Effect of Metabolizable Energy Intake on Metabolism and Reproduction of Broiler Breeders Fed by a Precision Feeding System

• Author / Creator

  Sheila Hadinia

• The objectives of the first study were to investigate metabolizable energy (ME) partitioning and energetic efficiency in Ross 308 broiler breeders. An empirical ME model was derived to describe ME used for total heat production
  (HP), growth (ADG), and hen-day egg production (HDEP). From 10 to 23 wk of age, pullets were assigned to 2 treatments: precision feeding (PF) or conventional skip-a-day feeding (CON). From 23 to 34 wk of age, the CON birds were fed on
  conventional daily restricted feeding; the PF system allowed birds to enter stations voluntarily at any time if their BW was less than the target BW. Energetic efficiency was evaluated using residual feed intake (RFI), defined as the difference between observed and predicted ME intake (MEI). From 10 to 23 wk of age, for CON and PF treatments, respectively, MEI was 194 and 174 kcal/d (P < 0.001); ADG was 15.3 and 15.4 g/d (P = 0.94); HP was 129 and 111 kcal/kg0.68 (P < 0.001); FCR was 4.888 and 4.057 (P < 0.001). The CON pullets had similar ADG, but higher MEI and higher cumulative FCR relative to PF pullets. The PF pullets lost less energy as heat, likely because they were fed continuously, reducing the need to store and mobilize nutrients compared to CON pullets. Thus, increased feeding frequency increased PF pullet efficiency. From 23 to 34 wk of age, the energy partitioning model (P < 0.05) predicted MEI = A × BW0.67 + 1.75 × ADG + 0.75 × EM + ε. The coefficient A was a vector of age-specific HP coefficient (155 kcal/kg0.67/d); the energy requirement for growth and egg mass (EM) was 1.75 and 0.75 kcal/g respectively. Overall for CON and PF hens respectively, MEI was 366 and 354
  kcal/d (P = 0.006); RFI was -5.9 and 6.7 kcal/d (P = 0.01); HP was 86.4 and 88.7%iii of total MEI (P < 0.001); HDEP was 65.5 and 55.2% (P < 0.001). Although the CON hens had higher MEI, they lost less energy as HP, had more nutrients available
  for egg production and were more energetically efficient than the PF hens. Production-related feed increases for individual PF hens occurred only after they laid an egg, whereas feed allocation increases for the CON hens resulted in increasing MEI for all CON hens at the same time. Therefore, we hypothesized that current BW recommendations are too low for PF hens, and increasing MEI of the PF hens before they reach onset of lay is likely needed to stimulate onset of
  production. To assess the effect of MEI on rate of sexual maturation, a second study was conducted. Ross 308 broiler breeder pullets were assigned to two treatments
  from 22 to 26 wk of age and fed using a PF system: 1) Low MEI (2,807 kcal/kg diet, feed restricted), and 2) High MEI (3,109 kcal/kg diet, not restricted). Daily cloacal palpation was used to detect sexual maturity via the presence of a hardshelled egg in the shell gland. Expression of gonadotropin releasing hormone-I (GnRH) and gonadotropin inhibitory hormone (GnIH) genes in hypothalamus, and GnRH receptor (GnRH-RI) and GnIH receptor (GnIH-R) genes in the anterior pituitary gland of each pullet was evaluated from 22 to 26 wk of age using
  quantitative real time-PCR. Blood samples were taken weekly and luteinizing hormone (LH), follicle stimulating-hormone (FSH) and 17-beta-estradiol (E2) determined using commercial ELISA kits. The protein and lipid content of the
  whole carcasses was determined. Data was analyzed using the MIXED procedure in SAS. High MEI pullets had 2.3-fold higher GnRH and 1.8-fold higher GnRH-RI
  mRNA levels than Low MEI pullets. MEI affected neither expression of GnIH and GnIH-R genes, nor carcass protein content. From 22 to 26 wk of age (P < 0.05); LH, FSH, E2 concentrations, and carcass lipid content were 1.9, 1.6, 1.6, and 1.3% times higher respectively for High MEI (489 kcal/d) compared to Low MEI (258 kcal/d). The onset of lay for High MEI was advanced such that 100% had laid by
  26 wk of age, compared to 30% in Low MEI. We concluded that High MEI advanced activation of the hypothalamic-pituitary-gonadal axis, increased body lipid deposition, and stimulated reproductive hormone levels which overall accelerated puberty in broiler breeder pullets.

• Subjects / Keywords

  • Animal Science

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-m1hr-v070

• License

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