to P₄ was the result of decreased glycogenesis and increased glycogenolysis occurring concomitantly with reduced Insr expression. Mink uterine glycogen metabolism appears to be regulated in a reproductive cycle-dependent manner in part as a result of the actions of E₂ and P₄ on cellular responsiveness to insulin.

Opportunities and challenges associated with fecal progesterone metabolite analysis

Conventionally, plasma or milk progesterone evaluations are used to determine the reproductive status of female animals. Collection of such samples is often associated with difficulties of animal handling and restraint. Measurable quantities of progesterone metabolites are found in feces of animals. Their concentrations are known to be well correlated to plasma progesterone levels and are, therefore, used as non-invasive samples for assessing reproductive function in a wide range of animal species. Although the analysis of fecal progesterone metabolites has been widely accepted in many laboratories, several factors are known to affect the results from this valuable analytical technique. Some of these factors include storage/transportation media for fecal samples, type of solvent that is used for extraction of progesterone metabolites from feces, and the type and sensitivity of an assaying technique employed. Although fecal progesterone metabolites analysis is associated with some difficulties, it can effectively be used to monitor reproductive function in a wide range of animal species. This review aims to highlight the usefulness of fecal progesterone metabolite analysis as a non-invasive technique in monitoring reproductive function in animals. The article mainly focuses on the many opportunities and challenges associated with this analytical technique.

Estradiol stimulates glycogen synthesis whereas progesterone promotes glycogen catabolism in the uterus of the American mink (Neovison vison)

Glycogen synthesis by mink uterine glandular and luminal epithelia (GE and LE) is stimulated by estradiol (E2 ) during estrus. Subsequently, the glycogen deposits are mobilized to near completion to meet the energy requirements of pre-embryonic development and implantation by as yet undetermined mechanisms. We hypothesized that progesterone (P4 ) was responsible for catabolism of uterine glycogen reserves as one of its actions to ensure reproductive success. Mink were treated with E2 , P4 or vehicle (controls) for 3 days and uteri collected 24 h (E2 , P4 and vehicle) and 96 h (E2 ) later. To evaluate E2 priming, mink were treated with E2 for 3 days, then P4 for an additional 3 days (E2 →P4 ) and uteri collected 24 h later. Percent glycogen content of uterine epithelia was greater at E2 + 96 h (GE = 5.71 ± 0.55; LE = 11.54 ± 2.32) than E2 +24 h (GE = 3.63 ± 0.71; LE = 2.82 ± 1.03), and both were higher than controls (GE = 0.27 ± 0.15; LE = 0.54 ± 0.30; P < 0.05). Treatment as E2 →P4 reduced glycogen content (GE = 0.61 ± 0.16; LE = 0.51 ± 0.13), to levels not different from controls, while concomitantly increasing catabolic enzyme (glycogen phosphorylase m and glucose-6-phosphatase) gene expression and amount of phospho-glycogen synthase protein (inactive) in uterine homogenates. Interestingly, E2 →P4 increased glycogen synthase 1 messenger RNA (mRNA) and hexokinase 1mRNA and protein. Our findings suggest to us that while E2 promotes glycogen accumulation by the mink uterus during estrus and pregnancy, it is P4 that induces uterine glycogen catabolism, releasing the glucose that is essential to support pre-embryonic survival and implantation.