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1 Institute of Animal Science, Department of Dairy Science, ARO, The Volcani Center, Bet Dagan 50250, Israel
2 Institute of Agricultural Engineering, ARO, The Volcani Center, Bet Dagan 50250, Israel
Corresponding author: J. Miron; e-mail: jmiron{at}volcani.agri.gov.il.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: pelleted soy hulls and gluten feed • starchy grain • feeding behavior • performance of dairy cow
Abbreviation key: AMS = automatic milking systems, CGF = corn gluten feed, ECM = economically corrected milk, HST = high starch pellets, SH = soy hulls, SHCG = SH + CGF 2:1, pellets
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Beyond the context of TMR, an additional issue of interest is whether pellets composed of nonroughage NDF-rich by-products, served as a supplement to high-producing cows, can effectively replace starchy pellets. This issue is of special interest in dairy herds using automatic milking systems (AMS). In AMS, pellets made of starchy grains and containing 17% CP are usually fed individually into the robot at a level of up to 25% of DMI, in order to attract the cows to enter the AMS voluntarily. The rest of the diet (~75% of daily intake) is served free choice as a basic TMR (containing 17% CP) along the feeding lane (Morita et al., 1996; Halachmi, 1999; Wagner-Storch and Palmer, 2003). Concentrates feeding of cows being milked in AMS may allow the consumption of a high quantity of starchy grains within a short period of time. This in turn could affect not only the appetite and feeding behavior of the cows but also the rate and extent of NDF digestibility by ruminal bacteria (Miron et al., 1996; Morita et al., 1996; Friggens et al., 1998), leading to further reduction in voluntary DM and NDF intake and possibly on the utilization for milk fat production.
The hypothesis is that 17% CP-pelleted supplement made of nonroughage by-product rich in readily digestible NDF fraction, such as SH plus CGF (2:1), can successfully replace the starchy pelleted supplement (17% CP) while increasing dietary NDF intake and utilization for milk fat production.
The objective of this study was to examine this hypothesis by conducting in vitro digestibility measurements of either high starch pellets (HST) or pellets composed of SH + CGF 2:1 (SHCG), and by assessing feeding behavior and milking performance of high-producing dairy cows fed these 2 types of pellets as supplements (at 25% of dietary DM) to a basic TMR.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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. The 2 pellets slightly differed in their calculated NEL content (1.86 and 1.94 Mcal of NEL/kg of DM in SHCG pellets and HST pellets, respectively) and were consumed within 10 to 30 min after serving. However, HST pellets were ingested more rapidly by cows, compared to the SHCG pellets. The NEL values of the individual feeds used in this study were provided by the manufacturers and used to summarize the NEL content of the basic TMR and the 2 types of pellets.
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Basic TMR and the 2 kinds of pellets were sampled daily. The basic TMR and pellet samples were pooled on a weekly basis to produce 7 composites. The DMI was determined by oven drying a portion of the basic TMR, and pellets pooled samples at 105°C for 24 h. The weekly pooled samples of basic TMR and 2 types of pellets were oven dried at 60°C for 48 h, ground through a 1 mm screen, and used for the extent and rate of in vitro digestibility evaluation of the DM and NDF fractions and for chemical analyses.
Milk yield was recorded daily by automatic meters (Afimilk, Israel). Milk samples were collected during 3 sequential milkings on Wednesdays of each week during the 7-wk experimental period. Each set of milk samples for each cow was stored at 4°C in the presence of a conservation pill until analyzed for fat content, protein, lactose, urea, and SCC by infrared analysis (Dairy Milk Association Lab., Caesaria, Israel, using Milkoscan 4000, Foss Electric, Hillerød, Denmark).
Chemical Analyses and In Vitro Digestibility
Samples of oven-dried basic TMR and the 2 types of pellets (7 pool samples collected on a weekly basis) were assayed in triplicate for DM and OM (7.007 and 7.009, respectively) (procedures, respectively, in AOAC, 1980), and CP was determined according to a Kjeldahl method (7.021 procedure in AOAC, 1980). The NDF, ADF, and ADL content were determined in the basic TMR, and pellets in triplicate, as well as NDF, analyzed in the in vitro residues according to the method of Van Soest et al. (1991) with 
-amylase, without sodium sulfite, and by employing Ankom apparatus (Ankom Technology Corp., Fairport, NY) for extraction and filtering.
Extent of DM and NDF in vitro digestibility of the 2 pellets was analyzed in each weekly pooled sample in triplicate using 48 h of incubation with rumen fluid followed by an additional 48 h of incubation with HCl and pepsin, according to the 2-stage fermentation technique of Tilley and Terry (1963). Ruminal fluid free of saliva contamination was obtained before morning feeding via esophageal tube from 4 cows fed the SHCG diet and 4 cows fed the HST diet, combined to create one pooled sample and used for the in vitro measurements. Rumen fluid pH was 6.70 in the SHCG cows and 6.53 in the HST cows. Rate of in vitro DM and NDF digestibility of the 2 types of pellets was measured similarly, except that the first stage of incubation was conducted in triplicate during 0, 6, 12, 24, 48, or 72 h of fermentation with rumen fluid followed by an additional 48 h of fermentation with HCl and pepsin. Rate of DM and NDF digestion was determined as the slopes of a first-order kinetic equation describing the regression between loge (residual fraction percentage-undigested fraction percentage) against time of incubation (h), as shown by Mertens and Loften (1980).
Calculations and Statistical Analyses
The daily yield per cow of 4% FCM was calculated (4% FCM [kg] = 0.4 x milk [kg] + 15.0 x milk fat [kg]), and the payment equation (termed economically calculated milk [ECM]) was calculated according to the equation used by the Israeli Dairy Milk Association (2003): ECM (kg) = 9.436 x milk fat (kg) + 22.018 x milk protein (kg).
Differences between the 2 pellets regarding the extent and rate of DM and NDF in vitro digestibility were analyzed statistically (T test) (Little and Hills, 1978).
Data of feeding behavior of the individual cows included number of meals/d, meal duration (min), feeding duration (min/d), extent of feed consumption per meal (kg), rate of meal eating (g/min), and daily DM and NDF intake. Additionally, performance data included milk yield and composition, and BW were reduced to means per cow in the 35 d of the experimental period after a 14-d adaptation period to the diets. These data were analyzed by ANOVA using the general linear model procedure of SAS (1996). Data in Tables 3 and 4 are presented as means of the dietary groups ± standard error of the means. Repeated measures analysis on a weekly basis showed a lack of any effect of the duration of the trial on the significance of behavior and performance data.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). Total NDF content was higher in the SHCG pellets than in the HST pellets (50.1 and 18.8%, respectively), and this was reflected by a higher NDF content of the SHCG ration compared with the HST diet (40.8 and 30.7%, respectively) (Table 2). Both diets contained a similar level of forage NDF (14.6%) (Table 2); however, in the SHCG ration, most NDF was of nonroughage origin (about 64%), whereas in the HST diet, about half of the NDF originated from roughage. This difference in dietary NDF content and origin exerted not only quantitative but also qualitative difference between the 2 diets, since the extent and rate of NDF in vitro digestibility of the added SHCG pellets (81.0 and 5.09%/h, respectively) were significantly higher (P < 0.03) than those of the HST pelleted supplement (65.7 and 4.33%/h) as shown in Table 2. The higher NDF digestibility of the SH pellets is a result of the high digestibility of soy hulls and corn gluten feed NDF-polysaccharides compared with that of NDF obtained from barley and corn grains (Ben-Ghedalia et al., 1987; Miron et al., 2001). On the other hand, the extent and rate of DM in vitro digestibility were higher in the HST pellets (85.3 and 5.97%/h, respectively) than in the SHCG pellets (83.7 and 5.16%/h, respectively) (Table 2). Thus, although the calculated energy and CP content of the 2 diets were almost similar (1.69 to 1.71 Mcal of NEL/kg DM and 17% CP), the above-mentioned quantitative and qualitative differences between the 2 kinds of pellets affected feeding behavior of the cows and their performance, as shown below.
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and Figures 1, 2, and 3. Figures 1 and 2 show that, during short meals (up to 15 min), the eating speed of the 2 diets was about the same, but in longer meals, the cows fed HST tended to consume more feed per meal. For example, in meals that lasted 40 min, the cows fed HST consumed about 14 kg of wet food (9.4 kg DM), whereas the cows fed SHCG ate only about 8 kg of wet food (5.4 kg DM) (Figure 1). Thus, in the SHCG group, 90% of the meals ended with the consumption of up to 5 kg of wet food/meal (3.36 kg DM), whereas in the HST group, 90% of the meals ended with ingestion of up to 6 kg of wet food/meal (4.03 kg DM) (Figure 2).
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, and data summarizing average number of meals per day, duration of meals, and DM consumed per meal and day are shown in Table 3. Cows fed the SHCG pellets ate significantly more meals per day than cows fed HST (14.0 vs. 10.3 meals/d, P < 0.02) (Table 3 and Figure 3); however, duration of average meal was similar in both groups (about 16 ± 0.92 min). The difference in number of meals per day was reflected by longer (P = 0.01) accumulated times in the feeding lane of the cows fed SHCG (223 min/d) compared with the HST group (161 min/d). However, in both groups, most of the meals occurred during the day between 0500 to 1800 h, and the distribution of feeding through the day was dominated by permanent events, including return from milking (0500, 1300, and 2100 h); pellets submission events at 0500, 1100, and 1700 h; and the dispensing time of basic TMR at 1000 h, as reflected by spikes of meals shown in Figure 3. The extra meals of the SH group occurred generally at peak times of feeding and milking mentioned above (Figure 3). This result is contrary to the study of Halachmi (1999), who found that in AMS the cows eventually balanced their meals through the day and night almost equally over the 24-h period. The conflict between studies can be explained by the different triggers that motivated cows to approach the feeding lane. In the present study, the triggers were external stimulating events, including feeding and return from milking, together with social stimulation of other cows, as demonstrated by Metz and Mekking (1978). In the study by Halachmi et al. (1999), the predominant triggers were restriction parameters dictated by the AMS.
The amount of feed consumed per meal by cows fed the 2 types of pellets (Figure 2 and Table 3) was significantly different (P = 0.03). The cows fed HST ingested more food per meal than the SHCG group (2.41 and 1.93 kg of DMI per meal), and this probably reflects both the advantage of the HST pellets in the rate of DM digestibility and NEL content (Table 2), and the fact that the HST pellets were of greater palatability to the cows and were consumed more willingly than the SHCG pellets.
The feeding behavior data in this experiment were in agreement with the study of Friggens et al. (1998), who found that cows fed a high-concentrate TMR had fewer but longer visits to the feeders and ate more feed per visit than did cows consuming a low-concentrate TMR. However, in contrast to our experiment, in the study of Friggens et al. (1998), dietary forage level differed between the 2 TMR, and therefore the cows fed the high-concentrate TMR had higher daily DMI than those fed the low-concentrate TMR.
Although feed-consumption rate per meal was higher in the HST group (Table 3), the accumulative DM and NDF intake per day were significantly higher in the cows fed SHCG (27.1 and 11.1 kg/d, respectively) compared with the HST group (24.8 and 7.61 kg/d, respectively). This difference reflects the longer daily eating duration and higher number of meals per day of cows fed SHCG (Table 3 and Figure 3). The increase in DMI of the SHCG group in this study (Table 3) is in contrast to some previous studies that showed reduced or similar DMI in cows fed SH as a replacement for 18 to 25% of corn grains (Firkins and Eastridge, 1992; Cunningham et al., 1993; Pantoja et al., 1994; Elliot et al., 1995). Possible explanations of the gap between studies are unique factors that were used in the present study, including lower content of roughage (<30%) (Table 1); pelleted supplements instead of TMR feeding system; the use of SH to replace fermentable barley in the diets instead of corn grain; and the higher level of milk production (over 44 kg/d) (Table 4) in the present study.
Three possible explanations are suggested for the differences in voluntary feed intake between the 2 dietary treatments (Table 3): (1) the higher extent and rate of NDF digestion of the SHCG pellets compared with the HST pellets (Table 2) may speed up passage from the rumen and enhance the feed intake of cows fed SHCG (Allen, 1997); (2) consumption of large quantities of starchy pellets per meal by the cows fed HST may inhibit the activity of ruminal cellulolytic population and further decrease the rate and extent of forage-NDF digestion of the basic TMR fed. This inhibitory effect of starchy feeds on NDF digestion occurs also in well-buffered rations of ruminant and is known as the "carbohydrate effect" (Ben-Ghedalia and Solomon, 1987; Miron et al., 1996); and (3) the higher rate and extent of DMI per meal (Figure 1 and Table 3) and DM digestibility of the HST pellets (Table 2) may supply more metabolites to the blood of the cows fed HST that may further reduce hunger feeling and inhibit short-term cow appetite, while increasing the interval between meals and reducing the number of meals per day and accumulated daily duration of feeding, as shown also in the study of Friggers et al. (1998).
Milk Yield and Composition
Average milk and milk-protein yields were similar in the cows fed the SHCG pellets as compared with the HST group (44.9 and 1.37 kg/d vs. 44.3 and 1.41 kg/d, respectively) (Table 4), possibly due to the advantage of the SHCG diet with respect to voluntary DMI (Table 3) that was compensated for by the advantage of the HST group in rate and extent of DM digestibility and calculated NEL content (Table 2). Notwithstanding, average concentration of milk fat and, accordingly, also yields of milk fat and 4% FCM were significantly greater in the SHCG group compared with the cows fed HST (3.31%, 1.49 kg/d, and 40.3kg/d vs. 2.79%, 1.24 kg/d, and 36.3 kg/d, respectively). Consequently, ECM yield tended to be greater in the cows fed SHCG compared with the cows fed HST (44.1 vs. 42.6 kg/d, P = 0.13). The advantage of the SHCG cows in FCM production may be due to the higher daily NDF intake and higher extent of NDF in vitro digestibility of that ration as compared with the HST group (Tables 3 and 2). More digestible cellulose and hemicellulose usually result in the production of more acetate by rumen cellulolytic bacteria (Chesson and Forsberg, 1997), which can be used as a precursor for milk-fat synthesis in the mammary gland. Thus, the positive effect on milk-fat yield obtained in the present study in the SHCG cows may have been the result of both the ingestion of more digestible NDF, cellulose, and hemicellulose components and the favorable conditions for microbial fiber degradation in the rumen of the cows fed the SHCG pellets.
Support for these performance data is given from previous studies that showed that replacement of corn grain with SH (18 to 20% of dietary DM) tended to increase FCM yield in lactating cows (Pantoja et al., 1994; Elliot et al., 1995; Ipharaguerre et al., 2002).
Despite the success of the SHCG pellets to replace HST pellets in the present study, the fact that the HST pellets were consumed more willingly and faster than the SHCG pellets suggests that more efforts should be invested in increasing the palatability of the SHCG pellets before applying this alternative in AMS.
Prediction of DMI
Measuring individual feeding behavior of high-producing cows fed 2 diets differing in source and content of NDF provides an opportunity to evaluate the NRC model for predicting DMI of cows based only on their milk and FCM yields, DIM, and BW data, while ignoring diet composition (NRC, 2001). Table 3 shows the predicted average DMI of cows fed the 2 dietary treatments calculated for each cow according to the model of NRC (2001) in comparison to the actual DMI measured in this study. Data show that the NRC model was quite successful in predicting DMI of the cows fed HST (predicted DMI 24.2 kg/d vs. actual DMI 24.8 kg/d, with a linear coefficient of regression = 0.88). However, when starchy grains were replaced by nonroughage highly digestible NDF by-products, prediction of DMI in the cows fed SHCG was underestimated by 5% and at a lower accuracy (linear coefficient of regression = 0.16).
Thus, it is suggested that prediction of intake based on cow performance, regardless of diet composition (NRC, 2001), is quite accurate for cows fed conventional diets, including the HST diet of the present study but not for rations based on bulky concentrates, such as the SHCG pellets.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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and 2). Data support our hypothesis, suggesting that the SHCG pellets may be recommended for AMS as a replacement for the conventional starchy pellets currently used, while avoiding possible reduction in FCM production.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Received for publication June 11, 2003. Accepted for publication October 10, 2003.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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