How to set the ratio of arginine to lysine in the diet of egg-laying hens under high-temperature summer conditions ？

Since poultry have feathers on their backs, it is difficult for them to dissipate heat, so high temperatures in summer can easily cause stress reactions in poultry. Studies have found that the optimum temperature for laying hens is 20-25°C. When the ambient temperature exceeds 27°C, the body metabolism of laying hens changes, such as cell damage, changes in enzyme activity, abnormal thyroid hormone secretion, and reduced blood calcium levels. At the macro level, this is manifested in increased breathing rate, increased body temperature, decreased feed intake, and reduced egg-laying performance in laying hens, which can even cause death in severe cases.

Due to the lack of a complete urea cycle pathway in the body, laying hens cannot synthesize arginine in their bodies, and arginine is mainly provided by the diet. Arginine is an amino acid with multiple functions, and its metabolite nitric oxide (NO) is a key nutritional factor for vasodilation and peripheral blood flow regulation, especially in the regulation of poultry body temperature under high temperature conditions. This paper mainly studies the effect of the ratio of arginine to lysine in the diet on the laying performance and reproductive performance of laying hens under high temperature weather, providing a reference for the formulation of summer laying hens diet.

[Experimental animals] 32-week-old Mandara hens and roosters. Mandara is a local breed in Egypt. The average annual egg laying hen is 280 eggs. The egg shell is white or milky white, and the egg weight is about 60g.

[Experimental design] 140 hens and 20 roosters were selected and randomly divided into 4 treatment groups, each with 5 replicates, 7 hens and 1 rooster in each replicate. Three diets with different arginine to lysine ratios of 125%, 137% and 150% were prepared using corn and soybean meal. The raw material composition and nutritional level of the diets are shown in the following table:

At a normal temperature (22-24℃), the 125% CON group was fed with a 125% Arg/Lys diet. The other three treatment groups were raised in a high-temperature environment and were fed diets with lysine ratios of 125%, 137%, and 150% respectively, as shown in the figure below:

【Test Period】

From 32 weeks of age to 44 weeks of age, a total of 12 weeks.

3.1Egg-laying Performance

When laying hens are exposed to a high-temperature environment, the mortality rate of the 125% CHS group (2.5%) is higher than that of the 125% CON group in the normal temperature environment; in the heat stress environment, when the Arg/Lys ratio of the diet is increased from 125% to 150%, the mortality rate of the hens returns to 0. In the heat stress environment, poultry may exhibit increased respiratory rate and dehydration as stress responses, which may subsequently lead to heatstroke death.

During the entire 32-44 week trial period, compared with the 125% CON group in a normal temperature environment, the egg production rate, egg weight and egg production volume of the 125% CHS group in a hot stress environment decreased significantly (P<0.05); in the hot stress environment, the egg production rate of the 137% CHS and 150% CHS groups with high crude protein ratio was significantly higher than that of the 125% CHS group and the 125% CON group (P<0.05), and the egg weight of the 137% CHS and 150% CHS groups recovered to the level of the 1.25% CON group (P>0.05). From the perspective of daily egg production, even in the high-temperature hot stress environment, the egg production of the 137% CHS and 150% CHS groups with high dietary crude protein ratio was significantly higher than that of the 125% CON group in the normal temperature group (P<0.05).

significant difference (P>0.05), but the feed-to-egg ratio (FCR) increased significantly (4.34 VS 5.12, P<0.05). Under high temperature, the FCR of laying hens in the 137% and 150% CHS groups was significantly lower than that in the 125% CHS group (P<0.05), and was even significantly lower than that in the 125% CON group under normal temperature (P<0.05).

There was no significant difference in the digestibility of crude fiber and crude fat among the treatment groups (P>0.05). Compared with the 125% CON group at room temperature, the high temperature environment significantly reduced the dry matter and protein digestibility of laying hens in the 125% CHS group (P<0.05); after increasing the arginine-lysine ratio in the diet, the dry matter and protein digestibility of laying hens in the 137% and 150% CHS groups increased significantly (P<0.05), and even the dry matter digestibility exceeded that of the 125% CON group at room temperature (P<0.05). The authors analyzed that the increased dry matter and protein digestibility caused by the high arginine-lysine ratio may be the main reason why the feed intake did not change and the feed-egg ratio was significantly reduced.

3.2 Changes in egg quality and plasma calcium and phosphorus levels 

The results showed that there were no significant differences in egg shape index, eggshell thickness, yolk color and Haugh unit among the treatment groups (P<0.05). However, compared with the 1.25% CON group in the normal temperature environment, the eggshell weight percentage of laying eggs in the 125% CHS group in the heat stress environment decreased by 8.8% (10.2% VS 9.3%), and reached a significant difference level (P<0.05). After increasing the arginine-lysine ratio in the diet, the eggshell weight percentage of laying eggs in the 137% and 150% CHS groups increased significantly (P<0.05), even exceeding the level of the 125% PC group in the normal temperature environment (P<0.05).

Compared with the normal temperature 125% CON group, the high temperature environment significantly reduced the plasma calcium and phosphorus levels of laying hens in the 125% CHS group (P<0.05). After increasing the arginine-lysine ratio in the diet, the plasma calcium and phosphorus levels of laying hens in the 137% and 150% CHS groups increased significantly (P<0.05), and reached the plasma calcium and phosphorus levels of the normal temperature 125% CON group (P>0.05).

Based on the changes in plasma calcium and phosphorus levels, the authors speculated that the reduction in eggshell weight was due to the reduced utilization of calcium and bicarbonate during eggshell formation under high temperature, which led to a decrease in plasma calcium and phosphorus levels, and then insufficient calcium and phosphorus absorption affected eggshell formation. Increasing the arginine-lysine ratio in the diet can restore the efficiency of calcium and phosphorus utilization in laying hens to a certain extent, thereby promoting eggshell formation.

3.3 Reproductive performance

Compared with the 125% CON group under normal temperature, the fertilization rate, total egg hatchability and fertilized egg hatchability of the 125% CHS group under high temperature decreased from 91.3%, 89.2% and 97.6% to 89.4%, 76.1% and 85%, respectively, and all reached significant differences (P<0.05); after increasing the arginine-lysine ratio in the diet under high temperature, the fertilization rate, total egg hatchability and fertilized egg hatchability of the laying hens in the 137% CHS group returned to the 125% CON level (P>0.05).

The authors speculate that there are several reasons why a high-arginine diet improves the reproductive performance of laying hens: 1) Arginine metabolite NO can promote vasodilation, increase blood flow to the reproductive organs, and improve the environment and vitality of sperm production; 2) Adding Arg can increase the sperm penetration rate of broiler breeders by 10%, and the fertilization rate is positively correlated with the penetration rate of sperm in the inner layer of the perivitelline membrane of the germinal disc; 3) Arg can also improve antioxidant capacity and maintain the stability of the embryo's internal environment; 4) Under heat stress, the level of T4 secreted by the thyroid gland increases abnormally, and a high Arg/Lys ratio (1.37Arg/Lys ratio) can stabilize the T3/T4 level and promote follicular development and implantation of fertilized eggs (data below).

3.4 Changes in antioxidant indices and plasma hormones

Compared with the normal temperature control group 125%CON group, high temperature environment increased the levels of plasma total lipids, cholesterol, low-density lipoprotein, triglycerides and propylene glycol in laying hens in the 125%CHS group (P<0.05); after increasing the Arg/Lys ratio in the diet, the above plasma indices of laying hens in the 137% and 150%CHS groups returned to the levels of the normal temperature 125%CON group (P>0.05).

Compared with the normal temperature 125%CON group, high temperature environment significantly reduced the catalase (CAT) activity of laying hens in the 125%CHS group (P<0.05); after increasing the semolina-lysine ratio in the diet, the CAT activity of laying hens in the 137% and 150%CHS groups increased significantly (P<0.05).

 

 

There was no significant difference in blood triiodothyronine (T3) in laying hens among the treatment groups (P>0.05). Compared with the 125% CON group at normal temperature, the high temperature environment significantly increased the blood T4 level of laying hens in the 125% CHS group (P<0.05); the 137% and 150% Arg/Lys ratio diets significantly reduced the blood T4 level (P<0.05). The authors summarized previous studies and found that high temperature weather reduced the thyroid activity of poultry, and the circulating concentrations of T3 and T4 would also change accordingly. Arginine supplementation enhances the antioxidant capacity of poultry and can also mitigate the adverse effects of high temperature stress on poultry hormones.

1) High temperature heat stress environment reduces laying performance, reproductive performance, protein digestibility, eggshell weight percentage and antioxidant capacity of laying hens;

2) In high temperature heat stress environment, increasing the Arg/Lys ratio of the diet from 125% to 137% can restore the laying rate, egg weight, egg production, fertilization rate and hatching rate of laying hens to the normal temperature control group (125% Arg/Lys ratio), and even the fertilization rate and hatching rate exceed the normal temperature control group;

3) The effect of high arginine-lysine ratio diet (137%) on improving laying performance and reproductive performance of laying hens under heat stress environment is related to the role of arginine in improving the antioxidant capacity of laying hens, increasing plasma calcium and phosphorus levels, and regulating the balance of thyroid hormone T3/T4.

References

Attia, Youssef A., et al. "Arginine: lysine ratio influences on performance, egg quality, haematology, biochemistry, antioxidant status and immunity of dual-purpose breeding hens exposed to cyclic heat stress." Italian Journal of Animal Science 23.1 (2024): 200-214.