Nitrogen and phosphorus consumption, utilisation and losses in pig production: Denmark

Livestock Production Science 58 (1999) 225–242

Nitrogen and phosphorus consumption, utilisation and losses in pig production: Denmark a, *, H.D. Poulsen a , S. Boisen a , H.B. Rom b ´ J.A. Fernandez b

a Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark Danish Institute of Agricultural Sciences, Research Centre Bygholm, P.O. Box 536, DK-8700 Horsens, Denmark

Abstract Swine production in Denmark has increased by more than 50% in the past 20 years and in this time the structure of production has changed markedly towards larger units. This has resulted in a serious threat to the local environment. Consequently, legislative measures with a progressive degree of restriction have been introduced. The annual production of slurry from pigs amounted to about 12.5 million tons in 1995, containing about 104 000 tons of N and 25 000 tons of P. Ammonia emission from pig buildings in 1996 was about 16 000 tons. Production of one standard pig (about 100-kg live weight) generated a total excretion of about 5 kg N and 1.2 kg P in 1997. Sows, weaners and growing pigs contributed 22, 13 and 63% to N excretion and 26, 15 and 59% to P excretion, respectively. Nitrogen and phosphorus losses from pig production in Denmark are discussed in relation to legislative and nutritional measures.  1999 Elsevier Science B.V. All rights reserved. Keywords: N and P excretion; Ammonia emission; Legislation; Research

1. Introduction

1.1. Basis, structure and development of pig production Denmark comprises a land area of 4.3 million ha, of which 2.7 million ha were cultivated in 1995. It is expected that the cultivated area will be reduced to about 2.5 million ha by 2010 (Danish Farmers’ Union, 1993). The ‘Winter-green’ area has increased from 62% of the total cultivated area in 1980 to 79% in 1994 (Danish Farmers’ Union, 1995). *Corresponding author. Tel.: 1 45-8-999-1217; fax: 1 45-8999-1919.

Swine production in 1994 amounted to 20.5 million pigs (Table 1), which means that the total production has increased by more than 50% since 1980. The pig sector has undergone a marked development towards specialisation and larger production units. From 1982 to 1994 the number of pig herds decreased by more than 50%, while the number of pigs produced increased. In 1990, about 67% of pigs were kept in farms with a herd size of more than 500 animals. This proportion increased to 80% in 1994–1995, with an expected further increase to 90% by the end of the century (Table 1). Pig population is concentrated in Jutland (79%). This is also reflected in the animal density, which in Jutland is 0.45 Animal Units (AU) for pigs and 1.17

0301-6226 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00011-1

´ et al. / Livestock Production Science 58 (1999) 225 – 242 J. A. Fernandez

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Table 1 Structure of pig production in Denmark

b

6

Pig production, total 3 10 Herd size distribution b , % of pigs: , 50 50–199 200–499 . 500 Average herd size a , pigs Pig population, pigs a 3 10 6 Islands, % Jutland, % a b

1994–1995

2000 a

1990

1992

16.5

18.5

20.5

21.5

2.0 10 20.6 67.4 318 9.5 24 76

1.4 7.7 16.5 74.4

1.3 6.0 12.9 80.1 527 11.0 22 78

90 794 11.5 21 79

10.5 23 77

Danish Farmers’ Union (1993, 1995). Federation of Danish Pig Producers and Slaughterhouses (1991, 1993, 1995).

AU for all farm animals. The corresponding values for the rest of the country are 0.32 and 0.63, respectively (Dalgaard, 1997).

1.2. Average production level of pig herds Production levels have increased continuously. The number of growing pigs produced per sow was 11.8 in 1975 increasing to 17.4 in 1990. Similarly,

the number of feeding days from birth to slaughter (90 kg) was reduced from 239 to 196 (Danish Farmers’ Union, 1993). Current production levels of herds are shown in Table 2. The data were obtained from the efficiency control and monitoring programme run by the National Committee for Pig Breeding, Health and Production (1996). This programme includes about 10% of herds but comprises about 30% of produced

Table 2 Average production level of pig herds in Denmark a 1993

1994

1995 b All

Worst 25%

Best 25%

Sows, piglets (–7.5 kg): Litters / sow / year Pigs born alive / litter Pigs weaned / litter Weaning age, days Weaning live weight, kg Feed produced / pig, MJ ME

2.3 11.0 9.8 29 7.4 757

2.3 11.0 9.8 29 7.3 750

2.3 11.1 9.8 29 7.3 767

2.2 10.7 9.2 32 7.8 868

2.3 11.4 10.3 27 6.9 623

Weaners (7.5–30 kg) Pigs produced / sow / year Daily gain, g Feed / produced pig, MJ ME

21.6 434 577

21.6 431 571

21.7 422 576

19.0 433 661

23.7 403 475

Growing pigs, (30–100 kg): Feed, MJ ME / day Gain, g / day Weight at slaughter, kg Feed / gain, MJ ME / kg Lean, %

26.9 706 100 38.1 60.1

27.5 735 97 37.4 59.8

28.0 744 97 37.6 59.8

27.4 676 99 40.6 59.7

28.4 810 97 35.0 59.8

a b

Data from the National Committee for Pig Breeding, Health and Production (1996). Classified according to gross marginal income.

´ et al. / Livestock Production Science 58 (1999) 225 – 242 J. A. Fernandez

pigs. Production levels of herds remained constant during the last 3–4 years with regard to reproduction (sows and weaners up to 30 kg), while there was a tendency towards higher daily gain and better feed conversion efficiency in the case of growing pigs (30–100 kg). Variation between herds (1995) is illustrated by the average of the worst 25% and of the best 25%, characterised by their gross marginal income.

1.3. The global output of N and P Faecal and urinary output of N and P in 1995 can be estimated from the number of pigs produced (Table 1), the number of sows involved (pig produced per sow per year, Table 2) and from average production data for weaners and growing pigs (Table 2). The method of calculating the contribution of each animal category is described later in this report. The total annual excretion is shown in Table 3.

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ing their yearly production of piglets up to 25 kg). From December 1999, one animal unit will be equivalent to a maximum of 100 kg manure-N produced (ex store). There are no corresponding regulations for phosphorus. In general, the current law permits the delivery of pig manure from 1.7 animal units per hectare of arable land. Farmers can exceed the animal density limitation, provided that an agreement is made with neighbouring farms with respect to access to additional land. Production of more than 250 animal units require approval of special procedures. A substantial number of farms need additional land to support their animal density. It has been calculated (Danish Farmers’ Union, 1995) that the country’s land deficit for all species amounted to 205 000 ha in 1994, of which pig units accounted for 163 000 ha. Only 55% of pig farms had enough land to meet the animal density requirement.

1.4. Legislation

2. Nitrogen and phosphorus economy

The law on environmental protection was revised in 1981. At that time it was pointed out that nitrogen and phosphorus threatened the quality of ground water and surface water. Various actions have since been introduced to reduce the N and P load. In agriculture, guidelines regarding the storage and application of manure were formulated. Furthermore, restrictions on animal density were imposed together with a requirement for improved utilisation of nitrogen from manure. For pig slurry, solid manure from deep-straw bedding and for other manure types the requirements in 1997 were 50, 15 and 45%, respectively. Currently, one animal unit corresponds to the manure production from 30 growing–finishing pigs (25–95 kg body weight) or from three sows (includ-

2.1. Contents of N and P in commercial diets for pigs

Table 3 Calculated mass of excreta, excreted N and P and emission of NH 3 in Danish pig production in 1995 (1000 tons)

Faeces Urine Total a

Mass

N

2953 9596 12 549

31.2 73.2 104.4

NH 3

P

16 a

20.1 4.7 24.8

Yearly emission from pig buildings in 1996.

Dietary content of N and P decreased during recent years. A survey of marketed feed mixtures throughout the country was carried out by the National Committee for Breeding, Health and Production (Kjeldsen, 1997). The survey comprised more than 80% of industrial pig feed. The results are shown in Table 4.

2.2. Utilisation of dietary N and P by different pig categories The accumulation of N and P in the body of piglets (0–7.5 kg body weight) and in the body weight (BW) gain of sows and weaners (7.5–30 kg BW) were taken from the available literature. The values are shown in Table 5 together with the estimated variation for sows and piglets. The body composition of weaners, growing pigs and of BW-gain was determined by comparative slaughter experiments carried out at the Danish Institute of Agricultural Sciences during the last 15 years. The pooled data from earlier experiments were

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Table 4 The content of N and P in commercial pig diets

Sows Weaners Growing pigs

ME, MJ / kg

Nitrogen, g / MJ ME

Phosphorus, g / MJ ME

13.57 14.72 13.72

1.88 2.19 2.03

0.49 0.54 0.42

Table 5 The content of N and P in the body of piglets and in the body weight gain of sows and weaners

Sows a , g / kg BW-gain Piglets (7.5 kg), g / kg BW Weaners (7.5–30 kg BW), g / kg EBW-gain

N P N P N P

Content

Min.

Max.

Reference

25 5 24 5 29

20 4.7 23 4.7 –

30 5.1 24 5.0 –

3, 4, 5, 7, 8 bd 4b 1, 2, 4, 6 d 1, 2, 4, 6 d

–

–

5.7

c

c

a

BW-gain was estimated on the basis of experimentally determined average weight gain of sows over several parities and added the contribution under practical conditions of boars, replacement gilts and dead piglets ( , 2-kg LW) to 60 kg / sow / year. b Combined with unpublished Danish results. c Calculated on the basis of the body content of piglets and the body content of weaners (see Table 6). EBW, empty body weight. d 1. Becker et al. (1979); 2. Berge and Indrebø (1954); 3. De Wilde (1980); 4. Everts and Dekker (1991); 5. Everts and Dekker (1994); 6. Nielsen (1973); 7. Walach-Janiak et al. (1986); 8. Whittemore and Yang (1989).

published by Jørgensen et al. (1985b). The data used in this report have been partially published by ´ Fernandez et al. (1985), Just et al. (1985a, 1985b, 1985c, 1985d), Jørgensen et al. (1985a, 1986, 1988) and Oksbjerg et al. (1990, 1996). Basically, the experiments consisted of feeding littermate pigs from 20 to 90 kg BW with balanced rations differing in chemical composition.

Digestibility and balance experiments (3–5) were performed. The pigs were subsequently sacrificed, dissected, ground and analysed. One pig from each litter was sacrificed and analysed at the beginning of the experiment in order to obtain initial values for the nutrient contents of the body. In Table 6 are shown the mean and variation of the nutrient content of weaners, growing pigs and the calculated corre-

Table 6 Nitrogen and phosphorus content in the empty body weight (EBW) of young pigs (n 5 37), growing pigs (n 5 151) and empty body weight gain of pigs (n 5 151) determined by comparative slaughter experiments Young pigs

Live weight at slaughter, kg Empty body weight, % of live weight Nitrogen, g / kg EBW Phosphorus, g / kg EBW

Growing pigs

Gain

Mean

S.D.

Mean

S.D.

Mean

S.D.

21.4

2.8

88.2

3.9

–

–

89.9 27.7 5.7

2.3 1 0.3

94.5 28.8 5.8

1.2 1 0.4

– 29.0 5.7

– 1 0.5

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sponding values of BW-gain. All values are given in relation to empty body weight (live weight minus content of digestive tract).

2.3. N and P flow in pig and sow production The flow of N and P in the production of a standard pig was calculated on the basis of the mean production levels in practical pig production (Table 2), the content in the feed (Table 4) and the retention by the pig (Tables 5 and 6). Total loss was obtained

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as the difference between consumption and retention. Partition of total loss between faeces and urine was carried out by assuming that protein digestibility is 80% in sows and growing pigs and 85% in weaners. Mean digestibility of phosphorus was assumed to be 45% for all feeds (Poulsen, 1994, 1996). The N and P flows specified for various pig categories are shown in Tables 7 and 8. The flows of N and P in breeding sows were also calculated in reproductive cycles (weaning to weaning) and in production per sow per year, using a

Table 7 The consumption, retention and losses of nitrogen in the production of a standard pig a (kg) Losses Days

N in feed

Piglet (0–7.5 kg) Weaner (7.5–30 kg) Growing pig (30–100 kg)

161 53 94

1.42 1.26 5.35

Total Relative

308 –

8.03 100

Retained N

Faeces

Urine

Total

Relative

0.25 0.59 1.97

0.28 0.19 1.07

0.89 0.49 2.31

1.17 0.67 3.38

22 13 65

2.81 35

1.54 19

3.69 46

5.22 65

100 –

a Conditions and assumptions (rounded figures). Piglet: calculated on the basis of a sow / year: weaning 22 piglets containing 24 g N / kg body weight; gain sow / year 5 60 kg, containing 25 g N / kg gain; yearly consumption of 16 640 MJ ME containing 1.88 g N / MJ ME. Weaner: consumption of 576 MJ ME containing 2.19 g N / MJ ME. Retained 29 g N / kg empty body weight gain. Empty body weight: 90% of live weight. Growing pig: consumption of 2634 MJ ME containing 2.03 g N / MJ ME. Retained 29 g N / kg empty body weight gain. Empty body weight: 95% of live weight. Digestibility of protein assumed to 80% for sow and growing pig diets and 85% for weaner diets.

Table 8 The consumption, retention and losses of phosphorus in the production of a standard pig a (kg) Losses Days

P in feed

Piglet (0–7.5 kg) Weaner (7.5–30 kg) Growing pig (30–100 kg)

161 53 94

0.37 0.31 1.11

Total Relative

308 –

1.79 100

Retained P

Faeces

Urine

Total

Relative

0.05 0.12 0.39

0.20 0.17 0.61

0.12 0.02 0.11

0.32 0.19 0.72

26 15 59

0.56 32

0.98 55

0.25 13

1.23 68

100 –

a Conditions and assumptions (rounded figures). Piglet: calculated on the basis of a sow / year: weaning 22 piglets containing 5 g P/ kg body weight; gain sow / year 5 60 kg, containing 5 g P/ kg gain; yearly consumption of 16 640 MJ ME containing 0.49 g P/ MJ ME. Weaner: consumption of 576 MJ ME containing 0.54 g P/ MJ ME. Retained 5.7 g P/ kg empty body weight gain. Empty body weight: 90% of live weight. Growing pig: consumption of 2634 MJ ME containing 0.42 g P/ MJ ME. Retained 5.7 g P/ kg empty body weight gain. Empty body weight: 95% of live weight. Phosphorus digestibility assumed to 45% for all diets.

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Table 9 The consumption, retention and excretion of N and P in sow production a (kg)

Days

Lactation Dry 1 gestation Total per cycle Total / sow / year Relative a

28 133 161 365

Consumption

Utilisation

Losses

In feed

Retained body

Faeces

Urine

N

P

N

P

N

P

N

P

4.50 9.10 13.60 30.83 100

1.17 2.37 3.54 8.03 100

1.47 0.91 2.38 5.40 18

0.27 0.22 0.49 1.11 14

0.90 1.82 2.72 6.17 20

0.65 1.30 1.95 4.42 55

2.13 6.37 8.50 19.26 62

0.25 0.85 1.10 2.50 31

Conditions and assumptions. Lactation: consumption of 2394 MJ ME; dry 1 gestation: consumption of 4841 MJ ME.

simplified model. Consumption during lactation was obtained from the standard feeding scale for lactating sows currently used in Denmark. Subsequently, the consumption during dry 1 gestation period was calculated by difference from total feed consumption (Table 2). Retention in the body weight gain of sows (60 kg / year), and in newborn piglets (mean 1.4 kg BW containing 19 g N and 6.6 g P/ kg; Nielsen, 1973) was allocated to the dry 1 gestation period, while the retention in the gain of piglets from 1.4 to 7.5 kg BW was taken as retention during lactation. The results of the calculations are shown in Table 9.

3. The basis for optimising P and N utilisation in practical pig production

3.1. Optimising the utilisation of dietary phosphorus The low net utilisation of P in Danish pig production (until now) is mainly due to two factors. Firstly, the P digestibility in pig diets is usually quite low, resulting in a high faecal excretion of P. Secondly, the dietary P recommendations were based on total P. As such, they were imprecise and included large safety margins, resulting in massive urinary excretion of surplus P. Therefore, a more precise basis for P recommendations would be digestible P instead of total P. In 1992 specific research was started in Denmark to define more precise P requirements based on digestible P and to develop ways of improving the overall P utilisation. The regulation of P homeostasis in the body occurs mainly through control of P excretion in urine

and P absorption. Physiologically, fractional P absorption decreases and the urinary P excretion increases when pigs are fed above their requirement. Conversely, fractional P absorption increases and the urinary P excretion decreases when pigs are fed below their P requirement. When pigs are fed P according to their physiological requirement, urinary P excretion is very low. These are the most important preconditions for the determination of P digestibility in feedstuffs, feed phosphates and compound diets. Danish studies on P digestibility are based on the apparent digestibility of P measured by 7 days total separate collection of faeces and urine (by insertion of bladder catheters). The P content in representative samples of faeces, urine and diet is analysed, and the apparent P digestibility is determined. A method for defining the P digestibility in feed phosphates and meat and bone meal has been ´ developed (Oksbjerg and Fernandez, 1987; Poulsen, 1995). A standard basic diet (semi synthetic) with a very low content of P (1.5 g / kg) is used. Based on this diet, five experimental diets with increasing additions of the test phosphate are prepared for each phosphate source and fed to six pigs per phosphorus level. The content of P in all diets is adjusted to levels calculated to be equal to or below the pigs’ requirement. The digestibility of P in the tested feed phosphate is determined by linear regression of P intake on apparent digestible P (Poulsen, 1995). The slope obtained is defined as the P digestibility coefficient of the tested phosphate. The calcium (Ca) content in all five experimental diets is adjusted to 6 g / kg diet by inclusion of calcium carbonate. The P digestibility coefficients obtained are used in prac-

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tice. The amount of digestible P in the most common feedstuffs is now studied by the same principles as described for feed phosphates. All experiments are carried out with growing pigs. As much as two-thirds of the P in grains and seeds that are used in pig feeding is present as phytate-P (Boisen, 1987). Without hydrolysis phytate-P is almost indigestible for pigs. The hydrolysis of phytate is catalysed by phytase, and this enzyme is present in many feedstuffs of plant origin (intrinsic phytase). As phytase is inactivated by heat, usually no activity can be detected in heat-processed feeds such as soybean meal etc. Phytase is also available commercially as microbial phytase produced by microorganisms. The effect of microbial phytase supplementation on P digestibility depends primarily on the composition of the diet, i.e. the content of intrinsic phytase. In Danish experiments addition of phytase increased P digestibility by about 20 percentage units in diets based on barley and by 5 to 9 percentage units in diets based on wheat (Poulsen, 1996). These test diets were not heat treated, which means that the intrinsic phytase activity was higher in the wheat diets than in the barley diets, resulting in the different efficiencies of supplemented microbial phytase. In none of these cereal-based diets P digestibility exceeded 65%. Until now, the use of microbial phytase supplementation in Denmark is negligible. In 1995 new Danish recommendations for digestible P were introduced for growing pigs (Table 10). Combined growth and balance studies were made to determine the P requirement. The latter were carried out in order to determine the exact content of

231

apparent digestible P in the test diets used in the performance studies (Poulsen, 1994). In May 1997, recommendations for digestible P were introduced for piglets and sows (Table 10). The new recommendations are based on results from performance and balance studies to determine the apparent digestible P content (piglets: Jørgensen et al., 1997; sows: Sørensen and Poulsen, 1997) and theoretical calculations based on information on the capacity for P retention in the body. P retention approximates 5.0, 5.5 and 5.5 g per kg gain for sows and piglets ´ (Poulsen, 1997) and for growing pigs (Fernandez, 1997), respectively. The total endogenous P loss (faecal and urinary) is not well documented. Usually the endogenous P loss is expected to be very low but ´ may be influenced by diet composition (Fernandez, 1995a). In May 1997 the recommendations for dietary Ca were revised, resulting in lower Ca recommendations (Table 10). Excessive dietary Ca may reduce P digestibility in some diets; furthermore Ca affects the absorption and metabolism of trace elements (Poulsen, 1993). Until now, mainly performance characteristics have been used in defining the P and Ca requirement in pigs. However, as P and Ca are central in the bone mineralisation processes, it is necessary to establish specific criteria to evaluate ´ bone quality (Fernandez, 1995b).

3.2. Optimising the utilisation of dietary nitrogen During the last 5 years the general protein level in pig diets has been reduced, leading to an assumed reduction in N-excretion of about 15%. This reduc-

Table 10 Recommendations for digestible phosphorus and total calcium in Danish pig diets Digestible phosphorus g / FUp Weaners (7–30 kg) Growing pigs: 30–50 kg 50–100 kg 30–100 kg Sows: Pregnant Lactating a

a

Calcium g / MJ ME

g / FUp

g / MJ ME

3.2

0.25

7.5

0.59

2.2 2.2 2.2

0.17 0.17 0.17

7.0 7.0 7.0

0.55 0.55 0.55

2.2 2.7

0.17 0.21

7.0 7.0

0.55 0.55

FUp, Danish feed unit for pigs: 7.72 MJ NE ¯ 12.8 MJ ME.

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tion has primarily been obtained by a general improvement of the protein quality, achieved by supplementation with industrial amino acids (lysine, methionine, threonine and tryptophan), especially in commercial feed mixtures. The commercially available amino acids are also those which usually are the first limiting amino acids in unsupplemented pig diets. However, when using supplementation of these amino acids, all essential amino acids can potentially be limiting (Fig. 1). The Danish recommendations for faecal digestible amino acids, which until 1996 included only the above amino acids, include now all essential amino acids (Table 11). The common feeding practice is still to use only one diet throughout the growing–finishing period from 30 kg live weight until slaughter at about 100 kg, although the amino acid requirements decrease gradually in relation to the energy requirement (Fig. 2). Furthermore, rather high safety margins are generally included in the recommendations for digestible essential amino acids, in order to avoid risk of undersupply. This appears to be necessary due to limitations in the present Danish protein evaluation system, which is based on values for digestible amino acids calculated from the faecal digestibility of N. Therefore, the final development and implementation of a new protein evaluation system, based on ileal digestible amino acids, has a high priority. The

Fig. 1. Standardised ileal digestible amino acids in a pig diet (contribution to ideal protein relative to that of lysine). The figure illustrates the potentials and limitations for improving the protein quality of pig diets by amino acid supplementation. In the example, the diet can be improved by supplementation of lysine (60 to 75%) and lysine 1 threonine (75 to 83%). The histidine level limits further improvement. (BV, theoretical biological value.)

Table 11 Danish recommendations for faecal digestible amino acids in diets for growing pigs (25–100 kg live weight)a

Lysine Methionine Methionine 1 cystine Threonine Tryptophan Isoleucine Leucine Phenylalanine Phenylalanine 1 tyrosine Valine

g / FUp b

g / MJ ME

7.3 2.3 4.6 4.8 1.4 4.2 8.3 4.2 8.3 5.4

0.57 0.18 0.36 0.38 0.11 0.33 0.65 0.33 0.65 0.42

a

Recommendations for two-phase feeding (25–50 kg and 50– 100 kg) are also given according to 0.61 g LYS / MJ ME and 0.55 g LYS / MJ ME, respectively. Recommendations for sows during gestation and lactation are given according to 0.27 g LYS / MJ ME and 0.47 g LYS / MJ ME, respectively. b FUp, Danish feed unit for pigs: 7.72 MJ NE ¯ 12.8 MJ ME.

Fig. 2. Nitrogen (N) balance in growing pigs when using one mixture throughout the growth period. The figure illustrates the N distribution in faeces, urine and body at different live weights during the period from 20 to 120 kg (Boisen and Hall, 1989).

theoretical basis for the new system has recently been described in a series of publications (Boisen and Moughan, 1996a, 1996b; Boisen, 1997, 1998). The principle in the new protein evaluation system

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is a step-wise characterisation and determination of the protein value according to the following steps.

3.2.1. Total amino acids Total contents of amino acids in actual feed batches are based on: 1. tabulated mean values for single feedstuffs, or 2. analysis of single feedstuffs and calculation by either simple specific conversion factors or by specific regression equations, or 3. direct amino acid analysis of feed mixtures.

3.2.2. Digestible amino acids Digestible amino acids are defined and determined as standardised ileal digestible amino acids. These are basically determined from in vivo measurements by correcting values of apparent digestibility and can be obtained from:

233

Table 12 Amino acid composition (g per 160 g N) for ideal protein and the ileal endogenous protein loss. Suggested standard values

Lysine Methionine Cystine Methionine 1 cystine Threonine Tryptophan Isoleucine Leucine Histidine Phenylalanine Tyrosine Phenylalanine 1 tyrosine Valine

Ideal protein

Endogenous protein

70 18 – 36 45 12 40 80 25 40 – 80 52

30 10 16 – 45 12 25 40 15 30 20 – 35

1. tabulated mean values for individual feedstuffs are obtained from in vivo apparent digestibility after correction for a standardised basal endogenous protein loss, or 2. direct determinations in actual batches of feedstuffs and pig diets are attempted to be obtained from in vitro digestibility of N (Boisen and ´ Fernandez, 1995) after correction for a calculated extra feed-specific endogenous protein loss. The calculation of the extra feed-specific endogenous protein loss (EEPL) is based on a determined relationship to in vitro undigested dry matter (UDM): EEPL 5 0.0106 3 UDM, g kg 21 DM intake. The real digestibility of amino acids is assumed to be identical to in vitro digestibility of N, while a standard amino acid composition of endogenous protein is suggested for calculation of the standardised digestible amino acids (Table 12). The two calculation methods are illustrated in Fig. 3.

3.2.3. Protein value The protein value of pig diets is characterised by the following. 1. The amount of ideal protein from standardised digestible amino acids. The suggested amino acid

Fig. 3. Calculations of standardised (‘true’) ileal digestibility of crude protein (CP) in pig feeds. The value can be calculated from either in vivo apparent digestibility by correcting for the basal endogenous protein loss or from in vitro digestibility by correcting for the extra endogenous protein loss. The values are typical for soybean meal.

composition of ideal protein for growing–finishing pigs is based on critical evaluation of literature data and also on the amino acid composition of sow’s milk. The composition given in Table 12 is assumed to be constant during the period from 30 kg live weight until slaughter at about 100 kg). 2. Digestible surplus-N.

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NH 3 emission from livestock farms in Europe increased from 2.2 to 4.7 Mt (Asman et al., 1998; Anonymous, 1994). From 1960 to 1980 the wet deposition flux of ammonia increased by approximately 25% in Europe (Buijsman and Erisman, 1988; Berckmans et al., 1992). Livestock buildings contribute 30 to 35% of the total ammonia emission from livestock enterprises. According to Knudsen (1997) 54 840 tonnes nitrogen are lost annually in Denmark from livestock buildings. Cattle houses contribute 28 000 tonnes and pig units contribute | 16 000 tonnes of which | 10 000 tonnes come from growing pig units. Two main effects of ammonia evaporation in agriculture can be considered. Fig. 4. Flow-sheet for a complete definition and calculation of the nutritional value of dietary protein in pig feeds (Boisen, 1998).

3. Indigestible N. The new protein evaluation system will be integrated in a new feed evaluation system, in which the physiological energy value of surplus amino acids is calculated and, thus, the complete nutritional value of the dietary protein is considered (Fig. 4). Furthermore, the new feed evaluation system will include a computerised pig model for calculating all relevant production data, comprising also digestion, metabolism, utilisation and excretion of N. This model is under development at this institute.

4. Ammonia emission

4.1. Status The effect of ammonia on the environment due to acidification and eutrophication can be severe. Ammonia and chemical combinations of it (NH x ) are important components responsible for acidification in addition to sulphur compounds (SO x ), nitrogen oxides (NO x ) and volatile organic components (VOC). Emission, transport and deposition processes of ammonia are such that acidification related to ammonia is not only a regional issue but it is a transboundary phenomenon that has to be handled as an international task. From 1870 to 1980 the annual

• The indoor ammonia concentration, which affects the health of the workers and of the animals. • The emission of ammonia from livestock buildings into the atmosphere, which contributes greatly to air pollution (Sommer, 1985; Klarenbeeck and Bruins, 1987; Rom, 1994, 1995).

4.2. System analysis of ammonia flow in confinement buildings The ammonia produced in livestock production derives from nitrogenous matters contained in faeces and urine. Both the quantity and the composition of the faeces and urine are of interest when studying ammonia emission. The main source of ammonia volatilisation from slurry is urea contained in pig urine. During hydrolysis of urea by the exoenzyme urease, ammonium and carbonate are produced. Approximately 70% of the total nitrogen produced by pigs is connected to total ammonia-nitrogen (TAN 5 NH 3 1 NH 1 4 ). The hydrolysis of urea is rapid at high temperatures and in the presence of moisture (Vlek and Carter, 1983) and urea collected in liquid manure, solid manure and slurry produced in animal houses is converted to ammonia within a few hours after excretion (Voorburg and Kroodsma, 1992). Ammonia emissions are therefore basically determined by the amount of nitrogen excreted in the urine. This corresponds to the amount of feed nitrogen that is digested but not retained in the pigs. The coefficient of utilisation of feed protein has

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increased in recent years from 30% for pigs (Nielsen, ´ 1993) to 36% (Fernandez, 1997). A system analysis of ammonia flow was performed in order to quantify the ammonia flow in pig buildings and to identify and quantify the most important factors influencing them (Fig. 5). The flow of manure excreted by the pigs in the unit can be divided into the following three sections. Flow hAj is urine deposited on floor and slats. A hydrolysis process will start as soon as urea comes into contact with the solid manure (faeces), thereby producing ammonia, which will evaporate into the building. Flow hBj is urine deposited into the slurry channel and mixed with old slurry. The hydrolysis process that takes place in part of the urine will cause a development of ammonia in the upper layer of the

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slurry, from where the ammonia will evaporate into the atmosphere of the building. Part of the urine will mix with the slurry, which will lead to a slower release and subsequent ascent of ammonia to the surface. Flow hCj is mainly faeces. Primarily found at the bottom of slurry channels and partly on floors and slatted surfaces. The microbial nitrogen turnover in the slurry is a controlling factor for generation and release of ammonia. Owing to the vertical concentration gradient in the slurry, the released ammonia will slowly ascend to the surface, where evaporation will take place. This part of the ammonia evaporation has minor significance for total ammonia evaporation from livestock buildings. Some of the most important factors influencing ammonia losses from pig units are:

Fig. 5. Diagram for the ammonia-nitrogen flow in a pig confinement building (TAN, total ammonia-N).

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• concentration of ammonia in the manure • the gas emitting surface area • air movement close to the emitting surface of the slurry • surface / volume ratio • the acidity of the slurry • storage period of the slurry in the building • slurry temperature.

4.3. Laboratory facilities In order to measure ammonia emission quantitatively, under the dynamic conditions created by the interaction between animals, housing design and manure handling, a Gas Emission and Climate laboratory was established at The Research Centre Bygholm. The laboratory was equipped with two almost equal experimental sections. One section was equipped with partially slatted floor and the other section with totally slatted floor, thus allowing the influence of slurry management and building design to be determined. Each section had accommodation for 40 fattening pigs divided into four pens. Each fattening period lasted | 10 weeks. Experimental pigs were fed to appetite through one feed dispenser in each pen. The gas concentration measurements were carried out with a Multi-gas Monitor Type 1302, a Multipoint Sampler and Doser Type 1303. The ventilation rate was recorded in the exhaust duct by means of a calibrated full size measuring impeller (Rom and Dahl, 1995). The measuring impeller was calibrated according to Pedersen and Strøm (1995). The measuring device overestimated ammonia emission by | 7%. This systematic positive overestimation might be due to the interference of minor concentrations of nitrogen gases in the indoor air. The animal activity was measured by means of a newly developed activity interface (Pedersen and Pedersen, 1995).

4.4. Research layout and results Experimental measurements were carried out during several fattening periods. Ammonia emission was measured with various types of floor design and various handling procedures for the slurry, while

feed composition was kept constant. Also, dietary influences on ammonia emission were studied with partially slatted floors and standard handling of the slurry. In the studies of ammonia emission as a function of floor design and slurry management, the total quantity of Kjeldahl-nitrogen (N K ) ingested was on average for all experimental periods 5.7 kg / pig. On the assumption that 30% of N intake was retained in the pigs, the excreted quantity was estimated to be 3.9 kg / pig. The results of ammonia emission measurements in the Gas Emission and Climate Laboratory showed that the average ammonia emission for all periods in the two sections increased from 5–6 g / pig / day for pigs weighing 30–35 kg up to 13–15 g / pig / day for pigs weighing 90–95 kg (Fig. 6). Total ammonia emission (average of experimental periods) was 0.66 and 0.73 kg per pig for partially slatted and totally slatted floors, respectively. The average pH of the slurry during the experiments was 7.3 to 7.6. Ammonia emission was found to be 7 to 11% higher in the section with a totally slatted floor compared to the section with a partially slatted floor. Experiences from the laboratory showed that urine or faeces on the solid floor would lead to an increase in the ammonia emission from the building, primarily due to the greater evaporation surface. The most important factors influencing ammonia emission from livestock buildings proved to be the pH and surface temperature of the slurry, as well as the age of the pigs, the area of wet floor surface and the ventilation rate. The temperature and humidity of the outdoor and indoor air, animal activity and amount of bedding seem to have little influence on ammonia emission.

4.5. The influence of diet composition on ammonia emission The role of complex dietary carbohydrates (sugar beet pellets) as inhibitors of ammonia emission from growing pigs was studied in an experiment in which sugar beet pellets replaced 15% of the test feed cereal content. The results are summarised in Table 13. The average outdoor temperature during the first trial was 12.48C. In the section with the control

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Fig. 6. Effect of the type of floor on ammonia emission during the growing period.

Table 13 The effect of dietary substitution of cereals with 15% sugar beet pulp on ammonia emission from growing pigs Live weight Section First trial (June to July) Control Test Second trial (August to September) Control Test a

Dietary

Slurry

Start kg

Final kg

Gain, g / day

Feed / gain FUp a / kg

protein, %

N Tot , g / kg

NH 41 -N, g / kg

Ammonia emission, g / pig / day

56.6 56.2

96.3 93.6

0.944 0.852

2.79 3.03

19.2 19.4

4.4 5.2

3.6 3.1

15.9 13.9

49.8 51.1

107.0 103.2

1.082 0.984

2.52 2.75

19.2 19.4

4.5 4.6

3.5 3.6

14.7 12.9

FUp, Danish feed unit for pigs: 7.72 MJ NE ¯ 12.8 MJ ME.

group the average room temperature was 17.58C. The slurry surface temperature was 17.68C and the average pH was 7.8. The average ventilation rate was 3.680 m 3 / h. In the section with the test group, the room and slurry surface temperature was 17.08C, the pH was 6.9 and the average airflow was 3.328 m 3 / h. pH was lower in the slurry from the test group than from the control group. The slurry from the test group became extremely sticky and consequently the floors and slatted floor beams in the test section were substantially fouled. The second trial was carried out in the period from August to September with an average outdoor temperature of 20.78C. Indoor temperature for the con-

trol group was 18.58C. The slurry surface temperature was 18.98C, and the pH was 6.8. The average ventilation rate was 4.245 m 3 / h. For the test group the indoor temperature was 18.58C and the slurry temperature was 18.98C. The pH of the slurry surface was 6.2, and the ventilation rate was 4.392 m 3 / h. The average daily ammonia emission for the entire period was 14.7 g / pig for the control group and 12.9 g / pig ? day for the test group. The pH was slightly lower in the slurry from the test group compared to the control group. The results showed that the ammonia emission was reduced by | 13% as a consequence of replacing 15% of the diet cereals with sugar beet pellets.

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The pH in the slurry from the test diet was | 10% lower compared to the control diet.

5. Current consumption and utilisation of nitrogen and phosphorus in practice

the reason is the modest response achieved in practical experiments in relation to the investment necessary to change from one- or two-phase to multiphase feeding.

5.2. N and P excretion in practice

5.1. Farming practices Pig feeding in Denmark is mainly based on industrially produced complete diets and premixes. Sales of complete diets for pigs in 1995 amounted to 2733 million kg (Kjeldsen, 1997), which covered the feeding of about 44% of growing pigs and 42% of sows. In addition, 40% of growing pigs and 42% of sows were fed with industrially produced premixes (protein, minerals and vitamins) diluted (71 and 76%, respectively) with on-farm grown cereals. There are no available statistics about the distribution of feeding practices. However, from the records of the Danish Agricultural Advisory Centre, National Committee for Pig Breeding, Health and Production, some estimates can be made. Feeding ad libitum is used primarily up to 50 kg LW (80–90% of pigs), decreasing to about 60% in the last period (50–100 kg LW). Dry feeding is still the dominant feeding system, although wet feeding is expected to increase from the present 20–30% of pigs. In spite of the obvious theoretical advantages of multi-phase feeding with respect to N and P excretion, feeding practices in Denmark are still dominated by single diet feeding (growing pigs 75%, sows 85%). Among younger pigs (7–30 kg LW) 60% are fed two diets and 20% three diets. Probably

The N and P excretion of pigs in different categories is shown in Table 14. The total excretion of these pigs was calculated using the data presented in Tables 2, 7 and 8. The difference between the average excretion for all pigs and the average of the worst 25% and best 25% of herds was 1 16% and 2 16% for N and 1 15 and 2 15% for P, respectively. The largest relative differences were found for weaners (N: 1 28% and 2 33%; P: 1 26% and 2 26%). Since the differences shown in Table 14 are only due to differences in overall performance, these results indicate that improving management offers a large potential for reducing N and P losses. The significance of improving single variables (dietary protein concentration, growth rate, feed / gain, and protein utilisation) can be illustrated by calculating the N excretion after a 10% improvement of each variable in turn. As indicated in Table 15, a 10% reduction of dietary protein, increase of growth rate, improvement of feed conversion or improvement of protein utilisation can each reduce N losses by 13–15%. The above variables are, however, strongly interrelated, as demonstrated by the results (Table 16) of correlation and regression analysis of the data on growing pigs presented in Table 6. Therefore an additive effect of improving several variables cannot

Table 14 Calculated a excretion of N and P of pigs in different categories (kg / pig) based on performance results from practical pig production in 1995 All N Piglet, –7.5 kg Weaner, 7.5–30 kg Growing pig, 30–100 kg Total Relative a

Worst 25% P

N

Best 25% P

N

P

1.17 0.67 3.38

0.32 0.19 0.72

1.37 0.86 3.80

0.37 0.24 0.80

0.93 0.45 3.01

0.26 0.14 0.64

5.22 100

1.23 100

6.03 116

1.41 115

4.39 84

1.04 85

Excretion was calculated on the basis of performance results shown in Table 2 and the conditions given in Tables 7 and 8.

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Table 15 The significance of improving production variables (610%) on the nitrogen excretion of growing pigs Variable

Change

N excretion, kg

Relative

Reference (Table 15) Dietary N, g / kg Growth rate, g / day Feed / gain, kg / kg Retained N, % of intake

0 2 2.80 1 74.0 2 0.27 1 3.70

3.38 2.86 2.91 2.91 2.85

100 85 87 87 86

Table 16 Partial correlation coefficients a between variables related to protein metabolism in growing pigs

Growth rate, g / day Feed / gain, kg / kg Retained N, % of intake a

Dietary N, g / kg

Growth rate, g / day

Feed / gain, kg / kg

0.29 *** 2 0.28 ** 0.16

2 0.71*** 0.49 ***

2 0.80 ***

Multivariate variation analysis: sex, experiment, treatment within experiment, and empty body weight.

be expected. For example, the effect of reducing dietary protein concentration (Table 15) was calculated on the assumption that the reference pig consumed protein in excess of requirements. Reducing excess dietary protein can also influence energy utilisation. Provided that the diet is optimised with respect to energy / protein ratio, feed conversion will also be improved with an extra reduction of N loss as a result. Therefore, the calculated reduction of N loss in this case is probably underestimated. Furthermore, increased growth rate (g / day) is associated with a better feed conversion. Consequently, the number of days required to achieve 70 kg live weight gain were calculated first, then total feed consumption was recalculated, assuming that daily feed intake was the same as for the reference pig. There is a close relationship between feed conversion and protein utilisation. This offers the possibility of estimating protein utilisation in specific cases by its relation to feed conversion, which is usually known in practice. Regression analysis showed that improvement of protein utilisation by 1% reduces feed consumption per kg gain by 60 g. Thus, increasing dietary protein utilisation by improved diet formulation (i.e. by fortification with

industrial amino acids) has not only a positive effect on the environment but also brings a substantial economic return to the producer.

6. Research priorities

6.1. Phosphorus • Studies on P digestibility of individual feed phosphates and feedstuffs together with mixed diets. • Studies dedicated to improve the efficacy of phytase (intrinsic and microbial). • Studies to improve our knowledge on bone mineralisation and how to define bone quality. • Development of an in vitro method to determine the dietary content of digestible P

6.2. Nitrogen • Continuous determinations of ileal digestibility of amino acids in selected feedstuffs and complete diets. • Investigations on additivity between digestible

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amino acids in single feedstuffs and their contributions in complete diets. • Investigations of endogenous protein loss, its amino acid composition and factors (ANFs, dietary fibre) influencing the loss. • Validation of a new in vitro technique for predicting the amino acid digestibility in actual batches of feedstuffs and diets. • Development of a computerised pig model based on inputs of the available amounts of those nutrient fractions that are relevant according to their digestion, metabolism and utilisation in the pig.

6.3. Ammonia emission • Determination of ammonia and greenhouse gas (nitrous-oxide and methane) emissions and nutrient flows in pig confinement buildings including low indoor temperatures (0 to 158C) similar to the outside winter temperatures. • Quantification of ammonia and greenhouse gas emission and nutrient flows in deep litter systems for growing pigs. • Evaluation of the effect of a feed additive (Micro Aid) on ammonia emissions in growing pig production. • Reduction of ammonia emission in livestock buildings by floor and pit surface treatments and by improved techniques for daily removal of slurry.

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