There is renewed interest in utilising food waste as animal feed due to its potential benefits in reducing feed cost and environmental impact while improving global food security.
The study ‘Feeding recycled food waste improved feed efficiency in laying hens from 24 to 43 weeks of age’ was conducted by researchers from the University of New England to examine the efficacy of recycled food waste-based feed for laying hen performance, egg quality and nutrient digestibility.
Following are excerpts taken from the research, which has been published on Scientific Reports and can be viewed in full at nature.com/articles/s41598-023-34878-2
It is estimated that about one-third of all food produced globally is lost as waste, causing a loss of $A1.48 trillion annually.
In Australia, approximately 7.3 million tonnes of food is disposed in landfill per year, which costs more than $20.67 billion to the Australian economy.
This waste also contributes to more than 5 percent of Australia’s greenhouse gas emissions, leading to substantial environmental and economic losses.
As food is wasted, the costs associated with the production, processing, delivery and selling of that food are also lost.
Moreover, the global warming potential caused by 1 tonne of food waste in landfill is more than five times higher than that of recycling food waste into dry animal feed.
Simultaneously, poultry feed occupies a major cost to producers and its price has increased due to rising prices of raw materials.
Previous studies have illustrated the possibility of producing feed from food waste that meets nutritional requirements for poultry, as well as hygiene and chemical safety standards.
A comprehensive review concluded that food waste can be effectively and safely utilised in commercial production systems.
Some processed food waste streams such as spent brewers grain, fish offal and spent brewers grain blend, and meat and bone meal may replace costly grains, oil and protein meals in poultry diets, thus reducing feed cost significantly.
Creating poultry feed from food waste is also expected to lower carbon and greenhouse gas emissions in the production of chicken meat by 35 and 25 percent respectively, and in eggs by 75 and 76 percent respectively.
Similarly, recycling food waste into pig feed may lead to better public health and environmental effects compared to other processing methods, such as anaerobic digestion and composting.
Therefore, there is great economic and environmental opportunity in the creation of poultry feed from food waste.
While this concept is new to many countries, using food waste-based feed has been an ongoing practice for many years and is supported by local governments in Japan and South Korea.
It is estimated that approximately 40 and 46 percent of mixed food waste are recycled as livestock and poultry feed respectively in these countries.
Others including Taiwan and the US have already used processed food waste as animal feed.
This study aimed to investigate the efficacy of recycled food waste-based feed on laying performance, egg quality and nutrient digestibility of laying hens by comparing a commercial diet with a food waste diet and a 50:50 blend of the two.
It was hypothesised that laying hens would perform up to the breeder specifications when fed diets containing 100 percent food waste.
Experimental design and diets
The study was implemented at the University of New England Laureldale cage layer facility in Armidale NSW.
One hundred and fifty Hy-Line Brown pullets were purchased from a commercial laying hen farm in Tamworth NSW at 15 weeks of age.
Birds were fed a pre-lay diet (2800kcal ME/kg, 16.7 percent crude protein, 2.6 percent calcium, 0.48 percent available phosphorus) from 15 to 19 weeks of age and a commercial layer diet from 19 to 22 weeks of age (2750kcal ME/kg, 16.5 percent crude protein, 3.6 percent calcium, 0.4 percent available phosphorus – Barastoc Premium Top Layer Mash, Ridley Corporation Ltd).
At 23 weeks of age, birds were weighed and randomly allocated to three dietary treatments:
- Standard control feed based on wheat, sorghum and soybean meal
- Recycled food waste-based feed
- A 50:50 blend of control and food waste-based feed.
There were 50 replicate hens per treatment, housed individually.
The average starting hen weights were not different between the dietary treatments (P > 0.05).
Experimental diets were gradually increased during a 10-day adaptation period and were then fed to birds from week 24.
Feed intake from 15 to 22 weeks of age was employed to formulate the experimental diets according to Hy-Line Brown nutritional requirements.
The study was implemented over a 20-week period until the hens were at 43 weeks of age.
Birds were housed individually in cages (30cm wide x 50cm deep x 45cm high) in a curtain-sided house.
There were two nipple drinkers and one feeder per bird.
Birds had free access to feed and water.
A lighting program of 16 hours light and 8 hours dark was maintained throughout the study.
Temperature and relative humidity in the hen shed were recorded daily throughout the study but were not controlled.
The average hen house temperature and relative humidity by weeks are shown in Figure 1.
All diets met the minimum nutrient requirements of Hy-Line Brown hens (2700kcal ME/kg, 14 percent crude protein, 4 percent calcium, 0.4 percent available phosphorus) according to Hy-Line Brown nutritional recommendations for the laying period.
Diets were offered as mash and contained two feeding periods – 24 to 37 weeks and 38 to 43 weeks.
Feedstuffs were analysed for particle size distribution and nutrient content including dry matter, gross energy, crude protein, amino acids, crude fat, crude fibre and mineral composition using standard procedures prior to diet formulation.
The particle size distribution of the diets was measured by dried sieving using a shaker provided with eight sieves.
Metabolisable energy and total and digestible AA levels of wheat, sorghum, soybean meal, canola meal and meat and bone meal used in the control diet were obtained from near-infra red reflectance spectroscopy and standardised with Evonik Aminonir Advanced calibration.
The metabolisable energy and digestible AA levels of the food waste materials were estimated at 65 percent based on previous reports.
Dry matter, GE, CP, AA, crude fat, crude fibre, ash content and mineral composition of mixed control and food waste-based diets were analysed by standard methods to confirm the accuracy of the dietary composition.
Food waste materials were collected from breweries, hospitals, nursing homes, bakeries, pubs and restaurants, abattoirs, fish processing facilities and vegetable and fruit markets.
After removing foreign objects, collected food waste was separated into general classifications including spent brewers grain, fish offal and spent brewers grain blend, hospital and nursing home meal, pub and restaurant meal, vegetable and fruit meal, meat and bone meal, bakery meal and oyster shell meal.
Each food-waste stream was processed by Food Recycle Limited using their patented production process to create a granular powder, which was then in a suitable form to feed to poultry.
Then, waste streams were blended into a complete mash feed.
Steam heating to exceed 100C for 30 minutes was used during the food waste processing to ensure the inactivation of pathogenic and spoilage organisms.
Minors such as crystalline AA, xylanase, phytase, red and yellow pigments, antioxidant and layer vitamin-mineral premix were added to all diets.
The analysed nutrient content of the dietary treatments showed that the mixed diets met the minimum nutrient requirements of Hy-Line Brown hens according to the breed recommendation.
Thus, the main feed formulation objective of this study was achieved.
However, the nutrient composition of the control and recycled food waste-based diets were different.
Of concern was the high sodium, phosphorus and fat levels in the food waste-based diets.
These nutrients were reduced as much as possible during feed formulation.
However, it was not possible to produce 100 percent food waste-based diets with the same nutrients as the control diets.
The objective of the study was to determine how laying hens would perform on 100 percent food waste-based diets.
The protein, fat, sodium and phosphorus levels of various food waste streams such as pub and restaurant meal, hospital and nursing home meal, fish offal meal and meat and bone meal were high.
Due to the nature of the food-waste streams, previous studies might not attempt to make food waste-based diets isonitrogenous or isocaloric compared to the control diets.
Similar to this study, the protein and fat content in the food waste-based diet reported by Garnida et al were also higher than the control diet.
Egg weight, hen day egg production and egg mass were recorded daily.
Feed consumption was recorded weekly.
The feed conversion ratio was calculated by dividing feed intake by egg mass.
Mortality rate was recorded daily throughout the study.
Individual hen weight was recorded every fifth week beginning on week 24.
At weeks 34 and 43, fresh, clean and normal-shaped eggs from all hens were collected for egg quality measurements.
At week 43, 10 hens per treatment with body weights close to the average body weight of the treatment were chosen for measurements of DM, GE, CP, crude fat digestibility, apparent metabolizable energy, apparent metabolisable to gross energy ratio and N-corrected AME using the total excreta collection method according to Dao et al.
Egg quality measurement
Eggshell reflectivity was measured by the TSS QCE-QCM equipment.
Egg length and width were measured by a digital caliper.
The egg shape index was calculated as a ratio of egg width to egg length.
Eggshell breaking strength, shell thickness, albumen height, Haugh unit, yolk colour, yolk height, yolk diameter and yolk index were measured by a digital egg tester.
The egg yolk was collected on filter paper and weighed.
Eggshell was rinsed, dried thoroughly and weighed.
The albumen weight was calculated by subtracting the weights of egg yolk and eggshell from the total egg weight.
Then egg proportion was calculated by dividing the weight of each egg component by the intact egg weight.
Excreta samples collected at 43 weeks of age were freeze-dried and milled to pass through a 0.5mm screen.
Gross energy and protein content of the feed and excreta was determined using a Parr adiabatic oxygen bomb calorimeter and a nitrogen analyser respectively.
Crude fat of the feed and excreta was measured using Soxhlet method adapted as outlined by Holman et al.
Apparent DM, GE, CP and crude fat digestibility were calculated following equations described by Dao et al.
Apparent metabolisable energy, AME:GE and AMEn were calculated following equations described by Moss et al.
All data were calculated on a DM basis.
Environmental condition, analysed dietary nutrient composition and mortality rate
The temperature and relative humidity inside the hen shed during the study are shown in Fig. 1.
The average indoor temperature was 15.2C, ranging from 10 to 19.7C, while the average relative humidity was 63.4 percent, ranging from 49.4 to 76.1 percent, during the experimental period.
The maximum daily temperature ranged from 13 to 29C, average 20.4C, while the minimum daily temperature ranged from 4 to 14C, average 10.4C.
The fish offal and spent brewers grain blend, pub and restaurant meal, and meat and bone meal waste contained high levels of CP, crude fat and total phosphorus.
The sodium content of the pub and restaurant meal was 2.29 percent, being high relative to the requirement.
Whereas, spent brewers grain and vegetable and fruit waste contained high fibre levels – 17.3 and 14.8 percent respectively.
The final diets formulated with waste streams met the formulation objectives in terms of meeting the nutritional requirements of Hy-Line Brown laying hens.
The analysed nutrients of the control diet were similar to the calculated values.
In the food waste diets, the analysed CP, crude fat, calcium and sodium levels were lower, while crude fibre level was higher than the calculated values.
Nevertheless, it was notable that when formulated to meet the minimum nutrient requirements of the breed, food waste-based diets contained higher concentrations of CP, crude fat, crude fibre, total phosphorus and sodium compared to the control diet.
Additionally, the analysed free sugars were lower and total non-starch polysaccharide was higher in the food-waste diets compared to the control diets.
As the study progressed and new batches of food waste were utilised, closer nutritional levels between the control and food-waste diets were observed in the second period of the study from weeks 38 to 43, compared to the initial period weeks 24 to 37.
The particle size distribution test showed that certain amounts of over-size particles (≥ 4mm) were still observed in bakery meal, recycled meat and bone meal, pub and restaurant meal, fish offal and spent brewers grain blend, hospital and nursing home meal and oyster shell meal.
Whereas, high percentages of fine particles (≤ 0.5mm) were detected in spent brewers grain (72.8 percent) and vegetable and fruit meal (72.3 percent).
Over the entire study, birds in all dietary treatments were visibly healthy.
The mortality rates of the control, food waste and 50:50 blend treatments from 24 to 43 weeks of age were 0, 0 and 2 percent respectively.
There was only one mortality recorded in the 50:50 blend treatment and the mortality was not related to dietary treatment.
Hen weight and laying performance
Lower body weight was observed in hens offered the food waste-based diets compared to those offered the control diets at weeks 29 and 39 (P < 0.05).
Hen weight in the 50:50 blend treatment was intermediate between the control and food waste treatment.
Hens offered the food waste-based diets had lower weight gain compared to those fed the 50:50 blend diets over the entire study from 24 to 43 weeks (P < 0.01) and specifically from weeks 24 to 29 (P < 0.001) and 34 to 39 (P < 0.05).
Also, lower weight gains were observed in hens offered the food waste based-diets compared to those fed the control diets from weeks 24 to 29 (P < 0.001) and 39 to 43 (P < 0.001).
The laying performance of dietary treatments from weeks 24 to 43 is given in Figure 2 and Table 8.
Hens offered the food waste-based diets had similar egg weight, hen day egg production and egg mass but lower feed intake (P < 0.001), resulting in a lower FCR (P < 0.001) compared to those fed the control diets from 24 to 43 weeks of age.
Specifically, hens fed the food-waste diets had approximately 15 points lower FCR compared to those fed the control diets from 24 to 43 weeks of age.
The 50:50 blend treatment had an intermediary response over weeks 24 to 43.
Similar findings were observed in laying performance from weeks 24 to 33 and 34 to 43.
Hens offered the food waste-based diets exhibited lower shell breaking strength (P < 0.001), shell thickness (P < 0.001), shell weight (P < 0.001) and shell proportion (P < 0.001) compared to the control and 50:50 blend treatments at week 34.
However, all other egg quality parameters were not significantly different between the dietary treatments at week 34.
At week 43, higher yolk colour score was observed in hens offered the food waste-based diets compared to those fed the control and 50:50 blend diets (P < 0.001), but all other parameters, including shell measurements, were not significantly different between the dietary treatments.
Excreta moisture and nutrient digestibility
Hens offered the food waste-based diets had higher excreta moisture than hens offered the control diets (P < 0.01).
Hens offered the food waste-based diets had a lower retained DM (P < 0.01) and digestibility (P < 0.05) compared to those fed the control diets at week 43.
Hens fed the 50:50 blend diets exhibited a lower DM intake (P < 0.05) and retained DM (P < 0.01), but similar DM digestibility compared to those fed the control diets at week 43.
Hens offered the food waste-based diets tended to have a higher energy consumption (P = 0.056) but lower energy digestibility (P = 0.056), and thus had a higher energy excretion (P < 0.01) compared to those fed the control and 50:50 blend treatments.
Higher AME and AMEn were observed in hens fed the food-waste diets compared to the control diets (P < 0.001).
Hens offered the food waste-based diets had a higher protein intake (P < 0.05) and tended to have higher retained protein (P = 0.066) compared to those fed the 50:50 blend diets.
Noticeably, hens offered the food waste-based diets had a higher fat intake, retention and digestibility compared to those offered the control diets (P < 0.001).
Hens fed the 50:50 blend diets showed an intermediary response (P < 0.001).
Laying hen diets that sustained production were successfully formulated from food-waste materials.
Furthermore, hens fed the recycled food waste-based diet had higher feed efficiency compared to those fed the commercial control diet.
The current study demonstrated that food waste not only has great potential as an alternative feed ingredient within poultry feed but can meet the nutrient requirements of laying hens.
Further study to determine the nutrient digestibility, calcium and phosphate availability, and optimal particle size of the food waste streams and the economic efficiency – cost-benefit analysis – of feeding food waste-based diets is necessary to facilitate a precise feed formation and optimise the food waste-based diets for practical commercial use.
Additionally, examining the effects of feeding food waste-based diets on the organoleptic properties of poultry products is crucial to facilitate the adoption of the poultry industry on the food waste-based feed.
All experimental procedures were approved by the University of New England Animal Ethics Committee and the study was performed in accordance and full compliance with the approved guidelines and regulations.