Growth heterogeneity in broiler breeder pullets is settled before the onset of feed restriction but is not predicted by size at hatch

• Uniform growth is a desirable trait in  all large-scale animal production systems because it  simplifies animal management and increases profitability.  In parental broiler flocks, so-called broiler  breeders, low growth uniformity is largely attributed  to the feed competition that arises from quantitatively  restricted feeding. As feed restriction is crucial to  maintaining healthy and fertile breeders, several practices  for reducing feed competition and the associated  growth heterogeneity have been suggested and range  from nutrient dilution by increasing fiber content in  feed to intermittent fasting with increased portion size  (“skip a day”), but no practice appears to be entirely  effective. The fact that a large part of the heterogeneity  remains even when feed competition is minimized  suggests that some growth variation is caused by other  factors. We investigated whether this variation arises  during embryonic development (as measured by size at  hatch) or during posthatch development by following  the growth and body composition of birds of varying  hatch sizes. Our results support the posthatch alternative,  with animals that later grow to be small or large  (here defined as >1 SD lighter or heavier than mean  BW of the flock) being significantly different in size as  early as 1 d after gaining access to feed (P < 0.05). We  then investigated 2 possible causes for different postnatal  growth: that high growth performance is linked 1) to  interindividual variations in metabolism (as measured  by cloacal temperature and verified by respirometry)  or 2) to higher levels of social motivation (as measured  in a social reinstatement T-maze), which should reduce  the stress of being reared in large-scale commercial  flocks. Neither of these follow-up hypotheses could  account for the observed heterogeneity in growth. We  suggest that the basis of growth heterogeneity in broiler  breeder pullets may already be determined at the time  of hatch in the form of qualitatively different maternal  investments or immediately thereafter as an indirect  result of differences in incubation conditions, hatching  time, and resulting fasting time. Although this potential  difference in maternal investment is not seen in body  mass, tarsometatarsal length, or full body length of  day-old chicks arriving at the farm, it may influence  the development of differential feed and water intake  during the first day of feeding, which in turn has direct  effects on growth heterogeneity.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

broiler breeders

feed restriction

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