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Effect of exposure on the chemical composition and in vitro dry matter digestibility of untreated and formalin treated green chop
Animal Feed Science and Technology, 44 (1993) 275-280
275
0377-8401/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Effect of exposure on the chemical composition and in vitro dry matter digestibility of untreated and formalin treated green chop L.D. Snyman 1 Department of Agricultural Development, HighveMRegion, Potchefstroom, South Africa (Received 16 December 1991; accepted 11 January 1993)
Abstract
Green chop, made from babala (Pennisetum typhoides) and forage sorghum (Sorghum bicolorsudanense) which were each harvested from six different rows at the pre-bloom and bloom stages of maturity, were exposed to the environment with and without formalin treatment (4.9 + 0.8 g formaldehyde per 100 g crude protein) for a period of 21 + 3 h. This was done at laboratory scale in a room at 27 °C. These treatments were compared in a complete randomized design with each other and with a corresponding non-exposed fresh green chop treatment. Exposure without formalin treatment caused a significant increase (P<0.05) in the acid detergent fibre (ADF) content (41.0 vs. 38.3%) and a concomitant decrease (P<0.05) in the in vitro dry matter digestibility (IVDMD) (63.1 vs. 66.6%) when compared with the non-exposed fresh material. This was accompanied by an increase (P< 0.05 ) in the non-protein nitrogen (NPN) fraction (41.6 vs. 32.4% ). Exposed material treated with formalin had a higher (P<0.05) total dry mass (58.6 vs. 51.6 g) and a lower (P<0.05) ADF content (39.2 vs. 41.0%) than exposed untreated material. The decrease in IVDMD caused by exposure was totally prevented by formalin treatment. The IVDMD of exposed formalin-treated material was 67.8% in comparison with 63.1% (P< 0.05) and 66.6%, respectively, for the exposed untreated and the nonexposed fresh material. The NPN contents for exposed material being treated and untreated were the same (40.5 vs. 41.6%) while the nitrogen fraction appearing in ADF was higher (P< 0.05 ) for formalin-treated material (22. l vs. 12.8%). It is concluded that the exposure of green chop led to some deterioration of forage quality, which was largely prevented by formalin treatment.
Introduction
The feeding of green chop, made from babala, forage sorghum and other thick-stemmed forage plants, to dairy cattle is an established practice worldwide. The making of green chop not only improves pasture management but also provides a mixture of plant components the quality of which can be predicted much more accurately for the purpose of diet formulation than can be done with grazed forage plants. Green chop is usually fed in cribs once or twice a day. Enough forage is fed Ipresent address: Onderstepoort Veterinary Institute, Onderstepoort 0110, South Africa.
2 76
L.D. Snyman ~Animal Feed Science and Technology 44 (1993) 275-280
to last until the next feeding. This could result in some deterioration of forage quality. It is known that newly harvested crops are subjected to some catabolic activity of the plant enzymes (McDonald, 1981 ). Formalin was successfully applied to limit the breakdown of water-soluble carbohydrates and proteins (Wilkins et al., 1974) during ensilage. An application rate of 3-5 g formaldehyde per 100 g crude protein (CP) for grass silage, was suggested to be safe for ruminants (Wilkinson et al., 1976). In a coincidental observation in our laboratory, it was noticed that formalin-treated chopped forage sorghum, after some days in a crib still had a fresh, rigid appearance, in contrast with chopped untreated forage sorghum which appeared wilted and mouldy. Little is known about the deterioration ofbabala and forage sorghum green chop and the effect of formalin treatment thereon. This paper reports a preliminary trial to investigate the matter. Materials and methods Babala ( Pennisetum typhoides ) and forage sorghum (Sorghum bicolor sudanense) plants were each harvested at the pre-bloom and bloom stages of maturity. Babala plants were harvested at the early bloom and forage sorghum at the full bloom stage. Each forage species at each maturity stage was harvested from six different rows, giving a total of 24 samples. The material harvested was chopped with a forage cutter into 1-cm pieces. Formalin (40 g formaldehyde per 100 ml solution) was applied to part of the chopped material (1 kg) to obtain an estimated treatment rate of 5 g formaldehyde per 100 g CP. Forage harvested at the pre-bloom and bloom stages were treated with 2.8 ml formalin per kg forage and 3.3 ml formalin per kg forage, respectively. Based on the analysed CP values, the real treatment rates were afterwards calculated to be 4.0 g formaldehyde per 100 g CP, 4.6 g formaldehyde per 100 g CP, 5.2 g formaldehyde per 100 g CP and 5.9 g formaldehyde per 100 g CP, respectively, for babala in the pre-bloom, babala in the bloom, forage sorghum in the pre-bloom and forage sorghum in the bloom stage of maturity. Treatment was performed by spraying the estimated amount of formalin with a syringe onto the chopped material, which had been scratched open in a plastic bag. The bag was then closed and the contents thoroughly mixed. The treated material was left for another 15 min in the closed bag, whereafter a 300 g sample was transferred into a small plastic bag. The opening of the bag was folded back and left opened to expose the contents directly to the environment. The same amount of untreated sample was exposed in a similar way in another plastic bag. Exposure of both treated and untreated samples took place in a room at a temperature of about 27 ° C. Samples were exposed for a period of 21 ___3 h, except for two samples of forage sorghum which were exposed for a period of 42 ___2 h and two samples of ba-
L.D. Snyman / Animal Feed Science and Technology 44 (1993.) 275-280
277
bala which were exposed for 73 _ 1.5 h. At the end of the exposure period, samples were heated up in a microwave oven (3 min at maximum irradiation) for instant inactivation of plant and microbial enzyme activity, and dried in a force draught oven at 65 °C for 48 h. For each treated and untreated sample taken to be exposed, a corresponding control sample was taken and dried similarly in the non-exposed fresh state. Sample treatments took place within about an hour after being harvested. All dried samples were milled through a 1 m m sieve and chemically analysed according to the following procedures: acid detergent fibre (ADF) (Van Soest, 1963 ), in vitro dry matter digestibility (IVDMD) (Tilley and Terry, 1963; as adapted by Engels and Van der Merwe, 1967), CP (Clare and Stevenson, 1964), non-protein nitrogen ( N P N ) (Marais and Evenwell, 1983 ) and nitrogen associated with the acid detergent fibre (ADF-N) (Goering et al., 1972). Statistical analysis was performed using Anova. Exe (H. van Ark, personal communication, 1992). Data of forage qualities were analysed in a completely randomized design. Contrasts between treatment means were analysed with the method of Bonferroni. Methods are described by Van Ark (1981). Comparisons among treatments were done on samples being exposed for 21 _+3 h only. A linear regression was performed between duration of exposure and the change in IVDMD, including the 42 _+2 h samples and the 73 _ 1.5 h samples of forage sorghum and babala, respectively. Results and discussion
The effect of exposure on the chemical composition and IVDMD of untreated and formalin-treated green chop, compared with non-exposed fresh material, is shown in Table 1. The data indicate a small non-significant decrease in total dry matter mass of green chop exposed without formalin treatment. Exposure with formalin, however, resulted in a significantly higher total dry matter mass compared with untreated exposed material. The data in Table 1 furthermore indicate that the ADF content of untreated green chop increased during exposure. No significant increase took place during exposure of formalin-treated material. In agreement with these results, the IVDMD of untreated green chop decreased during exposure while the IVDMD of formalin-treated material remained the same as that of the non-exposed fresh material. In contrast to its effect on the above-mentioned forage qualities related to forage energy value, exposure without formalin treatment had no effect on the CP content and total CP mass of green chop (Table 1 ). Formalin treatment, however, caused a small decrease in the CP content of exposed material. This may be explained as an indirect effect due to formalin's effect on the total dry matter mass, as it had no effect on the total CP itself. Exposure without formalin treatment resulted in a deterioration of protein quality with
278
L.D. Snyman / AnimaI Feed Science and Technology 44 (1993) 275-280
Table 1 Comparison of the chemical composition and IVDMD in non-exposed fresh green chop and green chop
exposed with and without formalin treatment Chemical composition I and IVDMD
Total dry matter (g) ADF (g per 100 g D M ) IVDMD(gperl00gDM) CP (g per 100 g D M ) Total CP (g) NPN (g per 100 g N ) ADF-N (g per 100 g N )
Number of samples per treatment
20 8 20 20 20 20 8
Treatment 2 Non-exposed (fresh)
54.5 a,b 38.3 a 66.6 a 15.8 a 7.6 ~ 32.4 ~ 10.3 a
SEM
Exposed (21 + 3 h) Without formalin
With formalin
51.6 a 41.0 b 63.1 b 15.9 a 7.3 a 41.6 b 12.8 a
58.6 b 39.2 a 67.8 a 14.8 b 7.6 a 40.5 b 22.1 b
4.47 0.88 1.80 0.97 0.67 3.73 2.40
~Dry matter ( D M ) content of the fresh material was 17.0 _+4.5%. 2Values in the same horizontal row with common superscripts do not differ significantly ( P < 0.05 ). Table 2
Effect of treatment on the non-protein nitrogen content (g per 100 g N ) o f b a b a l a and forage sorghum green chop, individually Forage species
Babala
Forage sorghum
Number of samples per treatment
10 10
TreatmenP Non-exposed (fresh)
37.7 a 27.1 a
SEM
Exposed ( 2 1 + 3 h ) Without formalin
With formalin
39.9 a,b 43.3 b
44.3b 36.6 c
1.13 1.60
~Values in the same horizontal row with common superscripts do not differ significantly ( P < 0.05 ).
respect to NPN as the NPN fraction of total nitrogen was increased. An analysis on the data of babala and forage sorghum separately, indicate that they reacted differently with respect to changes in the NPN fraction. The effect of exposure with and without formalin treatment on the NPN fractions of babala and forage sorghum separately, is shown in Table 2. The data show that the NPN fraction ofbabala in the non-exposed fresh state was high compared with that of forage sorghum and did not change significantly during exposure without formalin treatment while the NPN fraction of forage sorghum increased significantly. This indicates some fundamental difference between the two forages which may be of practical significance. Formalin treatment partly inhibited NPN formation during exposure of forage sorghum, but not during exposure ofbabala. Protein quality with respect to ADF-N (Table 1 ) was not influenced by exposure without formalin treatment. Exposure with formalin treatment, however, drastically increased the ADF-N fraction.
L.D. Snyman / Animal Feed Science and Technology 44 (1993) 275-280
279
12
~10
e~
Time (hours) Fig. 1. Relationship between the mean ( _+SD) time and the mean ( _ SD) IVDMD decrease for green chop exposed for periods of 21 + 3 h (n = 20), 42 + 2 h (n = 2 ) and 73 + 1.5 h (n = 2 ).
The relationship between the time duration of exposure and the decrease in IVDMD of green chop is shown in Fig. 1. The simple coefficient of correlation (r) for the individual samples (n = 24) was 0.69. The figure indicates a linear relationship between the time duration of exposure and the extent of IVDMD decrease, showing a decrease of 1 percentage unit for every 7 h exposure period. The overall data show that the exposure of green chop led to a deterioration of some energy-related forage qualities. Crude protein, within an exposure period of 21 h, was deteriorated only with respect to crude protein quality, namely an increase in the fraction of NPN. Degradative plant enzymes probably played an important role in these changes (McDonald, 1981 ). According to the change in IVDMD, a decline in the energy value, linearly related to time over a 72 h period, may be expected. When extrapolated to the practical feeding situation, these findings predict an under-provision of nutrients with respect to animals' feeding requirements, as degenerative changes during the feeding period are not usually taken into account in diet formulations. The results obtained with formalin-treated material showed that the deterioration of exposed green chop can be largely prevented when treated with formalin at a rate of 4.9 g formaldehyde per 100 g crude protein at the time of harvesting. The deterioration of energy-related forage qualities was prevented though CP quality was little influenced. In fact, the increase in ADFN measured reflects an increase in the fraction of unavailable nitrogen (Goering et al., 1972; Thomas et al., 1972 ). At relatively low rates of formalin treatment (3-5 g formaldehyde per 100 g CP), this detrimental effect, however,
280
L.D. Snyman / Animal Feed Science and Technology 44 (1993) 275-280
m a y be o u t w e i g h e d by a suspected increase in the fraction o f u n d e g r a d a b l e protein (Wilkinson et al., 1976; M c D o n a l d , 1981; S n y m a n et al., 1990) which m a y lead to an increase in the net a b s o r b t i o n o f a m i n o acids (Beever et al., 1977). The results o f this investigation s h o w e d s o m e degenerative changes d u r i n g the exposure o f green chop a n d s h o w e d t h a t it could be largely p r e v e n t e d if t r e a t e d with formalin. The significance o f these results for the practical feeding situation, however, should be p r o v e d u n d e r such c o n d i t i o n s in an a n i m a l feeding trial. F o r m a l i n m a y be carcinogenic a n d should be h a n d l e d with care. T r e a t m e n t o f green chop with f o r m a l i n / a c i d m i x t u r e s or with acids alone, m a y be other o p t i o n s to investigate. A t t e m p t s for effective stabilization o f green chop seem to be necessary, n o t only to p r e v e n t d e t e r i o r a t i o n in the cribs b u t also to increase the logistical efficiency o f feeding by less f r e q u e n t feeding.
References Beever, D.E., Thomson, D.J., Cammell, S.B. and Harrison, D.G., 1977. The digestion by sheep of silages made with and without the addition of formaldehyde. J. Agric. Sci. (Cambridge), 88: 61-70. Clare, N.T. and Stevenson, A.E., 1964. Measurement of feed intake by grazing cattle and sheep. X. Determination of nitrogen in faeces and feeds using an Auto Analyzer. NZ J. Agric. Res., 7: 198-204. Engels, E.A.N. and van der Merwe, F.J., 1967. Application of an in vitro technique to South African forages with special reference to the effect of certain factors on the results. S. Afr. J. Agric. Sci., 10: 983-995. Goering, H.K., Gordon, C.H., Hemken, R.W., Waldo, D.R., van Soest, P.J. and Smith, L.W., 1972. Analytical estimates of nitrogen digestibility in heat damaged forages. J. Dairy Sci., 55: 1275-1280. Marais, J.P. and Evenwell, T.K., 1983. The use of trichloroacetic acid as precipitant for the determination of"true protein" in animal feeds. S. Afr. J. Anim. Sci., 13:138-139. McDonald, P., 1981 . The Biochemistry of Silage. John Wiley, Chichester, New York, pp. 4261. Snyman, L.D., van der Merwe, H.J. and Van Schalkwyk, A.P., 1990. Effect of formalin preservation on the fermentation characteristics, chemical composition and protein properties of maize silage. S. Afr. J. Anim. Sci., 20:118-123. Thomas, J.W., Yu, Y., HiUman, D., Huber, J.T. and Lichtenwalner, R., 1972. Unavailable nitrogen in haylage and hays. J. Anim. Sci., 35:115. Tilley, J.M.A. and Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc., 18:104-111. Van Ark, H., 1981. Eenvoudige biometriese tegnieke en proefontwerpe met spesiale verwysing na entomologiese navorsing. Wetenskaplike pamflet no. 396. Departement van Landbou en Visserye, Pretoria, pp. 31-51. Van Soest, P.J., 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. J. Assoc. Off. Anal. Chem., 46: 829-835. Wilkins, R.J., Wilson, R.F. and Cook, J.E., 1974. Restriction of fermentation during ensilage: the nutritive value of silages made with the addition of formaldehyde. Proc. 12th International Grassland Congress, Moscow, 1974, pp. 675-690. Wilkinson, J.M., Wilson, R.F. and Barry, T.N., 1976. Factors affecting the nutritive value of silage. Outlook Agric., 9: 3-8.
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0377-8401/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Effect of exposure on the chemical composition and in vitro dry matter digestibility of untreated and formalin treated green chop L.D. Snyman 1 Department of Agricultural Development, HighveMRegion, Potchefstroom, South Africa (Received 16 December 1991; accepted 11 January 1993)
Abstract
Green chop, made from babala (Pennisetum typhoides) and forage sorghum (Sorghum bicolorsudanense) which were each harvested from six different rows at the pre-bloom and bloom stages of maturity, were exposed to the environment with and without formalin treatment (4.9 + 0.8 g formaldehyde per 100 g crude protein) for a period of 21 + 3 h. This was done at laboratory scale in a room at 27 °C. These treatments were compared in a complete randomized design with each other and with a corresponding non-exposed fresh green chop treatment. Exposure without formalin treatment caused a significant increase (P<0.05) in the acid detergent fibre (ADF) content (41.0 vs. 38.3%) and a concomitant decrease (P<0.05) in the in vitro dry matter digestibility (IVDMD) (63.1 vs. 66.6%) when compared with the non-exposed fresh material. This was accompanied by an increase (P< 0.05 ) in the non-protein nitrogen (NPN) fraction (41.6 vs. 32.4% ). Exposed material treated with formalin had a higher (P<0.05) total dry mass (58.6 vs. 51.6 g) and a lower (P<0.05) ADF content (39.2 vs. 41.0%) than exposed untreated material. The decrease in IVDMD caused by exposure was totally prevented by formalin treatment. The IVDMD of exposed formalin-treated material was 67.8% in comparison with 63.1% (P< 0.05) and 66.6%, respectively, for the exposed untreated and the nonexposed fresh material. The NPN contents for exposed material being treated and untreated were the same (40.5 vs. 41.6%) while the nitrogen fraction appearing in ADF was higher (P< 0.05 ) for formalin-treated material (22. l vs. 12.8%). It is concluded that the exposure of green chop led to some deterioration of forage quality, which was largely prevented by formalin treatment.
Introduction
The feeding of green chop, made from babala, forage sorghum and other thick-stemmed forage plants, to dairy cattle is an established practice worldwide. The making of green chop not only improves pasture management but also provides a mixture of plant components the quality of which can be predicted much more accurately for the purpose of diet formulation than can be done with grazed forage plants. Green chop is usually fed in cribs once or twice a day. Enough forage is fed Ipresent address: Onderstepoort Veterinary Institute, Onderstepoort 0110, South Africa.
2 76
L.D. Snyman ~Animal Feed Science and Technology 44 (1993) 275-280
to last until the next feeding. This could result in some deterioration of forage quality. It is known that newly harvested crops are subjected to some catabolic activity of the plant enzymes (McDonald, 1981 ). Formalin was successfully applied to limit the breakdown of water-soluble carbohydrates and proteins (Wilkins et al., 1974) during ensilage. An application rate of 3-5 g formaldehyde per 100 g crude protein (CP) for grass silage, was suggested to be safe for ruminants (Wilkinson et al., 1976). In a coincidental observation in our laboratory, it was noticed that formalin-treated chopped forage sorghum, after some days in a crib still had a fresh, rigid appearance, in contrast with chopped untreated forage sorghum which appeared wilted and mouldy. Little is known about the deterioration ofbabala and forage sorghum green chop and the effect of formalin treatment thereon. This paper reports a preliminary trial to investigate the matter. Materials and methods Babala ( Pennisetum typhoides ) and forage sorghum (Sorghum bicolor sudanense) plants were each harvested at the pre-bloom and bloom stages of maturity. Babala plants were harvested at the early bloom and forage sorghum at the full bloom stage. Each forage species at each maturity stage was harvested from six different rows, giving a total of 24 samples. The material harvested was chopped with a forage cutter into 1-cm pieces. Formalin (40 g formaldehyde per 100 ml solution) was applied to part of the chopped material (1 kg) to obtain an estimated treatment rate of 5 g formaldehyde per 100 g CP. Forage harvested at the pre-bloom and bloom stages were treated with 2.8 ml formalin per kg forage and 3.3 ml formalin per kg forage, respectively. Based on the analysed CP values, the real treatment rates were afterwards calculated to be 4.0 g formaldehyde per 100 g CP, 4.6 g formaldehyde per 100 g CP, 5.2 g formaldehyde per 100 g CP and 5.9 g formaldehyde per 100 g CP, respectively, for babala in the pre-bloom, babala in the bloom, forage sorghum in the pre-bloom and forage sorghum in the bloom stage of maturity. Treatment was performed by spraying the estimated amount of formalin with a syringe onto the chopped material, which had been scratched open in a plastic bag. The bag was then closed and the contents thoroughly mixed. The treated material was left for another 15 min in the closed bag, whereafter a 300 g sample was transferred into a small plastic bag. The opening of the bag was folded back and left opened to expose the contents directly to the environment. The same amount of untreated sample was exposed in a similar way in another plastic bag. Exposure of both treated and untreated samples took place in a room at a temperature of about 27 ° C. Samples were exposed for a period of 21 ___3 h, except for two samples of forage sorghum which were exposed for a period of 42 ___2 h and two samples of ba-
L.D. Snyman / Animal Feed Science and Technology 44 (1993.) 275-280
277
bala which were exposed for 73 _ 1.5 h. At the end of the exposure period, samples were heated up in a microwave oven (3 min at maximum irradiation) for instant inactivation of plant and microbial enzyme activity, and dried in a force draught oven at 65 °C for 48 h. For each treated and untreated sample taken to be exposed, a corresponding control sample was taken and dried similarly in the non-exposed fresh state. Sample treatments took place within about an hour after being harvested. All dried samples were milled through a 1 m m sieve and chemically analysed according to the following procedures: acid detergent fibre (ADF) (Van Soest, 1963 ), in vitro dry matter digestibility (IVDMD) (Tilley and Terry, 1963; as adapted by Engels and Van der Merwe, 1967), CP (Clare and Stevenson, 1964), non-protein nitrogen ( N P N ) (Marais and Evenwell, 1983 ) and nitrogen associated with the acid detergent fibre (ADF-N) (Goering et al., 1972). Statistical analysis was performed using Anova. Exe (H. van Ark, personal communication, 1992). Data of forage qualities were analysed in a completely randomized design. Contrasts between treatment means were analysed with the method of Bonferroni. Methods are described by Van Ark (1981). Comparisons among treatments were done on samples being exposed for 21 _+3 h only. A linear regression was performed between duration of exposure and the change in IVDMD, including the 42 _+2 h samples and the 73 _ 1.5 h samples of forage sorghum and babala, respectively. Results and discussion
The effect of exposure on the chemical composition and IVDMD of untreated and formalin-treated green chop, compared with non-exposed fresh material, is shown in Table 1. The data indicate a small non-significant decrease in total dry matter mass of green chop exposed without formalin treatment. Exposure with formalin, however, resulted in a significantly higher total dry matter mass compared with untreated exposed material. The data in Table 1 furthermore indicate that the ADF content of untreated green chop increased during exposure. No significant increase took place during exposure of formalin-treated material. In agreement with these results, the IVDMD of untreated green chop decreased during exposure while the IVDMD of formalin-treated material remained the same as that of the non-exposed fresh material. In contrast to its effect on the above-mentioned forage qualities related to forage energy value, exposure without formalin treatment had no effect on the CP content and total CP mass of green chop (Table 1 ). Formalin treatment, however, caused a small decrease in the CP content of exposed material. This may be explained as an indirect effect due to formalin's effect on the total dry matter mass, as it had no effect on the total CP itself. Exposure without formalin treatment resulted in a deterioration of protein quality with
278
L.D. Snyman / AnimaI Feed Science and Technology 44 (1993) 275-280
Table 1 Comparison of the chemical composition and IVDMD in non-exposed fresh green chop and green chop
exposed with and without formalin treatment Chemical composition I and IVDMD
Total dry matter (g) ADF (g per 100 g D M ) IVDMD(gperl00gDM) CP (g per 100 g D M ) Total CP (g) NPN (g per 100 g N ) ADF-N (g per 100 g N )
Number of samples per treatment
20 8 20 20 20 20 8
Treatment 2 Non-exposed (fresh)
54.5 a,b 38.3 a 66.6 a 15.8 a 7.6 ~ 32.4 ~ 10.3 a
SEM
Exposed (21 + 3 h) Without formalin
With formalin
51.6 a 41.0 b 63.1 b 15.9 a 7.3 a 41.6 b 12.8 a
58.6 b 39.2 a 67.8 a 14.8 b 7.6 a 40.5 b 22.1 b
4.47 0.88 1.80 0.97 0.67 3.73 2.40
~Dry matter ( D M ) content of the fresh material was 17.0 _+4.5%. 2Values in the same horizontal row with common superscripts do not differ significantly ( P < 0.05 ). Table 2
Effect of treatment on the non-protein nitrogen content (g per 100 g N ) o f b a b a l a and forage sorghum green chop, individually Forage species
Babala
Forage sorghum
Number of samples per treatment
10 10
TreatmenP Non-exposed (fresh)
37.7 a 27.1 a
SEM
Exposed ( 2 1 + 3 h ) Without formalin
With formalin
39.9 a,b 43.3 b
44.3b 36.6 c
1.13 1.60
~Values in the same horizontal row with common superscripts do not differ significantly ( P < 0.05 ).
respect to NPN as the NPN fraction of total nitrogen was increased. An analysis on the data of babala and forage sorghum separately, indicate that they reacted differently with respect to changes in the NPN fraction. The effect of exposure with and without formalin treatment on the NPN fractions of babala and forage sorghum separately, is shown in Table 2. The data show that the NPN fraction ofbabala in the non-exposed fresh state was high compared with that of forage sorghum and did not change significantly during exposure without formalin treatment while the NPN fraction of forage sorghum increased significantly. This indicates some fundamental difference between the two forages which may be of practical significance. Formalin treatment partly inhibited NPN formation during exposure of forage sorghum, but not during exposure ofbabala. Protein quality with respect to ADF-N (Table 1 ) was not influenced by exposure without formalin treatment. Exposure with formalin treatment, however, drastically increased the ADF-N fraction.
L.D. Snyman / Animal Feed Science and Technology 44 (1993) 275-280
279
12
~10
e~
Time (hours) Fig. 1. Relationship between the mean ( _+SD) time and the mean ( _ SD) IVDMD decrease for green chop exposed for periods of 21 + 3 h (n = 20), 42 + 2 h (n = 2 ) and 73 + 1.5 h (n = 2 ).
The relationship between the time duration of exposure and the decrease in IVDMD of green chop is shown in Fig. 1. The simple coefficient of correlation (r) for the individual samples (n = 24) was 0.69. The figure indicates a linear relationship between the time duration of exposure and the extent of IVDMD decrease, showing a decrease of 1 percentage unit for every 7 h exposure period. The overall data show that the exposure of green chop led to a deterioration of some energy-related forage qualities. Crude protein, within an exposure period of 21 h, was deteriorated only with respect to crude protein quality, namely an increase in the fraction of NPN. Degradative plant enzymes probably played an important role in these changes (McDonald, 1981 ). According to the change in IVDMD, a decline in the energy value, linearly related to time over a 72 h period, may be expected. When extrapolated to the practical feeding situation, these findings predict an under-provision of nutrients with respect to animals' feeding requirements, as degenerative changes during the feeding period are not usually taken into account in diet formulations. The results obtained with formalin-treated material showed that the deterioration of exposed green chop can be largely prevented when treated with formalin at a rate of 4.9 g formaldehyde per 100 g crude protein at the time of harvesting. The deterioration of energy-related forage qualities was prevented though CP quality was little influenced. In fact, the increase in ADFN measured reflects an increase in the fraction of unavailable nitrogen (Goering et al., 1972; Thomas et al., 1972 ). At relatively low rates of formalin treatment (3-5 g formaldehyde per 100 g CP), this detrimental effect, however,
280
L.D. Snyman / Animal Feed Science and Technology 44 (1993) 275-280
m a y be o u t w e i g h e d by a suspected increase in the fraction o f u n d e g r a d a b l e protein (Wilkinson et al., 1976; M c D o n a l d , 1981; S n y m a n et al., 1990) which m a y lead to an increase in the net a b s o r b t i o n o f a m i n o acids (Beever et al., 1977). The results o f this investigation s h o w e d s o m e degenerative changes d u r i n g the exposure o f green chop a n d s h o w e d t h a t it could be largely p r e v e n t e d if t r e a t e d with formalin. The significance o f these results for the practical feeding situation, however, should be p r o v e d u n d e r such c o n d i t i o n s in an a n i m a l feeding trial. F o r m a l i n m a y be carcinogenic a n d should be h a n d l e d with care. T r e a t m e n t o f green chop with f o r m a l i n / a c i d m i x t u r e s or with acids alone, m a y be other o p t i o n s to investigate. A t t e m p t s for effective stabilization o f green chop seem to be necessary, n o t only to p r e v e n t d e t e r i o r a t i o n in the cribs b u t also to increase the logistical efficiency o f feeding by less f r e q u e n t feeding.
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