Tom Riddle, DVM, of Rood and Riddle Equine Hospital in Lexington, Ky., began the in-depth session on "The Foal: Birth to One Month" with a discussion on how to prepare the third-trimester mare for normal foaling. His discussion included his management procedures within his Kentucky veterinary practice, which deals mainly with Thoroughbreds. However, he said many of his points could be applied to any reproductive practice, regardless of breed or region.

Riddle said that most mares are outside all of the time or are only brought up for feeding until they reach one month before their expected foaling date. Whatever is preferred, broodmares thrive on routine. He said that some farms in his area will put their mares under lights in stalls or lighted paddocks beginning Dec. 1. Benefits include a decrease in the length of gestation by seven to 10 days, which allows more time to breed the mare in the breeding season, and a decrease in the chance the mare will stop cycling temporarily.

At 30 days before foaling, Riddle said mares are brought into the foaling barn with turnout for six to eight hours per day. On most of his clients' farms, mares are checked once each hour by farm staff. A veterinarian will examine all of the mares in late November or early December. Any mare which has undergone a Caslick's procedure to partially close the vulva will need to be opened around two weeks before her due date or when she begins to show signs of imminent foaling. Afterward, petroleum jelly will be applied to the vulva daily to prevent adhesions.

Throughout the pregnancy, a manager or groom will check the mare for udder development and unusual vaginal discharge. If abnormalities are noted, a veterinarian is contacted to examine her. Rectal palpation can confirm the pregnancy and help the veterinarian evaluate cervical tightness, fetal position and movement, and uterine distention.

Riddle suggested that transrectal ultrasonography be performed in order to measure the combined thickness of the uterus and placenta at the cervix, look for placental edema (fluid buildup) or separation, evaluate the allantoic and amniotic fluids, and observe the amnion and measure its thickness.

Since the fetal heart cannot be seen with transrectal ultrasonography, Riddle recommended transabdominal ultrasonography. An average heart rate of 68-82 beats per minute has been recorded, with this decreasing as the fetus gets closer to term. If the heart rate drops below 50 beats per minute or rises above 100 beats per minute, it is a sign of a compromised pregnancy. In addition to monitoring the heart, transabdominal ultrasound allows the veterinarian to evaluate the placenta, amnion, and umbilical cord, said Riddle.

He also suggested that assays measuring total estrogens be used to determine viability of the fetus between 150-300 days of gestation. He recommended that estradiol and its metabolites be measured. Total estrogens should be greater than 1,000 pg/ml. If a veterinarian receives a report that levels are under 500 pg/ml, then abortion is likely to be imminent, and treatment is usually futile. Levels between 500 and 800 pg/ml indicate compromise, with 50% of cases going to term. Levels between 800 and 1,000 pg/ml indicates a fetus under mild stress, with 75% going to term. In the latter two scenarios, Riddle said he prefers to treat mares with a double dose of altrenogest, along with pentoxifylline and systemic antibiotics. He does not recommend examination with a vaginal speculum in these mares since contamination of the mare's reproductive tract is possible.

Between 250 and 305 days of gestation, plasma progestins can be measured to identify an impending abortion. Three weeks prior to delivery, progestins rise dramatically, falling again 48 hours before birth. Any abnormal rise in progestins between 250 and 305 days of gestation can indicate to the veterinarian that a fetus is stressed or might be premature. An abnormal fall in progestin levels can indicate an acute fetal crisis and impending abortion. Measurements should be taken every two to three days until three have been performed with the relative change in values compared.

Vaccination of Pregnant Mares
Vaccination is imperative for the broodmare, said Riddle, not only to protect the mare, but so the foal will be protected through her colostrum. Riddle recommended that mares be vaccinated four to six weeks before foaling to ensure the highest level of antibodies for passive transfer. If there is a failure in passive transfer of antibodies to the foal from the colostrum, then the foal will need to receive colostrum or plasma from a donor mare. Riddle vaccinates mares against influenza, rhinopneumonitis, tetanus, rabies, Eastern and Western encephalomyelitis, West Nile virus, botulism, and rotavirus. On some farms where strangles outbreaks have occurred, some farm managers will request vaccination against Streptococcus equi; however, Riddle said this is not recommended for the general equine population and, in his opinion, is unlikely to be helpful on those farms with a history of strangles.

Riddle recommends the modified live virus vaccine for the prevention of rhinopneumonitis. Only three mares he has vaccinated have aborted due to the disease, and two of them were purchased at a sale where the risk of exposure was increased. Mares are given the vaccine every two months throughout the year.

"When vaccinating for influenza, it is important to use a vaccine that includes a viral strain isolated in the 1990s," he said. "We recommend that the influenza vaccine be given 30 days before expected foaling. Although intranasal vaccines have proven effective in preventing infection, an intramuscular form must be used before foaling to stimulate production of systemic immunoglobulin G (IgG) for passive transfer to the foal."

Riddle has seen no adverse reactions with the West Nile virus vaccine and considers it very safe. It should be given 30 days before foaling.

Since botulism is endemic in Kentucky, Riddle recommends vaccinating all horses in the area with the type B toxoid. Due to this practice, "loss of foals from properly vaccinated mares has been virtually eliminated," he said.

Vaccinating pregnant mares against rotavirus group A with the inactivated H2 strain has reduced the incidence of the disease and has caused a decrease in clinical signs of affected foals. Riddle vaccinates mares in the eighth, ninth, and 10th months of gestation.

Screening for Neonatal Isoerythrolysis
Neonatal isoerythrolysis (NI) occurs when a mare produces antibodies in the colostrum that react with a foal's red blood cells after the foal has ingested the colostrum. Even though the incidence of NI occurs in 1-2% of horses, Rood and Riddle screens all mares before foaling, thus preventing NI. Riddle said that maternal antibodies to the foal's red blood cells can be found from the eighth to the 10th months of gestation. It is recommended to screen within four weeks of foaling. If a reaction is found, the foal is muzzled and prevented from nursing from his dam, the dam is milked, and the milk is discarded. The foal is given colostrum from a donor mare for the first 24-36 hours. After that time, the antibodies should be gone from the mare's milk, and the foal can nurse.

Nutrition of the Broodmare
Riddle said the broodmare's diet will consist of concentrates, hay, and pasture. "Each component of the diet should be analyzed when formulating the nutritional program of the pregnant mare," he recommended. Excessive nutrition with the addition of stress has been linked to placental disease and edema (fluid swelling), he said.

Riddle recommended that the mare receive between 2.25-2.5% of her total body weight in feed (hay and concentrate) with 12-14% crude protein. The calcium:phosphorus ratio should not exceed 3:1, with 1.2-1.5:1 being ideal. He warned against diets high in calcium, since they could possibly cause osteochondritis in the foal. In instances where alfalfa hay is fed, a phosphorus supplement might be necessary to balance out the high calcium content of the hay.

Riddle commented briefly on the importance of copper and zinc; but, he said, "No advantage to foals was shown when mares were fed minerals in amounts greater than normal requirements."

"Because the majority of weight gain occurs in the last three months of gestation, proper nutrition at that time is critical," he continued. "Evaluation of the mare's body condition is probably the best guide to the quality of the condition program. Mares in moderately fleshy to fleshy condition have been shown to have higher live-foal rates and to produce more milk than thinner mares."

In conclusion, Riddle commented that management practices will differ based on a farm's region, economics, available resources, and skill of the personnel. "It should be stressed that a strong partnership between the veterinarian and the farm manager is necessary to maximize the likelihood of producing a healthy foal," he stated.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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