Agriculture Reference
In-Depth Information
of market value. Sehested (1996) reported that improving sow longevity by one parity had
a similar economic impact as improving lean meat content by 0.5%. Parson
et al.
(1990)
suggested that productivity of a stable pig herd (stable in terms of size) and its economic
status was not affected by parity distribution and its culling strategies; however, the
authors were making comparisons among herds where the percentage of first parity sows
was approximately 30%, which would be considered a much lower percentage compared
with the current approximation of 50% replacement rates on commercial herds.
Sow longevity plays an important role in piglet production for several reasons. First, the
length of productive life is directly related to the number of piglets produced during a
sow's productive lifetime. For instance, the number of pigs produced per litter from first
parity animals is less than the number of pigs produced by older sows and early removal
of sows from the herd results in higher infertility rates, less litters produced per sow, lower
mean litter size, lower number of pigs weaned per sow per year, and a higher number of
non-productive days (Anil
et al.
, 2009; D'Allaire and Drolet, 1999; D'Allaire
et al.
, 1987;
Dourmad
et al.
, 1994; Engblom
et al.
, 2007; Friendship
et al.
, 1986). Grandjot (2007)
reported that sows culled due to lameness produced 1.5 litters less than non-lame sows
over their productive life. King
et al.
(1998) reported that as percentage of gilts in the
inventory increases by 1%, average number of non-productive days increases by 2.6 d.
However, Stein
et al.
(1990) reported that shorter longevity can result in increased pigs
born live and weaned per litter because of the introduction of genetically superior females
with a higher average prolificacy.
Therefore, incentives to increase sow longevity would include: obtaining larger litter
sizes with heavier pigs from sows in older parities, fewer unproductive days, higher sow
salvage value, lower replacement cost, increase in gross income as older sows have more
piglets born alive which in turn is likely to result in more pigs marketed, and facilitating
animal welfare concerns (D'Allaire
et al.
, 1987; Stalder
et al.
, 2000, 2003).
19.3.3
Immunity
The introduction of replacement gilts into the breeding herd may pose health risks
among the existing females due to their immature immune system (Sanz
et al.
, 2002).
Farms with a large percentage of gilts often have more challenges with
Streptococcus suis
,
Actinobacillus suis, Haemophilus parasuis, Mycoplasma hyopneumoniae, Staphylococcus
hyicus
and Pasteurella organisms (Sanz
et al.
, 2002). Replacement gilts produced 'on-site'
are exposed to pathogens that are endemic in the herd and develop an immunity to them.
However, in modern pig production systems, many of the replacement gilts are raised
in multiple locations and it is likely that they will not be exposed to certain pathogens
until they are brought to a sow herd. Loula (2000) stated that this could be beneficial for
production but not for the development of immunity as the first exposure of gilts to some
organisms is when they enter the sow herd.
Regardless of the replacement gilts source, a period of isolation and acclimation is essential
for the long term productivity of the gilt in the breeding herd. Incoming replacement gilts
may appear healthy but could be incubating infections or acting as carriers of pathogens.
