One + One Shouldn't = One
Owing to their tropical origin, Pygmy goats are historically a prolific breed with an average litter size of two or three kids. Some does have more, and a few have even produced six healthy kids at a time.
When only one kid is born, it is usually a large one. If you have trouble with large singles, there are a number of things you can do to try to improve litter size. Most pregnancies should produce more than one kid.
A number of factors affect birth size and weight. Litter size, fetal gender, the dam's age, and genetics can all contribute to large kids that are difficult to deliver.
The Pygmy doe often cycles all year long in much of the United States. Declining
day length, called photoperiod, causes a surge in reproductive hormones and
sexual activity in both bucks and does as autumn approaches. Sexual urge
remains high for at least several months, and fertility is at its highest
level at this time.
Terminology and Definitions
Fetal oversize, absolute
Fetal oversize, relative
fetus too large for pelvis
dam's pelvis too small to deliver normal-sized fetus
either absolute or relative fetal oversize
feed more generously 2-3 weeks before breeding
the ovary's egg-containing structure which produces estrogen and other hormones
first birth, thereafter called a cow
rupture of eggs from the follicle at the end of the estrus cycle
the number of eggs shed in each estrus
Even though there are millions of sperm in each ejaculate, the buck is only rarely responsible for the conception. Many factors in the doe determine how many embryos are conceived, and much depends on her ovulation rate. This is influenced by different things. Ovulation rate increases until maturity and remains at that level for a few years until it begins to decline. Within the breeding season, it is higher early in the fall and winter and declines in the spring and summer. A reproductive life of 4-8 years doesn't leave the Pygmy doe much room for errors, if you want her to be as fertile as possible.
The high ovulation rate of the Booroola Merino ewe is due to the action of a single gene. The ovulation rate in Romanov ewes is controlled by many genes. These breed differences probably normally occur in most litter-bearing livestock species, like sheep, goats and swine. The twinning rate in sheep can be increased by 2% per generation by keeping ewes that produce larger litters, and I believe that the same prolificacy traits can be improved in goats. There is a positive association between ovulation rate and follicle stimulating hormone in blood plasma around the time of ovulation in very prolific breeds. This is a trait we may unwittingly be selecting for by keeping highly fertile does.
Both young and aged does have lower ovulation rates, as do fat or thin does. Deworming helps improve general condition before breeding. Flushing (see terminology) can be used to increase the ovulation rate of thin does. Does in poor condition respond to flushing early and late in the season, but not during mid-season. Does in already good body condition do not respond to flushing. However, if does are fat, helping them lose weight before breeding can increase the ovulation rate.
The doe generally has a lower conception rate during the spring and summer. Heat stress is caused by temperatures over 90o, especially when combined with high humidity, increased activity, and/or excess body fat. (See Breaching the Heat Stress Comfort Zone for a heat index chart.)
Does cycle more strongly in the presence or odor of a buck. This is called "the buck effect," and it may be helpful for owners who do not have a buck. If you do not want a buck on your property and intend to take your doe(s) out for breeding, you can still take advantage of the buck effect. Vigorously rub the smelliest parts of a buck with an old rag, and keep it inside a closed container. A few weeks before you wish to breed the doe, offer her the buck rag daily. She will show stronger signs of heat and let you know when she is ready for breeding.
The doe's estrus signs are due to a rise in estrogen produced by ovarian follicles. One ovum is released from each follicle. Each ovary may have multiple follicles ready to ovulate. In theory, more estrogen from multiple follicles result in stronger heats with more obvious signs. If this is true, a larger litter might be expected from breeding on very strong estrus cycles.
Other causes of low fertility are: high estrogen content in forages (alfalfa and subterranean clovers), internal parasitism, reproductive and other diseases, reproductive tract infections, and stress that alters hormone interactions.
Fertilization Failures and Embryonic Mortality
Good heat detection and timing of breeding are vital for good conception rates. Deficiency in the trace minerals copper, iodine, magnesium and selenium are reported to interfere with conception, in addition to protein and energy deficiencies.
The buck can be at fault if he has been used to excess, if heat stress renders him temporarily sterile, or if he is severely deficient in certain trace minerals. Temporary sterility from over-use and hot weather and high body temperature (illness) usually resolves within six weeks after the episode. It takes that long for new sperm to develop.
Embryonic mortality is responsible for many gestation failures. In general, ruminants normally lose from 25% to 40% of all embryos by 16 days after breeding. Possible causes include: inbreeding, aging, incompatible blood types, chromosome abnormalities, nutritional deficiencies, under- and overfeeding, high environmental temperatures, endocrine factors and multiple pregnancy. Losses like these are hard to recognize, as the doe either recycles or carries fewer embryos to term. Maintaining the same diet for one month after breeding may decrease some embryonic loss.
Abnormal development and reduced viability of the sperm or ovum increase with age. The older doe has a higher incidence of embryonic mortality due to poor egg quality and a less responsive uterus. Breeding every 12 hours to ensure good quality of the sperm and ova may maximize conception rates. An older buck may benefit from a breeding soundness examination if he has trouble settling does.
There are two different types of fetal oversize. In absolute oversize, the mother's birth canal is large enough to pass a normal-sized fetus, but the fetus is too large. The large fetus may have trouble starting into or negotiating passage through a normal-sized pelvis. A fetus that is not excessively large can sometimes be assisted vaginally. In relative oversize, the pelvis is too small for even a normal-sized fetus. Some issues overlap in both types of feto-pelvic relationships.
The major cause of calf death is due to fetopelvic disproportion. This is is largely a hereditary problem. 85% of all cattle dystocias occur in heifers - 66% due to a large calf and 15% to a small pelvis). Fetopelvic disproportion is the most common dystocia in sheep, especially caused by male fetuses. Ram lambs are 5% heavier than ewe lambs, and singles weigh 16% more than twins.)
A small or structurally abnormal pelvis or birth canal can cause repeated dystocia. It is never worth trying to improve this trait in offspring. Do not breed a doe with this problem, and do not sell her to anyone else.
Some sires cause high dystocia rates in females bred to them. A particular sire may produce abnormally large or overly-developed kids. He can also pass his own poor pelvic structure to his sons and daughters.
Select both parents based on their own and their parents' good obstetric traits. Breed large-for-age females with ample pelvic area. Select sires for their history of birthing ease, including: small to average sized offspring that grow into normal-sized adults, normal gestation length, and sires who have produced daughters that deliver easily. Do not keep smaller and smaller breeding stock in an attempt to decrease fetal size - this is a good way to breed fetopelvic disproportion into your herd, especially when they are outcrossed. If you don't know when to breed a Pygmy doe for the first time, wait until she is 18 months old or 75% of her expected mature size, whichever occurs first.
One study of the West African Dwarf Goat (WAD) showed that a small pelvis, especially in young does, and abnormal fetal postures were major causes of dystocia, and that either problem could occur in any pregnancy. Radiography was used to reveal the cause of fetopelvic disproportion (absolute or relative oversize) to determine a course of action. Pelvic bones do not change size after maturity. Fetal size, fat deposits and cervical dilation failure (hormones) can be problems that occur in adult does that have previously delivered without problems.
Overfeeding and lack of exercise lead to dystocia. Single-bearing ewes overfed in the last weeks of gestation increase birth weight of the fetus by 2.2# compared to ewes who were not overfed.
Underfeeding the young doe or breeding her too young can retard her skeletal development. This can result in reduced litter size and weak or dead newborns.
High levels of grain are unnecessary in the first 70 days or after 120 days due to fetal growth rates in the WAD, and probably other goat breeds. Malnutrition between days 61-120 is not reversed in later gestation and results in weak newborns, but a diet of good forage with a little grain does not significantly affect the body weight and health of the kids. A high concentrate diet in the last trimester leads to obstetric problems. (See A Study of Feeding During Pregnancy.)
When a certain type of dystocia seems to be fairly prevalent in particular family line or a breed, it is probably due to genetic factors. Several generations of inbreeding increases dystocia. The sire can affect gestation length resulting in a heavier fetus. Muscular hypertrophy (excess muscle development of the fetus) is a single-gene trait, but it is not known if it is a dominant or recessive gene. This has has been reported in Pygmy goats.
Heredity and diet can be big factors in fertility and dystocia. I cannot be emphasized strongly enough that if you keep does and/or bucks with poor reproductive traits, you will build a herd full of poor reproductive traits. Each breeder must learn feed appropriately and recognize and eliminate inferior traits for the welfare of future generations, if our breed is to meet the promise of its full reproductive potential.
Heat Detection for Hand Breeding
The Ins and Outs of Body Condition
Body Condition Scoring for Pygmy Goats
Causes of Dystocia (chart)
Pelvic Structure and Capacity in Pygmy Goats
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