The efficiency of utilization of dietary protein

Model predictions (Moughan and Smith, 1984) for the utilization of dietary crude protein and lysine (the first limiting amino acid) for a range of commercial pig grower diets, given to 50 kg live weight gilts (Pdmax = 115 g day-1) at two food intake levels (see Moughan, 1984, for details) are given in Table 11.3. The predictions show that the different diets, formulated for optimal growth, actually support very different rates of daily body protein deposition and illustrate the low and variable efficiencies of utilization. At the higher feeding level only three of the formulated diets supported maximal protein growth. The efficiency of utilization of dietary crude protein intake (Pe) ranged from 20 to 42% at the lower level of meal intake and from 22 to 34% at the higher level. On average the ingested dietary protein was utilized with an efficiency close to 30%. The equivalent of around 70% of the ingested nitrogen was excreted from the pig's body. Part of this inefficiency can be explained by dietary amino acid imbalance, which may be purposeful and economically justifiable. Lysine was the first-limiting amino acid in each of the six diets, so it is pertinent to examine (Table 11.3) the efficiency of utilization of ingested lysine (Le), whereby the effect of amino acid imbalance is removed. As expected, the values for Le are higher than the comparable values for Pe. On average the ingested lysine was utilized with an efficiency close to 44%, but still over half the dietary lysine was not used for the net deposition of lean tissue. Modelled data, such as these, highlight the importance of under

Table 11.3. Efficiency of utilization3 of dietary crude protein (CP) and lysine in six commercial pig growers diets, given at two feeding levels to 50 kg live weight gilts.

Diet

Table 11.3. Efficiency of utilization3 of dietary crude protein (CP) and lysine in six commercial pig growers diets, given at two feeding levels to 50 kg live weight gilts.

Diet

1

2

3

4

5

6

Feeding level = 1710 g meal day 1

Digestible CP intake (g day 1)

175

281

235

232

182

215

Protein deposited (g day 1)

48.9

110.0

73.5

106.9

74.3

115.0

Pe (%)b

20.4

30.0

23.1

33.3

32.3

42.1

Le (%)°

37.2

38.3

38,5

43.5

54.0

59.0

Feeding level = 2270 g meal day 1

Digestible CP intake (g day 1)

232

374

312

309

242

285

Protein deposited (g day 1)

71.4

115.0

104.1

115.0

105.2

115.0

Pe (%)b

22.4

23.7

24.6

27.4

34.4

31.7

Le (%)°

40.9

30.2

41.1

35.3

59.0

45.0

3Predicted values (Moughan, 1984) from a pig growth simulation model. Assumes healthy animals growing in a thermoneutral environment. bPe = Body protein deposited x IflQ Diet crude protein intake 1 _ Body lysine deposited x 100 Diet total lysine intake 1

3Predicted values (Moughan, 1984) from a pig growth simulation model. Assumes healthy animals growing in a thermoneutral environment. bPe = Body protein deposited x IflQ Diet crude protein intake 1 _ Body lysine deposited x 100 Diet total lysine intake 1

standing the physiological processes which lead to losses of amino acids from the body, thus allowing better estimation of amino acid requirements and refined dietary formulation.

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