Background of action plan for mating


This section describes the theoretical background, knowledge and experiences which form the basis of the suggestions and recommendations to the mating of mink. It comprises mating conditions, mating, late implantation as well as feeding and care of the mink. The special reproduction conditions of mink are relatively well documented (Hansson, 1947; Enders, 1952; Venge, 1973), and the description below is based on these sources if nothing else is mentioned.


Mating season

Female mink are usually in heat at the end of February or the beginning of March. It has been somewhat uncertain whether the mating development of the mink is cyclic or permanent. Today the opinion is that there are mature follicles all the time and that the females remain in heat until mating (Elofson et al. , 1989; Lagerkvist, 1992). After mating the mating season of the females is over, until new follicles can mature after approx. 8 days. Today's theory on the course of the mating season of mink in relation to the time of and the number of matings is illustrated in the figure below.


Schematic illustration of the course of the mating season in female mink being mated 0, 1 or 2 times

Course of heat in females mated 1 og 2 times


The willingness to mate is gradually increasing through the month of March (Elofson et al., 1989). Matings are therefore started on March 6-7 where the majority of the females are in heat. If one starts at an earlier date there is a risk that not all females are willing to mate.

It has been proven that the faster the animals start to mate after they have been put together, the better the breeding result will be. Females beginning to mate within 10 minutes at a remating thus gave birth to 1,3 kits more than females that started after more than 20 minutes (Åhman, 1966).

In practice it will be seen that some females, strains or colour types are less willing to mate than others. The reason for these differences has not been clarified, but it is possible that there are individual and genetic differences in the start of the mating season of the individual females and in the strength of the mating season of females and strains. As the length of the day controls the annual cycle of mink, the light conditions in the building may affect the mating season (Møller, 1989). According to the above it should help on both late and weak mating season to postpone the mating attempts to later in the season. As the mating willingness and the breeding result depend on each other, it is wise not to force matings through if the female is not ready.


Mating

At mating the female is moved to the male's cage as the mating would otherwise be prolonged since the male would start by examining the female's cage (Madsen, 1984; Venge, 1973). If the female is in heat, the courtship begins and after some time the male bites on to the neck of the female, and the mating starts. A successful courtship and mating is often indicated by a characteristic rhythmic chuckling.

Play the chuckling of mating mink:             

The ejaculation takes place after approx. 2 minutes of mating, while it takes 5 minutes of mating to provoke an ovulation. Furthermore, mating for 10-15 minutes will activate the transport of the sperm in uterus and oviduct (Adams & Rietveld, 1981). At remating after 9 days, 5 minutes are enough to lose the follicles from the first mating while mating in 15 minutes provokes a new ovulation and the transport of sperm (Adams, 1981). Ovulation can take place without mating which is why handling and mating attempts should be as gentle as possible. The first ovulation in young females can be uncertain (Elofson et al., 1989), just as the sperm quality can be reduced at the first matings. It is therefore important that young females are remated at the next mating season 8-9 days after the first mating, so that they get a new ovulation. In first-year females the remating frequency is increased, the litter size increases, and the sterility percentage decreases when the first mating takes place early in the period, March 1-12 (Lagerkvist, 1992). In older females the breeding result was best (0,5 more live born kits per litter) with mating on two consecutive days late in the period, March 10-25 (Lagerkvist, 1992). There was not found differences in breeding result in similar experiments on 4 mink farms in Denmark (Falkenberg et al., 1989). As the number of mature follicles apparently is slightly increasing throughout the mating period (Elofson et al., 1989); Lagerkvist, 1992), all females should be mated for the last time after March 15. The frequency of successful rematings resulting in a new ovulation decreases by 6% for each day the first mating is postponed after March 7 (Lagerkvist, 1992). Therefore, females mated for the first time after March 15 can rarely be remated on the 8th or 9th day. These females are tried every second day and are remated the day after, whereupon they have finished mating, irrespective of the success of the remating. Remating on the following day gives fresh sperm to the fertilization. It should not be necessary, but can result in an extra 0,2-0,3 kits (Einarsson, 1988).

The duration of the matings can vary from a few minutes in the start to several hours later in the mating season. The duration is increased by approx. 4.2 minutes per day in the mating season (Elofson et al., 1989). It can therefore be necessary to separate the animals if the male is supposed to mate with more females on the same day. Generally, no first time mating should last less than 10 minutes and no remating should last less than 15 minutes, and the animals should therefore not be separated until they have mated long enough.

If the number of sterile males has been large earlier, there may be reason to check the sperm quality. This is done by interrupting the mating after 10-15 minutes, draw a little sperm out of the female's vagina and examine it in a microscope (Jørgensen, 1984). If the sperm cells are deformed, immobile or dead, the male should be discarded. It is a very demanding and complicated task to take usable sperm samples on a large scale basis. Ready-to-use sperm sample instruments with microscope, glasses, heating box etc. can be bought, and the instructions should be followed carefully.


Mating order

In practice, the order in which the females are mated is of no importance (Møller, 1992), and the easiest is just to mate randomly. Females that seem willing but are not mated can be tried the day after, while unwilling females is tried every third day. If the first mating attempt has provoked an ovulation even though the female was not mated, she will be "remated" at the fourth attempt after 9 days. Females mated in the first period is tried again on the 9th day (1+9), which provokes a new ovulation. If the remating is unsuccessful, she can be tried again on the 10th day and then she is finished. If the female is unwilling to remate and it is late in the period (around March 19), the mating season may be over. The advantage of "forcing" through a mating should therefore be weighed against the risk of losing fertilized follicles from the first mating. In practice remating is almost exclusively tried around day 9.


Mating system

The traditional mating system where attempts are made with all females to mate them to obtain two ovulations (1+9) has been thoroughly tested and documented. It is a little illogical not to remate the day after a remating on the 9th day (1+9+1), but this is omitted because of the work pressure and the capacity of the males. The alternative mating system (young females 1+9 with the first mating before March 15, and old females 1+1 after March 15) has given good results in experiments (Elofson et al., 1989; Lagerkvist, 1992) and is primarily used in Holland and Sweden. A Danish experiment showed no difference in breeding results (Falkenberg et al., 1989). There should be no time problem even though the mating of old females are not properly started until after the young females have finished mating around March 18. Thus old females mated 1+1 give birth 5-6 days later than females mated 1+9. On the other hand there are less mating attempts and less strain on the males (Falkenberg et al., 1989).


If there are animals with different gradings in the breeding group, the mating of these animals should be made at random, as mating of best-to-best can increase the inbreeding and gives a systematic error in the index calculation of the breeding programmes (Berg, 1994, Pers. Comm.).


Late implantation

The actual ovulation happens approx. two days after mating and fertilization takes place in the oviduct shortly after. The fertilized follicles divide 7-8 times in approx. 6 days and are then called blastocysts. These hibernate (diapause), until they take root in the uterus (implantation) around the turn of the month March-April (late implantation). After this there is approx. 30 days to whelping. (See figure of intervals from mating until whelping). At a very early mating (in February) it can take up to 40 days before the blastocysts take root. At an early mating where the implantation is postponed more than approx. 10 days, the risk of losing blastocysts increases by as much as 0.4-0.5 per female (Einarsson, 1988). It is difficult to calculate the precise effect of the length of the diapause as the implantation time of the individual female is not known, and the litter size affects the period of gestation (Lagerkvist, 1992).


Feeding and care

The females are fed ad libitum until they have finished mating. Often the appetite will culminate after about a week and gradually decrease to approx. 200 Kcal/animal/day equivalent to approx. 160-170 g feed. When the males have started the mating, they too are fed ad libitum, and just like the females their appetite will decrease at some time during the mating period. The animals should have plenty of straw so they do not get cold, but otherwise there is no time for special care in the mating period.


See also


Internet version 1.3 updated 12/6 1997 by Steen Møller SteenH.Moller@agrsci.dk