Although miniature horses are members of the equine family, the differences between them and their large cousins are many. As these wonderful creatures become more popular and prevalent we continue to learn about them and their unique characteristics. Veterinary research and owner familiarity are slowly but steadily contributing to our understanding of the miniature horse. This article will attempt to share some information on a few aspects of miniature horse reproduction and general health maintenance and highlight the unique differences of miniature horses. For the sake of brevity we’ll refer to standard sized horses simply as horses or mares. The space available is limited as is the scope of this article; we hope the reader will find it of some benefit. Also because the miniature is predisposed to particular problems we will concentrate on these medical questions. Don’t let this information frighten or discourage you, they are wonderful animals and most of these problems although more common in miniature horses, are rare.

Pregnancy and foaling
Because most of you have already bred your miniature mares this year, the specifics of breeding miniatures will be discussed in greater depth next Fall. Once pregnant, the length of a mini’s pregnancy (gestation) is shorter than the horse and averages 319 days. Pregnancy can be confirmed by rectal palpation, ultrasound ,or measurement of the hormone estrone sulfate in the blood. Because mini’s can be very small some veterinarians are uncomfortable with rectal palpation and may prefer to use the blood tests which are very accurate.

Predicting the delivery time or foaling in miniatures is more difficult than horses. Unlike mares, mini’s rarely have “waxed teats” (the accumulation of dried milk at the nipple openings). Daily observation of the udder is still helpful sometimes, and you can look for changes in their consistency or discharge. Any dramatic change, for example an udder softening, or becoming engorged and tight should alert you to watch the mare more closely the next day or two. Examination of milk calcium levels has been shown to be helpful in predicting the delivery in mares and may be useful in the mini too.

Abortion and problems of birthing
Although the majority of pregnancies are without complication, miniature mares do seem to have more problems with certain aspects of pregnancy. Horses experience the majority of pregnancy losses before day 40, mini’s lose their foals more frequently after the 40th day of pregnancy. Not many studies have been done on the subject, but one report showed a range for abortion between day 120-215 which as mentioned is not the time most foals are lost in mares.

Dystocia or difficult delivery, as might be expected, is much more common in mini’s than horses. Miniature horses have genes for large foals and occasionally dystocia occurs because a foal is too large for its mare. Although size mismatch is a common cause of dystocia in dogs, it is extremely rare in the mare. Often after a dystocia, miniature mares revert to the non cycling segment of their reproductive cycle and are commonly referred to as “in transition”. Transitional mares cannot become pregnant; perhaps this is a safety mechanism in the mini to effectively induce reproductive rest after a traumatic incident. Another possible consequence of dystocia in mini’s is a higher incidence of uterine and vaginal adhesions. These adhesions or scars are often the direct result of dystocia and serve to increase the potential for dystocias in the future because they often decrease the size of the birth canal..

Another complication of pregnancy in mini’s seems to be the increased incidence of premature placental separation and failure to “break water”. The placenta is the connection between the mares uterus and the fetus. It is responsible for supplying the fetus with nutrients and oxygen. During the birth process a foal usually doesn’t try to breathe until they are fully delivered. If the placenta is attached properly regardless of whether the foal breathes or not it is still getting oxygen from the placenta. The consequences of premature placental separation is that the foal is deprived of oxygen and can suffer brain damage in a very short time. The failure to break water is actually the placenta not opening at the proper time to allow delivery of the foal. The effects on the foal are unfortunately similar to premature separation.

Congenital abnormalities: type A vs. type B

Although many of the problems described above are more common in minis than horses type A miniatures are more prone to many of these abnormalities than type B. Miniatures are classified into 2 categories according to size; type A are less than 34 inches and type B are 34 - 38 inches tall. Type A mares fail to break water more frequently and have more embryonic losses. Type A 2 and 3 year olds also have lower conception rates. Lower conception rates mean that the mare must be bred more times during the breeding season to achieve a pregnancy. Type A mares also have more dystocia and foals with congenital problems (abnormalities developed during the pregnancy) like dwarfism and jaw malalignment. Dwarf foals are minis which look like dwarfs rather than miniature horses. They may have one or all of the following: domed head, short leg to body, short stubby necks and large heads. Some foals grow out of these abnormalities as they mature.

Another abnormality observed in many miniature foals are flexural limb deformities in two or more legs. Flexural limb deformities are abnormal contractions of the tendons in the front legs which result in the foal not being able to straighten its legs. Frequently, exercise and corrective shoeing and trimming eliminates the problem. The kneecap is also an area of particular weakness in minis as is the eye; problems in these parts of the mini are all too common.

Basic healthcare maintenance in mini’s

Dentistry
An absolute essential necessity in good mini management is close attention to their dental condition. Mini’s have frequent bite alignment problems and as a consequence routinely don’t shed their deciduous (baby) teeth. Also, because their bite is often malalligned, they need more frequent teeth “floating”. If you would like more information on equine dentistry please call our office and request the handout on dentistry.

Feeding : General rules of thumb
Good quality hay and feed is essential. If in doubt have it analyzed. Many miniatures are overfed and obese. Pot bellies however, are not always a sign of overfeeding; very poor quality hay can cause pot bellied yearlings and weanlings.

For general feeding recommendations we recommend:

For weanlings, prior to weaning: creep feed a ration with 15% protein. With a good legume hay 14-16% protein is OK, with poor quality legume hay increase the protein to 16-18%. Ensure the ration has 0.9% calcium and 0.8% phosphorus. Ground limestone or dicalcium phosphate are good sources for these minerals. Copper in the concentrate should be 30-50 ppm, and zinc should be approximately 80-120 ppm in the mix. After weaning, feeding recommendations are very similar to horses (as are the above recommendations) and protein levels do not need to be as high as mentioned above.

Selenium should be in the supplement as concentrations of selenium are very variable from area to area and can differ significantly between farms in the same locale. Selenium blood concentrations should be examined if it is suspected as a source of a problem. Deficiency of selenium can cause muscle stiffness, lameness, listlessness, muscle pain, and foals can die from respiratory failure.

This article was published in Northwest Miniature Horse Club Newsletter, July-Aug 1996, Vol. 1, no. 67