Sow longevity - The Gestating and Lactating Sow - page 414

the replacement rate may be higher than the removal rate. Conversely, when reduction
in herd size occurs, the replacement rate may be lower than the removal rate. Therefore,
population dynamics should be considered when analysing these rates.

The mean parity of sows at removal indicates the average length of time that sows stay
in the herd. Several studies reveal that the average parity at removal is between 2 and
5.6, but it can be as high as 8 (D'Allaire et al. , 1987; Koketsu et al. , 1999; Lucia et al. ,
2000b; Pedersen 1996; Stein et al. , 1990). In North America, the reported mean removal
parity ranges from 3.1 to 4.1 (D'Allaire et al. , 1987; Koketsu, 2003; Lucia et al. , 2000b;
Rodríguez-Zas et al. , 2003). In Dutch, Irish, Swedish, and Japanese commercial herds,
sows completed 4.3 to 4.6 parities by removal (Boyle et al. , 1998; Dijkhuizen et al. , 1989;
Engblom et al. , 2007; Koketsu, 2007).

At a minimum, breeding females should be kept in the herd until the investment cost
associated with their replacement is recuperated. According to Lucia et al. (2000a),
maximum removal parity associated with profitability ranged from 5 to 8. Rodríguez-
Zas et al. (2006) reported that culling sows at parity 4 or 5 would be optimal in order
to maximize profitability in breed-to-wean herds. Furthermore, Abell et al. (2010)
determined that the genetic loss of retaining a sow in the herd for additional parities had
a relatively low economic value, and therefore the optimal removal parity was greater
than 7 in U.S. commercial herds.

Furthermore, Hurnik and Lehman (1985) suggested that longer longevity is an indicator of
animal welfare and of whether animal needs are being satisfied. Conversely, high removal
rates are a welfare concern since some of the causes of culling and mortality could be
indicators of a welfare compromise for the animals involved (Barnett et al. , 2001). Shorter
longevity is often associated with an increased mortality rate involving some level of
suffering, and culling reasons due to some painful pathology such as leg problems (Deen,
2003). Moreover, it is not ethically acceptable from an animal welfare perspective to base
pork meat production on sows that are not capable of handling the physiological stress of
piglet production over numerous parities (Serenius and Stalder, 2006).

19.3 Economic importance of sow longevity: effects on the

sow herd

19.3.1 Parity distribution

The parity distribution of a breeding herd indicates when sows are more likely to be
removed as it influences biologic and economic performance of the sow herd. Pinilla
and Lecznieski, (2014) defined the 'ideal' parity distribution as a mathematical function
of sow removal rate, gilt availability, hog market price and feeding costs. According to
D'Allaire et al. (2012), the 'ideal' parity profile for a breeding herd is function of the
maximum number of parities that sows are allowed before automatic culling occurs and
annual culling rate, and once these two values are known, the distribution or percentage
of sows culled in each parity is a linear function.