Use of Crystalline Amino Acids and High Quality Protein

Lowering the dietary protein level and supplementing with certain crystalline amino acids is a well-established method of formulating diets to achieve a more ideal amino acid pattern, and it is very effective in reducing nitrogen excretion. Also, using highly 'digestible' feed-stuffs, a high quality protein source with superior amino acid balance, and formulating diets to achieve an ideal protein basis reduces the excretion of nitrogen and other nutrients. Both procedures reduce excesses of unneeded amino acids, which otherwise are degraded and excreted as urea nitrogen.

Table 24.2. Effect of reducing dietary crude protein and supplementing with amino acids on nitrogen excretion. (Average of experiments reported by Bridges et al., 1995.)

Diets

Table 24.2. Effect of reducing dietary crude protein and supplementing with amino acids on nitrogen excretion. (Average of experiments reported by Bridges et al., 1995.)

Diets

+ 1.59 Lys kg-1

100 g CP kg 1 + 3.0 g Lys kg 1 + 0.8 g Thr kg 1 + 0.39 Trp kg 1

N intake (g day-1)

46.9

40.2

35.2

N digested (g day-1)

42.3

36.0

30.3

N excreted in faeces (g day-1)

4.5

4.3

4.9

N excreted in urine (g day 1)

17.7

13.7

10.9

Total N excreted (g day-1)

22.2

18.0

15.8

N retained (g day 1)

24.6

22.3

19.5

Reduction in N excretion %

18.9

28.8

Table 24.3. Impact of added amino acids on N excretion in pigs. (From Nonn and Jeroch, 2000.)

Weight range

25-60 kg 60-85 kg 85-110 kg 25-110 kg

N excretion (g N day1)

Controls

Added amino acids

Females Castrates Females Castrates

33.7

43.3

25.0

29.5

Based on a review of several papers, Kerr and Easter (1995) suggested that for each percentage unit reduction in dietary crude protein combined with amino acid supplementation, total nitrogen losses (faecal and urinary) in pigs could be reduced by approximately 8%. Although the application of such crystalline amino acids in practical situations is generally straightforward, it is recognized that there will be limits to their use compared with intact protein. For example, nitrogen retained is often less when amino acids are supplemented and the crude protein level is reduced to a large extent. This is especially so when three or more amino acids replace four percentage units of crude protein.

Conversely, the use of low-quality protein sources markedly increases nitrogen excretion. Also, the inclusion of high levels of crude fibre in the diet reduces the efficiency of nitrogen utilization (Kornegay and Verstegen, 2001).

In most of the above-mentioned studies there were only small changes in faecal nitrogen losses because the added amino acids are very highly digestible. Several nutritional means are available to improve the nitrogen balance considerably. The use of added amino acids often crystaline AA, at present lysine, methionine, threonine and tryptophan, can reduce N excretion with manure in, for example, pigs by about 35%.

In poultry there is also an abundance of literature on reduction of protein levels with simultaneous addition of amino acids. Studies by Summers et al. (1992), Fancher and Jensen (1989) and Holsheimer and Janssen (1991) reported impaired weight gain and in broilers with low protein and extra amino acids. Other studies of (Moran et al., 1992;

Aletor et al., 2000) found nearly similar performance with added amino acids and less protein. If changes occurred these pointed mostly to more abdominal fat in the body. In addition, Aletor et al. (2000) found increased efficiency when protein in broiler diets was reduced to 153 g kg-1 with extra AAs. About 41% less N was excreted. By reducing the ratio of non-essential to essential AA content Ten Doeschate (1995) found a further reduction. If diets reduce amounts of endogenous AA this will give another possibility to reduce N surpluses. Gahl et al. (1995) demonstrated the diminishing returns in response to increasing nutrient input, but the responses in terms of reduction were not linear.

Feeding strategy also includes reducing feed waste and phase feeding. Estimated from various studies Van Heugten and Van Kempen (1999) quoted values of 2-12% in the United States, 1.5-20% in Great Britain, and 3-5% in Denmark.

Phase feeding can be applied to adjust the available AA content to the specific weight of the animal. The requirement of animals for most available amino acids expressed as part of the total diet decreases as animals grow heavier if the diet is not changed. Thus changes in diet formulation if properly adjusted can meet the nutrient needs of pigs more efficiently. Adjustments in diets with increase in weight can result in reduced intake of AAs and thus, reduced excretion of nitrogen. Phase feeding, as some have described it, is a way to meet more precisely the nutrient needs of growing and finishing pigs. This concept applied to dietary crude protein is illustrated in Table 24.4 and Fig. 24.2.

Table 24.4. Effect of feeding strategy during the growing-finishing period (25-105 kg) on N output. (Adapted from Henry and Dourmad, 1993.)

Single-feed

Two-feeds3

Three-feeds'3

170 g CP kg-1

170-150 g CP kg-1

170-150-130 g CP kg-1

N output (g day-"1)

31.9

29.0

26.7

Percentage of two-feed strategy

110

100

92

aCrude protein changed at 55 kg body weight. bCrude protein changed at 50 and 75 kg body weight.

Weight of pigs (kg)

20 110 Weight of pigs (kg)

Fig. 24.2. Example of a one-phase (a) and a nine-phase (b) feeding programme for the growing and finishing phase. (Kornegay and Harper, 1997, cf. Kornegay and Verstegen, 2001.)

Weight of pigs (kg)

20 110 Weight of pigs (kg)

Fig. 24.2. Example of a one-phase (a) and a nine-phase (b) feeding programme for the growing and finishing phase. (Kornegay and Harper, 1997, cf. Kornegay and Verstegen, 2001.)

Protein requirements may change (perhaps weekly) as pigs grow. Therefore, the formulation of the diet can also change as the nutrient requirements change. The nutrient needs of the animal can be met more precisely and in this way the total quantity of nitrogen excreted can be reduced.

These changes, however, have a danger that the animals will have to adapt their digestive processes to these diets often with, as a result, reduced availability of nitrogen. The study by Henry and Dourmad (1993) showed that nitrogen excretion could be reduced approximately 15% when feeding a 140 g CP kg-1 diet was initiated at 60 kg body weight, rather than continuous feeding of a 160 g CP kg-1 grower diet to final weight. Another French study (Chauvel and Granier, 1996) reported a 9% reduction in nitrogen excretion when a two-phase was changed into a multiphase system. The proportions of 189 and 149 g CP kg-1 diet (4.1 and 2.6 g digestible lysine MJ1 net energy, respectively) were changed weekly from 24 to 107 kg in the multiphase system versus a two-phase system in which a 181 g CP kg-1 (0.85 g lysine MJ-1 net energy) diet was fed until 66 kg and a 161 g CP kg-1 (7.4 g lysine MJ-1 net energy) diet was fed from 66 kg to 107 kg. According to Henry and Dourmad (1993) this change should be made gradually by changing the ratio in which a 'high' protein grower diet is mixed with a 'low' protein finishing diet. In a recent Dutch study a 14.7% reduction in urinary nitrogen excretion was reported when a multiphase feeding programme was compared with a two-phase feeding programme (Van der Peet-Schwering et al., 1996). They also found that ammonia emission was reduced 16.8%. Their multiphase feeding programme was achieved by mixing, on a weekly basis, a high protein diet with a low protein diet in decreasing proportions as pigs grew. Under such precise feeding conditions, the total quantity of nitrogen fed can be reduced as well as excreted N.

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