Does Diet Nutrient Density and Hen Size Impact Hen Productivity and Egg Quality at 50 Weeks of Age?

Optimum BW is an important consideration in achieving early maturity, high productivity and uniformity in laying hens (Lacin et al., 2009). Parkinson et al. (2015) noted that it was common for Australian flocks to have an average body weight (BW) 100-300 grams above the breed standard weight (BSW). This higher BW is indicative of bird obesity and is associated with the production of excessively large eggs with consequently lower eggshell quality and poorer persistency of lay compared to the smaller sized birds. Parkinson et al. (2015) suggested that aligning BW more closely to BSW or even a slightly lighter weight could significantly improve egg production and laying persistency.

Increasing the diet nutrient density for birds at the beginning of their laying period and as they progress towards peak production could be beneficial as it may facilitate consumption of the required nutrients but within a smaller quantity of feed. This may achieve both immediate and longer term benefits for smaller sized hens with innately lower feed intake (FI) compared to larger birds. Understanding whether a higher nutrient density (HND) diet fed to late stage pullets of different weights could improve their persistency of lay, eggshell quality and feed efficiency through to mid lay compared to a lower nutrient density (LND) diet could offer growers options in managing hens as they transition from point of lay to peak lay.

Therefore, this study was designed to compare the performance of BSW and LW ISA Brown hens when fed either a HND or LND diet from point of lay for 6 weeks, on their egg production, FCR and egg quality at 50 woa.

This study was a 2 × 2 factorial arrangement consisting of 2 nutrient densities (HND and LND) and 2, 18 woa bird weight groups: mean weight 1.58 kg (BSW) and 1.40 kg (LW). When 16 woa, 240 ISA Brown commercial strain pullets were purchased from a certified grower, transported to University of Sydney, Camden and housed individually in 25 × 50 × 50 cm cages with individual feeders and waters within a high rise layer shed. They were fed the LND diet ad libitum and allowed to acclimate for a 2-week period. At 18 woa all birds were weighed and 120 pullets allocated to both weight groups (BSW or LW). Sixty pullets from each weight group were then randomly allocated to either a HND (formulated on 90g FI/day; 2900 kcal/kg, 0.83% SID.Lys) or LND (formulated to 110g FI/day; 2725 kcal/kg; 0.74% SID.Lys) diet. All hens were fed the experimental diets from 18 to 24 woa. At 25 woa hens on HND diet were consuming at least 100g FI/day and so all were moved to the LND diet. The dietary nutrient specifications meet the recommended requirements of the ISA Brown to 50 woa. From 18-50 woa individual hen egg production (EP), egg weight (EW) and FI were measured to allow weekly determination of FCR. Cumulative measures of production were then also calculated. At 50 woa 10 eggs/treatment group were assessed for egg quality. Data was analysed using a factorial ANOVA with 18 woa BW and diet nutrient density as the main effects.

At 16 woa pullets at the rearing facility were above BSW and hence the slightly heavier weights of these birds from the start of the study. Hen production is presented in Table 1. At 50 woa average BW, average daily FI and cumulative FI (CFI) of BSW birds were significantly higher (P < 0.05) than the LW birds. Birds of the 18 woa BSW group consumed on average 12% more feed from 18-50 woa than the LW hens. Similarly, unpublished findings of Christmas and Harms referred to in Harms et al. (1982) report up to a 12% difference in FI between the heaviest and lightest strains of birds. There was no effect of treatments on percent egg production (EP), but BSW birds had notably higher cumulative egg mass (CEM) (P=0.06) at 50 woa. The latter is in agreement with Leeson and Summers (1987) where higher BW birds produced significantly greater EM compared to LW birds.

Birds have been seen to adjust their FI based on the nutrient density of the diet (Morris, 1968) but this is unlikely to be in perfect alignment (Leeson et al., 2001). In this study, significant differences in FI were associated with bird weight only, not dietary treatment. This positive association of bird weight on FI has also been observed in brown egg-laying hens by Perez-Bonilla et al. (2012), but the reasons diet density had no significant effect on FI in this study are not immediately clear.

There was an interaction between 18 woa BW and diet nutrient density on CFCR. LW birds fed the HND diet until 24 woa had the lowest CFCRC, being significantly lower than LW birds fed the LND diet. The CFCR for both BSW groups was significantly higher than both of the LW groups. This demonstrates a clear benefit of the HND diet for the LW birds through to 50 woa.

The effects of BW and diet nutrient density on egg quality at 50 woa is presented in Table 2.

Table 1 - Hen production from 18 to 50 weeks of age.

There were no treatment effects on yolk % - YP (yolk weight as % egg weight), shell %- SP (shell weight as % egg weight) nor shell thickness (ST), however there is a tendency (P = 0.06) for higher shell thickness in the LW birds that received the HND diet compared to all BSW birds. Mean EW was significantly higher (P= 0.05) in BSW birds irrespective of diet. There was a treatment interaction for Haugh units (P = 0.01) where BSW birds that had received the HND diet had the highest Haugh units and LW birds on the HND diet had the lowest Haugh units. Haugh units of the LW birds on the LND were not different to the BSW birds that had received the HND diet.

The yolk colour score was highest for birds on the LND diet (P= 0.001) compared to HND diet. Our observed production of lighter weight eggs by LW birds compared to BSW birds of the same flock has been reported by others (Leeson et al., 1997). The variation in yolk colour associated with diet density in this study could be a characteristic of individual hens or due to differences in FI and therefore pigment intake (Karunajeewa et al., 1984). In this regard, birds fed the LND diet had a higher CFI to 50 woa, though that increase was not statistically significant. The egg quality observations presented here are from a single assessment on 10 eggs per treatment group. Interestingly combined egg quality assessment across several weeks leading up to 50 woa (i.e. from 45-50 woa) have also demonstrated a tendency (P= 0.08) to darker yolk colour in hens fed the LND diet (data not shown).

Table 2 - Egg quality at 50 weeks of age.

While BSW birds have the highest EW and cumulative egg mass at 50 woa the benefit of the HND diet for LW bird on shell thickness and CFCR is of particular interest. This study is continuing until birds are 90 woa allowing for ongoing evaluation of egg production and quality due to BW and diet nutrient density through to very late lay.

ACKNOWLEDGMENT: This research was funded by Australian Eggs.