Effects of Feeding Corn-lablab Bean Mixture Silages on Nutrient Apparent Digestibility and Performance of Dairy Cows

Field management and silage preparation

Field experiments were carried out at Mudanjiang Shuangfeng farm (44°36′ latitude N, 129°35′ longitude W), Heilongjiang, China, from May 2009 to September 2009. We used hilly albic soil mixed with sand at a 30 cm average soil depth. Soil fertility levels at the location were maintained at optimal levels for corn silage production. Silage corn (Longfudan 208) was sown alone or intercropped with lablab bean at a planting density of 80/40 thousand corn/lablab bean plants/ha. On 10 May 2009, silage corn (Longfudan 208) was sown in two different 10 ha herbicide-free areas. After 2 d, lablab beans were sown in rows 15 cm apart from the rows of corn in a randomized 10 ha area. Chemical herbicide application was completed in 5 d. Corn and corn-lablab bean mixtures were harvested on 23 September 2009 at a corn maturity stage of 2/3 milk line.

The monoculture corn and corn-lablab mixtures were chopped to a theoretical cut length of 15 mm using a forage harvester and then ensiled in two individual bunker silos for 50 d. At the time of ensiling, two 1,000 g fresh samples were taken for the initial characterization of corn and corn-lablab bean mixture. After 50 d of storage, two 1,000 g samples of silage were taken from each silo and frozen to −20°C until analysis.

Corn and corn-lablab bean mixture silages were analyzed for pH in triplicate by placing a 20 g sample in 100 ml distilled water, and blending for 60 s in a high-speed blender. The diluted sample was filtered through three layers of cheesecloth, and pH was measured with a pH meter (Mettler Toledo Delta320, Switzerland). A 20 ml aliquot was centrifuged at 25,000×g for 20 min at 4°C, and supernatant was decanted into 20 ml scintillation vials and stored at −20°C for later analysis of organic acids and ammonia-N. The organic acids (lactate, acetate, and butyrate) were analyzed by high performance liquid chromatography (column: Sodex RS Pak KC-811, Showa Denko K.K., Kawasaki, Japan; detector: DAD, 210 nm, SPD-20A, Shimadzu Co., Ltd, Kyoto, Japan; 1.0 ml/min; temperature: 50°C). Concentration of ammonia-N was measured using the indophenolblue method.

Corn and corn-lablab bean mixture silages samples were dried at 55°C for 72 h in a forced-air drying oven and then ground in a Wiley mill to pass through a 1 mm screen (FZ102, Shanghai Hong Ji Instrument Co. Ltd, Shanghai, China). Dry matter, Ca, P, ash and ether extract (EE) contents of silage samples were determined by following the procedure of AOAC (1990), and N content was determined by the Kjeldahl method (AOAC 1990), CP was calculated as N×6.25. The neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed according to the methods described by Van Soest et al. (1991). Concentrations of Water Soluable Carbohydrate (WSC) in silage samples were measured using the anthrone technique (Thomas, 1977).

In situ ruminal nutrient degradabilities

The corn silage (Longfudan 208) and corn-lablab bean mixture silages were ground with a mill to pass through a 2.5 mm screen (FZ102, Shanghai Hong Ji Instrument Co. Ltd, Shanghai, China). Duplicate samples weighing 5.0 g were placed into nylon bags (9×16 cm, 50μm pore size, Beijing Feidi Business Co. Ltd, Beijing, China) and heat sealed. The nylon bags were then incubated in the rumen of three ruminally cannulated Holstein cows (two bags per treatment per time period per cow) for 0, 4, 8, 12, 24, 48 and 72 h. The cows were fed ad libitum a 51:49 forage:concentrate total mixed diet that contained (DM basis) 92.3% DM, 10.8% CP, 28.7% ADF, and 45.8% NDF. Zero-hour disappearance was estimated by washing duplicate bags containing samples. At the end of the incubations, all bags were removed from each cow and were manually rinsed in cold tap water until the rinsing water was clear. Washed bags were dried at 65°C for a constant weight. Residues from the nylon bags were analyzed for DM, CP, NDF, and ADF as previously described.

Kinetic parameters of nutrient disappearance in the rumen were estimated using an iterative least squares method of the nonlinear regression procedure of SAS (2001) by fitting the following model (Ørskov and McDonald, 1979): y = a+b×(1−e^−ct), where y is ruminal nutrient disappearance at time t; a is soluble fraction (%), b is slowly degradable fraction (%), c is fractional degradation rate constant at which b is degraded and t is the time of incubation (h). Effective degradability (ED) was calculated from the equation: ED = a+bc/(c+k), where k is the ruminal outflow rate (0.036/h) and a, b, and c are as described above.

Production study

Sixty multiparous lactating Holstein cows selected from Heilongjiang dairy farm were stratified on the basis of milk production and were randomly divided into two groups of 30 cows each. The cows were housed in tie stalls with water freely available. Two diets were formulated with a 59:41 forage: concentrate ratio to meet the nutrient requirements of dairy cows (NRC, 2001). The forage part of the diets consisted of 39.3% corn silage (Longfudan 208) or 39.3% corn-lablab bean mixture silages, with the remaining 60.7% consisting of Chinese wildrye hay in both diets (Table 1). The experimental period lasted for 70 d, including a 10-d adaptation period and a 10-d metabolism trial. The diet was fed ad libitum per d at 04:00, 11:00, and 17:00 h, and the animals were milked daily at 05:00 and 18:00 h.

Table 1.

Ingredients and chemical composition of dietary treatments

Five cows from each treatment group with similar food intake were housed in metabolism crates designed to collect total fecal excretion during the last 10 d of the experiment. The cows were acclimatized to their assigned diets for 5 d, followed by 5 d of fecal collection. The weight of the total daily feces was recorded for each cow and a 10% aliquot was stored at 5°C every morning of the collection period. Feed offered and feed refusals were also recorded daily for each cow. At the end of the collection period, feed offered, feed refusals, and all feces from a cow were thawed, mixed thoroughly, and subsampled for subsequent analysis. The analysis of DM, CP, NDF, and ADF concentrations in the feeds and feces was used to determine nutrient digestibility. The analytical procedures were the same as previously described.

Individual milk yields were recorded electronically at each milking (HerdMaster Galaxy Management System, Alfa-Laval Agri Inc., St. Louis, MO, USA). Milk samples were obtained for each milking on day 0, 15, 30, 45, 60 and analyzed for milk fat, milk protein, solids non fat (SNF), and milk somatic cell count (SCC). The content of fat, protein and SNF, respectively, was analyzed by spectroscopic mid infrared technique (MilcoScan FT 120. Foss Electric, Hillerød, Denmark) according to Lakic et al. (2009). The SCC was analyzed in fresh milk with no additives by fluorescence-based electronic cell count (Fossomatic 5000. Foss Electric, Denmark) according to Burriel (2000).

Statistical analysis

The data were analyzed using the GLM procedure of SAS program package (SAS Institute, version 9.1). The following model was used: Yij = μ+Ti+ɛij, where Yij is the dependent variables; μ is the overall mean; Ti is the fixed effect of group or treatment; ɛij is the random error. Duncan’s multiple range tests were used to detect statistical significance between treatment groups.

Silage fermentation characteristics, chemical composition and effective ruminal degradability

The fermentation characteristics and chemical composition of corn silages and corn-lablab bean mixture silages are presented in Table 2. The lactic acid and acetic acid concentrations of corn-lablab bean mixture silages were higher compared with those of corn silage (p<0.05). The pH and ammonia-N concentrations of all silages indicated well-fermented silage (p>0.05).

Table 2.

Fermentation characteristics and chemical composition corn silages and corn-lablab bean mixtures silages

Dry matter, CP, ash, Ca, EE, NDF, and ADF concentrations were significantly different between corn silage and corn-lablab bean mixture silages (p<0.05). Dry matter, CP, ash, Ca, and EE concentrations of corn-lablab bean mixture silages were 1.04%, 0.45%, 0.87%, 0.25%, and 0.34% greater than those of monoculture corn silage, respectively (p<0.05). Moreover, NDF and ADF concentrations of corn-lablab bean mixture silages were 12.78% and 7.57% lower than those of corn silage, respectively (p<0.05). The P and WSC concentrations were similar between monoculture and mixture silages (p>0.05).

In situ ruminal digestion kinetics and ED of corn silage and corn-lablab bean mixture silages are shown in Table 3. Ruminal DM, CP, NDF, and ADF degradability of corn-lablab bean mixture silages were higher than corn silage (p<0.05).

Table 3.

In situ ruminal nutrient degradabilities of corn-lablab bean mixtures silages relative to corn silage (%, X±SD)

Nutrient apparent digestibility

Effects of feeding corn-lablab bean mixture silages on nutrient apparent digestibility of dairy cows are presented in Table 4. The digestibility of DM, CP, NDF, and ADF was different between two dietary treatments (p<0.05). The digestibility of DM, CP, NDF, and ADF for cows fed corn-lablab bean mixture silages was 7.67%, 7.84%, 5.18%, and 8.54% greater than for those fed corn silage, respectively (p<0.05).

Table 4.

Effects of feeding corn-lablab bean mixtures silages on nutrient apparent digestibility of dairy cows (%, X±SD)

Performance

No significant differences in milk yield between two dietary treatments (p>0.05) were observed in the first 15 d of the experiment. However, in the next 16 d to 60 d, cows fed corn-lablab bean mixture silages produced a higher milk yield compared with cows fed corn silage (p<0.05). During the 60-d experimental period, the overall mean of milk yield was 3.02 kg/d greater for cows fed corn-lablab bean mixture silages than for those fed corn silage (p<0.05). Milk proteins were greater (p<0.05) in the milk of cows fed corn-lablab bean mixture silages than in the milk of cows fed corn silage. Milk fat and SNF content were similar for both dietary treatments (p>0.05). However, milk somatic cell counts for cows fed corn-lablab bean mixture silages were lower than for those fed corn silages (p<0.05).

Economic benefit

During the experimental period, the prices of each ingredient (yuan/kg) were as follows: corn silage, 2.8; Chinese wildrye hay, 1.2; and mixture concentrate, 2.57. Experiments were carried out at Heilongjiang dairy farm, which belongs to Wandanshan Milk production base. According to the provisions of Wandashan fresh milk purchase price, milk purchase price was 2.97 yuan/kg.

Effects of feeding corn-lablab bean mixtures silages on economic benefit are shown in Table 6. The two diets containing corn silages and corn-lablab bean mixture silages had the same cost. But the economic benefit for cows fed corn-lablab bean mixture silages was 8.43 yuan/d/cow higher than that for those fed corn silage.

Table 6.

Effects of feeding corn-lablab bean mixtures silages on economic benefit (yuan/d/cow)

Silage fermentation characteristics, chemical composition and effective ruminal degradability

Legumes are expected to have higher organic acid concentrations than grasses because of their greater buffering capacity (McDonald et al., 1991; Albrecht and Beauchemin, 2003; Muck et al., 2003). In the present experiment, corn-lablab bean mixture silages contained higher lactic acid and acetic acid concentrations than monoculture corn silage. The higher buffering capacity of lablab bean may have extended the fermentation period, resulting in greater lactate and acetate concentrations. Similar observations have been recorded by Contreras-Govea et al. (2009a), who observed an increase in lactic acid and acetic acid concentrations when corn was ensiled in mixture with lablab bean. Meanwhile, in the present study, the pH value, and ammonia-N concentrations of silages indicated that the monoculture corn (Longfudan 208) and corn-lablab bean mixture silages were well-fermented silage. This result is in agreement with earlier studies conducted by Mazaheri (1979) and Anil et al. (2000).

As expected, corn-lablab bean mixture improved the nutrient value of silage compared with monoculture corn. Combining corn with lablab bean increased CP concentrations and decreased fiber concentrations in silage. These results can be attributed to the greater protein and lower fiber content of legumes compared with grasses (NRC, 2001). Kaiser and Lesch (1977) revealed similar results, demonstrating that the increase in CP concentration can reach as high as 78% from a monoculture corn to an intercrop corn with lablab bean. Similarly, Contreras-Govea et al. (2009b) compared the chemical composition of corn-lablab bean mixture silage with corn silage and found that the mixture silage has 13% greater CP concentration than corn alone. In another study, Armstrong et al. (2008) intercropped corn with lablab bean and concluded that adding lablab bean in low-density corn stands can increase the CP concentration and feed nutrient value of the forage.

In the present study, in situ ruminal nutrient degradabilities of corn-lablab bean mixture silages were greater than those of corn silages. This result may be attributed to the difference in protein composition and structure between corn silage and corn-lablab bean mixture silages, which altered the fermentation substrate of the rumen microbial population and thus improved nutrient degradability. For corn-lablab mixture silage, a higher CP content may mean a high concentration of buffer soluble CP and a low concentration of slowly degradable fractions. The high effective degradabilities of DM, NDF and ADF maybe due to its higher soluble in situ soluble DM, NDF and ADF fractions than monoculture corn silage. Other researchers also reported higher rates of ruminal degradation of DM, NDF and ADF derived from higher CP legumes than grasses (A. F. Mustafa et al., 2000).

Nutrient apparent digestibility

Corn for silage is a major forage source for dairy cows in northern China. The composition and content of various nutrients in the silage directly affect cow digestibility and production. In this experiment, cows fed corn-lablab bean mixture silages increased the digestibility of DM, CP, NDF, and ADF compared with those fed corn silage. This results was derived from lower NDF, ADF content and higher CP concentration in corn-lablab mixture. This finding is in agreement with Mupangwa et al. (2000a), who found that lablab bean supplementation improves the apparent digestibility of DM and NDF in the basal diet compared with the control diet of growing goats.

The cell wall constituents NDF (hemicellulose, cellulose, and lignin) and ADF (cellulose and lignin) are negatively correlated with NDF and ADF digestibility (Theander and Westerlund, 1993). Legumes, including lablab bean, contain higher CP and lower NDF content than grasses, such as corn (NRC, 2001), which may elicit an effect on digestibility. Thus, higher CP and lower NDF and ADF concentrations of corn-lablab bean mixture silages may lead to remarkable higher digestibility of DM (up to 76.7 g/kg DM), CP (up to 78.4 g/kg DM), NDF (up to 51.8 g/kg DM) and ADF (up to 85.4 g/kg DM) compared with monoculture corn silage (p<0.05). Similar observations were recorded by earlier studies (Paterson et al., 1994).

Performance and economic benefit

The performance of dairy cows can be estimated primarily from milk yield and milk composition, which are affected by genetic and environmental factors, including bio-geophysical (such as photoperiod), nutritional, and management factors. Generally, variations in animal nutrition elicit the most important environmental effect on performance. In this study, milk yield was greater for cows fed corn-lablab bean mixtures silages than for those fed corn silage. Dietary NDF contents are major factors affecting the milk yield of dairy cows (Allen, 2000). The reduction in milk yield, for cows fed the corn silage diet can be attributed, at least in part, to the greater (7.2% more) NDF content of the corn silage diet relative to that of the corn-lablab bean mixture silage diet.

Moreover, milk protein content in the milk of cows fed corn-lablab bean mixture silages was increased. By contrast, Mugwenti et al. (2006) found that feeding mixed cereal-tree forage legume silages does not elicit an effect on milk yield and composition in lactating dairy cows. Our result may differ because feeding corn-lablab bean mixture silages diet increased CP concentration and digestibility compared with corn silage diet. As a result, milk yield and milk protein were improved.

Methods to reduce production costs and obtain the highest possible income are still the main focus for animal nutrition researchers studying dairy cows. In this study, feeding corn-lablab bean mixture silages diet had 8.43 yuan/d/cow higher economic benefit compared with corn silage diet.