College of Veterinary Medicine DVM Candidates 2019
Hypothermic Lambs: How to defrost before they’re in the freezer
Winter has already been harsh this year, making it only fitting to write about hypothermia in lambs. Even with the best management, this is bound to be an issue for many sheep producers. Hypothermia has many causes and can affect lambs at different ages. In newborn lambs less than five hours old, hypothermia often occurs due to prolonged exposure to cold temperatures.
Difficult or premature births can cause weak lambs which contributes to hypothermia because these lambs do not get up and nurse warm colostrum as readily as lambs that have a normal birth. Poor mothering can also lead to hypothermia if an ewe fails to thoroughly lick her lambs dry or if she abandons a lamb. If the ewe has poor body condition and there was a lack of adequate nutrition during gestation the risk for hypothermia increases as lambs born from these ewes are often weak and colostrum production is decreased.
Hypoglycemia, or low blood sugar, often accompanies hypothermia in newborn lambs because they have not ingested colostrum which is both a source of immunity and glucose. Lambs are born with brown fat that provides an energy source prior to colostrum ingestion but this fat is gone around five hours after birth. Therefore, lambs that have not nursed colostrum within five hours after birth are at a higher risk for hypoglycemia and will need glucose supplementation before warming. Lambs that failed to receive enough good quality colostrum in a timely manner are also at risk of sepsis associated hypothermia which occurs secondary to lack of maternal immunity. Lambs that are septic will not respond to basic hypothermia and hypoglycemia treatment and should be seen by a veterinarian as soon as possible.
Diagnosis of hypothermia in any age lamb is straightforward. The number one clinical sign of hypothermia is a subnormal body temperature of 100°F or less. As a reminder, the normal body temperature of a lamb is 102-103°F. Always have a clean, functioning thermometer on hand to take the body temperature of a lamb at the first suspicion of hypothermia. These lambs are will be very weak and lethargic. In severe cases, they may lack a suckle response and will be unable to hold their head up.
Treatment of hypothermia varies based on the severity and the age of the lamb. A lamb with mild hypothermia, a body temperature of 99-100°F, should first be thoroughly dried off before receiving colostrum via a stomach tube. It is a better option to tube hypothermic lambs since they often lack a suckle response. Giving colostrum via bottle without a suckle reflex may result in aspiration pneumonia and subsequent death of the lamb. Contact your veterinarian or experienced shepherd to learn how to tube a lamb. If warm, fresh colostrum cannot be obtained from the ewe, use a commercially available colostrum replacer. Do not use a colostrum supplement because it does not have a high enough concentration of antibodies as a replacer.
Often these replacers are made for calves but will work well for lambs also. Mixing instructions will be the same for calves and lambs but obviously a lamb does not need as much volume as a calf. A lamb should receive 10% of its body weight in colostrum over at least a few meals during the first six hours of life. Another option is to keep fresh-frozen colostrum on hand. Fresh-frozen
bovine colostrum can be used but try to make sure it comes from a healthy herd since Johnes disease transmission through the milk to lambs is possible. Some producers will choose not to use cow colostrum or ewe colostrum from other flocks due to this risk, so consider retaining fresh-frozen colostrum from your own ewes.
Lambs that are severely hypothermic with a body temperature of less than 99°F require more aggressive treatment. A lamb that is less than five hours old and severely hypothermic needs to be dried and warmed before giving colostrum via stomach tube. Warming can be accomplished using commercially available warming boxes or simply using blankets or towels. It is especially helpful if these materials can be warmed in a dryer prior to use. Another method is to place warm jugs of water or heating pads under the lamb. Do not use a hair dryer to attempt to dry and warm lambs as the high-pressure air will result in evaporative cooling rather than warming.
Lambs that are severely hypothermic and greater than five hours old must receive colostrum first before drying and warming. Lambs more than five hours old do not have any brown fat reserves left. If these lambs are warmed before receiving glucose in the colostrum, they will convulse and likely die. Again, a stomach tube should be used to give colostrum.
However, if the lamb cannot hold its head up, tubing can be a challenge and there is an increased risk for aspiration pneumonia since it is more likely for the tube to enter the trachea and lungs instead of the esophagus and stomach. In this case, Karo corn syrup can be rubbed on the gums of the lamb because absorption of sugar across the gums occurs rapidly. Alternatively, an intraperitoneal glucose injection can be given if the producer is comfortable doing this.
However, inexperienced shepherds should not attempt intraperitoneal injections without instruction from a veterinarian since there can be severe complications with incorrectly injecting any solution into the abdomen of any animal. After these lambs have been given some energy, begin the drying and warming process. It is recommended to tube these lambs again after their body temperature has increased.
Overall, it is important to remember that the best treatment for hypothermia in lambs is prevention. Ensure that lambs are born in clean and dry environments such as a well bedded lambing pen. Knowing when an ewe will lamb will help a producer predict when to move ewes into an appropriate lambing area since most of the time ewes are sheltered in colder environments such as a three-sided shed on pasture. Careful observation of breeding dates and aging fetuses at the time of pregnancy diagnosis will aid in knowing due dates. Neither of these methods are perfect so frequent monitoring for signs of parturition is necessary. The lambing area should also be free from drafts. Heating lamps are a common recommendation but make sure that they are secured to reduce fire risk. Most of the time though, the heat from the dam and her colostrum will be enough for a lamb to maintain body heat if the lamb is born in a well- insulated and appropriately ventilated barn. Wishing everyone the best of luck during this lambing season.