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Save Lambs

Keep “Good-Mom” Ewes

By Alan Harman

While the starvation/hypothermia complex is the leading cause of death in most regions, vigorous lambs that receive adequate colostrum and milk—5% to 10% of their body weight—in the first few hours after birth can withstand a significant amount of cold.

Losses are largely a function of the time of year when lambs are born.

But Ohio State University Extension veterinarian Bill Shulaw says in a report posted on the OSU website some literature from other parts of the world refers to this problem as SME—starvation, mismothering, and exposure.

“This terminology emphasizes the ewe’s contribution to the problem,” he says. “Research and practical experience indicate that selection for ewes with sound udders, desirable teat placement, and strong mothering instincts can significantly reduce the impact of this problem.

“Likewise, large birth weights and dystocia [difficult births], also conditions we can select against, contribute to less vigorous lambs that don’t find the ewe’s udder without assistance.”

Shulaw says if a pregnancy is carried to term, most losses occur in the first three to four days of life, and if lambs survive the first four weeks, most usually make it to market.

Uncrowded, good mothering ewes—plus fresh air and sunshine—equal top production. Photo by Nathan Griffith.
Uncrowded, good mothering ewes—plus fresh air and sunshine—equal top production. Photo by Nathan Griffith.

How To Cut Three Types Of Losses

Most losses, he says, can be grouped in three general categories—starvat­ion/hy­p­o­ther­mia (chilling to death), pneumoni, and scours (diarrhea).

“To a large degree, these losses are related to management factors we control, and therefore, a proportion of this loss is preventable,” he says.

Shulaw says because lambs have small body weight in relation to their surface area, hypothermia will always be a potential cause of loss, even in lambs born in mild or warm weather.

“However, we can reduce its impact in our flocks by altering our selection and management practices,” he says.

Pneumonia is the second leading cause of death in young lambs and transmission to the lamb is usually by aerosolized droplets, containing the bacteria, originating from carrier ewes.

Shulaw says this transmission is favored by inadequate exchange of air and moisture as is often seen in barns. Poor ventilation, combined with a significant proportion of the ewe flock with chronic infection of the respiratory tract, generally results in pneumonia being a significant cause of mortality in young lambs. Producers should consider culling ewes with a chronic cough.

“Increasing the rate of air exchange will, of course, tend to make the barn colder in winter and could increase the risk of hypothermia in lambs,” he says. “However, starvation/hypothermia problems can be minimized with appropriate selection and management.”

Pneumonia not only causes significant mortality in young lambs, but also leads to chronic infections in older lambs and ewes. Pneumonia is a leading cause of death and reduced performance in feedlot age lambs. Many infections in these lambs are already established in the respiratory passages, long before lambs reach the feedlot, and only need the stresses of transportation and the feeding program to result in clinical disease.

Refinements in building design and reduced animal density in confinement situations are more effective long-term measures to control pneumonia than antibiotic usage.

“Experience suggests that flocks which lamb outdoors in the spring tend to have a low incidence of lamb pneumonia,” Shulaw says.

Diarrhea in young lambs is caused by several kinds of bacteria, viruses, and protozoa and Shulaw says lambs that do not receive adequate colostrum are at greatest risk of developing diarrhea.

“However, even animals that received adequate amounts may still develop diarrhea if the colostrum did not contain specific antibodies to these agents,” he says. “In addition, colostral antibody can be overcome by a severe buildup of infectious agents in the environment.”

Lambs with diarrhea may shed hundreds of millions of infectious organisms in every teaspoonful of manure. For many infectious organisms, ingestion of only a few is necessary to cause disease.

“For example, fewer than 10 Crypto­spor­i­dium parvum oocysts are needed to cause a productive infection,” Shulaw says. “As if all this weren’t bad enough, some ewes act as unapparent carriers of these infectious agents and seed the environment with low numbers.”

Also, The Right Habitat

Shulaw says healthy, vigorous lambs with adequate colostrum and in a relatively clean, well-ventilated environment may withstand exposure to low levels of many infectious agents and not get sick.

“In fact, this is a necessary process in order to ensure their

immune system responds to these low level challenges and develops resistance,” he says. “This exposure process eventually results in replacement animals that successfully make and pass protective

antibodies to their own lambs. This is a dynamic situation. It is when things get out of balance that clinical disease becomes evident.”

Shulaw says overcrowding, excessive moisture or humidity, lack of bedding, and poor sanitation all contribute to raising the overall level of contamination by infectious agents to levels that result in disease.

“Infectious agents in the environment are not only acquired by the lamb nosing about the pens, but also by nursing udders which are contaminated by dirty environments,” he says. “In addition, once a scours outbreak is in progress, much of the environment rapidly becomes contaminated, and many lambs get exposed.

Isolating ewe/lamb pairs when diarrhea occurs in the lamb can help reduce the number of cases that develop. Likewise, good overall sanitation with dry, relatively deep bedding can reduce the amount of exposure lambs get to disease-causing organisms.”

Most flocks harbor many of the common infectious agents responsible for the bulk of lamb losses caused by infectious disease, Shulaw says.

“These agents are either in the environment or harbored by the animals themselves. Whether or not clinical disease occurs is usually a function of the interactions between animals with their environment. Our role in minimizing management factors that contribute to disease development is crucial to the health status of our flocks.”

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