Colostrum and milk production - The Gestating and Lactating Sow - page 168

ascending phase of lactation, nursing frequency doubles, going from 17 to 35 nursings
per day between days 2 and 10 of lactation (Jensen et al. , 1991). The quantity of milk
obtained at each nursing also increases from 29 to 53 g between the first and the third
week of lactation (Campbell and Dunkin, 1982). Milk production on day 4 of lactation
ranges between 5 and 10 kg/day with an average of approximately 8 kg/day (Toner et al. ,
1996), being approximately twice the total yield of colostrum produced. The duration of
the ascending phase may vary from 14 to 28 days, depending on factors such as breed,
nutrition, parity or method used to estimate milk yield (Elsley, 1971; Harkins et al. ,
1989). According to a recent meta-analysis, the mean time to peak lactation in sows using
numerous studies published since 1980 was 18.7 days (Hansen et al. , 2012). During that
ascending phase, milk yield is adjusted to the needs of the piglets with piglets of greater
birthweight ingesting more milk at each nursing than their lighter littermates (Campbell
and Dunkin, 1982). Nevertheless, milk yield is limiting for growth rate of the nursing
pigs. Indeed, the weight of suckling piglets supplemented with artificial milk replacer
from day 3 until weaning was increased on days 7, 14 and 21 of lactation compared with
that of non-supplemented pigs (Wolter et al. , 2002). In modern swine husbandry systems,
sows normally do not reach the descending phase of lactation because they are weaned
during the plateau phase.

8.4.2 Milking frequency

During lactation, cyclical nursings start approximately 10 hours after the onset of
farrowing (Lewis and Hurnik, 1985) and develop gradually (Algers and Uvnäs-Moberg,
2007). Nursing frequency has a major role in determining milk output and reaches
a maximum around days 8 to 10 of lactation and decreases thereafter (Puppe and
Tuchscherer, 2000). Nursing intervals of 36 to 40 minutes were reported in early lactation
(day 5 or 6) and of 39 to 48 minutes at peak lactation (day 18 or 20) (Farmer et al. , 2001;
Fisette et al. , 2004). Removal of milk from the mammary glands is of utmost importance
in order to maintain milk secretion (Theil et al. , 2005). It has been suggested that as milk
components accumulate in the alveolar lumen, there is also accumulation of an autocrine
factor which would be responsible for inhibiting lactation (Peaker and Wilde, 1987). Yet,
this protein has never been purified or sequenced, despite numerous attempts. Refilling
of the mammary glands with milk is almost complete within 35 minutes after suckling
(Spinka et al. , 1997), thereby demonstrating the importance for maintaining a nursing
interval as close to 35 minutes as possible. Prolonging the nursing interval only slightly
increases milk output per nursing (Spinka et al. , 1997).

8.4.3 How to measure milk yield

There are three frequently used methods to quantify sow milk yield, namely, the weigh-
suckle-weigh technique, the DO dilution technique, and prediction based on piglet or
litter weight gain. Milk yield can be measured directly using the weigh-suckle-weigh
technique. It implies that either the sow or the whole litter is weighed before and after
each suckling bout for a series of consecutive sucklings. For practical and precision
reasons, repeatedly weighing the litter is much more common than weighing the sow.
The weigh-suckle-weigh technique is applicable throughout lactation because the whole