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Some Thoughts On Hypothermia and Starvation In Newborn Lambs
J. S. Rook, D.V.M. MSUE & MAES If you’re a sheep producer…. you just might be an epidemiologist! Think about it, most of you have probably experienced and wisely noted the association between: 1) the presence of a dead pile behind the barn and lambing season, 2) flock expansion and the need for increasing the capacity of that dead pile and 3) increased frequency of trips to the dead pile when beastly winter weather and lambing season are in “harmony”. Like most things in life, you really didn’t need that PhD in epidemiology or that computer-generated p-value to tell you what you already gleaned from life’s experiences - not every lamb or ewe makes it through lambing season. In fact, 2% to 5% of the ewe flock and 5% to 30% of the lamb crop die during the month prior to and following lambing. In “real world” production settings, flock lamb mortality rates of less than 5% (remember this counts abortions, stillbirth, dystocia, etc.) are rare and producers consider a 5% to 10% loss figure as excellent. If these figures shock you, then one of us is likely: 1) using the “new” math, 2) in denial, 3) looks like Pinocchio or 4) all of the above (i.e. a real epidemiologist). Seriously, lambs die from a lot of different causes – infectious, man-made, weather-induced, mamma-induced, predator-induced - you get the picture. However, simple hypothermia and hypothermia secondary to starvation account for roughly 50% of all postpartum (i.e. lambs were born alive) lamb deaths occurring during the first week following birth. Therefore, as a producer (or epidemiologist), knowing a little something about hypothermia and starvation in newborn lambs would seem prudent. The significance of hypothermia, starvation and exposure is obvious when one recognizes that hypothermia, exposure and starvation account for 20% to 50% of all pre-weaning lamb mortality. Most of these losses occur during the first 3 days following birth and are influenced by producer management decisions and production practices. Losses due to hypothermia and starvation occur via two distinctly different physiological pathways. During the first 4 to 6 hours following birth, newborn lambs have relatively high blood glucose levels and do not initially suffer from simple starvation. Thus, if the ewe flock has been adequately fed, newborns have adequate fat reserves capable of providing for the energy needs of the lamb until colostrum is digested, absorbed and able to be utilized as an energy source. During warm weather, lambs born to well-fed ewes may survive for several days - or until internal fat supplies are depleted. However, when this same lamb is exposed to cold weather, increased demand for energy (to generate body heat) quickly depletes fat reserves by as early as 4 to 6 hours following birth. Thus, newborn lambs succumb to either: 1) simple hypothermia (usually occurs in lambs less than 6 hrs. old) or 2) hypothermia induced or secondary to starvation (occurs in lambs more than 6 hrs old). However, this 6-hour figure is influenced by both weather and the amount of body fat present in the newborn lamb. Furthermore, because starvation and exposure contribute to the hypothermia equation, hypothermia losses are often discussed as resulting from a complex or series of events related to age, weather and nutrition – but the end result is still dead lambs! Simple hypothermia (0 to 6 hours after birth) - The physiological processes that contribute to simple hypothermia mostly involve: 1) excessive loss of body heat and 2) reduced heat production. At this crucial time in a lamb’s life, factors that contribute to this excessive heat loss scenario include: 1) exposure to climatic factors, 2) evaporation heat loss due to a wet birth coat, 3) small body mass, 4) reduced mobility leading to reduced heat production, 5) dystocia related hypoxia and subsequent lack of thermoregulation, 6) poor mothering behavior and 7) lack of colostrum. In cases of mild hypothermia rectal temperatures range from 99‑102 o F and in severely hypothermic lambs often plunge to well below 97 o F - until death occurs. A digital thermometer (or your finger in a cold mouth) is a useful tool for identifying and treating affected lambs. Supplemental colostrum (administered via a stomach tube (@ 20mls/lb of body weight) is important for hypothermic newborn lambs, however, producers should recognize that nutrition alone is not the primary component of a simple hypothermia treatment program during the first few hours following birth. Treatment should stress supplemental warmth to reverse the excessive loss of body heat Starvation-induced hypothermia (lambs over 6 hours old) affects newborn lambs that survive the critical first 6 hours following birth - when deaths due to simple hypothermia are most common. Starvation and the resulting lack of energy needed to produce body heat is the cause of hypothermia in older lambs. Inadequate heat production - due to starvation - becomes a “catch-22” affair. Cold weather increases the demand for heat production in a system already depleted of energy (fat) reserves while starvation concurrently restricts re-supply of fuel needed for heat production. Thus, cold weather magnifies the urgency for a newborn lamb to suckle. Affected lambs exhibit extreme depletion of body fat stores and resulting low blood sugar. Correction of starvation-induced hypothermia in older lambs should address the following issues: 1) hypoglycemia, 2) hypothermia and 3) starvation. Starvation-induced hypoglycemia, commonly observed in these older lambs, must be addressed if treatment is to be successful - as sudden warming of a hypoglycemic lamb can lead to cerebral hypoglycemia and death. 
Simple Hypothermia (0 – 6 hrs. after birth) ü Move ewe and lamb to shelter or remove lamb from ewe ü If only one of a set of twins involved remove both from ewe while warming and return both lambs at same time. ü Dry wet lambs to prevent chilling due to evaporation ü Supplement warm, dry heat 100‑103oF max. temperature ü Tube feed colostrum at 20 ml/pound of body weight ü If lambs are strong enough to stand and nurse - return to ewe (rectal temperature normal @ 101-102oF in 1‑3 hrs) ü Assure future nutrition and warmth - recognize and correct initial problem (mastitis, environment, mamma, etc) to prevent re-occurrence. ü Decide if continued attention (labor) to non-responsive lambs warranted
Starvation-induced hypothermia (lambs over 6 hrs. old ) Not comatose Not “flat out” on side Able to hold head upright ü Same as for simple hypothermia
Starvation-induced hypothermia (lambs over 6 hrs. old ) Comatose “Flat out” on side Not able to hold head upright ü Inject 40 ml of 20% dextrose into peritoneal cavity one-half inch beside and one inch behind the umbilicus using a sterile needle and syringe ü Dry wet lambs to prevent chilling due to evaporation ü Supplement warm, dry heat 100‑103oF max. temperature ü Tube feed colostrum at 20 ml/pound of body weight ü If lambs are strong enough to stand and nurse return to ewe (rectal temperature normal @ 101-102oF in 1‑3 hrs) ü Assure future nutrition and warmth - recognize and correct initial problem (mastitis, environment, mamma, etc) to prevent re-occurrence. ü Move ewe and lamb to shelter or remove lamb from ewe ü If only one of a set of twins involved remove both from ewe while warming and return both lambs at same time. Decide if continued attention (labor) to non-responsive lambs warranted
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