BENEFITS OF AMINO ACID BALANCING IN DAIRY CATTLE DIETS

Precision feeding became an essential strategy to optimize income over feed cost in dairy herds, mainly through the increase in nutrient utilization and the corresponding benefits in milk and milk components production. Furthermore, the environmental impact of dairy herds is lessened when nutrient utilization is improved. All these benefits may be achieved through the formulation of diets targeting optimum amino acid balancing. For example, several research studies reported increases in milk and/ or milk protein production with supplementation of rumen-protected amino acids (RPAA). In addition, it was demonstrated that RPAA allows dairy nutritionists to formulate diets with lower CP content while maintaining or sometimes improving performance. These diets were often reported to reduce N excretion. Combined, all these results suggest that RPAA supplementation is desirable, especially in eras when or locations where protein feedstuffs are expensive.

Overall, a majority of the research studies were focused on the supplementation of lysine, methionine or a combination of both. And over the years not only supplementation but also the ratio between these two essential amino acids were consistently reported to be an important diet formulation strategy. Moreover, amino acids may be involved in other physiological processes and thus, proper amino acid balancing may bring other benefits to dairy cows, perhaps in areas such as health and reproduction. However, to quantify these benefits at the farm level is very difficult. Recently, two experiments from University of Wisconsin evaluated the benefits of methionine supplementation on embryo development. The first experiment reported alterations in gene expression of embryos when cows were supplemented with RP methionine and suggested that methionine may be a potential inducer of better embryo development. A follow-up study confirmed this hypothesis as cows fed RP methionine had greater embryo size and reduced embryonic losses. These data support the involvement of RPAA in reproductive physiological processes, and further research with other individual amino acids, especially lysine and histidine, is warranted. A recent study from the University of Illinois highlighted the benefits of amino acid balancing on health of transition dairy cows. These researchers observed lower systemic inflammatory state and enhanced liver function when cows were fed a diet containing adequate levels of methionine in comparison with a deficient diet supporting proper amino acid balancing during the transition period.

Although for many years lysine and methionine were considered to be the two most limiting amino acids when feeding corn-silage based diets, recent studies suggest that other amino acids may improve lactation performance of dairy cows. For example, a study from South Dakota State University evaluated supplementation of rumen degradable valine to late-lactation dairy cows. The authors observed an increase of approximately 6 lbs/ cow/day when cows were fed valine compared with the control group.

Similar effects were observed for fat- and energy-corrected milk as well as feed efficiency. For many years histidine was not considered a limiting amino acid when cows were fed corn silage/alfalfa hay based diets. Data from Penn State University, however, brought new insights about it. In that study, it was observed that supplementation of lysine and methionine attenuate the negative effects of diets deficient in metabolizable protein compared with the diet formulated for adequate metabolizable protein levels. However, the combination of lysine, methionine and histidine led to similar production levels between the adequate and the deficient metabolizable protein diets. Lastly, a Canadian study observed reduction in milk protein yield when cows were deficient in phenylalanine. These results underscore the importance of amino acid balancing beyond lysine: methionine ratio when formulating diets for dairy cows.