Agriculture Reference
In-Depth Information
parturition, therefore meeting the recommendation of Williams
et al.
(2005). They should
then have had the body reserves to withstand parity-one lactation without experiencing
any compromise in subsequent performance. Yet, categorically, approximately 25% of the
sows weighed less than 178 kg at weaning and gave birth to smaller litters in parity two. In
an alternative categorical assessment of the data, smaller second litter sizes occurred for
39% of the gilts that lost 10.1 to 25.0% of their body weight in parity one. It appears that
the achievement of first service targets proposed by Foxcroft (2002) and Williams
et al.
(2005) were inadequate. Schenkel
et al.
(2010) suggested that season, depressed lactation
feed intake (not reported), increased mobilization of body nutrients to a threshold, and
even first breeding targets could not protect against subsequent reproductive negative
outcomes. Body condition at first breeding is an inaccurate science because of the
variation in severity of reproductive experiences that follows. There exist all the extremes
with respect to feed, parturition, effective environment, and husbandry during phases of
reproductive cycles that follow first breeding.
Overall, long-term research using accurate measures of protein mass in gilts is lacking. In
assessing over 4,000 gilt records from Australia, Johnston
et al.
(2007) used a statistical
analyses called recursive partitioning and reported that in the two maternal genetic
lines of gilts studied, an increased longissimus thoracis muscle diameter at selection (22
weeks of age) marginally improved lifetime performance. Knauer
et al.
(2011) estimated
genetic correlations between loin muscle area at puberty and the likelihood of parity-one
farrowing, total number born in parity one, and wean-to-estrus interval after parity-
one lactation. Genetic correlations between these three reproductive outcomes and loin
muscle area at puberty (212 d of age and 137 kg body weight) were also estimated and
were 0.31, 0.01 and 0.10, respectively. It was concluded that more muscle at puberty
moderately increases the likelihood of parity-one farrowing. The importance of protein
mass for parity-one litter size was less apparent. It is often thought that body protein
reserves are important for the quick resumption of estrous activity post weaning, and the
low positive genetic correlation gives support to that hypothesis.
Relative to body protein, every so often the rate of lean accretion during rearing is
mentioned as a body condition variable that may be more important in the lifetime of
the sow than presently known. Citing the work of Stalder
et al.
(2000) and their own,
Johnston and Smits (2007) argued that if lean growth was too rapid then longevity would
be compromised.
1.4
Conclusions
Recent research, summaries, and commentaries suggest that the relationships between
phenotypic measures of body condition and subsequent reproduction will not grow more
precise in their predictive use. In other words we cannot narrow the weight range or the
backfat depth range or the age by weight combination range to bring about noticeable
improvements in lifetime productivity or longevity of the sow. Relatedly, at present there
is no convincing research to provide protein mass (precise longissimus thoracis muscle
depth or area) targeting.
