Agriculture Reference
In-Depth Information
4.7
Management strategies that can affect mammary
development
Litter size is known to affect milk yield (King, 2000) and it also has an impact on mammary
development (Kim
et al.
, 1999c). First-parity sows with a larger litter size (12 pigs) were
shown to have a greater total mammary mass on day 21 of lactation than sows with a
smaller litter size (6 pigs), however, the weight of each individual gland was lower in the
larger litter size (Kim
et al.
, 1999c). Wet and dry weights of total nursed mammary glands
increased linearly with litter size and doubling the litter size from 6 to 12 pigs led to a 65%
increase in total mammary wet weight, a 67% increase in total mammary DNA, and a
63% increase in total protein. These increases result from the greater number of lactating
glands since within individual nursed glands wet and dry weights as well as the amounts
of dry fat-free tissue, protein, DNA and fat decreased as litter size increased. Results
suggested that there are no differences in terms of cell density or cell size between nursed
glands from sows with differing litter size, rather there was greater mass of parenchymal
tissue in glands from sows with smaller litter sizes. An important finding was that an
increase in the size of mammary glands or in the amount of mammary protein had
a positive impact on piglet weight gain. This supports the importance of maximizing
mammary growth via feeding and other strategies during lactation.
Another management aspect which affects mammary development is teat use or lactational
history. That is, the extent to which a gland grows and lactates in one lactation may
impact that gland's growth and function in the subsequent lactation. Ford
et al.
(2003)
noted that mammary glands that were suckled during lactation were larger than non-
suckled glands at the end of the involution process, suggesting a possible beneficial effect
on redevelopment during the next gestation. Results from an earlier study did indicate
a likely effect of teat use or non-use in one parity on its productivity in the subsequent
lactation, yet, there was a confounding effect of treatment with teat location (Fraser
et al.
,
1992). Recent data permitted to clearly establish that non-suckling of a teat in first parity
impairs its development in second parity (Farmer
et al.
, 2012c). Either the same teats or
different teats were blinded during the first and second lactation and teats which were not
suckled in first parity had less parenchymal tissue and less parenchymal DNA and RNA
at the end of the second lactation than teats which were previously suckled. This indicates
the occurrence of both hyperplasia and increased metabolic activity of parenchymal cells
from glands that were previously used. Furthermore, piglets suckling previously-used
teats weighed 1.12 kg more at 56 days of age than piglets suckling previously unused teats
(Farmer
et al.
, 2012c).
4.8
Conclusions
Mammary development can be altered by many factors including nutrition and
endocrine status of the gilt or sow, but much still remains to be learned in order to
develop optimal management strategies for replacement gilts, gestating gilts and lactating
sows that will maximize their milk production. Table 4.1 and Table 4.2 summarize the
various treatments that can significantly affect mammogenesis in growing gilts and
