Menu
The hypothalamus plays an important regulatory role for feed intake and energy expenditure by interpreting information from internal physiological signals (hormones and nutrients) and external environmental cues (photoperiod, temperature, and stressors). The hypothalamus also plays a vital role in the reproductive system of birds. The hypothalamus controls the female reproductive life cycle by activating and inhibiting the hypothalamic–pituitary–gonadal (HPG) axis. The first objective of the current study aimed at assessing the effect of MEI on sexual maturity, specifically on (1) mRNA levels of GnRH-I and GnIH in the hypothalamus and their receptors in the anterior pituitary gland and (2) the plasma concentration of reproductive hormones (LH, FSH, and E2) in broiler breeders. The second objective was to evaluate the effect of MEI on the expression of POMC, NPY, and LEPR to understand how energy balance is regulated by the hypothalamus in broiler breeder pullets postphotostimulation and during sexual maturity. Finally, the third objective was to investigate the effect of MEI on carcass composition in broiler breeder pullets.
The focus of the current experiment was sexual maturity, and all pullets were fed using a precision feeding (PF) system. At 21 wk of age, 140 pullets were randomly selected and assigned to 2 treatments (2 replicate pens with 35 birds each per treatment): (1) Low-energy diet fed restricted according to the breeder-recommended Ross 308 BW target using a typical commercial diet (2,807 kcal/kg, low MEI) and (2) high-energy diet fed unrestricted (3,109 kcal/kg, high MEI). The current experiment was carried out from 22 to 26 wk of age. Four birds in each pen (8 per treatment) were randomly selected at 22, 23, 24, 25, and 26 wk of age and euthanized. Ileal digesta samples were collected Digesta samples were pooled for each experimental pen and analyzed. Palpation was performed every morning to detect sexual maturity via the presence of a hard-shelled egg in the shell gland. At 22 and 23 wk of age, 4 birds per treatment were randomly selected to collect hypothalamus and pituitary tissue samples. The samples were used for gene expression analyses. Blood samples were collected weekly for hormone assay and for gene expression analyses. The same birds were chosen for carcass composition analyses.
Higher MEI of pullets in the high MEI treatment resulted in greater BW relative to the pullets in the low MEI treatment from 22 to 26 wk of age. The high MEI pullets compared with the low MEI pullets had greater ovary weight as a percentage of BW from 22 to 26 wk of age (0.62% ± 0.07 and 0.32% ± 0.07 respectively; P = 0.003). The greater ovary weight of the high MEI pullets indicates that they partitioned more energy toward developing reproductive tissues for the onset of egg production than the low MEI pullets, and this is consistent with observed egg production data. The high MEI treatment had higher hypothalamic mRNA level of GnRH-I compared with the low MEI treatment at 23 wk of age and also overall from 22 to 26 wk of age. Overall, GnRH-I and GnIH mRNA levels were positively correlated (r = 0.36; P = 0.01). The concentration of plasma LH and FSH were higher in the high MEI treatment compared with the low MEI treatment at 22 wk of age. The overall concentration of plasma E2 was higher in the high MEI treatment relative to the low MEI treatment from 22 to 26 wk of age. Pullets in the high MEI treatment had higher lipid than the pullets in the low MEI treatment from 23 to 26 wk of age. All pullets in the high MEI treatment entered lay by 26 wk of age; however, only 30% of the pullets in the low MEI treatment entered lay by 26 wk of age. Moreover, total egg production was higher for the hens on the high target BW treatment compared with the standard target BW treatment at the end of wk 55 (129.4 vs. 92.8, respectively).
High MEI along with photostimulation can increase GnRH-I expression in the hypothalamus and GnRH-RI and LH expression in the pituitary. Therefore, in addition to increasing body lipid deposition, higher MEI enhanced the activation of the HPG axis which accelerated puberty in broiler breeder pullets. The results of the current experiment would suggest increasing the target BW for the broiler breeder pullets to help them to obtain all the cascades for the sexual maturity earlier and advance the onset of lay and also increase the productivity.