Agriculture Reference
In-Depth Information
measure and manage. In the past five years, the most consistent recommendations for
gilt development have been:
•
Relative to estrous activity prior to first service:
-
lifetime growth rate during rearing not slower than 550 g/d;
-
lifetime growth rate during rearing not faster than 850 g/d;
-
have 90% of gilts cycling within 6 weeks of puberty stimulation;
-
heat-no-serve recorded for all breeding females.
•
Relative to the timing of first service:
-
135 to 170 kg body weight;
-
220 to 270 d old;
-
growth rate during rearing not faster than 850 g/d;
-
backfat depth of 12 to 18 mm;
-
body condition score of 3 to 3.5.
In this body of writing, important questions about targets have led to consideration of
conditioning of the gilt for optimal reproductive performance. How have these targets
and their importance changed in the past 10 years? Have they become more effective
in maximizing lifetime productivity and minimizing gilt development costs? Has their
predictive power (repeatable practical value) improved?
1.2
Gilt body condition and estrous activity prior to first
service
In 1991, Beltranena
et al.
described the relationship between lifetime growth rate and age
at pubertal estrus using a quadratic curve. This showed that age at first estrus decreased as
growth rate increased from 0.4 to 0.53 kg/d, was unaffected as growth rate increased from
0.53 to 0.6 kg/d, but then increased as growth rate exceeded 0.6 kg/d. Puberty was delayed
in extremely slow growing and extremely fast growing gilts. Foxcroft
et al.
(2005) called
this curvilinear response of growth rate vs. age at puberty a tendency for the extreme
growth rates to be associated with a marginal delay in pubertal estrus. Rozeboom
et al.
(1995) reported that the occurrence of puberty in gilts given
ad libitum
access to feed
during rearing and initially exposed to mature boars at approximately 120 d of age was
not related to a specific rate of body tissue accretion
In the past 10 years, knowledge about the occurrence of pubertal estrus and lifetime growth
rate has been explored further. Bortolozzo
et al.
(2009) noted that gilts experiencing
greater lifetime growth rate during rearing (>700 g/d) attain puberty earlier and have
a lower incidence of anestrus between pubertal estrus and breeding. They concluded
that very fast growth rate (close to 800 g/d) does not delay the occurrence of pubertal
estrus. Others have supported this finding (Amaral Filha
et al.
, 2009; Kummer
et al.
, 2009;
Patterson
et al.
, 2010).
Overall, most recent research is in agreement that there is little relationship between
lifetime growth rate and age at first estrus. The interest in the relationship between growth
rate and age at puberty has been fostered by speculation that rate of fat and protein
