Agriculture Reference
In-Depth Information
From the point of view of the individual piglet, it is good to cooperate with other piglets
to stimulate sow milk production. At the same time, getting a preferential share of the
milk production is a beneficial strategy since it will support faster growth. This creates
space for sibling competition over the milk allocation. Additionally, a beneficial strategy
for the sow may be to allocate the milk equally to the viable progeny, the sow may thus
behave in such a way as to suppress sibling competition.
13.4.1
Colostrum/milk production and litter size
The most important function of the nursing interactions during the early postpartum
teat-sampling period is the provision of colostrum to piglets. The parturient and post-
parturient sows facilitate this function by exposing their udder through immobile lateral
lying, thereby enabling the piglets to sample all teats freely. Piglets fight a lot during teat
sampling and the proportion of fights won by a piglet has a positive, albeit weak, influence
on how frequently the piglet suckles during the first day postpartum, however it has no
influence on the number of teats suckled (de Passillé and Rushen, 1989; de Passillé
et
al.
, 1988a). Thus, it seems that passive exposure of the udder by the sow creates an even
playing field in which most piglets can have a proper colostrum intake. However, the
ability of the sow to provide a reliable source of colostrum for all piglets may reach a limit
as the number of piglets approaches or even surpasses the number of functional teats. The
factors affecting colostrum yield are covered in Chapter 8 (Quesnel
et al.
, 2015). With
relation to litter size, it is known that total colostrum yield is constant across different
litter sizes (Devillers
et al.
, 2007; Quesnel, 2011), but that colostrum intake per piglet
decreases with increasing litter size. Because milk yield among sows varies considerably,
it is estimated that about 35% of sows do not produce enough colostrum to adequately
supply all their piglets (Quesnel
et al.
, 2012). In addition, sows with high within-litter
variation in piglet birth weights produce less colostrum (Quesnel, 2011). As a result, low
birth weight piglets in large litters are at a heightened risk of not obtaining at least 200
g of colostrum, which is the amount needed for adequate immunoglobulin levels and
minimum growth. Andersen
et al.
(2011) proposed that neonatal mortality in large litters
is 'adaptive, i.e. that it is a strategy for sows facing a trade-of between the ofspring quality
and their quality or vitality. According to this 'litter reduction' hypothesis, the function
of maternal passivity is to allow free course for the sibling competition which results in
discarding the weakest offspring so that more resources are available for the surviving
majority of piglets. Although this view might be controversial, it highlights the fact that
the intense selection for large litter size at birth results in greater piglet mortality, and
thus, in ever smaller net gains in the number of weaned piglets (Milligan
et al.
, 2002).
Piglet mortality occurs mainly during the first 1-3 postnatal days so that individual litter
sizes are almost stable over the rest of lactation. This has important implications for milk
production because unsuckled glands regress rapidly within the first week (Kim
et al.
,
2001) and total milk production is affected (see Chapter 4 on mammary development for
more details (Farmer and Hurley, 2015)). The established litter size determines to a great
extent the ensuing milk production, as documented by the fact that mobilization of body
protein in sows increases linearly with litter size at week 3 of lactation. In smaller litters,
