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Report no. 467

Abstract
The effect of reducing the content of digestible crude protein in feed for growing-finishing pigs under the current standard (130 g per FEs) has been tested.

The test comprised the following treatments:

* 110 g digestible crude protein per FUp ( 1 FUp = 0.097 x MJ, ME – 0.244)
* 120 g digestible crude protein per FUp
* 130 g digestible crude protein per FUp

The feed mixes were composed so that the contents of the amino acids lysine, methionine, cystine,  threonine and tryptophan were calculated to be 5% above the current standard to secure against fluctuations in the content of crude protein in the ingredients. No requirements were made to the other  essential amino acids isoleucine, leucine, histidine, phenylalanine and valine in the feed optimizing. The test was carried out in one herd with growing-finishing pigs in the weight interval approx. 30-100 kg. Each test treatment consisted of 48 replicates, approx. 144 pigs per test treatment, in total.

The calculated and analysed contents of nutrients in the mixes showed good agreement. The content of digestible, essential amino acids in the mixes was calculated from the total, measured content of the individual amino acids and the content of digestible crude protein as measured by the EFN (enzymatic digestible nitrogen) method. The standards for all the essential amino acids were met in the feed mixes with 130 and 120 g digestible crude protein per FUp. In the mixture with 110 g digestible crude protein per FUp the calculations showed that the content of digestible leucine per FUp was 8% below the standard while the content of the other essential amino acids was level with or above the standard.

The production value for the three feed mixes was calculated from the production results and stated as gross margin per place unit per year at the same feed price for all mixtures.

A reduced content of digestible crude protein by 10 g per FUp in the interval 130-110 g per FUp resulted in a statistically significant decrease in the lean meat percentage of 0.4 pct. points. However, the reduced lean meat percentage did not result in a statistically significant decrease in the production value. Previous tests have shown that a higher content of digestible crude protein in the feed in the interval 130-155 g per FUp resulted in a decrease in the feed conversion ratio and weight gain. On the basis of this, the standard for digestible crude protein for growing-finishing pigs (25-100 kg) of 130 g per FUp is considered to be appropriate.

The excretion of nitrogen was reduced by lowering the content of protein in the feed. When the content of digestible crude protein in the feed was decreased by 10 g per FUp in the interval 130-110 digestible crude protein per FUp, the excretion of nitrogen decreased by 0.35 kg N ex animal. At the three protein levels (110, 120 and 130 g per digestible crude protein per FUp), the kilo N ex animal was 62, 74 and 83 percent, respectively, of the standard figure for growing-finishing pigs. The intake of water was also reduced, and the protein utilization increased by reducing the protein content in the feed.

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