36 Sheep & Goat Research Journal, Volume 19, 2004
the herd, or vice-versa, when scavenged
stillborns and aborted fetuses are mis-
taken as cases of depredation.
Feral swine usually follow a charac-
teristic feeding pattern that makes iden-
tification of depredation possible if the
entire carcass is not consumed (Pavlov
and Hone, 1982). Death typically occurs
by biting and crushing the skull or neck
(Frederick, 1998). A good indicator of
feral swine predation is that the prey’s
carcass will be skinned out with the
rumen or stomach contents consumed
(Wade and Bowns, 1985). Feral swine
tracks are distinct and may help decipher
cause of mortality when the soil and
nearby vegetation have been disturbed.
Feral swine cause serious economic
loss to the livestock industry, although
exact numbers and values are largely
unknown. This may be caused by
misidentification of the cause of preda-
tion. For example, signs of coyote (Canis
latrans) and feral swine predation appear
very similar; therefore cases reported as
coyote predation may actually be feral
swine. This is especially plausible in
Texas, where high densities of coyotes
and feral swine exist and target newborn
animals. Coyotes typically attack sheep
and goats with a bite to the throat, caus-
ing death from suffocation and shock,
then feed on their prey (Wade and
Bowns, 1985) starting at the flank or just
behind the ribcage. Coyotes typically
leave splintered bones, chewed ribs, and
scattered pieces of skin, fur, tendons, and
bones (Wade and Bowns, 1985). Con-
versely, black bear (Ursus americanus)
normally do not consume the rumen and
its contents, but the carcass will appear
skinned out (Wade and Bowns, 1985).
Black bears usually do not scatter their
prey, and the hide and skeleton will be
mostly intact. Large claw marks across
the shoulders and back may provide
additional clues.
The annual economic loss from feral
swine predation in the United States is
unknown; however feral swine predation
on livestock in the United States does
not appear to be as prevalent as in Aus-
tralia, where >$80 million is lost annu-
ally (Emmerson and McCulloch, 1994).
In Texas, Rollins (1993) reported that
33% of county agricultural agents listed
livestock depredation by feral swine as a
problem with losses directed towards
sheep and goats. In 1990, 1,243 sheep
and goats were documented as being lost
to feral swine in Texas, with an esti-
mated value of $63,000 (Rollins, 1993).
Barrett and Birmingham (1994) reported
1,473 sheep, goats, and exotic game ani-
mals were killed by feral swine in Texas
and California in 1991. In a more recent
survey, 23% of county agricultural com-
missioners in California reported live-
stock depredation by feral swine (Freder-
ick, 1998); total economic loss was not
estimated. Texas produces 1.1 million
goats annually, about 90% of the goats
raised in the United States (Scrivner et
al., 1985), and Pearson (1986) reported
that predators killed 18% of adults and
34% of kids. The number of goats lost to
feral swine predation is unknown, but is
likely substantial (>$1 million) consid-
ering $5.7 million was lost to coyotes in
the United States in 1990 (NASS
1991). Additionally in 1990, combined
sheep and lamb losses from coyotes were
valued at $18.3 million in the United
States (NASS, 1991). Where practical,
ranchers should closely monitor live-
stock and confine pregnant animals to
protected areas during calving and lamb-
ing seasons to reduce susceptibility to
predation. An understanding of field
sign and different behavioral cues can
help determine cause of mortality and
the impact of feral swine predation.
Feral Swine and Disease
Annual pork sales in the United
States exceed $11 billion with retail
sales exceeding $34 billion (Witmer et
al., 2004). Therefore, there is concern
relative to the role feral swine could pose
to the pork industry as a reservoir for dis-
ease. However, only 26% of Texas agri-
cultural extension agents were con-
cerned about disease transmission to
livestock (Rollins, 1993). Feral swine
can harbor at least 30 significant viral
and bacteriological diseases (Williams
and Barker, 2001) and feral swine in
Florida have been documented to have
as many as 45 different parasites and
infectious diseases (Forrester, 1991).
These include 37 parasites (12 proto-
zoans, 17 nematodes, 1 acanthocepha-
lan, 1 sucking louse, 4 ticks, and 2
mites), 7 bacteria, and 1 virus. Eight of
these parasitic and infectious diseases
can infect humans (brucellosis, lep-
tospirosis, salmonellosis, toxoplasmosis,
balantidiasis, trichinosis, trichostrongy-
losis, and sarcoptic mange). All four
species of ticks opportunistically infect
and feed on humans. The diseases of
most concern to the livestock industry
include pseudorabies, swine brucellosis,
bovine tuberculosis, leptospirosis, and
vesicular stomatitis (Becker et al., 1978;
Williams and Barker, 2001). These and
the possibility of an exotic disease out-
break, such as foot-and-mouth disease, a
contagious viral disease of ungulates
(e.g., pigs, sheep, cattle, goats, and deer)
(Pech and McIlroy, 1990), or classic
swine fever (a contagious viral disease of
wild and domestic swine), could have
serious repercussions for livestock indus-
tries (Hone et al., 1992). On the other
hand, feral swine may serve as a surveil-
lance tool for the early detection of
exotic diseases (Mason and Fleming,
1999; Witmer et al., 2004). These poten-
tial health aspects should be kept in
mind when considering feral swine range
expansion, translocation (Forrester,
1991), and tolerance around livestock
operations.
Crop Damage
Feral swine damage pasture and
agricultural crops by consumption, root-
ing, digging, and trampling. In Aus-
tralia, feral swine cause considerable
agricultural crop damage with >$100
million lost annually (Choquenot et al.,
1996). The greatest losses occurred in
wheat, sorghum, barley, oilseeds, sugar
cane, oats, and maize, in that order (Tis-
dell, 1991). In the United States, feral
swine damage $800 million in agricul-
tural crops each year, assuming that 4
million feral swine inhabit the United
States and cause $200 worth of damage
per pig (Pimentel et al., 2002). This
estimate is likely very conservative
because it does not consider livestock
predation, disease transmission, or envi-
ronmental degradation.
In Texas, the most common com-
plaint or concern (75%) in a survey con-
ducted by Rollins (1993) was damage to
agricultural crops including hay, small
grains (milo, rice, and wheat), corn, and
peanuts. Other crops affected were veg-
etables, watermelons, soybeans, cotton,
orchards, horticultural crops, and conifer
seedlings. Seventy-two percent of sur-
veyed extension agents reported addi-
tional damage to ranch facilities (e.g.,
fences, water supply, irrigation ditches,
and guzzlers).