J. Dairy Sci. 2009. 92:1272-1280. doi:10.3168/jds.2008-1443
© 2009 American Dairy Science Association ®
Forced traffic in automatic milking systems effectively reduces the need to get cows, but alters eating behavior and does not improve milk yield of dairy cattle
A. Bach*,
,1,
M. Devant,
C. Igleasias
and
A. Ferrer
* Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
Grup de Recerca en Nutrició, Maneig, i Benestar Animal, Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Unitat de Remugants, 08140 Caldes de Montbui, Spain
Servicio de Mejora Ganadera, Diputació de Girona, 17121 Monells, Spain
1 Corresponding author: alex.bach{at}irta.es
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ABSTRACT
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Eighty-five lactating Holstein dairy cows in loose housing conditions in 2 symmetrical pens, each containing 28 feeding places, 3 waterers, and 1 automatic milking system (AMS), were used to evaluate the effects of the traffic type imposed on lactating cows through an AMS on milking frequency, feeding behavior, and milk production. The study was a crossover design with 2 periods and 2 treatments. Each period lasted 3 mo, with 1 mo of adaptation within each period. All cows were fed a partial mixed ration twice daily and up to 3 kg/d of a concentrate during the visits to the AMS. Treatments consisted of allowing free traffic of cows throughout the pen or forcing cows to pass through the AMS to access the feed troughs (forced traffic). Individual eating behavior and feed consumption were continuously monitored throughout the study using a computerized system. Individual milk production was recorded at each milking, and milk composition was recorded monthly. In addition, the number of cows brought to the AMS was recorded. The number of daily meals was less, whereas meal duration and meal size were greater with forced traffic (6.6 ± 0.3 meals/d, 20.4 ± 0.65 min/meal, and 2.7 ± 0.09 kg/meal, respectively) than with free traffic (10.1 ± 0.3 meals/d, 15.7 ± 0.65 min/meal, and 1.8 ± 0.09 kg/meal, respectively). Total dry matter intake (21.1 ± 0.5 and 20.4 ± 0.58 kg/d, respectively) and milk production (29.8 ± 0.79 and 30.9 ± 0.79 kg/d, respectively) were similar in the 2 systems. The number of voluntary and total daily milkings was greater with forced traffic (2.4 ± 0.04 and 2.5 ± 0.06 milkings/d, respectively) than with free traffic (1.7 ± 0.06 and 2.2 ± 0.04 milkings/d, respectively). Forced traffic improved the number of voluntary milkings, but altered milk quality and eating behavior of dairy cattle.
Key Words: behavior • feeding • management • traffic
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INTRODUCTION
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The number of dairy enterprises with automatic milking systems (AMS) has steadily increased in Europe in recent years. One of the most common reasons for producers to invest in AMS is the expectation of a decreased need for labor and an increase in milking frequency, which should positively affect milk production (Wagner-Storch and Palmer, 2003). Still, AMS result in large variation in milking intervals because cows do not visit the AMS the same number of times nor at the same time of the day throughout their lactation, forcing the udders to store different amounts of milk depending on the regularity of the actual milking intervals. Irregular milking or visits to the AMS impairs milk production, especially in multiparous cows (Bach and Busto, 2005). Svennersten-Sjaunja and Pettersson (2008) evaluated the advantages and disadvantages of AMS and concluded that establishing adequate cow traffic was essential to attain an optimal number of milking visits. To improve the number of visits and decrease the need for labor and variation in milking intervals, AMS manufacturers frequently recommend offering high amounts of concentrate, but there is no scientific evidence that this practice is effective (Halachmi et al., 2005; Bach et al., 2007). Another proposed alternative consists of forcing cows to visit the AMS before they can reach the feedbunk. Ketelaar-de Lauwere et al. (1998) compared a free-traffic with a forced-traffic scheme in a simulated AMS and reported that the forced-traffic scheme increased the number of visits to the AMS. Hermans et al. (2003) compared a forced-traffic with a semi-forced-traffic scheme where cows had access to a TMR but had to visit the AMS to gain access to additional concentrate after an elapsed time since a previous milking. Those researchers concluded that the semi-forced traffic was preferred over forced traffic, although no differences were found in milk production. More recently, Melin et al. (2007) reported that forced traffic resulted in negative effects on feed intake and cow welfare compared with free traffic. In addition, forced traffic may result in long waiting lines, which may have a negative effect on cow welfare, especially for animals with a low social rank (Thune, 2000).
The studies that directly compare free- vs. forced-traffic schemes are available only as summaries (Metz-Stefanowska et al., 1992; Harms et al., 2001; Forsberg et al., 2002) except for that of Melin et al. (2007). None of the available studies on traffic schemes focus on the economic problem (i.e., labor costs) associated with the need of getting cows to the AMS. In addition, these previous studies did not evaluate potential changes in milk components with the 2 types of traffic. The objective was to evaluate the consequences of a forced- or a free-traffic scheme imposed through an AMS on milking frequency, obtaining cow needs, feeding behavior, and milk production and composition of dairy cattle.
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MATERIALS AND METHODS
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Animals and Treatments
Eighty-five lactating Holstein dairy cows (DIM 203 ± 2.53, mean ± SE; 44 primiparous and 41 multiparous) were used over a period of 6 mo from November 2006 to May 2007. All cows were kept at the experimental research farm of Institut de Recerca i Tecnologia Agroalimentàries (IRTA) located in Monells (Girona, Spain) in loose housing conditions distributed in 2 symmetrical pens, each containing 28 feeding places, 3 waterers (200 x 60 cm and 140 x 45 cm), and 1 AMS (VMS, DeLaval, Tumba, Sweden). Each pen held about 50 animals at any time, but not all animals were included in the study because their stage of lactation would not allow them to be present in both periods. The 85 cows were present throughout the entire experiment, 42 in 1 pen and 43 cows in the other. The maximum number of animals at any time in each pen was 53 cows. Parity and DIM were evenly distributed in both pens, not only among the 85 cows, but also considering the rest of the cohorts not included in the analysis. On average, during the duration of the study, 1 pen held 52 cows, 40% primiparous and 60% multiparous, with an average DIM of 173 d, and the other pen held 53 cows, 43% primiparous, and 57% multiparous, with an average DIM of 173 d. Because DIM might affect the need for cows to visit the AMS, DIM distributions for the entire duration for all cows that participated in each pen are in Figure 1
. Cows were on straw bedding (replaced every 2 d) and milked with an AMS. Animals were maintained and handled under the supervision of the Animal Care Committee of IRTA. All animals received the same partial mixed ration (PMR) and the same concentrate at the AMS (Table 1). Cows were fed the PMR twice daily (to attain 3% orts) at 0800 and 1600 h. In addition to the PMR, cows received up to 3 kg/d of concentrate (containing 50% corn and 50% soybean meal, as-fed basis) during the visits to the AMS.
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Figure 1. Distribution of DIM of cows in pen 1 and pen 2 at the beginning of the study to evaluate a free- or forced-traffic treatment for cows milked with an automatic milking system.
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Table 1. Ingredient and nutrient composition of the partial mixed ration and concentrate offered during automatic milkings
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Treatments were applied to each pen following a crossover design with 2 periods and 2 treatments. Each period lasted 3 mo, with 1 mo of adaptation at the beginning of the first period and 1 mo of adaptation between the end of the first period and the beginning of the second period (6 mo total). Treatments consisted of allowing free traffic of cows throughout the pen or forcing cows to pass through the AMS before access to the feed troughs could be reached (forced traffic). The forced-traffic treatment was achieved by installing a physical barrier between the resting area (and entrance to the AMS) and the exercise area and feed troughs (Figure 2). The physical barrier had 2 one-way gates that allowed cow traffic into the resting area, but blocked the access from the resting to the feeding area, forcing the animals through the AMS before they could reach the feed troughs. Regardless of treatment, all cows had free access to the AMS 22.5 h/d (1.5 h/d were needed to clean the AMS). Cows were allowed to access the AMS after 6 h from the previous milking, unless a milking failure occurred, in which case cows would be allowed permission to be milked again immediately. In general, for any particular cow, when the time elapsed since last milking was more than 12 h, that cow would be brought in and milked in the AMS. The milking frequency of each cow was controlled at 0700, 0900, 1230, and 2030 h daily for both treatments. Cows with more than 12 h elapsed since the last milking were fetched and brought to the AMS only at these hours.
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Figure 2. Design of the research facilities used to impose a free- or a forced-traffic to cows milked with an automatic milking system (AMS). The 2 types of cow traffic were applied to both pens in different periods.
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Measurements
Individual eating behavior including time, number, and duration of visits to the feed troughs, as well as individual feed consumption at each visit were continuously monitored throughout the study using a computerized system (Bach et al., 2004). On a daily basis, a grab sample of fresh PMR and a grab sample of refusals from the previous day were obtained to determine DM content of PMR and refusals. Then, assuming that the moisture loss rate of the PMR throughout the day was constant, each meal consumed was adjusted to the predicted DM content corresponding to the time of the day at which consumption occurred. Chemical composition of the PMR and concentrate was determined twice a week. Also, milking frequency and pattern and time of day were recorded. Individual milk production was recorded at each milking by the AMS, and individual milk composition (fat and protein) was determined monthly at an official laboratory (ALLIC, Cabrils, Spain). In addition, the identification number of each cow that was brought to the AMS and time of this event were recorded daily.
Calculations and Statistical Analyses
To group consecutive visits to the feed troughs into a single meal, meal criteria and maximum amount of time between visits to the feed troughs to consider a visit as a part of the same meal were calculated using a model composed of 2 normal distributions resulting from the natural logarithm of time (in seconds) between feed trough visits as described by Bach et al. (2006).
The weekly coefficient of variation (CV) of milking intervals was calculated by dividing the standard deviation of the milking intervals of a given week by the mean milking interval of that week for each individual cow. Thus, there were 12 CV for each cow and period. Energy-corrected milk was calculated by standardizing actual milk production to 3.5 and 3.2% milk fat and protein contents, respectively: ECM, kg = (0.3246 x kg of milk) + (12.86 x kg of milk fat) + (7.04 x kg of milk protein).
All data collected daily (DMI, yield, eating behavior, visits to the AMS) were summarized by week within period. Stage of lactation of each cow was classified as a 4-class ordinal variable using the quartiles of the DIM distribution as cut-offs. The number of involuntary milkings, milkings as a result of fetching cows, and the time elapsed between the exit of the AMS and the first visit to the feed troughs were not normally distributed and these data were log-transformed before conducting the statistical analysis. To ease the interpretation of the results, these data are presented as nontransformed means, but the significance level was obtained from the log-transformed data.
This study followed a crossover design with 2 pens, 2 treatments, and 2 periods. Within each pen there were 42 and 43 cows that were monitored individually for DMI, behavior, milk production, and milk frequency. To correctly account for the dependence or correlation of the measurements from each cow within each pen across time, a 3-level mixed-effects model was used (Rabe-Hesketh and Skrondal, 2005). Level 3 was the pen, level 2 was the cow, and level 1 was the occasion when measurements were obtained (week). Thus, the mixed-effects model accounted for the random effects (1 df) of each pen, period, and each cow within pen, and the fixed categorical effects type of traffic (1 df), parity (primiparous vs. multiparous; 1 df), stage of lactation (3 df), week (11 df), and the 2-way interactions between the type of traffic (free or forced) and week (11 df), stage of lactation (3 df), and parity (1 df). Week entered the model as a repeated measure using a compound symmetry variance-covariance structure. This model yielded a denominator degrees of freedom for the F statistics test for the type of traffic of 82; however, readers are cautioned that the interactions (random) between period and pen and pen and treatment cannot be predicted with the current experimental design and statistical analysis used. This was an unsolvable limitation when trying to assess the effect of forced traffic with 2 AMS. If these random interactions were accounted for, at least 4 robotic milking units and 4 different pens, or conducting the experiment for 2 more periods would be necessary. The first approach was economically unfeasible, and the second was biologically limited because of the length of lactation and duration of each period.
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RESULTS AND DISCUSSION
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Milking Attendance, Milk Production, and Feed Intake
The number of daily visits to the AMS was greater (P < 0.001) for forced traffic than with free traffic (Table 2). Primiparous cows (every 10.47 ± 0.21 h) visited the AMS with a greater frequency (P < 0.05) than multiparous cows (every 11.33 ± 0.22 h) irrespective of the traffic scheme imposed; consequently, the number of daily milkings was greater (P < 0.001) in primiparous than in multiparous cows (2.4 ± 0.04 vs. 2.2 ± 0.04/d, respectively). Previous studies (Ketelaar-de Lauwere et al., 1998; Melin et al., 2007) reported increased milking frequency with forced-traffic compared with free-traffic schemes. Other studies of cow traffic reported a decrease in visits to the AMS when the number of cows was close to the maximum density that the AMS could handle (Harms et al., 2001; Thune et al., 2002). In the current study, each AMS milked about 50 cows, and the maximum milking capacity of the AMS (about 70 cows) was far from being reached.
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Table 2. Number of voluntary, involuntary, and total daily milkings of cows milked with an automatic milking system under a free- or a forced-traffic treatment
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Milking failures are a common problem with AMS. These failures may affect the number of visits and milking intervals of dairy cattle (Stefanowska et al., 2000; Bach and Busto, 2005). In the current study, 8.9% of the total milkings resulted in some type of failure (from 1 to all 4 glands failing to be completely milked). The occurrence of a failure affected the subsequent milking interval. Cows that experienced a failure during milking showed a shorter (P < 0.05) milking interval after the failure (633.8 ± 3.40 min) than when no failure occurred (674.2 ± 11.03 min). Nonetheless, there were no differences in the proportion of milking failures between the types of traffic, and the interaction between the occurrence of a milking failure and the type of traffic was not significant for the subsequent milking interval.
Cows with elapsed times from previous milking <6 h were able to access the AMS but no milking or delivery of concentrate would occur. Overall, 2.4% of the AMS visits fell in this no-milking category. Still, the proportion of no-milking visits to the AMS was greater (P < 0.05) for the forced- than with the free-traffic treatment (3.4 vs. 1.4%, respectively). This difference was likely because of the urge of cows under the forced-traffic treatment to gain access to feed and water.
The difference in milking attendance between the traffic situations in daily milkings was greater when voluntary visits were considered. Overall, 51% of the involuntary (fetching cows for milking) visits occurred at 0700 h, 36% at 0900 h, 11% at 1230 h, and the remaining 2% at 2030 h, with this pattern being similar in both traffic situations. Cows on the free-traffic treatment had to be fetched 0.5 times daily, whereas cows on the forced-traffic treatment had to be fetched for milking 0.1 times a day (Table 2
). Therefore, forced traffic not only increased the number of voluntary milkings, but effectively diminished the need for bringing cows to the AMS. The reduction in the need to fetch cows with the forced- compared with the free-traffic treatment was not affected by parity, stage of lactation, or week of study. However, the number of voluntary visits to the AMS was greater (P < 0.001) and the number of involuntary milkings was less (P < 0.001) in primiparous (2.2 ± 0.06 and 0.2 ± 0.05/d, respectively) than in multiparous (1.8 ± 0.07 and 0.4 ± 0.04/d, respectively) cows.
Because of the increased number of daily milkings, milking interval was reduced (P < 0.001) with forced traffic compared with free traffic (Table 2). Despite the increased milking frequency and number of voluntary milkings, daily milk production was not greater (P = 0.32) with the forced- than with the free-traffic situation (Table 3). This lack of response could be related, in part, to the variation in milking frequency. Despite the shorter milking interval with forced traffic, the weekly CV of milking intervals was greater with the forced-traffic than with the free-traffic situation (Table 2). The increased CV with forced traffic was due to a broader range of milking intervals, with a maximum milking interval of 23.6 h compared with 21.8 h for free traffic. Bach and Busto (2005) reported that increases in variation of milking intervals negatively affected milk yield.
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Table 3. Dry matter intake and milk production of cows milked with an automatic milking system as influenced by the type of cow traffic imposed
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Consumption of PMR and total DMI were not different (P = 0.24 and 0.22, respectively) in cows under the free-traffic treatment compared with those in the forced-traffic treatment (Table 3). In contrast, Melin et al. (2007) reported increased concentrate and total DM intake with cows on a forced-traffic scheme compared with a free-traffic scheme. One explanation for this difference could be that cows in the current study had access to a PMR in the feeding area, whereas in the study of Melin et al. (2007), cows only had access to forage. Another explanation could be that in the current study, cows under forced traffic did not have access to water until they accessed the AMS. Several studies reported a decrease in DMI when water access was restricted to steers and lactating cows (Utley et al., 1970; Senn et al., 1996).
The observed changes in milk yield and DMI might lead to the apparent conclusion that efficiency of milk production could be improved in a forced-traffic situation. Nonetheless, milking efficiency should be calculated based on actual milk components rather than crude milk yield (Linn et al., 2004). When ECM was used to determine milk efficiency, no differences were found between the treatments (Table 3). There were no differences in milk efficiency between parities, and the interactions between type of traffic and parity, stage of lactation, and week of study were not significant.
Milk Quality and Eating Behavior
Milk protein content was lower (P = 0.05) in cows under the forced-traffic treatment compared with cows in the free-traffic treatment (Table 3). There was no interaction between traffic scheme and parity on milk components, but primiparous cows had a lower (P < 0.05) milk fat content (3.40 ± 0.08%) than multiparous cows (3.69 ± 0.08%). Melin et al. (2005) reported no differences in milk components when comparing several traffic schemes imposed using control gates based on milking interval, but to our knowledge, there are no reports in the literature comparing milk components of cows in a free- versus forced-traffic situation. The change in milk protein observed in the current study could be due to the change in eating behavior of cows in the forced-traffic treatment compared with those in the free-traffic treatment (Table 4). In the present study, the total time that cows devoted to eating was similar with both types of traffic, and the eating rate was similar in both situations (Table 4). Contrary to this observation, Hermans et al. (2003) reported that cows on a semi-forced-traffic protocol ate for longer periods than cows on a forced-traffic protocol. Still, other researchers reported a tendency for cows on a forced-traffic scheme to spend less time chewing (Melin et al., 2007) and eating (Ketelaar-de Lauwere et al., 1998) compared with cows on a free-traffic scheme, and Uetake et al. (1997) reported that a controlled cow traffic imposed on cows milked in an AMS resulted in a decrease in the time spent eating compared with cows milked in a traditional milking parlor. In the current study, primiparous cows (176 ± 6.85 min/d) spent more (P < 0.001) time at the feed bunk than multiparous cows (144 ± 6.05 min/d), but primiparous cows consumed feed more (P < 0.05) slowly than multiparous cows (179 ± 5.54 vs. 214 ± 4.88 g as fed/min, respectively), independently of the traffic scheme imposed. Despite the relatively low number of feed trough spaces (28) in each pen (holding about 50 cows), primiparous cows did not have difficulty accessing feed (Figure 3), and they visited the feed troughs with a similar pattern as multiparous cows within each type of traffic scheme imposed. Feed availability was not likely to affect the results between treatments, as the feed refusals were 73 ± 30.1 and 73 ± 31.2 kg/d for the free- and forced-traffic treatments, respectively, with the minimum amount of feed left at any particular time being 25 and 27 kg for the free- and forced-traffic treatments, respectively.
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Table 4. Feeding behavior at the feed troughs1 of cows milked with an automatic milking system under a free- or a forced-traffic treatment
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Figure 3. Time distribution of the visits to the feed troughs of primiparous and multiparous cows on a free- or a forced-traffic situation. Arrows indicate the times when feed was delivered.
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The number of daily meals was less (P < 0.001) with cows on the forced-traffic treatment compared with the free-traffic treatment (Table 4). Contrary to these findings, other researchers (Ketelaar-de Lauwere et al., 1998; Melin et al., 2007) reported no differences in the number of meals between a simulated free- and a simulated forced-traffic scheme. These discrepancies could be attributed to 1) the duration of the study or 2) the conditions under which the studies were conducted such as a simulation of an AMS with no milking activity or the use of a control gate to direct cow traffic. A decreased number of meals with a forced-traffic situation could be expected because cows would only be able to consume feed after visiting the AMS, whereas in a free-traffic scheme cows could visit the feedbunk at any time. Meal duration was longer (P < 0.001) for cows on the forced- than on the free-traffic treatment. The increase in meal duration with forced traffic could be expected and explained by the longer interval between meals that the cows on this traffic scheme showed compared with cows on the free-traffic treatment. The interactions between type of traffic and week, parity, and stage of lactation did not affect eating behavior.
Although eating rate was not affected by the cow traffic imposed, the amount of feed consumed (meal size) was greater (P < 0.001) with forced-traffic cows (that had long meals) than with free-traffic cows (that had short meals). Cows on water restriction decreased feed consumption (Utley et al., 1970; Senn et al., 1996). This decrease in DMI under water restriction was attributed to a reduction of meal size (Burgos et al., 2001). Cows under the forced-traffic scheme experienced some degree of water restriction, but meal size did not decrease. This increased meal size was probably due to both feed and water restriction and the effect of a potential mild dehydration on feeding behavior, which might have been overcome by the effect of a relatively prolonged feed restriction.
The decreased meal frequency in conjunction with longer and larger meals could result in rumen upsets such as rumen acidosis, and this in turn could induce a decrease in milk fat. Both eating and ruminating increase saliva secretion (Cassida and Stokes, 1986) and a reduction of salivary buffer secretion may lead to decreased ruminal pH and altered ruminal fermentation patterns (Mertens, 1997). As observed with eating behavior, DMI was not affected by the interaction between treatment and parity, stage of lactation, and week of study.
The time elapsed between cows leaving the AMS and first visiting the feed troughs (data not shown) was shorter (P < 0.001) on the forced-traffic treatment (12.9 ± 1.06 min) than on the free-traffic treatment (28.2 ± 1.06 min). This shorter interval between milking and visiting the feed troughs was expected, as cows on the forced-traffic treatment probably visited the AMS because of an urge to consume feed.
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CONCLUSIONS
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Forcing cows through an AMS as the only way to access feed is an effective method to increase the daily number of voluntary and total milkings compared with a free-traffic scheme. Nevertheless, forced traffic alters the eating behavior of cows, decreasing the number of daily meals. The increased milking frequency obtained with a forced-traffic scheme is not likely to improve milk production, and milk protein content may be reduced.
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ACKNOWLEDGEMENTS
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The authors thank Ministerio de Educación y Ciencia for partial funding support to conduct this study through the grant AGL2004-07223-C02-01. Special thanks to Natàlia Ràfols (IRTA-Unitat de Remugants, Caldes de Montbui) for her valuable collaboration in this study.
Received for publication June 10, 2008.
Accepted for publication October 29, 2008.
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ABSTRACT
INTRODUCTION
