Colostrum and milk production - The Gestating and Lactating Sow - page 173

around parturition. The data also suggest that a high feed intake is favourable for milk
output in late lactation, although milk yield was not significantly reduced in sows fed ad
libitum from day 14 only compared to those fed ad libitum from day 7 of lactation.

Body condition is another important trait for sow milk yield, and capacity of body
mobilization seems to be more important than a high feed intake (Beyer et al. , 2007;
heil et al., 2012). Especially after peak lactation, the persistency of lactation seems
to be related to body condition, as indicated by a high level of backfat (Hansen et al.,
2012a). Kim et al. (2009) demonstrated that the ideal amino acid profile for lactating sows
depends on the extent of body weight loss during lactation, and sows with a high weight
loss required more threonine and leucine (relative to lysine) than sows that did not lose
weight throughout lactation. These findings indicate that the dietary ratios of essential
nutrients and the feeding curve are important traits for improving the sow milk yield.

Endocrine status

Milk yield is affected by hormonal status and various hormonal treatments were used in
an attempt to increase sow milk yield. Injections of thyrotropin-releasing factor (TRF)
either increased (Wung et al. , 1977) or had no effect on piglet weight gains (Dubreuil et
al. , 1990). Addition of TRF in the diet of lactating sows increased piglet weights but also
increased the weaning to oestrus interval, making such a treatment inadequate for swine
producers (Cabell and Esbenshade, 1990). When looking at the impact of exogenous
growth hormone (GH) on sow milk yield, an early study reported a 15-22% increase in
milk yield (Harkins et al., 1 989), however, those results could not be reproduced in later
studies (Cromwell et al. , 1992; Toner et al. , 1996). The use of growth hormone-releasing
factor increased circulating GH but did not affect sow milk yield, milk composition,
or piglet performance (Farmer et al. , 1992). Another hormone, prolactin, is of special
interest for lactating sows. Indeed, inhibition of prolactin during lactation inhibits milk
production in sows (Farmer et al. , 1998). Furthermore, sows with spontaneous lactation
failure were shown to have abnormally low concentrations of prolactin (Whitacre and
Threlfall, 1981) and an 8% increase in litter weight gain was later observed in gilts (but
not sows) receiving a single injection of porcine prolactin on day 1 of lactation (Dusza et
al. , 1991). Yet, daily injections of porcine prolactin to sows from days 2 to 23 of lactation
did not increase piglet weight gains (Farmer et al. , 1999). This was likely due to the fact
that all prolactin receptors were already saturated in control animals, thereby preventing
any beneficial effects of further increasing prolactin concentrations.

8.5 Conclusions

Even though the quantities of colostrum and milk produced by the sow are crucial for
piglet survival and/or performance, much still remains to be learned about the factors
controlling them. With respect to colostrum yield, future research should focus on
the impacts of sow nutrition and metabolic status during late gestation as well as on
the potential impact of mammary development. Regarding milk yield, future research
endeavours should concentrate on amino acid requirements of hyperprolific sows,