Agriculture Reference
In-Depth Information
1.3.2
Growth rate
Most of the research work related to gilt development, body condition, lifetime prolificacy,
and longevity has focused on the importance of weight but, simultaneously, much of the
research has also focused on growth rate; or the rate of body tissue accretion. Tummaruk
et al.
(2001) reported that growth at too slow a rate during rearing compromises litter
size and weaning-to-oestrus interval in parities one to five. Johnston
et al.
(2007) in
retrospective analyses of data found that pigs produced and productive days over a
lifetime were decreased in females that grew too fast during development and were too
heavy at first service. Bortolozzo
et al.
(2009) reported that there is no advantage in
breeding gilts weighing more than 150 kg. They assert that the incidence of locomotive
failure increases for gilts with excessive weight gains prior to first breeding (>150-170 kg).
Kummer
et al.
(2009) reported no effect of lifetime growth rate on first parity reproductive
performance (pregnancy rate, ovulation rate, total embryos, viable embryos, and embryo
survival). Amaral Filha
et al.
(2010) suggested that fast growing gilts should be stimulated
to express puberty earlier (between 150-170 d of age) and be bred between 185 and 210
d of age to not become too heavy by the time of service and experience less productivity
later in life. Lastly, Knauer
et al.
(2011) reported a positive genetic correlation (r=0.52)
between growth rate to 114 kg and likelihood of farrowing a first litter; whereby very
fast-growing gilts were less likely to farrow their first litter.
Because weight at first service is often confounded with growth rate during rearing,
separating the effects of weight and growth rate is difficult. Knauer
et al.
(2010) concluded
that the relationship between growth rate and sow reproductive lifetime remain unclear.
Bortolozzo
et al.
(2009) wrote 'It is difficult to discern the real effects of age, weight,
and backfat and estrus number at first insemination on reproductive performance and
longevity. Flowers (2005) also stipulates that:
it is generally accepted that the development of the reproductive organs
during sexual maturation in gilts is positively correlated with their growth
rate. In other words, at the same chronological age, the reproductive organs
are more developed in heavy versus light gilts. While this probably still
holds true in most cases, it is important to recognize that there appear to be
some situations in which the development of reproductive organs becomes
uncoupled with growth rate. In these situations, growth rate and, thus age
and weight, at first mating could be similar among replacement females, yet
their reproductive performance as adults could be quite different.
1.3.3
Body fat
In 2005, Aherne wrote that 'there is no convincing evidence that backfat thickness, by
or of itself, has an inluence on sow reproductive performance. He also mentioned that
there is ample academic and on-farm evidence that females experience excellent lifetime
productivity even though they have thin layers of backfat at the beginning of their first
parity (Young
et al.
, 2004). Therefore, backfat (when conceiving the first litter) by itself
would not be a reliable predictor of subsequent sow reproductive performance. Aherne
