Reversing antibiotic resistance
may become possible

Noting that pathogen resistance to antibiotics is a rapidly
growing problem, researchers with the Sackler School of Medicine at Tel Aviv
University in Israel said a method that will “resensitize pathogens to approved
antibiotics holds key advantages.”

In an article in the journal Applied & Environmental
Microbiology, the researchers presented a proof-of-principle for a system
that restores antibiotic efficiency by reversing pathogen resistance by using
temperate bacteriophages to introduce by lysogenization two genes that confer
sensitivity in a dominant fashion to the antibiotics streptomycin and nalidixic
acid.

Researchers Rotem Edgar, Nir Friedman, Shahar Molshanski-Mor
and Udi Qimron said they believe that transfer of the sensitizing cassette by
constructed phages will “significantly enrich for antibiotic-treatable pathogens
on hospital surfaces.”

Edgar et al. added that broad usage of the proposed system will
potentially change the nature of nosocomial infections toward being more
susceptible to antibiotics rather than more resistant.

A research abstract can be found at http://aem.asm.org/content/early/2011/11/18/AEM.05741-11.abstract.

By TIM LUNDEEN

REPLACEMENT heifers are the future of every dairy operation,
so the calf and heifer management program needs the right pieces to ensure the
future wellness of the herd and the associated dairy business.

A key piece of that puzzle is pneumonia management. Pneumonia
causes the second-highest number of cases of illness and death in young dairy
calves, behind only scours. Calves that do survive pneumonia are likely to face
a lifetime of diminished performance.

According to Dr. Lance Fox with the Pfizer Animal Health
Cattle Technical Services unit, research shows that replacement heifers affected
by bovine respiratory disease (BRD) in the first three months of life are more
likely to experience significantly increased mortality, have reduced average
daily gain, calve later than healthy herd mates and produce less milk in at
least their first lactation.

“It is important that producers work with their veterinarians
to look at their calf and heifer management program and make sure they are
properly managing BRD,” Fox said. “There are several steps for pneumonia
management, and all are interconnected; having one without the other can cause
health issues.”

These steps include:

* Set the stage with proper nutrition. Bolstering a
calf’s immune system is important for pneumonia resistance and starts with
feeding at least four quarts of high-quality colostrum within two hours of
birth, Fox said. An excellent colostrum feeding program is the cornerstone of
healthy calf rearing and helps jump-start the immune system, better preparing it
for vaccination.

* Vaccinate to help prevent BRD. Work with a
veterinarian to set up a vaccination program for young calves. Dairy producers
should ask about introducing a vaccine that helps protect against the three
major viral pathogens that cause pneumonia in dairy calves: bovine respiratory
syncytial virus, infectious bovine rhinotracheitis virus and para-influenza 3
virus. Vaccines are an important part of helping the immune system fight off
BRD.

* Use strategic antibiotic control. Implementing a calf respiratory identification protocol can
help initiate treatment earlier in disease progression. A veterinarian can help
set up an antibiotic control protocol to minimize the effects of pneumonia
during high-risk situations such as seasonal weather changes, overcrowding or a
move to group housing, Fox noted.

* Manage the environment. Utilize an all-in/all-out
approach, and sanitize hutches and pens between calves to limit pathogen
exposure to incoming animals, Fox added. Also, be sure to provide enough clean,
dry bedding, especially as the weather gets colder.

Sneaky salmonella

The clinical signs of salmonella are easy to identify: sudden
weight loss, weakness, fever, diarrhea and dehydration.

While these symptoms signal clinical salmonella on a dairy
operation, they are only the tip of the iceberg. The majority of salmonella
infections in herds are sneaky and often can go undetected for long periods of
time in the form of subclinical salmonellosis, Pfizer said. These cases show no
visible clinical signs of disease, so they are difficult to identify yet reduce
a herd’s productivity. What’s worse, salmonella pathogens can spread from animal
to animal throughout an operation for months without detection.

Data from the U.S. Department of Agriculture “tell us that
nearly half of all dairies are infected with salmonella, and in herds with more
than 500 cows, that number jumps to 61%,” Dr. Gary Neubauer, Pfizer Animal
Health Cattle Technical Services senior manager, explained. “Most of those
infections are subclinical, resulting in decreased milk production and cattle
that are more susceptible to other diseases, especially right after
calving.”

A subclinical case of salmonellosis can develop as a result of
exposure to three different types of pathogen carriers: (1) active carriers that
shed the salmonella organism in manure and/or milk, (2) symptom-free carriers
that infrequently shed organisms and (3) dormant carriers that harbor salmonella
but do not shed bacteria.

Neubauer pointed out that cattle can often move among these
carrier states. For example, a dormant carrier may become an active carrier, and
vice versa. Carriers can infect the rest of the herd through fecal-oral
contamination of bacteria shed during periods of stress.

He recommended taking the following steps as part of a
salmonella control plan:

* Maintain clean facilities. Evaluate the fresh cow,
transition and calving pens. Apply fresh bedding on a consistent schedule, and
remove all manure from the facilities.

* Sanitation is key. Feeding equipment and loaders
should not be used for manure handling. Reduce the spread of bacteria by using
products such as chlorhexidine to clean calf feeding utilities and oral
treatment equipment on a regular basis.

* Enforce biosecurity measures. Insist that all
visitors, including veterinarians, wear clean boots and clothing. Wash boots
regularly with orthophenylphenol, and launder work clothes daily. Ideally, work
attire should be left at the dairy.

Gram-negative mastitis

Research from Cornell University, recently published in the
Journal of Dairy Science, shows an 89% cure rate of mild or moderate
Escherichia coli mastitis infections — characterized by the cow not
being sick or off feed but with visible signs of mastitis — when treated with
extended intramammary antibiotic therapy, according to a separate release from
Pfizer Animal Health.

Conducted at five large dairy herds of 500 or more cows in New
York, the trial looked at mild and moderate cases of Gram-negative mastitis and
evaluated the efficacy of treating for five consecutive days with ceftiofur
hydrochloride (SPECTRAMAST LC Sterile Suspension). The results showed that
treated cows had significantly higher cure rates than untreated cows, Pfizer
said.

In this randomized study, researchers evaluated both clinical
and complete cures, with bacterial strain-typing performed to classify
infections as “new,” “persistent” or “cure” across the course of treatment and
recovery. After completion of the treatment and at equivalent time points for
untreated control cows, two follow-up milk samples were cultured and
strain-typed after the last treatment.

“Until now, no research has so vividly demonstrated treatment
success of mastitis infections caused by Gram-negative bacteria like E.
coli,” said Dr. Roger Saltman, Pfizer Animal Health Cattle Technical
Services group director. “Our team set out to determine how well such infections
would respond to extended antibiotic therapy, and we found that, in the majority
of cases, they responded very well.”

The results support a new way of thinking — that antibiotic
treatment of Gram-negative mastitis can be successful. Pfizer said specific
revelations from the research include:

* For clinical mastitis caused by E. coli, 89% of the
treated cows showed bacteriological, or complete, cures, compared with 53% of
untreated control cows.

* Cows that were completely cured gave an additional 8.8 lb.
of milk at the second test day versus cows that were not cured.

* Herd survival also was significantly higher in completely
cured animals versus animals that were not cured.

“These results dispel the belief that Gram-negative bacteria
do not respond to intramammary antibiotic therapy or that these infections will
self-cure,” Saltman said. “For those already putting an extended duration of
therapy protocol into practice for Gram-negative infections, the results have
always been apparent. Now, however, research clearly supports such treatment
decisions.”

Coliform mastitis can cause adverse impacts on dairy
operations, Pfizer explained, noting that Gram-negative bacteria, like E.
coli, cause 40% of all clinical mastitis cases.

Managing mastitis

Reducing the somatic cell count (SCC) on a dairy operation is
not just a matter of regulations and rulings; it’s a matter of animal health and
good management.

“We know that lower somatic counts are a reflection of
improved animal health and less mastitis in the herd,” Linda Tikofsky, a
professional services veterinarian with Boehringer Ingelheim Vetmedica Inc.,
said. “Whether or not there is a regulation on SCC limit, producers should
strive to reduce their SCC for the good of their cows and their milk check.”

Tikofsky said there are several management practices that
contribute to lower SCC:

* Improve udder preparation. Complete and proper udder
preparation involves stimulating milk letdown by stripping, pre-dipping and
wiping teats dry before attaching the milking unit. Always wear gloves, sanitize
gloves between cows and use single-service paper towels to dry teats. Hang units
squarely beneath the cow, and ensure that there are no air leaks or “squawks.”
There should be a 60- to 90-second delay between stripping and unit
attachment.

* Keep cows clean. Reducing infection and SCC is easier
when cows are kept in a clean, dry environment. Bedding should be refreshed and
stalls groomed frequently.

* Maintain good records. Keep track of cows with a
history of high SCC and mastitis. A good record-keeping system will help when
making treatment and culling decisions.

* Treat those you can, but cull those you can’t.
Repeated treatment of cows with chronic mastitis and high SCC doesn’t make
economic sense.

Methionine

As the dairy industry moves toward balancing rations based on
the cow’s amino acid requirements, selecting the right methionine supplement in
the ration becomes more important.

“With the high cost of feed ingredients, the risk is too high
to have animals not reaching their greatest potential by making the most of
their rations,” said Ed Galo, a national sales manager with the Novus
International Inc. Dairy Business Unit.

Amino acids are the building blocks of proteins. Cattle need
many different amino acids to optimize milk and milk protein production. If just
one of those amino acids is deficient, overall performance will be limited.

Methionine and lysine are the two most limiting amino acids
for dairy cows. Feedstuffs can be balanced to provide the amino acid requirement
of dairy cows. However, with current technologies, balancing amino acids with
feed ingredients alone may not be the optimal feeding strategy for dairy cows to
achieve the most efficient productive performance.

Galo said Novus’ ALIMET feed supplement supplies rumen-bypass
methionine as well as rumen-effective methionine, which may improve milk
production and increase milk fat and protein yield.

“Balancing rations for amino acids with just feed ingredients
might result in adding more or too much protein and nitrogen to the diet, which
is inefficient and uneconomical with today’s high feed prices,” Novus ruminant
nutrition research manager Geoff Zanton added. “By balancing with supplemental
methionine, producers can use less crude protein to meet amino acid
requirements. This results in a reduced ration cost and improved overall
efficiency of the diet and nitrogen utilization.”

Amino acid balancing

Among dairy nutritionists, balancing rations for specific
amino acids has become a best practice, especially when using updated ration
formulation software that simplifies the process, according to Adisseo.

When the ration’s amino acid levels are matched to the cow’s
biological needs, the cow’s nutritional status improves. To achieve this goal,
the ration fed typically includes a rumen-protected, metabolizable methionine,
and the most common result is an increase in milk protein — the best known
benefit of amino acid balancing, according to Dr. Dan Luchini, manager of
ruminant products technical services at Adisseo.

He explained that other benefits exist, such as increases in
both milk volume and milk fat and a decrease in nitrogen excretion. To quantify
the response to amino acid balancing in a single number, the figure for
energy-corrected milk is often used.

Balancing amino acids supports more efficient nitrogen so less
crude protein needs to be fed. Reducing crude protein helps reduce feed costs
and makes room for more high-quality forage while decreasing nitrogen excretion,
Luchini said.

In recent research (Table), one group of cows was fed a 16.8%
crude protein diet that provided an estimated 2,590 g of metabolizable protein
with a lysine-to-methionine ratio of 3.33. Another group of cows was fed a 15.7%
crude protein diet that delivered 2,450 g of metabolizable protein for a
lysine:methionine ratio of 2.98.

The 16.8% crude protein ration contained an additional 140 g
of metabolizable protein, yet its amino acid levels were out of balance, Luchini
said. Both rations delivered similar amounts of metabolizable lysine. The 15.7%
crude protein ration, however, provided an extra 6 g of metabolizable methionine
from 40 g of a dry rumen-protected methionine (MetaSmart).

The cows fed the 15.7% crude protein diet produced an extra 2
lb. of milk with better fat and protein percentages, Luchini reported. They had
a significant 3.5 lb. of extra energy-corrected milk and had lower plasma urea
nitrogen and milk urea nitrogen levels, which confirm better efficiency of
nitrogen utilization, he concluded.

a) Scientific Evidence: 
What are our sources of evidence for global, regional, and local climate
impacts? What methods and resources do we use that can be shared with others to
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