Some abstracts do not have video files because ASAS was denied recording rights.
1504
Meta-analysis to predict amino acids limiting dairy cattle performance
Meta-analytic methods were used to provide statistical relationships between estimated metabolizable protein (EMP) amino acid supply (g or g/ME) and milk protein content, milk protein percentage, and milk yield in lactating dairy cows. Sixty-three research publications (258 individual observations) were identified through a search of published literature using 3 search engines and met the criteria for inclusion in the meta-analysis. An advanced nutrition model (CNCPS 6.5 with NDS platform, RUM&N Sas, Italy) was used to determine dietary nutrient parameters including EMP amino acids. Two approaches were used to analyse the data: 1) mixed models weighted analysis with a random effect of study to determine whether the explanatory variables predicted cow responses and 2) classical effect size meta-analytical evaluation of responses to treatment. Regardless of the analytical approach or method of expression (g or g/ME), EMP Met increased milk protein yield, milk protein percentage, or milk yield, confirming that it can be first-limiting in lactating dairy cow diets. With a difference of 0.07 units EMP His (g/ME) (1.13 vs. 1.20 for control and treatment, respectively), effect size analysis determined that each additional unit of EMP His (g/ME) increased milk protein yield by 1.72 kg, identifying His as a possible limiting amino acid. Milk yield increased by 3.28 kg per unit of EMP Trp (g/ME) (0.60 vs. 0.616 for control vs. treatment, respectively). Milk true protein yield was improved by EMP Leu (g). Estimated MP Lys (g or g/ME) did not increase responses in production outcomes. However, mean EMP Lys supply was lower than typically recommended and the change with treatment was minimal (157 vs. 162 g; 6.36 vs. 6.38% MP). This meta-analysis supports other research indicating the positive impact of Met and His as limiting amino acids for protein synthesis and suggests Leu, Trp, and Lys be given greater consideration in future research.
Keywords: amino acids, milk protein, meta-analysis