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* Key Laboratory of Subtropical Agro-Ecological Engineering, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan 410125, P. R. China
Graduate University of the Chinese Academy of Sciences, Beijing 100039, P. R. China
Agricultural University of Hebei, Baoding 071001, P. R. China
Central South University of Forestry and Technology, Changsha, Hunan 410004, P. R. China
1 Corresponding author: zltan{at}isa.ac.cn
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Key Words: steam-flaked corn • milk composition • digestibility • dairy cow
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Inclusion of SFC in diets for dairy cows could increase milk yield, milk protein yield, FCM, SNF, and lactose when compared with diets containing finely ground corn (FGC) and corn processed by other methods (Oliveira et al., 1993; Chen et al., 1995). Theurer et al. (1999) reported that starch digestibility in the whole gastrointestinal tract was increased by 10%, and milk yield and milk protein yield were increased by 6 and 8%, respectively, in cows fed SFC compared with those fed steam-rolled corn. Nikkhah et al. (2004) demonstrated that FCM yield was 2.3 kg greater for cows fed diets containing steam-flaked sorghum than for cows fed its ground form.
Little information exists on effects of substituting SFC for FGC on the response of lactating dairy cows. The purpose of this trial was to evaluate the effects of substituting different levels of SFC with equal amounts file, and lactating performance in early lactation dairy cows.
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MATERIALS AND METHODS |
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Feeding and Management of Cows
The use of the animals and the experimental procedure were approved by the Animal Care Committee, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, China. Eight multiparous Holstein cows (550 ± 50 kg of BW, parity 3), 4 fitted with rumen cannulas and 4 intact cows averaging 30 ± 10 DIM at the start of the trial, were fed the 4 experimental diets in a replicated 4 x 4 Latin square design. The fistulated cows formed 1 replicate within each treatment.
Experimental diets were formulated to meet the NRC (2001) requirements for energy, protein, Ca, and P, and diets were prepared weekly (Table 1
). Dietary formulations were adjusted weekly, if necessary, to account for changes in DM content of ingredients. The ratios of FGC to SFC in diets were 40:0, 30:10, 20:20, and 0:40, respectively, of the diet DM. Energy and protein were maintained similar among treatments. All ingredients were purchased and prepared once before the start of the experiment. Alfalfa hay was chopped to about 5 to 10 cm in length and mixed with other ingredients in a TMR machine.
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Cows were milked twice daily at 0600 and 2130 h. Before milking, all animals were allowed to walk outdoors for 1 h. Milk weight was recorded daily by an automatic milking machine (model HP101 milking machine, Alfa Laval Agricultural Corp., Guangzhou, China) for each cow.
Sampling Procedure and Sample Preparation
Over the last 3 d of each period, fecal grab samples (300 to 500 g fresh basis) were taken 4 times daily from the rectum of each cow at 0600, 1100, 1700, and 2200 h on d 19; at 0500, 1000, 1500, and 2000 h on d 20, and at 0400, 0900, 1400, and 1900 h on d 21. Feed and orts were sampled daily. The daily feed, orts, and fecal samples were composited by dietary treatment, period, and cow; subsampled; and stored at –20°C until analysis. At the end of the experiment, all the samples were thawed and dried at 65°C for 48 h. The dried sample was ground through a 1-mm screen (Wiley mill, Arthur H. Thomas, Philadelphia, PA) for analysis later. Milk samples were collected during the morning and afternoon milking over the last 3 d of each period. The composition of milk samples was analyzed immediately by an automatic milk analyzer with mid-infrared wave-band procedures (MILKYWAY-2, Zhejiang University, China).
Over the last 3 d of each period, blood samples (20 mL) from each cow were taken from the jugular vein at 2.5 h postfeeding into EDTA-treated tubes. Blood samples were allowed to clot for a minimum of 30 min at room temperature and were then centrifuged at 3,000 x g for 15 min at 4°C to harvest plasma. Plasma samples were stored at –20°C until analysis.
Ruminal fluid samples were collected from the 4 cannulated cows using a 50-mL syringe connected to a plastic tube that passed through the cannula plug and down into the ventral sac of the rumen at 0, 2, 4, 8, 12, 16, and 20 h after the morning feeding over the last 3 d of each period. Ruminal liquor samples were strained through 4 layers of cheesecloth, and pH was determined immediately after collection (6250 membrane pH meter, Yibo Instruments Corp., Shanghai, China). Strained ruminal fluid samples (15 mL) were transferred into plastic vials containing 0.3 mL of 50% sulfuric acid, mixed, and stored at –20°C for NH3-N analysis.
Chemical Analysis and Calculations
Dry matter, ether extract, OM, and CP of diets, orts, and feces were analyzed according to the procedures of AOAC (1990). The contents of NDF and ADF were determined by the method of Van Soest et al. (1991) using a heat-stable amylase but without sodium sulfite and were expressed inclusive of residual ash. Starch content was determined according to the following procedure as described by Poore et al. (1991). Samples (0.2 g for grain, 0.4 g for mixed feeds, and 0.75 g for feces) were gelatinized by autoclaving for 1 h in 2 mL of a 20% solution of CaCl2 (pH = 2.0) in 18-mL screw-cap test tubes covered with marbles. After cooling, 8 mL of amyloglucosidase solution (Diazyme L-200, Miles Inc., Elkhart, IN; 50 diazyme units were dissolved in 1 L of 0.1 M acetate buffer, pH = 4.2) was added, and samples were incubated for 14 h with hourly shaking during the first 3 h in a 60°C water bath. The solutions were then diluted up to 100 mL. Glucose released during the incubation was quantified with immobilized glucose oxidase-peroxidase in a glucose analyzer (model 27, Yellow Springs Instruments Inc., Yellow Springs, OH).
The acid-insoluble ash ratio technique was used to determine the apparent total tract digestibilities (D, %) of dietary nutrients. The acid-insoluble ash in the diets (Ad, g/kg) and feces (Af, g/kg) were analyzed by the method described by Van Keulen and Young (1977). With the concentration of a nutrient in diet (Nd, g/kg) and feces (Nf, g/kg), the apparent digestibility of a nutrient in the gastrointestinal tract of cows was calculated using an equation as follows:
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Milk samples were analyzed for fat, protein, lactose, and SNF by the MILKYWAY-2 analyzer (manufactured by the University of Zhejiang, China). Milk urea N concentration was determined using the pH difference method according to ISO Standard 14637 (ISO, 2004). Milk composition was expressed on the average weighted milk yield at a.m. and p.m. milking. The 4% FCM was calculated as follows: FCM = milk yield x (0.4 + 0.15 fat content). The average fat and protein yields were calculated by multiplying the milk yield by the fat and protein content in the milk sample on an individual cow.
The concentrations of glucose, cholesterol, and urea N in plasma were determined using the Jiancheng kit (Jiancheng Regent Corp., Nanjing, China) in a UV-visible Recording Spectrophotometer (UV3600, Daojin Corp., Japan) according to the procedures of AOAC (1990). The ruminal fluid samples were thawed and centrifuged at 30,000 x g at 4°C for 20 min. The supernatants were used to determine NH3-N using the alkaline phenolhypochlorite colorimetric procedure of Chaney and Marbach (1962).
Statistical Analysis
Data on nutrient intake, milk composition, apparent digestibility, ruminal fluid pH, urinary and fecal pH, ruminal NH3-N, and blood metabolites were analyzed using the GLM procedure of SAS Institute (1996). The following model was used for the analysis of data on a replicated 4 x 4 Latin square design:
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where Yijkl = dependent variable; µ = overall mean; Pi = effect of period i; Cj(l) = effect of cow j within square l; Tk = effect of treatment k; Sl = square effect (l = 1 or 2); STlk = interaction between square l and treatment k; and Eijkl = the random residual error.
For ruminal pH and NH3-N, which had repeated measures over time, the following model was used:
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where Yijkl = dependent variable; µ = overall mean; Pi = effect of period i; Cj = effect of cow j; Tk = effect of treatment k; Hm = effect of hours postfeeding analyzed as repeated measures; HTmk = interaction between hour m and treatment k; and Eijkm = the random residual error.
The observed means were compared by Tukey’s range test. Statistical significance was declared at P 
0.05. Orthogonal polynomial contrasts were used to examine the responses (linear and quadratic) to increasing the substitution level of SFC for FGC in the diets. In orthogonal polynomial analysis, coefficients were corrected because of unequal spacing of treatments.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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). Yu et al. (1998) observed a similar result; cows fed a SFC diet had greater DMI than cows fed a FGC diet (27.0 vs. 23.1 kg/d). Chen et al. (1994) also reported that DMI of dairy cows tended to increase with increasing proportions of SFC and steam-flaked sorghum in diets. The increased DMI may have been caused by the greater ruminal disappearance of starch (Poore et al., 1991; Oliveira et al., 1995).
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). There were no significant differences between 20 and 40% SFC diets or between 0 and 10% SFC diets. Yield of FCM had a quadratic response (P = 0.004) to SFC substitution as the proportion of SFC increased, with the greatest value being for the 20% SFC diet. Despite no significant difference in milk lactose concentration, milk lactose yield changed quadratically (P = 0.046) as the percentage of SFC in diets increased, with the peak value at the 20% SFC diet. The increase in milk lactose yield in SFC diets may be attributed to a greater availability of starch from SFC, which could provide more VFA, particularly propionic acid, and improve nutrient uptake by the mammary gland (Joy et al., 1997; Santos et al., 1997; Nikkhah et al., 2004).
Milk protein content (P = 0.004) and yields (P < 0.001) changed quadratically as the proportion of SFC increased in diets (Table 2). Milk protein concentration reached the plateau for cows on the 20 and 40% SFC diets, and milk protein yield reached the peak in the 20% SFC diet. These findings were supported by earlier studies (Poore et al., 1993a; Simas et al., 1997) in which milk protein concentration and yield increased with increasing levels of rumen-fermentable carbohydrates and nonstructural carbohydrate content of the diet. In the current study, the increase in milk protein from cows on greater-SFC diets is likely due to the increased supply of neoglucogenic precursors resulting from the increase in SFC starch digestibility (Dhiman et al., 2002).
Milk fat concentration (P = 0.005) and yield (P = 0.002) changed quadratically as SFC increased in diets, with the greatest amount reached in the 20% SFC diet (Table 2). Milk SNF content (P < 0.001) and yields (P = 0.001) increased linearly as SFC increased in diets. Our results were supportive of those of Yu et al. (1998), who reported that milk fat percentage of cows fed SFC was greater than of those fed FGC. On the contrary, increased starch availability in the rumen decreased milk fat content in other studies (Poore et al., 1993b; Overton et al., 1995).
A quadratic effect (P < 0.001) was observed in the concentration of MUN as SFC increased in diets, and the 40% SFC treatment had a greater (P < 0.05) MUN concentration than the other 3 treatments (Table 2). In contrast, Dann et al. (1999) reported a lower MUN concentration of cows fed SFC than of cows fed cracked corn.
Apparent Digestibility of Nutrients
Apparent total tract digestibilities of OM and ADF linearly decreased (P < 0.001) with the increment of SFC in diets (Table 3). Apparent digestibilities of DM (P = 0.026) and NDF (P = 0.009) were affected quadratically as SFC increased in diets. Apparent digestibility of ether extract did not differ among the 4 diet treatments (P > 0.05). The decline in NDF digestibility accounts for about 92% of the decrease in DM digestibility and increased with the increasing level of SFC, which may reflect greater ruminal fermentation of starch.
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). Our results are similar to findings from the study by Dhiman et al. (2002). They demonstrated that starch digestibility in the FGC diet was in the range of 95.6 to 96.1%, and starch digestibility in the SFC diet was 99.2% in dairy cows. Ørskov (1986) noted that when corn was fed to ruminants as whole or crushed forms, up to 40% of corn starch would escape fermentation in the rumen, but if corn starch was steamed before feeding, then virtually all corn starch was fermented in the rumen. Our findings were in agreement with the previous studies (Kotarski et al., 1992; Poore et al., 1993a; Cooper et al., 2002).
There was a quadratic response in apparent total tract CP digestibility (P = 0.009) with the increasing levels of SFC in diet (Table 3), and the peak value was on the 20% SFC diet. Results from this study are consistent with earlier studies (Simas et al., 1997, 1998; Nikkhah et al., 2004). Kotarski et al. (1992) suggested that steam-flaked grains in dairy diets increase the ruminal hydrolysis of feed protein, because steam-flaking disrupts the protein matrix in the endosperm.
pH of Ruminal Fluid and Feces and Ruminal NH3-N
The average ruminal fluid pH was not affected by treatments (Table 4). There was a quadratic response (P = 0.002) in feces pH as the proportion of SFC increased, with the greatest fecal pH being for 20% SFC. Chen et al. (1994) demonstrated that the fecal pH may decrease in cows fed low-degradable starch from FGC, because the incompletely digested starch easily escapes to the hindgut.
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). Decrease in the ruminal fluid NH3-N in cows fed SFC is also an indication of increased capture of NH3 by ruminal microbes and thus improved N utilization in the rumen. A similar result was reported previously by Aldrich et al. (1993), who suggested that increasing the amount of rumen-degradable starch by substituting steam-flaked grain could decrease ruminal fluid NH3-N concentration.
Blood Metabolite Parameters
Plasma glucose concentration changed quadratically (P = 0.04) as the proportion of SFC increased, peaking in the 40% SFC diet (Table 5). This was probably related to a greater availability of starch in SFC, which provided more glucogenic products (propionic acid) than starch in FGC. Plasma cholesterol decreased in a quadratic manner (P = 0.022) as SFC increased in diets, with the greatest value being for the 40% FGC diet. The concentration of plasma urea N (PUN) changed quadratically (P < 0.001) as SFC increased in diets, peaking in the 40% SFC diet. The value of PUN is usually used to indicate the efficiency of N utilization in the body, and MUN is used as an indicator of protein utilization and a predictor of N excretion (Kauffman and St-Pierre, 2001). The greatest PUN and MUN values were observed in cows fed the 40% SFC treatment diet.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication December 17, 2007. Accepted for publication June 23, 2008.
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