Lysine (Lys) is an essential amino acid for milk production in dairy cattle.
To evaluate the effects of feeding two rumen-protected lysine products on milk performance, we enrolled 990 Holstein cows (3 ± 1.2 lactations [mean ± SD], and 158 ± 65 days in milk [DIM]) in a completely randomized pen trial with 2 periods of 60 days. During period 1 cows were supplemented with 45 g/d of AjiPro®-L (50% HCl-Lysine; Ajinomoto; Itasca, IL, United States) and during period 2 cows were supplemented with Relys®50 (50% HCl-Lysine; Vetagro; Reggio Emilia, Italy). Products were mixed with the TMR and provided 11.5 and 13.2 g/d of metabolizable Lys, respectively for AjiPro®-L and Relys®50.
Individual milk yield was recorded daily, and milk tank components were analyzed for protein and fat daily. Data were analyzed under a mixed model with the random effect of cow and the fixed effects of parity, season, DIM, and treatment.
No significant changes were detected in milk yield, however energy-corrected milk (ECM) tended to increase with Relys®50. Milk fat %, milk protein % and yield did not change among treatments. Milk fat yield tended to increase with Relys®50 compared to AjiPro®-L.
We conclude that both rumen-protected Lys products showed a similar milk performance. However, Relys®50 tended to increase yields of milk fat and ECM and that may probably be attributed to the greater Lys bioavailability compared to AjiPro®-L.