Nutritional balance in practice

In European feed formulas, threonine is usually the second limiting amino acid after lysine for pigs and the third one after sulphur amino acids (methionine + cysteine) and lysine for poultry. As lysine, threonine is an indispensable amino acid for body protein deposition and growth. Thus, deficiency in threonine affects the utilization of dietary lysine and consequently animal growth. 

Besides its utilization for protein synthesis, threonine is involved in other biological functions such as gut integrity and immunity. Thus, a deficiency in threonine leads also to disorders in the digestive physiology which can, in turn, increase the frequency of digestive problems. As a consequence, threonine requirement varies depending on the relative importance of these different functions. It is therefore important to determine the threonine requirement which corresponds to each physiological stage to improve the balance and efficiency of feeds.

Additionally, endogenous losses are very rich in threonine. For instance, threonine to lysine (Thr:Lys) ratio in endogenous losses have been measured to be 120% in pig endogenous losses and in poultry, 174% in ileal juice and 132% in excreta. This specific threonine trait linked to its metabolic functions, underlines the importance of using standardized (or true) digestibility (SID in pigs and TD in poultry) because this system takes into account endogenous losses.

Threonine requirement in pig

To estimate the SID Thr:Lys ratio that optimizes growth performance in pigs, a literature review on the effect of the SID Thr:Lys ratio on pig performance was performed. In these trials, all the diets were supplemented with L-Threonine to refine the threonine requirement. Figure 1 illustrates the example for grower pigs (15-70 kg, 17 trials).

Figure 1. Effect of the standardized ileal digestible threonine to lysine (SID Thr:Lys) ratio on the average daily gain (ADG, % of the best performance) and feed conversion ratio (FCR, % of the best performance) for pigs between 15 and 70 kg live weight.

An increase in the optimal SID Thr:Lys ratio as the pig is getting heavier is described in the literature. This increase could be explained by an increase of the maintenance requirement of heavier animals.

Threonine requirement in broiler

Threonine requirement in broilers has been extensively studied over the last decade. To estimate the optimal SD Thr:Lys ratio of broilers between 0-42 days, 81 trials (reported after 1980) were compiled in a database. In these experiments, L-Threonine was supplemented to estimate the threonine requirement. 21 dose-response studies were selected based on the amino acid profiles. A curvilinear-plateau model was used to predict the threonine requirement of broiler chickens and estimated that at least 67% SD Thr:Lys was necessary to ensure maximal performance of broilers.

Figure 2. Effect of the true digestible threonine to lysine (TD Thr:Lys) ratio on the average daily gain (ADG, % of the best performance) and feed conversion ratio (FCR, % of the best performance) for broiler chicken between 0 and 42 days.

For both, pig and broiler, the dose-response curves (Figures 1 and 2) show that increasing the Thr:Lys ratio through L-Threonine supplementation allows the optimization of pigs and poultry performance (weight gain and feed efficiency).

The tables below give a summary of Ajinomoto Animal Nutrition Europe proposals concerning threonine requirements per species and per growth stage when justified. These requirements, in accordance with the concept of the ideal protein, are expressed relative to lysine on a SID basis for swine and on a TD basis for poultry.

Growing pigs
Piglets Grower Finisher
SID Threonine:Lysine (%) 65 67 68
Lactating sows
SID Threonine:Lysine (%) > 70
Broiler chicken Laying hens
0-42 days 42-56 days
TD Threonine:Lysine (%) 67 67 70

As for L-Lysine, L-Threonine supplementation in monogastric feeds represents a simple, effective and accurate way of adjusting threonine content to animal requirements to optimize the technico-economic results of the production. L-Threonine supplementation also contributes to a better utilization of lysine and of the feed in general. In association with L-Lysine, the use of L-Threonine makes it possible to further reduce the dietary crude protein content and, as a consequence, to reduce nitrogen excretion from animal husbandry in the environment. As L-Lysine, L-Threonine is 100% digestible, so its utilization by the animal is far greater than that of protein-bound threonine from vegetable proteins.

For further information, please read our technical bulletins: numerous experimental results are reported.