Agriculture Reference
In-Depth Information
Landrace, Large White), which produce more milk than meat type breeds (i.e. Duroc,
Pietrain). The heritability of sow milk yield is moderate, i.e. 0.27 for daughter-dam
regression (York and Robison, 1985), which explains the positive impact of selection on
milk yield over the years. Indeed, in 1971, Elsley (1971) reported sow milk yields of 5.2
kg/day whereas Sauber and Stahly (1996) reported values of 10.3 kg/day in 1996 and King
and Eason (1998) reported values of 11.6 kg/day in 1998. Milk yield values have then
remained quite stable with values of 9.6 kg/d reported in 2011 (De Oliveira Junior
et al.
,
2011). It is interesting to note that the total number of teats and the number of functional
teats (i.e. not inverted or blind) in females can also be selected against, having respective
heritabilities of 0.36 to 0.42 and 0.29 (Chalkias
et al.
, 2013). The association between
genetics and sow milk yield was also illustrated in a study where sows were genetically
modified to overexpress alphalactalbumine by inserting the bovine gene in the sow
genome (Noble
et al.
, 2002). These transgenic sows produced approximately 50% more
alphalactalbumin than control sows and their milk yield was 13 to 23% greater on d 3, 6,
and 9 of lactation. Milk yield is also affected by parity of the sow with multiparous sows
producing more milk than primiparous sows and milk yield being greatest in parities 2
to 4 and decreasing thereafter (Dourmad
et al.
, 2012). Speer and Cox (1984) estimated
that milk yield from second-parity sows is 35% greater than that of first-parity sows. The
number of functional teats remains stable from 1
st
to 7
th
parity whereas the number of
unused teats at weaning decreases from 1.3 to 0.5 between parities 1 and 7 (Caugant
et
al.
, 2000).
Litter size and suckling intensity
The number of suckling piglets is the major determinant of sow milk yield. Indeed, milk
production was found to be proportional to the number of suckled mammary glands
(Auldist
et al.
, 1998). Typical sow production curves for varying litter sizes are shown in
Figure 8.1, demonstrating the greater milk yield as litter size increases (Toner
et al.
, 1996).
Nevertheless, the amount of milk ingested per piglet decreases as litter size increases
with 14 piglets ingesting 1.11 kg/day instead of the 1.63 kg/day ingested when litter size
is 6 (Auldist
et al.
, 1998). The role of piglets in determining milk output is described
in detail in the review by Auldist and King (1995). Not only number of piglet but also
size of individual pigs affects milk yield. Van der Steen and De Groot (1992) clearly
demonstrated that birth weight has a substantial effect on milk intake and pre-weaning
growth rate of piglets. King
et al.
(1997) also reported a positive relationship between
piglet body weight and milk consumption, indicating that older, heavier piglets are able
to remove more milk from the mammary glands of lactating sows. Suckling intensity
per se also seems to play a role for milk production in early lactation. Algers and Jensen
(1991) reported a relation between the duration and intensity of teat stimulation and
subsequent milk yield from that teat on days 1 to 3 of lactation. However, such was not the
case in later lactation as there was no correlation between the duration of post-ejection
udder massage on days 11 and 18 of lactation and subsequent milk yield (Thodberg and
Sorensen, 2006). It is nevertheless apparent from all reported findings that the demand
of piglets for milk during lactation has a direct effect on milk yield. This was elegantly
illustrated in a study by Auldist and King (1995) where sows nursed either 6 piglets, or
two litters of 6 piglets which alternately had access to suckled every 30 min.
