NorFor update - focus on Amino acids

NorFor has not, until now, given any recommendations concerning amino acids. There has been a demand for such recommendations and during 2013 NorFor has made a development work with data from the literature in order to set up recommendations for methionine, lysine and histidine.

A dataset with data from 17 production trials where the effect of adding rumen protected amino acids was investigated and data from infusion trials, in total 27 trials with 128 treatments. The cows were 70 to 180 days in milk. Data about the cows and feedstuffs were put into NorFor in order to investigate relationships between amino acid supply and milk protein response.

When only data from the production trials were used there was no relationship between the levels of methionine (% of total AAT) in control feed rations and the response in milk protein yield (g/day). Note that the variation in methionine among the feed rations were small, between 2.1 to 2.35 % of total AAT. The conclusion from this analysis was that cows in mid- and late lactation with a content of methionine of 2.1 2.3 % of total AAT don´t need any supplementation with rumen protected methionine to increase protein yield or milk yield.

The complete dataset were put into NorFor to see if milk protein yield was dependant of the methionine content of the ration. A logistic regression model was used and according to figure 1 the maximum milk protein yield will be achieved with a methionine content of 2,2 % of AAT for cows in mid or late lactation.

The dataset contained only a minor set of treatments with rumen protected lysine and most often in combination with rumen protected methionine. There was no response in milk protein yield by increasing the level of lysine in the feed ration, according to the studied data.
The cows in these trials were all in mid and late lactation. Data from literature indicate that milk production in cows in very early lactation can benefit from supplementing with rumen protected amino acids. However, a very limited number of studies are available.

Based on these data analyses, a recommended minimum level of 2.2 % methionine of total AAT is now applied in the NorFor model. The recommendations for histidine and lysine are set relative to the content of methionine in milk. The content of histidine in milk protein is the same as the content of methionine, therefor NorFor recommends a minimum histidine level of 2.2 % total AAT. The lysine content in milk protein is 2.9 times higher than methionine. NorFor recommends a minimum lysine level of 6.4 % of total AAT.

This recommendation for amino acids was included in the latest update of the NorFor model, FRC 1.76.

For more information contact Nicolaj Ingemann Nielsen

Figure 1. Relationship between milk protein yield (g/d) and methionine supply (% of AAT) of the cow calculated in NorFor. The response function is modelled with logistic regression based on 128 treatments from 27 experiments, where methionine was added by infusion or as a rumen protected amino acids or in combination with other essential amino acids.

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