Agriculture Reference
In-Depth Information
7.2.8
Time of the onset of lactation
During the first 48 h after parturition, the amount of mammary secreta (colostrum and
milk) changes considerably. During the initial 12 to 15 h after birth of the 1
st
piglet
colostrum is abundantly available, but subsequently the amount of secreted colostrum
drops (Krogh
et al.
, 2012; Krogh
et al.
, unpublished data). The amount of mammary
secreta is then low until the onset of copious milk production, which on average occurs
33 to 34 h after birth of the 1
st
piglet (Krogh
et al.
, 2012). It is unclear why colostrum
becomes scarcely available after 15 h, but it is likely linked to a drop in oxytocin
concentration in sow plasma when farrowing ceases. Interestingly, we have found that
onset of lactation may happen as early as 23 h postpartum in some sows or as late as 39 h
in other sows. Currently, we can only speculate on what causes this variation among sows.
We have tested whether time for onset of lactation may be linked to feed composition
or feed intake of sows in the transition period, body weight or backfat thickness of sows
at parturition, farrowing length or litter size during the colostrum period, but none of
these characteristics could explain the individual differences observed (Vadmand
et al.
,
unpublished data). Thus, the reason for the difference in the timing of lactation onset
between sows remains to be elucidated. It may be linked to when the litter establishes a
teat preference and, in a concerted action, successfully massages the udder and induces
milk letdown. Interestingly though, an early onset of lactation was associated with higher
milk yields in weeks 1, 2, 3 and 4 of lactation (Vadmand
et al.
, unpublished data). The
onset of lactation has a great impact on sow physiology because the energy and protein
balances drop abruptly once milk production is initiated (Hansen
et al.
, 2012b, 2014).
7.2.9
Milk synthesis
Milk production is a major investment for the lactating sow, and at peak lactation half the
amounts of nitrogen (52%) and energy (50%) from the feed are transferred to the piglets
via milk (Theil
et al.
, 2004). Consequently, synthesis of milk is the reproductive trait which
has the greatest impact on the daily sow nutrient requirements. The nutrient requirements
for milk synthesis depend on both the yield and composition of milk, and both traits are
affected by the stage of lactation (Theil
et al.
, 2002, 2004; Hansen
et al.
, 2012b), however,
without doubt milk yield has the greatest impact on the nutrient requirements.
The sow lactation curve was recently described using a mathematical model (Hansen
et
al.
, 2012b). The developed mathematical model predicts milk yield based on the litter
weight gain and litter size, and with these simple inputs, milk yield can be estimated for
each day of lactation. The mathematical model takes into account all published data on
milk yield from 1980 to 2012, where sow milk yield has been measured at least twice
during the lactation period. The lactation curve is characterized by an increase in milk
yield from the onset of lactation (milk yield of approximately 5.7 kg at d 2) to the end of
the transition period (d 10 of lactation) when it averages 11-14 kg/d. After the transition
period, milk yield peaks at around d 17 to 19, depending on the litter size and litter weight
gain (Hansen
et al.
, 2012b), and the best performing sows produce 15 to 17 kg/d. As a
consequence of the secretory activity of the mammary glands, the mammary plasma
flow increases from approximately 3,500 l/d 10 d before parturition to 6,000 l/d 3 d
