The first week postpartum is the period of greatest loss for U.S.
swine producers, with most morbidity and mortality attributed to
malnutrition and scours. In addition, long-term swine growth
potential can be permanently reduced by malnutrition or disease
during the suckling period. Improving milk quantity and quality are
likely to improve, piglet performance, however, little progress has
been made in this area through conventional means. Thus, transgenic
technology, or the insertion of foreign genes into an organism, may
provide an effective means for addressing the problem of low milk
production and its detrimental impact on swine production. We developed
two separate lines of transgenic swine with mammary- and
lactation-specific overexpression of bovine a-lactalbumin (a-LAC) or human
insulin-like growth factor-I (IGF-I). These two proteins were chosen for
their roles in lactose synthesis and milk production (a-LAC) and mammary
development, milk production and neonatal intestinal development (IGF-I).
The IGF-I construct consisted of the IGF-I gene inserted directly behind
the a-LAC signal peptide coding sequence to allow for secretion of IGF-I
into milk. Outcomes assessed were milk composition, milk yield, piglet
growth and intestinal development. First parity a-LAC gilts had higher
milk lactose content in early lactation and 20 to 50% greater milk yield
on days 3, 6, and 9 of lactation than non-transgenic gilts. Weight gain of
piglets suckling a-LAC gilts was greater from d 9 and 21 postpartum than
control piglets. IGF-I concentrations were ~10-fold higher in colostrum
of first parity IGF-I transgenic gilts than non-transgenic gilts and
elevated milk IGF-I was maintained throughout lactation at levels which
are bioactive in piglet intestine (1 mg/L). Milk yield may also be
enhanced in IGF-I transgenic sows on d 3 vs. nontrangenic sows. Thus,
transgenic over-expression of milk proteins may provide a means to improve
swine lactation performance.