Degradation characteristics and energy value of grains, oil seed cakes and agroindustrial by-products

In ruminant animals, rumen microbes utilize different fractions of protein, non-fiber carbohydrate and structural carbohydrate (CHO) at different rates. When rate of protein degradation exceeds the rate of CHO fermentation, large quantity of N is lost as NH₃. On the other hand, when rate of CHO fermentation exceeds protein degradation rate, there is inefficient microbial protein production. Therefore, estimation of CHO and protein fractions in the feedstuffs as well as their degradation rates provides more precise information about the availability of nutrients to rumen microbes and the animal. Cornell net carbohydrate and protein (CNCP) system assumes that feedstuffs are composed of protein, carbohydrate, fat, ash, and water while protein and carbohydrate are further subdivided by chemical composition, physical characteristics, ruminal degradation and post ruminal digestibility characteristics. This system provides the basic structure necessary to predict more accurately the ruminally degraded carbohydrate and nitrogen fractions and absorbed amino acids from microbial and feed protein. Few data are available (Jeya Prakash et al., 2003; Kamble et al., 2010 and Gupta et al., 2011) regarding the CNCP fractions of Indian feeds.

So, in the current study carbohydrate and protein fractions and subsequently the rumen degradable (RDP) and undegradable CP (RUP) and energy values of feeds using prediction equations (NRC, 2001) based on their composition were determined. 

The samples viz. maize, pearl millet, barley, wheat, cotton seed cake (CSC), groundnut cake (GNC), mustard cake-deoiled (DOMC), mustard cake, jatropha cake, karanj cake, sesame cake, soybean meal, sunflower cake, rice polish, rice bran, maize gluten meal (MGM), deoiled rice bran (DORB), guar churi, maize bran, guar korma, gram churi, tamarind seed and mangoseed kernel were collected from local market of Karnal (Haryana), Directorate of Wheat Research (DWR), Karnal and other parts of India, dried in a hot air oven at 60ºC until constant weight, ground to pass through 1mm sieve using electrically operated Willey mill and stored in plastic sample bottles for further analysis. Apart CF and NFE, the proximate (AOAC, 2005) and fiber composition (Van Soest et al. 1991) of feed samples were analyzed. NDF was assayed without a-amylase and expressed exclusive of residual ash. ADF was also expressed exclusive of residual ash. Lignin was estimated by hydrolysis of acid detergent residue in 72% H₂SO₄ for 3h (Van Soest et al. 1991). Starch was estimated as per the procedure applicable to grains, stock feeds, and cereals given in AOAC (2005). Neutral detergent insoluble protein (NDICP) and acid detergent insoluble protein (ADICP) were estimated by analyzing the CP content of the residual NDF and ADF (Licitra et al. 1996). Phosphate buffer soluble protein (SOLP) was estimated from the CP analysis of the residue obtained after treating 0.5g of sample in borate phosphate buffer. Similarly TCA precipitable protein was analyzed (Licitra et al. 1996). Carbohydrate fractions viz. soluble carbohydrates i.e sugars and organic acids (CA), soluble available fiber (CB₁), insoluble available fiber (CB₂) and unavailable fiber (CC) and protein fractions viz. non-protein nitrogen (PA), instantly soluble (PB₁), readily degradable (PB₂), slowly degradable (PB₃) and indigestible (PC) were calculated using equations given by Sniffen et al. (1992). Non structural CHO (NSC) was calculated as the difference of the sum of CB₂ and CC from total CHO. TDN and ME were calculated from chemical composition (CP, EE, NDF, NDICP, non fibrous carbohydrate (NFC)) based equations proposed by NRC (2001).

The RDP and RUP were analyzed from the protein fractions as per NRC (2001). The fractional degradation rate of the three B fractions are B₁ (120-400 %/h), B₂ (3-16 %/h) and B₃ (0.06-0.55 %/h) (NRC. 2001). The median value of the given range of Kd is used in the equation 1 and 2 to calculate the RDP and RUP of the feeds whereas the ruminal outflow rate (kp) is assumed to be 0.05h-1 for concentrates.

RDP = A + B₁ [kdB₁ / (kdB₁ + kp)] + B₂ [kdB₂ / (kdB₂ + kp)] + B₃ [kdB₃ / (kdB₃ + kp)] (1)

RUP = B₁ [kp / (kdB₁ + kp)] + B₂ [kp / (kdB₂ + kp)] + B₃ [kp / (kdB₃ + kp)] + C (2) 

Among grains, the highest OM was found in pearl millet (98.03%) and lowest in maize (97.87%). The CP content was maximum in wheat (15.77%) and minimum in barley (11.63%) whereas EE values ranged from 2.15% (wheat) to 6.25% (maize). CP values of maize, barley and wheat were similar to earlier reported values (Trivedi et al. 2007; Kamble et al. 2010). CP content of oil seed cakes ranged from 18.12% (jatropha cake) to 47.35% (SBM). Proximate composition of CSC, GNC, mustard cake and SBM agrees with the findings of Trivedi et al. (2007). Comparable CP content of GNC, mustard cake, and CSC has been reported earlier (Kamble et al. 2010). Among agroindustrial by-products, CP content was highest in MGM (62.12%) and the lowest in mangoseed kernel (3.75%) whereas the highest EE was recorded in rice bran (16.1%) and the lowest in maize bran (1.72%). Among grains NDICP (%CP) ranged from 13.65% (pearl millet grain) to 26.00% (barley grain) whereas ADICP (%CP) ranged from 3.91% (wheat) to 5.12% (pearl millet). Starch (%NSC) ranged from 74.19% (wheat) to 90.60% (maize). SOLP (%CP) varied from 18.29% (maize grain) to 47.98% (barley grain). Of the total soluble nitrogen (%SOLP) NPN portion was maximum in barley grain (96.96) and minimum in maize grain (42.84). SOLP (%CP), ADICP (%CP), NPN (%SOLP) and NDICP (%CP) in barley and maize grain were comparable to the findings of Sniffen et al. (1992) and starch (%NSC) of barley and maize grain agrees to the findings of Fox et al. (2003). Guevara-Mesa1 et al. (2011) reported similar fiber bound CP of SBM to present finding. MGM, maize, pearl millet, GNC and guar churi were highly energy rich with ME value exceeding 3 Mcal/Kg and TDN ranging from 77-80%. Jatropha (1.90 Mcal/Kg) and sesame cake (1.94 Mcal/Kg) had lowest ME value. Suksombat et al (2007) reported more or less similar TDN1X value of soybean meal and rice bran present findings. 

Table 1. Chemical composition, fiber and protein fractions and energy value of feeds (% DM basis)

Among grains, the highest CA and CB₁ fraction was observed in wheat (10.72% and 69.57%, respectively) whereas the lowest CA fraction was found in maize (4.08%) and that of CB₁ in barley grain (57.89%) (table 2). Barley had the highest (27.52%) and wheat had lowest (12.79 %) CB₂. Pearl millet and barley grain had the highest (7.59%) and lowest (6.22%) values for CC, respectively. Due to less CC fraction (<8% of total carbohydrate), most of the CHO derived from grains are digestible in the animal. Maize grain contained negligible amount of fraction C (0.6%) (Chen et al., 1999). Among energy sources highest CHO has been reported in barley grain by Trivedi et al. (2007). Almost similar pattern for CHO fractions of oil seed cakes has been reported by Trivedi et al. (2007). Among oil seed cakes, the highest CHO content was present in jatropha cake (71.70%) followed by karanj cake (67.11%) and sesame cake (63.77%). The fraction CA was the highest in mustard cake (49.05%) and lowest in sesame cake (23.68%). The maximum CB₁ fraction was observed in karanj cake (28.97%) and minimum in sunflower cake. (13.63%) while CB₂ level was the highest in jatropha cake (37.58%) and lowest in mustard cake (6.67%). Fraction C ranged from 6.17% (SBM) to 37.69% (sesame cake). Total CHO among agro-industrial by-products was the highest in mangoseed kernel (88.71%) followed by maize bran (87.42%). The highest CA was observed in guar korma (42.27%) and the lowest in maize bran (5.68%). The maximum value of CB₁ was of tamarind seed (47.07%) and minimum of MGM (9.46%). CB₂ fraction was the lowest in tamarind seed (4.05%) and highest in mangoseed kernel (57.59 %). Among agro-industrial by-products, fraction CB₁ was highest in rice polish.

Among grains, maize had the lowest PA (7.83) and highest PB₂ (62.98%) whereas barley had the highest PA (46.52) and lowest PB₂ (26.02%). Fraction PC was the highest in pearl millet (5.12%) and lowest in wheat (3.91%). The highest PA (46.52) and PB₃ (21.72%) was found in barley. PB₁ (16.50%) was the highest in pearl millet. PA + PB₁ ranged from 14.28 to 23.86% in grains. The PA + PB₁ and PB₂ fractions of grains were comparable to the findings of Sharma and Singh (1997). PB₃+PC fraction of maize grain was in corroboration with the findings of Lanzas et al. (2007). The protein fractions of barley grain were supported by the findings of Fazaeli et al. (2012). In GNC, PB₂ (14.15%) was observed to be lower compared to other oil seed cakes. The level of PB₂ in mustard cake, sesame cake, DOMC and CSC was found to be 37.65, 42.05, 62.98 and 63.05%, respectively. The PC fraction was very low (1.07 to 8.61) in oil seed cakes. The protein fractions of oil seed cakes are similar to previous findings (Gupta et al. 2011). The nitrogen fractions of GNC estimated by Singh et al. (2002) were different from the present finding which might be due to difference in variety, processing methods etc. Lower PC fraction reflects the fair availability of nitrogen to the animal from oil seed cakes. The PB fractions (PB₁, PB₂ and PB₃) of CSC corroborated with the findings of Guevara-Mesa et al. (2011). RUP (%CP) varied from 17.12% to 44.94% whereas, RDP (%CP) varied from 55.07% to 82.88%. The RDP (%DM) was lowest in mango seed kernel (2.07%) and guar korma (43.46%) and MGM (40.69%) had highest value for it whereas, RUP (%DM) was lowest in mango seed kernel (1.69%) and highest in MGM (21.43%). Similar RDP and RUP of rice bran and soybean meal were reported by Suksombat et al. (2007). 

Maize grain, pearl millet had higher ME (3.1 Mcal/ kg) and guar churi and MGM had about 50% bypass protein. Agro industrial byproducts viz. rice polish, rice bran, MGM, DORB, guar churi and guar korma had good proportion of instantly soluble and degradable CHO. Their combination with the oil cakes viz. GNC, mustard cake, karanj cake and sunflower cake having higher PA+PB₁ fraction would result in efficient ration formulation. The grains were rich in CB fraction whereas cakes viz. CSC, GNC, DOMC, jatropha cake, sesame cake and soybean meal were rich in PB (true protein) fraction. 

Table 2. Carbohydrate and protein fractions of the feeds as per Cornell Net Carbohydrate and Protein System and their rumen degradable and undegradable protein fractions

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