Abstract
The study was conducted to optimize lighting schedule for pre-pubertal (12 to 22 weeks) Chinese native breed Pengxian yellow pullet. A total of 414 healthy pullets (10 weeks), with similar body weight were randomly distributed into three groups (n = 138) and housed in individual cages for up to 12 weeks of age in light controlled rooms and provided normal lighting schedule (10L:14D). At 12 to 18 weeks of age, pullets were housed in three rooms, having varying lighting schedule viz. G1 (8L: 16D), G2 (10L:14D), or G3 (12L:12D). From 19th week onwards lighting schedule was gradually increased every week in incremental manner till all groups started receiving 16L:8D lighting schedule. The age at first egg, weight of first egg laid, percent peak hen day egg production, concentration of plasma luteinizing and follicle-stimulating hormones and expression of genes regulating synthesis or/and secretion of hypothalamic gonadotropin-releasing hormone-I (GnRH-I), and pituitary LH-β and FSH-β were studied during experimental period (12 to 43 weeks of age) of this study. The result indicated that pullets of long day length (G3) group had higher plasma levels of FSH and LH and also better mRNA expression that regulates synthesis or/and secretion of GnRH-I, FSH-β, and LH-β before egg laying. The age at first egg (151.3 days) in pullets of G3 group receiving longer lighting hours (12L:12D) was 8.8 days less (P<0.05) compared to pullets of G1 group, while it was 6.9 days less (P>0.05) compared to G2. However, significantly higher (P<0.05) plasma levels of LH and FSH in pullets of G1 as compared to pullets belonging to G3 group corresponded with the higher (P<0.05) cumulative egg production during the experimental period, while these attributes in G2 group didn’t differ from either G1 or G3 groups. Pullets of G1 group had significantly higher levels (P<0.05) of GnRH-I, FSH-β, and LH-β mRNA abundances at 43 weeks of age than other two groups and this corresponded with the percent (hen day) peak egg production (75.38%) in pullets in this G1 group that was attained at 32 weeks of age, while the peak production of 71.24% was attained at 30 weeks of age in G3 group. There was no effect of lighting schedule on body weight of pullets, recorded during experimental period, at all occasions; belonging to three groups (G1,G2 and G3) and receiving varying hours of photo-stimulation (P>0.05). It was inferred that the optimum lighting schedule for Chinese native breed Pengxian yellow pullets during 10 weeks of pre-pubertal growth period is short hours of photo-stimulation (i.e 8L:16D).
Highlights
The age at which pullets sexually mature has a direct influence on their laying performance, and genetic stocks have optimal ages at which they reach sexual maturity to produce the maximum possible egg mass [1]
Among the numerous factors that can affect the time of sexual maturation, the light program to which a flock of laying hens is subjected during the growth and production phase seems to play a critical role [2]
Egg production rate rapidly increased in G3, and peaked at 30 weeks, which was 2 weeks earlier than other two treatments (32 weeks), but the rate (71.22%) at peak was lower than that in G1 (75.38%) and G2 (72.77%)
Summary
The age at which pullets sexually mature has a direct influence on their laying performance, and genetic stocks have optimal ages at which they reach sexual maturity to produce the maximum possible egg mass [1]. Among the numerous factors that can affect the time of sexual maturation, the light program (day length and light intensity) to which a flock of laying hens is subjected during the growth and production phase seems to play a critical role [2]. Pullets grown in light-proof houses are usually not held on constant day lengths during rearing, but are given some pattern of photoperiods, and most lighting programs have recommended combinations of decreasing and increasing photoperiods during different stages of the pullet’s life [3]. Koelkebeck reported that if leghorn pullets and broiler breeder pullets are grown under an increasing daylength, sexual maturity will be enhanced which can cause egg production and blowout problems in the layer house. Managers should continually evaluate the optimal light stimulation based on age for pullets, even if they are using the same strain, because there is constant selection by breeders
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