EFFECT OF BODY CONDITION AND DIETARY ENERGY SUPPLY ON REPRODUCTIVE PROCESSES IN THE FEMALE MINK (MUSTELA-VISON)

This paper reviews a series of experiments regarding the influence of body condition and dietary energy supply on reproductive processes in the female mink. The reporting is based on 1905 sets of reproductive performance data and on data regarding number of corpora lutea, implantation rate, plasma progesterone and oestradiol, luteinizing hormone (LH) release and ovulation rate, and the early development of the fertilized ova. Generally, treatment effects were more pronounced in yearling females than in adults; furthermore, adults responded less to varied energy supply by changes in body weight. A weight reduction of > 300 g during the winter resulted in poor reproductive performance in yearling females. A long-term study indicated better reproductive longevity for females on a low-intensity feeding regimen, whereas females on a high-intensity feeding regimen tended to have larger litters until 3 years of age. Nutritional flushing was carried out by a 2-week period of moderate energy restriction followed by feeding ad libitum from 3-5 days before initiation of matings until matings were completed for the individual females. Mainly in yearlings, but also in adults, litter sizes were improved for females with a first mating early in the breeding season, which was confirmed by an increased number of corpora lutea. The interval between the first recorded increase in plasma progesterone and the day of the peak progesterone concentration was decreased. Plasma oestradiol concentrations were higher in flush-fed females; age-dependent differences in the appearance of the profiles were also found. LH release tended to be more synchronized and distinct in flush-fed females. The early development of fertilized eggs was advanced, documented as a higher percentage of eggs reaching the four-cell stage or more within 3 days after mating. It was thus concluded that flushing induces changes in the concentrations of the reproductive hormones which in turn lead to a more synchronized and advanced embryonic development, resulting in increased litter sizes.