Evaluation of pellets from different industrial processing of dehydrated lucerne in dairy cattle feeding

Animal Feed Science and Technology 99 (2002) 13–24

Evaluation of pellets from different industrial processing of dehydrated lucerne in dairy cattle feeding G. Cozzi∗ , G.M. Burato, P. Berzaghi, I. Andrighetto Department of Animal Science, University of Padova, Agripolis, 35020 Legnaro, PD, Italy Received 28 November 2001; received in revised form 2 April 2002; accepted 12 April 2002

Abstract The research evaluated three pellets from different industrial processing of dehydrated lucerne. Pre-bloom cut lucerne was dehydrated and pelleted to obtain the Control product. The second pellet was produced by mechanical pressing of the forage before dehydration to extract a juice rich in soluble proteins and carbohydrates used by the poultry feeding industry. This pellet had a higher neutral detergent fibre (NDF) content than the control one. Urea (2.5% of forage DM) was added to the forage between dehydration and pelleting to produce the third pellet. All the tested pellets had a mean geometrical diameter lower than 0.20 mm and, due to their small particle size, they should be classified as protein concentrates rather than forage sources in dairy ration formulation. The degradability trial used three non-pregnant, non-lactating Holstein cows fitted with ruminal cannulae which were fed three diets formulated to satisfy the nutritional requirements of lactating cows, each containing one of the tested pellets. Cows received the diets in three following periods of 28 days according to a 3 × 3 Latin square experimental design. Ruminal degradation kinetics of pellets dry matter (DM), cell contents (CC), crude protein (CP), NDF, cellulose (CE) and hemicellulose (HE) was determined in situ by incubating the pellets within nylon bags for different time periods. Passage rate from the rumen was measured by mordanting each pellet with sodium dichromate. The different industrial processing did not affect the pellets rate of passage in the rumen. Based on the in situ degradation kinetics, 611 g/kg of Control DM were available in the rumen mainly from microbial digestion of the CC. In comparison to Control, mechanical pressing prior to dehydration decreased the lucerne DM disappearance (546 g/kg DM) because of the lower contribution of the CC to the degradable pool. Urea treatment enhanced CP content of the pellet but it did not increased the ruminal availability of dehydrated lucerne DM (595 g/kg DM). The alkaline additive was not effective to increase the degradation of the fibrous constituents leading only to a peak of readily available nitrogen in the rumen. Regardless of the type of pellet, the cell wall constituents were Abbreviations: C, control pellet; P, pellet from mechanically pressed lucerne; U, pellet from lucerne added with urea ∗ Corresponding author. Tel.: +39-49-827-2662; fax: +39-49-827-2669. E-mail address: [email protected] (G. Cozzi). 0377-8401/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 2 ) 0 0 1 1 1 - 6

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always degraded at a lower rate and extent than the CC and among them, CE has shown to be the primary site of hydrolysis by the rumen microrganisms. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Lucerne; Dehydration; Pellet; Degradation kinetics; Dairy cattle

1. Introduction The high forage yield, the adaptability to different environments, and the high nutritive value make lucerne one of the most appreciated forage sources for ruminant feeding. As compared to grasses, lucerne has a lower neutral detergent fibre (NDF) content (Andrighetto et al., 1993) and, therefore, limiting the filling effect of the diet in the rumen, it may be advisable to stimulate a higher dry matter (DM) intake in high producing dairy cows. Lucerne has remarkable contents of crude protein (CP), vitamins and minerals, but the availability of these nutrients depends upon the harvesting conditions and the preserving method of the forage. In field-cured lucerne hay, handling losses during wilting are on average 15% of total DM, but adverse weather conditions during harvesting can extend the time spent by the forage in the field, increasing DM losses up to 30–40% (Scales et al., 1978). These losses regard especially the leafy parts of the plant where proteins are mainly located (Dermaquilly and Andrieu, 1988). The high nutritive value of lucerne can justify the adoption of more expensive alternative preserving systems in order to reduce DM and quality losses of lucerne. Forage dehydration leads to a fast decrease in free water content, lowering the moisture content below 8%. The fast drying helps to prevent both respiration of plant tissues and epiphytic bacteria activity, which contribute to the losses occurring during the field-curing. After dehydration, lucerne can be baled and directly incorporated in total mixed rations or, alternatively, it can be ground and then pelleted, allowing its easier transport and storage. The reduced particle size due to the grinding process leads to a higher exposure of forage surface to microbial attachment in the rumen and to a faster ruminal passage rate. In the ruminant, the most efficient energy utilisation from fibrous feeds occurs when they are available for microbial fermentation in the fore-stomachs. The above mentioned physical treatments carried out during dehydration and pelleting might affect the availability of lucerne nutrients in the rumen and consequently their contribution to the fulfilment of animal maintenance and production requirements. To evaluate the possibility of including dehydrated lucerne pellet products in dairy cattle formulation, the present study investigated chemical and physical properties, ruminal degradation and passage rate of three types of pellets processed by the feed manufacturing industry.

2. Materials and methods 2.1. Pellets production and chemical composition The research considered three pellets obtained from the industrial processing of dehydrated lucerne. The original forage was cut at pre-bloom stage of maturity, then roughly chopped and sent to the processing plant. To produce the control pellet (C), lucerne was

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processed in a rotational dehydrator operating at 700–800 ◦ C. The dehydrated forage came out from the dehydrator at a temperature of 65–75 ◦ C and then it was immediately ground, pelleted at about 80 ◦ C and cooled down to a temperature below 20 ◦ C, suitable for stable preserving. The second pellet (P), was obtained by mechanical pressing of the original forage before undergoing to the same dehydration and pelleting process. The extraction process produces a juice, rich in soluble proteins and carbohydrates, used by the poultry feeding industry. In the third pellet (U), urea was added to the original forage (2.5% of forage DM) as liquid solution between dehydration and pelleting. Original samples of the pellets were submitted to wet mechanical sieving to measure their particle size distribution and mean geometrical diameter was calculated according to Ensor et al. (1970). Samples of all the pellets were ground through a Wiley mill (Arthur H. Thomas, Philadelphia, PA) with 2 mm mesh screen and then analysed for CP, ash and ether extract content (AOAC, 1984). NDF, acid detergent fiber (ADF), and cellulose (CE) content were measured according to Van Soest et al. (1991). The content of non-fibrous carbohydrates was calculated as suggested by Mertens (1992), as 100 − (CP + ether extract + ash + NDF); cell contents (CC) were calculated as 100 − NDF and hemicellulose HE as NDF − ADF. 2.2. In situ degradability The degradability trial used three non-pregnant, non-lactating Holstein cows (595±34 kg BW) fitted with ruminal cannulae in a 3 × 3 Latin square experimental design, with periods of 28 days. The aim of the in situ trial was to evaluate the degradability of the three lucerne pellets in a condition as close as possible to the normal ruminal environment of lactating cows. Therefore, three isonitrogenous and isofibrous experimental diets, each including one of the tested pellets, were formulated to satisfy the nutritional requirements of lactating cows (Table 1). Diets were administered as total mixed rations at 9:00 h and ad libitum intake was reached allowing a daily feed residue of 5%. The cows were allowed to adapt to the diet during the first 2 weeks of each experimental period, while the last 2 weeks were used for in situ incubation and sample collection. Nylon bag technique (Ørskov et al., 1980) was used to determine ruminal degradation kinetics of the following feed chemical constituents: DM, CP, CC, NDF, CE, and HE. Samples of each pellet (4 ± 0.4 g), roughly crushed in a mortar to mimic size reduction occurring with initial mastication, were placed into 10×14 cm nylon bags (40 ␮m pore size), allowing a sample size:bag surface ratio of 14.4 mg/cm2 as suggested by Varga and Hoover (1983). The time periods of incubation considered in the study were 2, 4, 8, 12, 18, 24, 36, 48, 72 and 96 h. At each time period, four bags filled with one of the tested pellets were placed in the rumen of the cow consuming the diet containing the same pellet. The bags were suspended into the rumen using 50 cm long Teflon® bars (four bags per bar), anchored by a nylon cord to the cap of the cannula. Each incubation time was executed separately inserting the bags into the rumen before the morning feeding, this, in order to maintain a constant interval between the beginning of each incubation period and the consumption of the meal by the cows (Andrighetto et al., 1993). At the end of the incubation, the bags were recovered, rinsed with tap water to remove ruminal particles from their external surface and then dried to a constant weight in forced-air oven at 60 ◦ C. Four bags per treatment were washed without any previous ruminal incubation to estimate washing losses (0 h). The residues of the four

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Table 1 Feed and chemical composition of the experimental diets Dieta C

P

U

Feed composition (% as fed) Lucerne pellet Meadow hay Maize silage Maize meal Soybean meal Whole linted cottonseed Vitamin–mineral supplement

14.6 8.6 52.9 10.3 8.0 4.3 1.3

11.8 8.6 53.0 10.9 10.0 4.3 1.4

14.5 8.5 54.0 10.8 6.5 4.3 1.4

Chemical composition DM (%) Ash (% DM) CP (% DM) Non-fibrous carbohydrates (% DM) NDF (% DM)

51.4 7.5 16.5 36.0 36.0

52.0 7.6 16.5 35.3 37.0

51.8 7.4 16.6 35.3 36.7

a C: diet containing control pellet; P: diet containing pellet from mechanically pressed lucerne; U: diet containing pellet from urea treated lucerne.

bags, incubated in each cow at each time, were measured for the precision of duplication for DM disappearance and then combined within cow for subsequent chemical determinations. These residual samples were then ground (2 mm) and analysed for CP (AOAC, 1984), NDF, ADF, and CE (Van Soest et al., 1991). The degradation parameters of DM, CP, CC, NDF, CE, and HE of the three pellets were computed using DUD (the derivative-free iterative method) within the non-linear regression procedure PROC-NLIN of SAS (1989). The generalised kinetics equation (Mertens and Loften, 1980) was: Y = A + B(1 − exp−K(T −JT) ), where Y (%) is potential degradability, A (%) readily degraded fraction, B (%) fraction degradable at measurable rate, K (% per h) degradation rate, T (h) time and JT (h) is lag time. The iterative procedure adopted the following assumptions: JT = T when T ≤ JT, and JT = JT when T > JT. Effective degradability values for the same chemical constituents were calculated by adapting the above equation to the general model proposed by Van Soest et al. (1982). 2.3. Rate of passage To generate passage rate values (% per h) required for the calculation of the effective degradability, pellets samples were mordanted with sodium dichromate, according to Udén et al. (1980). A single dose of 150 g of each marked pellet was put via cannula into the rumen of the cow receiving the diet containing the same pellet. The marker administration was carried out before morning feeding on day 15 of each experimental period. Grab samples of

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faeces were taken 12, 24, 30, 36, 42, 48, 72 and 96 h after marker administration, weighed and dried at 60 ◦ C. Faeces were prepared for chromium content analysis according to Murthy et al. (1971) and the analysis were performed with an atomic absorption spectrophotometer. Passage kinetics of forage particles was then determined according to Grovum and Williams (1973). 2.4. Statistical analysis Chemical composition and particle size data were subjected to one-way ANOVA considering the effect of the type of pellet. Degradation parameters and passage rate values were submitted to ANOVA and cow, period and type of pellet were the factors included in the model. Both analysis were carried out with PROC GLM of SAS (1989); the two degrees of freedom of the type of pellet factor were used to test the difference between C and each treated pellet. Differences were considered significant at P < 0.05.

3. Results 3.1. Chemical composition and particle size In comparison to the chemical composition of C, mechanical pressing to extract the juice for poultry feeding, increased (P < 0.01) the content of the different fibrous constituents in the P pellet, lowering (P < 0.01) CP and non-fibrous carbohydrates content (Table 2). The pellet treated with urea had a greater (P < 0.01) CP, NDF, ADF, and CE content than C one. Pellets particle size distribution measured by wet sieving showed U having the lowest percentage of particles greater than 1.18 mm (Table 3). All the pellets had a mean geometrical

Table 2 Chemical composition of lucerne pellets Pelleta

Item

DM (%) Ash (% DM) CP (% DM) Ether extract (%DM) Non-fibrous carbohydrates (% DM) CC (% DM) NDF (% DM) ADF (% DM) HE (% DM) CE (% DM) Acid detergent lignin (% DM) a

Contrast (P<)

C

P

U

C vs. P

C vs. U

90.6 13.2 20.5 2.8 24.0 60.4 39.6 30.1 9.5 23.8 6.1

91.3 11.5 15.7 2.2 20.5 49.9 50.1 39.0 11.1 30.5 8.1

90.6 11.1 23.3 2.3 21.9 58.7 41.3 32.5 8.8 26.1 6.3

** ** ** ** ** ** ** ** ** ** **

NS ** ** * * ** ** ** * ** NS

C: control pellet; P: pellet from mechanically pressed lucerne; U: pellet from urea treated lucerne.

S.E.M.

0.2 0.1 0.4 0.1 0.5 0.3 0.3 0.1 0.1 0.3 0.1

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Table 3 Particle size distribution and mean geometrical diameter of lucerne pellets Pelleta

Item

Particle size (% DM) >1.180 mm >0.600 and <1.180 mm >0.300 and <0.600 mm >0.150 and <0.300 mm >0.075 and <0.150 mm >0.038 and <0.075 mm <0.038 mm Mean geometrical diameter (mm) a

Contrast (P<)

S.E.M.

C

P

U

C vs. P

C vs. U

22.50 12.65 15.58 9.50 3.82 0.86 35.09

23.81 12.24 14.67 9.74 5.05 1.34 33.15

12.23 13.38 18.37 13.08 5.78 1.81 35.35

NS NS NS NS NS NS NS

** NS NS NS * NS NS

2.78 1.90 1.48 1.36 0.72 0.41 2.24

NS

*

0.099

0.183

0.193

0.149

C: control pellet; P: pellet from mechanically pressed lucerne; U: pellet from urea treated lucerne.

diameter below 0.20 mm, and U was smaller than C (0.15 versus 0.18 mm; P < 0.05) due to its lower percentage of large particles. 3.2. Ruminal rate of passage and degradation The differences in particle size (Table 3) did not affect the ruminal passage rate of the pellets, as shown in Table 4. The ruminal in situ DM disappearance did not show any significant difference between C and each treated pellet (Table 4). Regardless of the type of pellet, no measurable JT was detected and the readily degradable DM fraction was always considerable resulting on average 30.1%. The effective DM degradability values of C (61.1%) and U (59.5%) were similar, while P had a reduced amount of DM available in the rumen (54.6%) than C (P < 0.01), because of the lower content of protein and other soluble constituent induced by the extraction process (Table 2). Consistent with the DM pattern, the degradation kinetics of CC was not affected by the type of pellet (Table 4). More than 50% of this feed fraction was readily degraded in the rumen and no measurable JT was detected. On average, 80.7% of CC was rumen degradable. Despite of the lower CP content (Table 2), the protein degradation kinetics of P was similar to C (Table 4). In comparison to C, the addition of urea enhanced the effective CP degradation of U (76.6 versus 68.1%; P < 0.01) by increasing the contribution of the A fraction (49.8 versus 26.7%; P < 0.05). The degradation parameters of the main cell wall constituents for the three lucerne pellets are reported in Table 5. Regardless of the type of pellet, all the fibrous fractions considered showed the lack of detectable A fraction, and a measurable JT required for microbial attachment. As compared to C, either the pellet produced after the extraction process, or the one added with urea showed a significant reduction of the B fraction of NDF (P < 0.01). Statistical contrasts between C and each treated pellet showed only P having a lower effective degradability of NDF (29.5 versus 33.0; P < 0.01). Consistent with NDF, CE and HE of both treated pellets had a lower fraction degradable at measurable rate, B than C (Table 5). However, the effective degradability values of these two structural carbohydrates were similar among pellets (Table 5).

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Table 4 Passage rate and in situ DM, CC and CP degradability parameters of lucerne pellets Itema

Pelletb C

Passage rate (% per h)

Contrast (P<) P

U

S.E.M.

C vs. P

C vs. U

4.5

4.0

5.0

NS

NS

0.3

DM A (%) JT (h) B (%) K (% per h) Effective degradability (%)

30.4 – 48.9 8.6 61.1

26.4 – 43.5 8.5 54.6

33.4 – 41.3 9.9 59.5

NS – NS NS **

NS – NS NS NS

1.4 – 1.5 0.8 0.4

CC A (%) JT (h) B (%) K (% per h) Effective degradability (%)

51.0 – 41.3 13.1 80.5

51.6 – 39.5 14.0 81.1

54.0 – 37.3 15.3 80.6

NS – NS NS NS

NS – NS NS NS

1.1 – 1.8 0.5 0.5

CP degradability A (%) JT (h) B (%) K (% per h) Effective degradability (%)

26.7 – 63.8 9.5 68.1

30.2 – 55.4 8.3 66.1

49.8 – 41.8 10.4 76.6

NS – NS NS NS

* – * NS **

2.1 – 2.0 0.9 0.4

a b

A: readily degraded fraction; JT: lag time; B: fraction degradable at measurable rate; K: degradation rate. C: control pellet; P: pellet from mechanically pressed lucerne; U: pellet from urea treated lucerne.

4. Discussion The chemical composition of dehydrated lucerne pellet was modified by both the industrial processes considered (Table 2). Mechanical pressing of the forage to extract the juice for poultry feeding reduced the amount of CP and other soluble constituents of P, whereas, U pellet had a higher CP content than C due to the addition of urea. Previous researches have shown that the moisture content of plant material at the time of the treatment with an alkaline source can affect the effect of the treatment on lucerne chemical composition. The forage treatment with a N-free alkaline source (NaOH) at the harvest reduced CP content (Canale et al., 1990; Canale et al., 1992). The result was likely due to leaching losses of water-soluble DM (including nitrogen) from plant material, which may have been increased by the alkaline treatment. On the contrary, when plant free water was reduced prior to the alkaline treatment, like in the case of U pellet, no reduction of CP content was observed (Mathews and McManus, 1976). Moreover, according to Mathews and McManus (1976), the alkaline treatment could also have caused the apparent increase of cell walls content observed in U (Table 2) by promoting the occurrence of Maillard reactions between carbonyl groups of carbohydrates and nitrogen. The extraction process to produce the P pellet did not modify its particle size distribution in comparison to C (Table 3). The contrast between C and U showed the latter pellet having

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Table 5 Cell wall constituents in situ degradability parameters of lucerne pellets Itema

Pelletb

Contrast (P<)

S.E.M.

C

P

U

C vs. P

C vs. U

NDF A (%) JT (h) B (%) K (% per h) Effective degradability (%)

– 1.1 61.2 5.9 33.0

– 0.4 51.6 5.7 29.5

– 0.1 52.8 6.7 30.2

– NS ** NS **

– NS ** NS NS

– 0.2 0.4 0.4 0.8

CE A (%) JT (h) B (%) K (% per h) Effective degradability (%)

– 0.6 67.8 6.3 38.3

– 0.7 58.2 6.2 34.2

– 0.3 61.1 7.3 35.8

– NS ** NS NS

– NS ** NS NS

– 0.2 0.3 0.4 0.7

HE A (%) JT (h) B (%) K (% per h) Effective degradability (%)

– 2.0 61.0 6.2 30.7

– 1.0 52.9 5.2 28.7

– 0.7 49.4 7.3 27.8

– * * NS NS

– * * NS NS

– 0.1 0.1 1.8 2.7

a b

A: readily degraded fraction; JT: lag time; B: fraction degradable at measurable rate; K: degradation rate. C: Control pellet; P: pellet from mechanically pressed lucerne; U: pellet from urea treated lucerne.

a smaller mean geometrical diameter due to a reduced percentage of particles greater than 1.18 mm. This might have been caused by the alkaline activity of urea that, partially attacking cell wall bonds, makes them more fragile and sensitive to crushing during the following grinding process. Poppi et al. (1985), working with sheep, indicated that the feed fraction retained by a screen with pores size of 1.18 mm is able to stimulate rumination and chewing. Based on their particle size distribution, all the tested pellets, and U, in particular, should be considered more as protein concentrates rather than forage sources. Mertens (1992) proposed to multiply the NDF content of a given feed (on DM basis) by the percentage of its particles retained by the 1.18 mm sieve to calculate the feed roughage value. As compared to reference roughage values reported by the same Author (1992) for various feedstuffs, C (8.9) and P (11.9) resulted similar to brewers grains (8.3) and high moisture ear maize (9.1), while U showed a lower value (5.1), close to that of coarsely ground maize (4.3). Consistent with these findings, Shaver et al. (1988) observed a reduced chewing activity when dairy cow in early lactating replaced either long or chopped hay with lucerne pellets. Moreover, milk fat depression was recorded when 50% DM from maize silage was replaced by an equal amount of lucerne pellets (Lessard and Fisher, 1980). The kinetics of DM degradation was similar among pellets and it showed a considerable A fraction and a lack of detectable JT (Table 4). Both results may have been influenced by the particle size of the tested products. About one-third of the particles of all the pellets passed through the 38 ␮m sieve (Table 3) and it is likely that a great part of it was able to escape from the bag as “mechanical losses” (bag pore size 40 ␮m) before being actually degraded.

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Among the different chemical constituents of the pellets, CC have shown the greatest ruminal disappearance (Tables 4 and 5). CC represented 50% or more of pellets total DM (Table 2) and the fine breakdown of the feed particles (Table 3) should have increased their fermentation by extending the feed surface available for microbial attachment (Weakley et al., 1983). All the pellets had a readily degradable CP fraction lower than corresponding A fraction of CC (Table 4), showing how the nitrogen compounds play only a minor role within the lucerne DM readily available in the rumen. Other forage constituents such as soluble carbohydrates and pectins are likely to be the main components of the CC fraction readily available for microbial degradation. Due to the extraction process, P had a lowered CP content than C (Table 2), but this difference did not affect the protein degradation kinetics of these two pellets (Table 4). Their effective CP degradability values resulted similar and close to reference value of 68.4 reported by NRC (2001) for lucerne meal (CP = 19.2% DM) in case of diets with low DM intake (2% of BW) and high concentrate content (75% of DM). Urea treatment enhanced the effective CP degradation of U by increasing the A fraction (Table 4). The nitrogen of the alkaline additive resulted readily available in the rumen and, therefore, diets formulated with the U pellet should include an adequate amount of readily fermentable carbohydrates to avoid the loss of ammonia N (Nocek and Russell, 1988). Consistent with previous in situ studies on lucerne (Hoffman et al., 1993; Andrighetto et al., 1995), cell wall constituents were slowly degraded in the rumen as compared to CC (Tables 4 and 5), and their effective availability for microbial degradation has been further limited by the short ruminal retention time caused by the small particle size of the pellets (Table 3). Structural carbohydrates are insoluble in water and their degradation requires a close adhesion by rumen microbes. As compared to C, the pellet produced after the extraction process showed a lower effective degradability of NDF (Table 5). Therefore, microbial growth on the fibrous substrate of lucerne was made more difficult by the removal of readily fermentable nutrients. Lucerne cell wall digestion was not increased by the addition of urea and this is in contrast to what has been observed with same treatment in grass species (Deschard et al., 1987; Chestnut et al., 1988) or by treating lucerne with other types of alkali products such as NaOH (Canale et al., 1992) or KOH (Mathews and McManus, 1976). The greater nitrogen availability induced by the urea treatment may have promoted a greater occurrence of Maillard reactions exceeding the positive effect of the alkali treatment on cell wall ruminal degradation. Consistent to the result of the present study, Glenn (1990) found no increase in potential cell walls degradability treating lucerne hay with anhydrous NH3 . Regardless of the type of pellet, CE showed a reduced JT and it was degraded at a faster rate than NDF and HE (Table 5). These findings, consistent with those reported by Andrighetto et al. (1993) for lucerne hay, indicate that CE may be the primary site of hydrolysis of lucerne cell wall by the rumen microbes. To further understand the nutritional implications of the degradation study, NDF and CC of each lucerne pellet were multiplied by the corresponding effective degradability coefficients to calculate the amount of these two feed constituents made available in the rumen per kg of pellet DM intake (Fig. 1). Feeding C, 611 g/kg of pellet DM, were degraded in the rumen. Within this aggregate, the contribution of NDF was minor than the CC one, confirming the previous observations by Andrighetto et al. (1993) and Hoffman et al. (1993) on 2 mm-ground lucerne hay. Therefore, dehydration and pelleting do not seem to

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Fig. 1. Amount of CC (䊐) and NDF (䊏) available in the rumen per kg of DM intake of C, P, and U. Significance of the contrasts (S.E.M.): CC, C vs. P**; C vs. U (NS) (1.5); NDF, C vs. P (NS); C vs. U (NS) (3.6).

substantially alter the pattern of ruminal degradation of dried ground lucerne forage. The addition of urea did not significantly modify the ruminal availability of the lucerne pellet NDF and CC (Fig. 1). On the contrary, the extraction process carried out in the production of P reduced the total DM available in the rumen by a drop (P < 0.01) in CC contribution to the degradable pool of the pellet.

5. Conclusions The pelleting process has shown to drastically reduce the physical effectiveness of the fibrous fraction of dehydrate lucerne and, therefore, all the tested pellets must be considered as protein concentrates rather than forage sources. This low roughage value could represent an important constraint on their inclusion in diets for high producing dairy cows in which feedstuffs rich in structural carbohydrates are basically required to stimulate an adequate chewing activity. The reduced particle size of the pellets can also affect their degradation pattern in the rumen by enhancing the substrate surface area accessible for microbial attachment. It must be pointed out, though, that fine particles are subjected to a faster rate of passage and this can limit the ruminal availability of slow degradable forage constituents such as the cell walls. This latter effect was particularly evident in the degradation kinetics of P which had the highest NDF content among tested pellets. The rumen disappearance of the cell wall constituents was not increased by treating dehydrate lucerne with urea before pelleting. The alkaline additive has shown to be weakly bound to the forage particles and, once in the rumen, it significantly increased the readily available CP. In dairy cattle feeding, this peak of ammonia N in the rumen fluid must be balanced by an adequate amount of readily fermentable carbohydrates to allow and efficient microbial growth, avoiding excessive nitrogen losses.

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