Christy
UKC Forum Member
Registered: Jun 2003
Location: Sylva, North Carolina (the far Western Tip of the State)
Posts: 10272 |
quote:
Originally posted by Jack Bingham
how do you know that maybe the stud has very low semen count. the stud is also 8-9 yrs old the female is 3.
THERE IS MORE THAT GOES INTO CONCIEVING A LITTER THAN THE SIRE'S SEMEN. FOUND THIS INFO ON A WEBSITE.
Litter Size in Dogs
Ultimately, many variables work collectively to determine litter size. Understandably we expect the dam to exert an influence, and it’s commonly thought that the sire, too, can impact litter size. Perhaps not so recognized is the impact the embryos themselves can make. Breeding management plays several roles in the number of offspring we can expect. And it’s not too hard to accept that genetics, environment and nutrition all have a part to play as well.
Dam
Now if we start with the dam, we can identify specific factors that will bear on litter size. Every litter starts with the estrous cycle. Within each cycle are four distinct stages which must work in harmony for optimal breeding results. The first stage, proestrus, is the initial signs that the female is coming in heat including the enlarging vulva and the bloody discharge. What we can’t see are the pheromones that the bitch is secreting to attract the attention of suitors, but we generally can observe the results. When she gets to the point where she will accept mating, she has transitioned into estrus, the second phase of the complete cycle. She is ovulating, and the number of viable ova available for fertilization is obviously going to exert a very strong influence on the final litter size. We may well have fewer puppies born than ova that were ovulated, but we will never have more pups that ova. Additionally, it is possible for the bitch to exhibit every sign of a fertile cycle, without actually ovulating. Unfortunately, unless we specifically look for evidence of ovulation using hormone assays or other diagnostics, we have no way of knowing whether or not ovulation occurred. When the bitch loses interest in accepting the male, she is beginning the diestrus phase. During this time the uterus, the mammary tissue, and dam’s metabolism is preparing for pregnancy, whether or not she is actually pregnant. During this phase the follicular cells on the ovaries are secreting progesterone to maintain a pregnancy. This stage will persist for about 60 days. Finally, her body shifts into the final stage of her estrous cycle, which is anestrus. It is commonly thought that this is a sexually quiescent time, with nothing in particular happening. Actually, it is a tremendously important phase when the uterus returns to a normal, non-pregnant state. We know that this phase requires at least 90 days for that repair and rejuvenation to reach completion. If the bitch we want to breed is cycling too frequently, her uterus may not be prepared to accept embryos, and the embryos die. It can appear that she was not successfully bred for whatever reason, when in fact she got pregnant, but early embryonic death (EED) occurred.
The age of the bitch can also affect litter size. Not surprisingly, very young and very old dogs produce smaller litters. The age of the bitch when she has her first litter induces an impact. When a bitch is 4 years old or older when she has her first litter, her litters will be smaller than a younger dog. With subsequent litters we see an overall decrease in litter size after 5 years of age in the majority of breeds. We expect the first litter for any bitch to be smaller. Litter size will increase with each litter generally through the third, sometimes the fourth litter. Then the number of pups decreases steadily.
Another factor the bitch owns is her breed. As one would expect, smaller breeds tend to have smaller litters, and vice versa. An important point however, is the breeder’s expectation. Often times the assumed average litter size is based on nothing more than conjecture and possibly the reports of other breeders. The problem with that is the population involved is too small to really reflect a true average value.
AKC performed a three year study involving 15 breeds, in order to gather data on litter sizes, ages of dam, number of litters, etc. A total of 728,271 litters were included in this time period. The representative data gathered is truly reflective of the breeds involved. Just to illustrate the information on some of the breeds, we’ll look at 2 breeds from each large, midsize and small breed dogs. Labrador Retrievers had a typical range of 5 to 10 puppies, with 7.6 average puppies, looking at over 85,000 litters. German Shepherds were evaluated with just over 44,500 litters, showing a normal range of 4 to 9 pups, and an overall average number of 6.6. In the American Cocker Spaniel breed, 39,000 litters provided data showing an average litter size of 5, with a normal range of 3 to 7 pups. Shetland sheepdogs produced over 28,400 litters in this 3 yr period, revealing a typical litter size ranging from 2 to 6 pups, and the average litter size was 4.3. Yorkshire terriers were represented by just over 53,000 litters, ranging from 2 to 5 puppies per litter with an average of 3.3. Chihuahuas had identical results based on 55,500 litters. The point being that if one expects a German Shepherd to consistently produce 8 pups with each litter, thinking that an "average litter size", he might conclude that she is not performing up to her potential if she’s producing 4, 5 or 6 pups, which is well within the normal range for that breed. Likewise, while Chihuahuas and Yorkies have a typical range of 2 to 5 pups, 80% of all litters are 4 pups or less.
We’ll leave the main issues involving the dam with the concluding thoughts that her health, reproductively, and in general, will act upon her ability to produce puppies.
Sire
So does the sire sway the litter size? Our usual method of evaluating the efficacy of a potential sire is by determining semen quality. The parameters by which that quality is judged are sperm concentration, morphology and motility. Normally, the concentration of sperm will be around 10 million sperm per pound body weight. We want to see 80% normal morphology at least. Motility needs to be not only movement, but effective movement linearly and with speed. Ideally 75 to 80% of the sperm on the slide will be traveling quickly in a linear manner. Not surprisingly, age does affect semen quality. Like the decreasing production seen in bitches as they age past 5, males will also show a decrease in semen quality as they get to be 6 or so. The assumption of semen quality impacting litter size is not really pertinent. Rather, it is the ability of a male to get a female pregnant at all. What we see when semen quality decreases, is fewer pregnancies resulting when breeding the male in question. In a young healthy male with good semen quality, we can expect 9, or even 10, out of 10 breedings to result in pregnancy (assuming breeding timing is appropriate). With lower semen quality, we may only see 3 or 4 pregnancies from 10 matings. So basically, if the semen has enough sperm to get one ovum fertilized, there is enough to get the other ova fertilized, again assuming the timing of the breeding is optimal.
Embryo
It can be difficult, if not impossible, to fully appreciate the differences between the number of fertilized eggs, developing embryos, and the fetuses that survive to birth. Early embryonic death claims a significant number of the "litter", with infectious diseases being the most common factor. If the embryo has a developmental defect, it may result in death and resorption. Developmental defects may result from genetics, trauma, exposure to drugs or vaccines, or infectious agents. Occasionally an embryo will inherit defective genes from both parents that kills it. In these ways, the embryo itself can affect the number pups delivered.
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01-19-2010 03:00 AM
