Effect of Increasing the Methionine Level and Reducing the Threonine Level in the Diet of Fast-Growing Rabbits

Abstract

The main aim of this work was to evaluate a novel combination of the first limiting amino acids (lysine, methionine, and threonine) in fast-growing rabbits (combination MHL, shown to minimise levels of plasmatic urea nitrogen in previous research, medium level of lysine, high level of methionine, and low level of threonine) and compare it with current recommendations (combination MMM, medium level of all amino acids). A total of 165 weaned rabbits (28 d old) from a paternal line selected for growth rate were used in the growth trial. The effect of the diet on apparent fecal digestibility, as well as the apparent and true ileal digestibility, were studied. Nutrient retention was also determined. Although no differences in digestibility between diets were observed, animals fed with Diet MHL improved the global average daily gain (+2.3 g/d; p = 0.0482) and feed conversion ratio (−0.10; p = 0.0229). Animals fed with Diet MMM reduced the protein-to-energy ratio retained (p = 0.0086). In conclusion, Diet MHL promoted an improvement in growth traits in a paternal line. Consequently, we propose its levels of 6.4, 5.4, and 5.0 g/kg DM of true ileal digestible lysine, methionine, and threonine, respectively.

A Trial Comparing Growing Rabbits Differing in 18 Generations of Selection for Growth Rate Reveals a Potential Lack of Effectiveness in the Genetic Selection Progress

“…As a result, the obtained sanitary risk index (37%) was comparable to other reported values in the literature for this same line (on av. 35%) [9,[19][20][21].…”

Biomarkers for ideal protein: rabbit diet metabolomics varying key amino acids

“…(ii) Oversized levels: Another hypothesis suggests that the levels of this amino acid are oversized, causing an excess that must be catabolised. This hypothesis seems to be less plausible, as there are recent works in growing rabbits of this same age and selected for similar traits that showed that the lysine levels used in this experiment match their requirements 57 , 58 . (iii) Higher digestibility of synthetic lysine: The increased degradation might be a consequence of the higher digestibility of the synthetic lysine added to Diet B by adding l -lysine HCl (4.7 g per kg).…”

“…(ii) Oversized Levels: Another hypothesis suggests that the levels of this amino acid are oversized, resulting in an excess that must be catabolised. However, this hypothesis seems less plausible, as the nutritional requirements for methionine are well established and closer to the higher levels 58 . (iii) Higher Digestibility of Synthetic Methionine: The increased degradation might be a consequence of the higher digestibility of the synthetic methionine added at each level.…”

“…Diet MHL was chosen for its demonstrated improvement in productive performance in the same animals, signifying a diet correctly tailored to their requirements 46 . Lastly, Diet LMM, known for its lysine deficiency and its impact on plasma urea levels in prior experiments, was also included 45 , 46 , 58 .…”