Optimal protein diet improves egg production and reproductive tract morphology

24-06 | |
Too much protein is costly and bad for the environment, too little eats into production performance. Photo: Jan Willem Schouten
Too much protein is costly and bad for the environment, too little eats into production performance. Photo: Jan Willem Schouten

A shortage of protein resources in poultry feed is an important limiting factor affecting poultry productivity. In addition, nitrogen emissions from the poultry industry is an increasing environmental concern affected by dietary amino acid balance. A key strategy to overcome these issues is to optimise protein raw material consumption and improve gut microbiota through proper high-quality protein intake.

A team of Chinese researchers determined the optimal protein supply in the diet for cleaner egg production and to foster more efficient, healthier breeding of laying hens. They published their findings in the Journal of Science of the Total Environment in a research article published in February 2024. In this article they evaluated the impact of graded dietary protein levels on egg production performance, gut microbiota and host metabolism in laying hens.

Data collection

The team used 360 commercial laying hens at 38 weeks of age for this trial and randomly allocated them into 4 treatment groups. The experimental diets were similar in apparent metabolisable energy and nutrient levels but varied in crude protein content, these being 13.85%, 14.41%, 15.63% and 16.30%, respectively. They recorded initial body weight, final body weight, total number of eggs and total egg weight every day. In addition, they calculated daily egg mass, egg weight, egg production, average daily gain, average daily feed intake and feed-egg ratio.

The team randomly collected 60 eggs before the experiment and 30 eggs from each treatment group during the experiment to assess egg quality parameters, including shell strength, shell thickness, eggshell colour, Haugh unit, yolk colour and egg weight, every 4 weeks. They further weighed the eggshell, yolk and albumen separately to calculate their percentage egg weight. The team evaluated nitrogen efficiency and emissions using acid insoluble ash as an endogenous indicator. They extracted DNA from cecal microbiota to profile the microbial community. Blood samples were also collected to analyse serum biochemical indices and they measured the weights of the liver, kidney, abdominal fat, fallopian tube and ovary after slaughter.

Impact of protein levels

Feeding laying hens 15.63% and 16.30% crude protein increased final body weight, average daily gain, egg production and daily egg mass but decreased the feed-egg ratio. Feeding laying hens 13.85% crude protein increased egg weight compared to feeding them 14.41% crude protein. In addition, feeding laying hens 15.63% crude protein enhanced eggshell thickness compared to that of the 14.41% crude protein group and eggshell strength compared to that of the 16.30 % crude protein group. Conversely, feeding laying hens 16.30% crude protein reduced the yolk colour compared to that of the 13.85% group.

Reproduction tract morphology

Laying hens fed with 14.41% crude protein had the smallest yellow follicles compared to the other treatment groups. Furthermore, the maximum oviduct length, ovary weight and ovarian weight were obtained when the diet was supplemented with 15.63% crude protein. Feeding laying hens 16.30% crude protein increased the serum concentration of urea and IgG and IgM levels. Feeding laying hens 15.63% crude protein also improved the antioxidant capacity. The amount (kgs) of diet nitrogen excretion, daily nitrogen excretion and egg nitrogen excretion increased with increasing dietary protein level, along with per egg nitrogen excretion.


Feeding laying hens 15.63% crude protein resulted in the highest bacterial species diversity and richness. Bacteroidetes, Firmicutes and Actinobacteria also accounted for more than 90% of the total gut microbial community. The authors concluded that laying hens’ production performance and reproductive tract morphology were improved at a protein level of 15.63%. Moreover, the 13.85% and 15.63% groups showed increased crude protein utilisation rates. Therefore, a dietary protein content of around 15.63% appears to be most beneficial for laying hens.

The article in the Journal of Science of the Total Environment was authored by Meiling Liu, Shunju Geng, Qingfeng Wang, Jinqiu Mi, Lihong Zhao, Jianyun Zhang, Cheng Ji, Qiugang Ma, and Shimeng Huang from State Key Laboratory of Animal Nutrition, College of Animal Science and Technology, China Agricultural University, and Feed Safety and Healthy Livestock, Beijing Jingwa Agricultural Innovation Center, and Hongliang Wang from College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, China.


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Samaneh Azarpajouh Author, veterinarian
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