Agriculture Reference
In-Depth Information
Body condition is a term used when considering the preparedness of the young female
for successful lifetime reproduction.
Relative to body condition, producers, production managers, veterinarians, geneticists,
and nutritionists, use 'target' indicators of bodily development to ensure that gilts
initiating reproductive activity are adequately developed before they are first serviced
and conceive. This is intended to provide a safeguard against too few gilts being serviced,
small litter sizes, inconsistent reproductive performance post-weaning, and early removal
from the herd. Some would like to think that targets are guarantees that females will
produce offspring in large quantities at a consistent or uninterrupted frequency. Body
condition, however, is only one aspect of gilt development. Other developmental aspects
include health and management of the gilt's external environment.
Applied research has sought to identify targets of ideal maturity (a combination of age and
body composition) for given genotypes. In swine literature, targets are often suggested
for age, weight, growth rate, and backfat thickness. Occasionally, longissimus thoracis
muscle diameter or area may also be included. Numerous target suggestions have been
published in journal articles, proceedings, magazines, bulletins, and company materials.
Noteworthy, thorough and insightful reviews summarizing the relationships between
body condition targets and reproductive success have been written in the last 5 to 7 years
by Gill (2007), Johnston and Smits (2007) and Bortolozzo et al. (2009).
There is genetic variation in body composition and in rates of tissue accretion. Maternal
lines, from which modern replacement gilts originate, have been selected primarily for
large litters (12 to 13 live born piglets) and exceptional milk production (litter weight
gains of 2.3 to 2.7 kg/d). These females are typically crossbred, with docile temperaments,
white in color and derived from varied genetic backgrounds including lines and crosses
from hybrid seedstock companies and independent breeding stock producers. In the
last decade of the 20 th century, the desire for lean market hogs resulted in maternal lines
also being very lean and with less appetite. Realizing this as an undesirable predicament,
selection and molecular genetics have been used in the past 10 years to develop maternal
females with greater fatness, greater feed intakes, possibly less muscle mass, and more of
that difficult-to-measure characteristic called 'robustness.'
Genotypic differences in body composition (rate of accretion and absolute mass of fat,
lean, and skeleton) and in reproductive traits are acknowledged (Johnson et al. , 2008;
Knauer et al. , 2010; Rozeboom, 1999). Unique body condition targets are believed
justified for each maternal genotype and most seedstock providers suggest them. In
depth discussion of these differences was not purposed here. The discussion herein
is based upon conclusions from reports about body condition where comparisons of
developmental treatments were applied within genotype.
Pinilla et al. (2103) suggest that the 'new normal' is 30 total piglets born in parity one and
two, and 78 total born in a lifetime of 5.2 parities. The desire is to have greater than 60%
of selected gilts bred from weeks 29 to 31 of age, and by 33 weeks of age to have greater
than 90% of selected gilts bred. Operationally, gilt development targets are fairly easy to
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