Better Pork - August 2016

Better pork

August 2016

HERD

HEALTH

hen we encounter re-

productive failures (e.g.

abortions), we almost

always expect they occurred because

of some infection (viruses, bacteria,

etc.). It may come as a surprise that

until the appearance of porcine re-

productive and respiratory syndrome

(PRRS) nearly 30 years ago, the

majority of reproductive failures had

nothing to do with infections. They

occurred from noninfectious causes

which are often difficult or impossible

to pinpoint.

Today, a large percentage of abor-

tions can now be attributed to PRRS

virus. We do know, however, of

some of the more frequent noninfec-

tious causes of reproductive failures

in swine which still occur. Here are

some which we can verify.

Small number of fetuses

Sometimes after a pregnancy has

been established and the fetuses suc-

cessfully implanted in a multiparous

species (species that produce litters

or large numbers of offspring in each

pregnancy) like pigs, there is a low

number of fetuses in the pregnancy.

At some point during early pregnan-

cy, a decision is made to terminate

the pregnancy and start over again,

hopefully getting a more acceptable

number of viable fetuses in the next

pregnancy.

High ambient temperatures

Anything that spikes a high tempera-

ture >39 C is capable of triggering

an abortion in sows. This can be the

result of an infection or just high am-

bient summer temperatures if some

sort of cooling is not made available

to the sow. There is some evidence

that low progesterone levels in the

sow may play a role in contributing

to the reproductive failure in the face

of the high temperature. I’ll address

the relationship to low progesterone

a little later.

Fall abortions (Autumn Abortion Syndrome)

An increase in abortions is observed

in temperate climate regions of pig-

producing countries. The abortions

are often associated with very cold

nights (≤0 C) following relatively

mild fall days (10-20 C). Abortions

occur in stalled sows located at the

ends of rows, near to doors or outside

walls. Several sows may abort over-

night. One theory to explain the rash

of abortions under these conditions

goes back to observing nature’s role

for the sow. Pigs in the wild produce

one litter a year. Breeding occurs in

the late summer and fall; sows are

pregnant over the winter and farrow

in the spring. Since sows are polyes-

trous (can come into heat throughout

the year), we have converted them to

being pregnant several times a year

and at any time of the year. High

levels of progesterone in mammals

is synonymous with maintenance of

pregnancy. Measurements of proges-

terone levels in the European wild

boar reveal high levels of progester-

one in the summer and fall. In late

winter and spring when farrowings

occur, progesterone levels fall off in

preparation for farrowing. In our

domestic swine, progesterone levels

are low and decreasing during late

summer and into fall, leading to

speculation that our sows are on a

tenuous threshold for maintaining

pregnancy at this time. Hence, any

adverse change to the pregnant sow

at this time (eg. stressors such as large

sudden fluctuations in temperature

overnight) combined with the low

levels of progesterone makes the sow

subject to aborting.

Mycotoxins

According to the Merck Veterinary

Manual, “The estrogenic mycotoxins

zearalenone and zearalenol interfere

with conception and implantation,

causing infertility, embryonic death,

reduced litter size, but rarely, if ever,

abortion. Another class of myco-

toxins, the fumonisins, causes acute

pulmonary edema in swine; sows that

reproductive failure from noninfectious causes

In the third of three articles, the author reviews the major noninfectious causes of reproductive

failure in swine.

by ERNEST SANFORD

In our domestic swine, progesterone levels are low and

decreasing during late summer and into fall, leading to

speculation that our sows are on a tenuous threshold

for maintaining pregnancy at this time.