An Evaluation of the Protein and Energy Requirements of Long-Life Laying Hens

Improved production efficacy in laying hens has been achieved by selecting individual birds that lay longer clutches of eggs (Dunn, 2013; Bain et al., 2016; Preisinger, 2018). In addition, the length of the productive life of hens has been extended to one hundred weeks of age or more. These 'long-life' layers were predicted to produce 500 eggs by 100 weeks of age (Bain et al., 2016; Hy-Line, 2020), and this is now being achieved commercially (Gautron et al., 2021). Primary breeding companies have used genomic tools to address several issues, including clutch lengths, control of egg size, reducing the decline in egg quality, improving shell breaking strength and bone quality and improving the oviduct's weight and efficiency (Bain et al., 2016; Preisinger, 2018).

Little research has been carried out into the nutrition and metabolism of the long-life hen, principally because the stock has not been available. Most of the information available is based on supposition and anecdotal evidence. In an attempt to better understand the nutrient requirements of long-life hens, an experiment was carried out using individually housed Hy-Line Silver Brown hens aged 80 to 90 weeks post-hatch. An evaluation of the protein and energy requirements and their impact on daily egg output and quality was conducted.

This study was approved by the Animal Ethics Committee of the University of KwaZulu Natal (AREC/044/017), and investigated three levels of dietary AMEn and four levels of SID Lys on production parameters in 192 individual Hy-Line Silver Brown layers, from 80 to 90 weeks of age. Data for the period 87 to 90 weeks of age were used for analytical and modelling purposes. The birds were housed individually in wire cages (500 mm depth × 450 mm height × 350 mm width) in an open-sided convection house. A completely randomised 3 × 4 factorial block design was used, with 16 replicates per treatment. Feed and water were supplied ad libitum, and the photoperiod was maintained at a constant 16 hours/d by artificial lighting.

Eggs were collected daily, and hen day production (% eggs produced per hen per day) was calculated. Egg weight (g) was measured three times per week, and the mean was determined. Feed intake (FI) was determined weekly, while body weight (BW) was determined before and after the four-week data collection period. The change in BW (g/d) was calculated for this period. Daily egg output was calculated as the product of egg weight × hen day production (g egg/hen day-1), and feed conversion ratio (FCR) was calculated as the ratio of average daily FI (g) to daily egg output (g/day). The daily intakes of AMEn and SID Lys were calculated as the product of FI and dietary level.

Diets were formulated using similar ingredients to provide three levels of AMEn (11.0, 11.75, 12.5 MJ/kg) and four levels of dietary SID Lys (6.0, 7.0, 8.0, 9.0 g/kg) (Kleyn et al., 2021). SID Lys was used as the reference amino acid (AA) but contained the same ideal AA profile. Feed analysis was undertaken by Evonik Africa (Pty) Ltd. Data were analyzed by full factorial ANOVA using JMP® Pro 14.2.0. (SAS Institute Inc., 2018). Each hen represented a single data point. Linear regression prediction equations were used to model FI, FCR, egg output and nutrient requirements. Any hen that fell outside the specified FCR range of 1.5 to 2.4 was excluded (Spek, 2018) to reduce the effect of body protein and energy on deposition or mobilisation and minimise the impact on SID Lys and AMEn utilisation.

The main effects for the period 87 to 90 weeks of age are shown in Table 1. There were no significant interactions between the protein and energy levels of any diets used. The transition from 11.0 to 12.5 MJ/kg dietary AMEn decreased daily FI by 15.7% (96.7 versus 111.9 g/day; p < 0.01), but there was no significant difference in AMEn intake. The FCR differed by 13.3% (2.72 versus 2.05; p < 0.001). The increase in dietary SID Lys from 6.0 to 9.0 g/kg increased daily SID Lys intake by 33.8% (683 versus 914 mg/day; p < 0.01), but this had no significant impact on egg weight or egg number. The SID Lys level of the diet had no significant impact on AMEn intake, FI, egg weight, egg mass or FCR, and no interactions were observed. Individual hens were able to adjust FI to meet their requirements (Eq. 1). Dietary SID Lys content was not significant and excluded from the model. AMEn intake was predicted with high accuracy (r2 = 0.796; p < 0.001) (Eq. 2), with body weight (p < .001), and daily egg output (p < .001) being the only factors that impacted energy intake. The prediction of daily egg output as determined by AMEn intake (kJ/d) is both significant (r2 = 0.780; p < 0.001) and linear (Eq. 3), whereas the impact of dietary energy level on egg out was NS (Eq. 4.) The energy requirement for maintenance was 193 kJ/kg body weight, and that of egg output was 18.6 kJ/g.

The response of daily egg output to SID Lys intake (mg/d) was significant (r2 = 0.274; p < 0.001), with the only variable having an impact being daily egg output (p < 0.001). Body weight had an NS impact and was excluded from the model (Eq. 5). Increasing the levels of dietary SID Lys from 6 to 9 g/kg, had a significant, linear but negative impact on egg output (r2 = 0.020; p < 0.040) (Eq. 6). Those hens consuming higher levels of AMEn consumed less SID Lys, but this had an NS effect on egg output. Egg weight remained the same regardless of the SID Lys intake achieved, which is at odds with the results in younger hens (Bouvarel et al., 2011; Spek, 2018; Kleyn et al., 2021).

The advantage of housing and measuring individual hens is that outcomes are not blurred by averaging the measurements from two or more individuals, giving rise to a more accurate measurement of underlying biological factors (O’Shea, 2019). Conversely, the social and spatial constraints between hens living in a colony of cohorts are absent. This social interaction likely limits FI under commercial, particularly cage-free conditions.

The finding that long-life hens can adjust their FI to match their requirements is contrary to the findings of other workers (Bouvarel et al., 2011; Classen, 2016), who suggested that modern genotypes may have lost the ability to regulate energy intake in this manner. These differences are likely explained by the fact that there is nothing to impede FI in individually housed hens, whereas this may not be the case when hens are housed in colonies, as found by Scappaticcio et al. (2022) The energy requirement for maintenance declined from 352 kJ/kg of body weight to 193 kJ/kg, while in the case of daily egg output, this value increased from 9.16 kJ/g to 18.6 kJ/g when compared to younger hens (Kleyn et al., 2021). This result may not be an accurate reflection of energy partitioning in long-life hens, as many of the individual birds had either gone out of production or were in the process of doing so, suggesting that body reserves were utilized for egg production.

The hens lost body weight. Thus, it was likely that some endogenous protein was available for egg production. Increasing the levels of dietary SID Lys from 6 to 9 g/kg, had little impact on long-life strain hens in terms of hen day production, even though those hens consuming higher levels of AMEn consumed less SID Lys. T those diets formulated to provide 6 g/kg of SID Lys may have exceeded the hen’s requirements. This would suggest that SID Lys was not deficient in any of the diets offered in this experiment. Contrary to expectation, higher dietary SID Lys levels lead to reduced performance. The protein requirement of long-life hens may be considerably lower than that of younger hens.

Long-life hens can meet their energy requirements by adjusting FI, much the same as hens of any age or genotype. This implies that nutritionists can make decisions about dietary energy levels in the same manner for hens of all ages and genotypes. Hens with a higher daily egg output consumed more SID Lys, but incremental increases in dietary SID Lys did not result in responses in daily egg output, while surplus dietary protein may well have a negative impact on performance. Thus, the protein requirements of the long-life layer differ from those of younger birds. It is likely that the current understanding of the energy and protein requirements of laying hens is applicable to the feeding of long-life layers, although care should be taken not to overfeed protein.