Protein is a vital component in precision nutrition for laying hens as it provides amino acids (AA) necessary for optimal growth, egg production, health, and welfare. Precision protein nutrition is the concept that hens receive the right amount of protein tailored to their specific needs, preventing both deficiencies and excesses that can lead to feed waste and inefficiency of nutrient utilisation. This thesis had an overarching goal of generating essential insights into precision protein nutrition to improve protein utilisation efficiency, production performance, and welfare conditions of laying hens. This overarching goal was supported by two key research objectives: to optimise 1) reduced protein (RP) diets and 2) AM/PM feeding regimes; focusing on optimising these feeding strategies to meet AA requirements cost-effectively. To achieve this, this thesis included a comprehensive review within the area of current understanding of RP diets and AM/PM feeding to identify the research gaps (Chapter 2), and three experiments to elucidate the effect of the interventions and their implications for the poultry industry. The first experiment aimed to identify the priority order of limiting AA beyond the well-established methionine (Met), lysine (Lys), and threonine (Thr) in Australian practical RP diets for laying hens, with the aim of exploring additional limiting AA for supplementation use to reduce reliance on traditional protein sources particularly soybean meal in feed formulation (Chapter 3). The order of limiting AA was determined in wheat-sorghum-based diets for Hy-Line Brown laying hens from 20 to 39 weeks of age (WOA) in individual cage experimental settings to identify which AA are essential to supplement in RP diets to achieve the ideal protein balance. Since the first three limiting AAs (Met, Lys, and Thr) have already been well-established in layer diets, the study was designed to supplement the rest of the eight essential AAs: tryptophan (Trp), valine (Val), isoleucine (Ile), arginine (Arg), leucine (Leu), histidine (His), phenylalanine (Phe), and glycineequivalent (Gly) in RP diets. Then, the subsequent deletion of each AA from the diet allowed determination of its impact on hen laying performance, egg quality, nutrient digestibility, bone quality, and gut health, prioritising their respective importance in RP diets. The study identified Ile and Val as the fourth and fifth AAs in wheat–sorghum-based RP diets, based on egg mass, respectively. However, Val emerged as the fourth limiting AA, while Trp, Ile, Arg, and His were identified as the co-fifth limiting AAs based on feed conversion ratio (FCR). The study demonstrated that deficiencies in these AAs negatively impacted egg mass and FCR. It also suggested that Leu, Phe, and Gly may not be essential in RP diets because of their minimal impact when absent, indicating potential cost-saving opportunities while formulating the RP diets. Moreover, the study demonstrated that reducing dietary crude protein (CP) levels by 2% with crystalline AA supplementation in RP diets effectively maintained laying hen performance and egg quality, while also lowering protein intake and excretion, thereby offering environmental benefits compared to a standard protein diet.
The second experiment (Chapter 4) was designed to investigate if feeding laying hens’ diets that match their specific nutritional and physiological needs at different times of the day is more advantageous than providing a single diet throughout the day, to further explore the protein requirement of hens. The aim of the experiment was to explore the dietary optimisation effects of AM/PM feeding strategy on nutrient utilisation and laying performance with cost-benefit outcomes, where hens received protein and energy-rich but low calcium (Ca) diets in the morning (AM) and low protein and energy but Ca-rich diets in the afternoon/evening (PM). The study was conducted on Hy-Line Brown laying hens from 34 to 53 WOA in a free-range experimental setting. Hens in the treatment group received the AM/PM diet, with the AM diet (2980 kcal/kg AMEn, 20.1% CP, 2.5% Ca) provided from 08:00 to 16:00 h, and the PM diet (2580 kcal/kg AMEn, 17.5% CP, 5.6% Ca) from 16:00 to 08:00 h. A conventional standard layer hen diet (2780 kcal/kg AMEn, 18.8% CP, 4.1% Ca), offered continuously throughout the day, served as the control. The study assessed hen laying performance, egg quality, nutrient digestibility, and included a cost-benefit analysis. Results showed that the AM/PM feeding strategy led to a 2.15% increase in egg mass and an 8.34% improvement in feed efficiency, reducing total feed cost per unit of egg mass by 1.2% compared to the conventional diet. This suggests that AM/PM feeding could be a practical, cost-effective method for implementing precision nutrition strategies and may be a complementary way to provide RP diets.
Leading from Chapter 4, the effects of AM/PM feeding on hen behaviour, range use and welfare indicators were investigated in a subsequent experiment in Chapter 5. The aim of the experiment was to investigate the effects of AM/PM feeding on behaviour and welfare indicators of laying hens to assess whether this feeding strategy can complement the concept of modern farming practices by supporting hen welfare directives. Hen behaviour within their home pens was observed using a detailed behavioural ethogram, while individual hen ranging patterns were tracked through radio-frequency identification (RFID) technology. Welfare indicators were evaluated through tests for fearfulness, stress levels, bone quality, and external health assessments. The results showed that AM/PM feeding reduced feather pecking behaviour and increased outdoor range use (2.85 vs 2.47 hrs/day) compared to a conventional all-day single diet, suggesting improved welfare conditions of free-range laying hens. Additionally, hens on the AM/PM diet exhibited improved bone health, as indicated by higher tibia ash content and bone-breaking strength. Overall, this thesis advances precision protein nutrition by exploring strategies to balance the lysine pool in laying hens, including the use of RP diets with synthetic AAs to optimise protein utilisation and timing nutrient absorption to align with hens' metabolic rhythms. These approaches collectively enhance efficiency, sustainability, and animal welfare in layer hen production, although further research is needed for wider commercial adoption.