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versus 145 kg). Bussières (2013) described the relationship between body weight at
first service and lifetime total born to be very similar to that reported by Williams
et al.
(2005). Total born over a lifetime for the 145-160 kg group of Bussières (2013;
Figure 1.1) was significantly more than for the lightest (115 to 130 kg) and heaviest
(175 to 190 kg) weight groupings, but not different from the 130-145 kg or 160-175 kg
groups. The suggested target range for body weight at first service was 130 to 175 for the
population of gilts studied.
Most consistent in the literature is the fact that very heavy gilts at first breeding are more
likely to experience lameness (Amaral Filha
et al.
, 2009; Kummer
et al.
, 2006; Patterson
et al.
, 2010; Williams
et al.
, 2005). The breakpoint in weight most frequently mentioned
is approximately 170 kg. Lyvers-Peffer
et al.
(2003) suggested that most of the culling for
lameness with heavy gilts at first mating would occur primarily before parity two. Quinn
(2013) also suggested that producers beginning the development of replacement gilts
should remove them from the grow-finish flow at 65 kg and then feed a gilt-development
diet from that time on. Reduction in lameness and claw lesions were attributed to the
use of a zinc, copper and manganese supplement in the gilt development diet. Increased
macroscopic articular surface deformations were reported by De Koning
et al.
(2013) for
gilts given
ad libitum
access to feed from 10 to 26 weeks of age, in contrast to restricting
feed intake (80% of
ad libitum
) for the same growth period. The deformations were
observed when gilts were slaughtered at 26 weeks of age and are purportedly indicative
of the development of osteochondrosis.
Relative to skeletal development there are few, if any, empirical measures available to
producers for assessing this. Enhancing bone mineralization is often mentioned as
the justification for not raising replacement females in the commercial finishing unit
with hogs to be sent to harvest. Rozeboom (2006) wrote that the justification for 0.1
percentage point greater requirement for calcium and phosphorus in order to maximize
bone mineralization was not indisputable. The recommendation which continues to be
made to producers presently is based on the research of Nimmo
et al.
(1981). Yet, there
were three other research groups who also studied bone mineralization in growing pigs
around that same time and their work did not support a similar conclusion To this day,
more research is needed into the mineral requirements for skeletal development of gilts.
65
60
55
50
45
40
115-130
130-145
145-160
160-175
175-190
Body weight at
rst breeding (kg)
Figure 1.1. Relationship between body weight at first breeding and total piglets born in the female's lifetime
(Bussières, 2013).
