Agriculture Reference
In-Depth Information
neutrophils are observed in colostrum, followed by declining neutrophil concentrations
as lactation progresses. Greater variability of reported neutrophil concentrations is
observed later in lactation. Average concentrations of macrophages and lymphocytes are
relatively constant throughout lactation, however, considerable variability exists among
reported differential cell counts. Eosinophils on average make up less than 2% of total
cells in mammary secretions. Proportions of epithelial cells change dramatically during
lactation, with low percentages observed in colostrum, followed by a rapid increase after
the colostrum phase. Weaning results in mammary secretions with 90 to 98% neutrophils
(Lee
et al.
, 1983).
9.12
Bioactive components
Colostrum and milk contain a wide array of biologically active factors, including
immunoglobulins and leukocytes (discussed above), enzymes, hormones and growth
factors, and others. Some of these components are briefly discussed here for sow
colostrum and milk.
Many hormones, growth factors and cytokines have been identified in milk of various
species (Baumrucker and Magliaro-Macrina, 2011; Pakkanen and Aalto, 1997). Many
of these biologically active components are thought to have effects in the neonate.
Concentrations of prolactin in colostrum are highest just prior to parturition and decline
rapidly during the first 24 h postpartum (Devillers
et al.
, 2004a). After the colostrum
period, prolactin slowly declines from about day 5 through the remainder of lactation
(Mulloy and Malven, 1979). Milk prolactin concentrations are affected by litter size, with
sows nursing litters of 8 piglets having lower milk prolactin concentrations compared
with sows nursing litters of 10 or 12 piglets (Mulloy and Malven, 1979). Concentrations
of serum prolactin and milk prolactin are positively correlated at least through day 13 of
lactation (Mulloy and Malven, 1979).
Relaxin is also found in sow milk (Yan
et al.
, 2006), secreted as the pro-form of the
hormone (Bagnell
et al.
, 2009). Concentrations of relaxin are highest in colostrum and
then decline over the first 4 to 6 d of lactation (Yan
et al.
, 2006). This milk-borne relaxin is
thought to be a route of maternal programming of neonatal development in the lactocrine
hypothesis (Bagnell
et al.
, 2009).
Concentrations of leptin in defatted mammary secretions decrease from parturition
to day 7 of lactation, and then remain unchanged through 22 d of lactation (Estienne
et al.
, 2000). However, leptin concentrations in whole milk are not affected by stage of
lactation (Estienne
et al.
, 2000). Neither whole nor skim milk leptin concentrations are
significantly affected by body condition, and they are not correlated with backfat thickness
or sow serum leptin concentration (Estienne
et al.
, 2000). Mean leptin concentrations in
mammary secretions during the initial 4 d of lactation are significantly greater in Yorkshire
(75%) × Meishan (25%) crossbred sows than in Meishan sows (Mostyn
et al.
, 2006).
