Body weight (BW) and backfat thickness (BT) were
measured at a maximum of 24 h after farrowing and again
at day 19 of lactation. Body weight of sows was also
measured on days 7 and 15 of lactation. Measurements
of BT were taken at P2 point on the last rib, 6.5 cm away
from the midline of the vertebral column with A-mode
ultrasonography (Renco Lean Meters-Renco Corporation,
Minneapolis, MN) within a range of 1 mm. Percentages of
body fat and body protein were estimated according to the
equations of Whittemore and Yang (1989). The loss of BW,
protein mass and fat mass, between parturition and weaning,
were expressed in kilograms and also as percentages in
relation to BW, body protein mass and fat mass at parturition.
Data regarding the weaning-to-oestrus interval (WOI),
farrowing rate, number of piglets born and culling of sows
were captured from the available production records. Data
concerning farrowing rate and subsequent litter size are
from the first insemination after weaning.
Piglets were identified with both ear tag and tattoo
and were individually weighed with a digital balance (5 g
of precision) at cross-fostering and at 7, 15 and 19 days of
lactation. The mortality of piglets was daily recorded.
Lactation efficiency was calculated according to the
following equation: lactation efficiency (%)¼energy output
100/energy input. Daily energy input and output
(MJ ME/d) were calculated using the equations described
by Bergsma et al. (2009) except for the weight of sows at
parturition and the weight of dead piglets, which were
not estimated but recorded during the study.