Features of the extended laying cycle of hy-line brown hens reared under different lighting and feeding regimens

I. INTRODUCTION

The physiological patterns of hen FI and BW trajectory are established by early lay (Muir et al. 2023a). Careful management of lighting and feeding patterns during rearing can regulate bird size and feeding habits by the end of rearing (Muir et al. 2023b). Whether this influences persistency of lay, efficiency of production and egg quality during an extended laying period is unknown. The lighting program during rearing can alter pullet age at first egg (AFE), the number of eggs produced and EW (Santiago-Anadón and Latorre-Acevedo, 2004; Arango et al. 2007). We have shown that a more RLR during rearing, which provides fewer hours of light/day, slows chick growth and on light stimulation will initiate earlier AFE, compared to a SL schedule in current brown egg-laying hen strains (Muir et al. 2023b). But the ongoing impact of the lighting and feeding programs employed during rearing on Brown egg-laying hens held in an extended laying cycle has not been evaluated. Therefore, this longitudinal study followed hens reared under different lighting and feeding programs (Muir et al. 2023b) until they were 100 WOA, including measurement of their FI, EP, EW and FCR. The quality of the eggs produced towards the end of their laying cycle was also evaluated.

II. MATERIALS AND METHODS

As described in Muir et al. (2023b) 900 Hy-Line Brown day-old chicks, that had been beak trimmed and vaccinated at the hatchery were placed in groups of 30 in floor pens (7 m2 ) at the Zootechny research facility, Austral, NSW, Australia. Each pen had a perch, automatic nipple drinkers and manually filled feed hoppers. The shed was brooded with space heaters, had side curtains, foggers, and dimmable lights with photoperiod control for each end of the shed. A light proof curtain traversed the centre of the shed separating 15 pens to each of the two lighting regimens. All birds were held under intermittent lighting during the first week (4hLight(L):2hDark(D)) then 20hL:4hD in the second week. For RLR the photoperiod was reduced as 16hL:8hD, then 12hL:12hD and finally held at 9hL/d from 4-16 WOA. Under SL program 20hL:4hD was maintained through to 3 WOA then reduced gradually to 10hL:14hD by 7 WOA and held there through to 16 WOA. All birds were fed ad libitum until 4 WOA when three feeding programs of five pens per lighting treatment were introduced. This was ad libitum (ad lib); feeding to achieve breed standard weight (BSW); and feeding to achieve 88% BSW (Managed) for age. Hence the study was a 2 × 3 factorial arrangement of 2 lighting and 3 feeding programs. All birds receive the same commercial crumble pullet starter (0-5 WOA) and grower (5-12 WOA) (Barastoc, Australia), then a developer mash (12-16 WOA). When 16 WOA, 75 pullets/treatment were moved into individual pens in a high-rise layer shed under a common lighting program with gradual increase to 16 h L/d at 33 WOA. From 16-17.4 WOA all pullets received pre-lay diet and from 17.5-100 WOA diets changed through feeding phases 1-5 as per Hy-Line Brown breed recommendation (Hy-Line International 2018). From 16 WOA all diets were mash and fed ad libitum. Bird BW was measured at 16, 72 and 100 WOA, FI, EP, EW, egg mass (EM) and FCR were measured when hens were 100 WOA, and their cumulative measures were calculated from 17.5–100 WOA. Eggs from 12 focal birds/rearing treatment were assessed for EW, HU, relative albumen weight, yolk colour, relative shell weight, shell thickness and shell breaking strength, during 96-100 WOA. All data were analysed using a factorial ANOVA with lighting and feeding regimens during rearing as main effects.

III. RESULTS AND DISCUSSION

At 16 WOA BW was highest in pullets of ad lib feeding under SL and lowest for pullets of Managed feeding under both SL and RLR (Table 1). Similar trends in BW were evident at 72 WOA but BW was above breed standard for age (1.97 kg) in all treatments. At 100 WOA hens from Managed feeding during rearing had the lowest BW but FI was similar for all treatments. The 17.5-100 WOA cumulative FI was approaching significance as birds from Managed feeding during rearing had the lowest FI (P = 0.073; Table 1). Egg production at 100 WOA was similar, ranging from 62.3–68.9% and essentially all hens produced 500 eggs by 100 WOA. At 100 WOA hens fed ad lib during rearing had higher FCR at 100 WOA compared to birds from restricted FI (BSW or Managed) rearing regimens (P = 0.004; Table 1). Further, cumulative FCR (17.5–100 WOA) was numerically lower in hens from Managed compared to ad lib feeding in rearing. Earlier in production, cumulative 17.5–61 WOA FCR had been significantly lower (data not shown) in lighter hens from Managed feeding during rearing, concurring with lower cumulative FCR of smaller hens from 18-69 WOA in a previous study (Muir et al. 2022) and then numerically lower FCR through to 89 WOA (Muir et al. 2023a).

Table 1 - Body weight at 16, 72 and 100 weeks, 100 week and cumulative (17.5-100 weeks) feed intake, egg production and feed conversion of Hy-Line Brown hens reared in different lighting and feeding regimens.

Based on average EW from all eggs produced by hens of each treatment group, SL eggs were heavier compared to RLR (P = 0.015). Whereas, when based on EW of eggs from focal hens only, differences were approaching significance (P = 0.061; Table 2). Relative albumen weight was higher due to SL during rearing. Eggs from hens reared within the Managed feeding regimen had the highest HU (P < 0.01) though all HU met the > 81 HU breed standard for age (Hy-Line International, 2018). Yolk colour was also above the recommended score of 11 (Roberts 2004). There were no differences in shell quality. Relative shell weight was > 9% and shell thickness > 0.35 mm for all treatments, minimizing the chances of shell cracks (Parkinson et al. 2008). Egg weight at 100 WOA remained around 65 g, aiding shell quality compared to larger (> 70 g) eggs.

This study illustrated the opportunity to program hens to different sizes during lay by managing their FI during rearing. Smaller hens had lower FCR while producing a similar number of eggs with higher HU, compared to larger-sized hens that have been fed ad lib throughout rearing. There may be opportunity to provide pullets of lower BW with a nutrient-dense diet during early lay to provide additional nutrients in preparation for a longer laying cycle (Muir et al. 2023a).

Table 2 - Egg weight from all birds at 100 weeks * and characteristics of eggs produced by Hy-line Brown focal hens between 96-100 weeks of age following rearing in different lighting and feeding regimens.