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Influence of increased feeding frequency on behavior and integument lesions in growing-finishing restricted-fed pigs¹

E. F. Hessel^*,2, M. Wülbers-Mindermann, C. Berg, H. F A. Van den Weghe and B. Algers

^* Institute of Agricultural Engineering, University of Goettingen, D-37075 Goettingen, Germany; and Department of Animal Environment and Health, Swedish University of Agricultural Sciences, SE-532 23 Skara, Sweden; and Swedish Animal Welfare Agency, SE-532 21 Skara, Sweden; and and Research Centre for Animal Production and Technology, University of Goettingen, D-49377 Vechta, Germany

	Abstract

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This study evaluated how feeding frequency affects behavior and the occurrence of skin lesions in growing-finishing pigs. One hundred eighty pigs (27 to 112 kg of BW) were reared in one environmentally controlled room (20 pens; 9 pigs/pen). Pigs in 10 pens were fed 3 times daily (reference group), whereas the others were fed 9 times daily (experimental group). Both groups received the same total amount of liquid feed. Rations were adjusted to the mean pen weights. Behavioral observations (scan sampling, as well as continuous focal pig observations) were made in wk 4, 10, and 14 of the growing-finishing period. After each observation, skin lesions were assessed individually for each pig. Pigs fed 9 times daily tended to lie laterally for less time (P = 0.083) and tended to be active (P = 0.054) during the day, especially in growing-finishing wk 4 (P = 0.007). With continuously observed focal pigs, no differences in time allocations for feeding were found between groups. During feeding in growing-finishing wk 4, focal pigs belonging to the experimental group displayed more aggressive actions (P = 0.019), tended to perform aggressive actions for a longer time (P = 0.076), and tended to be belly-nosed for a longer time (P = 0.083) compared with the reference group. In addition, in growing-finishing wk 14, pigs in the experimental group had greater scores for skin lesions (head, P = 0.001; belly, P < 0.001; caudal part, P < 0.001) and tended to be belly-nosed for a longer time (P = 0.084). In the case of pigs restricted-fed liquid feed, a greater frequency of feeding per day appears to be a condition that results in greater competitive feeding than with a lower feeding frequency.

Key Words: feeding behavior • feeding frequency • pig • skin lesions • social behavior

	INTRODUCTION

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Pigs living in a seminatural environment (including grass and woodland) spend 20% of the daylight period rooting and 30% grazing (Stolba and Wood-Gush, 1989).

In contrast, pigs that are restricted-fed and are housed conventionally spend only a few minutes each day for feeding when the feed is portioned out 2 to 3 times per day. This leads to a reduction in opportunities to satisfy chewing and biting needs and results in the sucking and nibbling of pen companions (Van Putten, 1978). Botermans et al. (2000b) demonstrated that many small meals, instead of 1 large meal per day, trigger a greater output of enzymes from the exocrine pancreas. The repeated intake of small portions of feed positively influences the digestibility of the feed (De Haer and De Vries, 1993). Frequent small meals have also been observed to result in a greater lean tissue content of the carcass (De Haer et al., 1993; Raemaekers et al., 1999).

Competition for food sources is a component of the behavior patterns displayed by pigs (Van Putten, 1978). In a study by Nielsen et al. (1996), a greater number of visits to the feeder was found to be positively correlated with less competition. Botermans et al. (2000a) reported more skin injuries and more forced withdrawals from the feeder in a highly competitive environment. From a welfare point of view, feeding systems resulting in a high level of competition may be detrimental when all individual pigs in the pens are taken into account, even though it is possible, on average, to achieve acceptable production results (Georgsson and Svendsen, 2002).

In this study, the hypothesis tested was that increasing feeding frequency facilitates the performance of natural behavior to a greater degree, thereby resulting in improved pig well-being, e.g., they would be more active, display fewer aggressive interactions and fewer skin lesions, compared with pigs fed less often. Therefore, this study focused on the influences of different feeding frequencies on behavior and integument lesions of growing-finishing pigs.

	MATERIALS AND METHODS

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Experimental Design
A total of 180 crossbred pigs [(Swedish Landrace x Swedish Yorkshire) x Hampshire] from 4 commercial pig herds were raised from an average BW of 27 to 112 kg at the Swedish University of Agricultural Sciences experimental station in southwest Sweden. The Research Animal Ethics Committee belonging to the Swedish Animal Welfare Agency, which is an official authority under the Swedish Ministry of Agriculture, approved the design of the study.

Pigs were weaned at 5 wk of age and moved to the growing-finishing unit at 14 wk of age. Pigs were randomly allocated to 2 treatment groups according to sex, BW, and herd of origin. All pigs were reared in groups of 9 animals/pen in one environmentally controlled room. Each pen was divided into 3 functional areas: the trough area (3.00 x 0.30 m), the lying area with concrete floor (3.00 x 1.80 m), and the dunging area with slatted floor (1.50 x 1.20 m). Pens measured 7.20 m² with a stocking density of 0.8 m²/pig, and trough space was, on average, 0.33 m/pig. Every day after the morning feeding period, between 0900 and 0930, the lying area was cleaned, and about 2 kg of chopped straw was scattered on the cleaned lying area of all pens.

Feeding.
All pigs received the same amount and type of feed each day. The feed was provided as a liquid, based on a compound feed for fattening pigs mixed with whey and water. The ratio between feed and whey plus water was 1 part feed:3 parts whey plus water. In total, 19% of the energy in the liquid feed mixture came from the whey. The CP content in the compound feed was analyzed to be 180 g/kg of feed, with an energy level of 12.6 MJ of ME/kg (DM basis). The analyzed Lys level was 10.9 g/kg of feed (DM basis), and the total amounts of Met and Thr were calculated to be 34 and 59% of the dietary Lys level, respectively. Pigs were restricted-fed in a trough, with a daily feed ratio of ME of 16.5, 19.0, 24.1, 29.0, and 34.1 MJ at 25, 30, 40, 50, and 60 kg of BW and thereafter to slaughter, respectively (based on Andersson, 1985). The feed ratio was calculated from the average BW of the pigs in each pen.

Pigs from 10 pens were fed 3 times daily (reference group), and pigs from the other 10 pens were fed 9 times daily (experimental group; Table 1). To provide a clear distinction compared with conventional feeding, the feeding frequency was increased from 3 to 9 meals/d. In the reference group, pigs received 1/3 of their daily ration per serving; in the experimental group, pigs were fed 1/9 of their daily ration per serving. During the complete growing-finishing period, a check was made on a daily basis to establish whether the pigs actually consumed their feed after each feeding period (morning, midday, evening). If the pigs did not empty the trough, the amount of feed was reduced in the next feeding period. In the behavioral observation periods, pigs in all pens emptied their troughs completely.

Six behaviors were recorded using scan sampling of diurnal behavior: standing, sitting, feeding, lying sternal, lying inclined, and lying lateral. In total, 12 behaviors of focal pigs were recorded continuously during the morning feeding period: standing, sitting, feeding, lying sternal, lying inclined, lying lateral, walking, as well as the additional behaviors rooting, belly-nosing, being belly-nosed, and the aggressive and displacement activities.

Standing behavior was defined as having taken place when the animal adopted an upright position with legs extended. Lying was defined to include lateral (on the side with all legs extended), inclined (lying not completely on the side, but with legs partly extended), or sternal (upright on the chest) recumbency, and involved contact of the body with the ground. Sitting behavior was defined as when the caudal portion of the body trunk was in contact with and supported by the ground. Feeding behavior was when the pig was standing at the trough with its head down. The head could be either in the trough or in front of the trough when pigs ate spilled feed. Walking behavior included any actions in which the pig moved at least 2 steps. Rooting behavior included pushing and sniffing movements, with the snout at floor level beyond the trough. Belly-nosing behavior was when the pig performed rooting snout movements toward the belly of a pen-mate. Being belly-nosed was when a pig was belly-nosed by pen-mates. Antagonistic behavior was defined as physical encounters between at least 2 pigs including head-to-head fights, biting another pig, as well as pushing or knocking another pig with the head. Antagonistic behavior was subdivided into the 2 categories aggression and displacement. The superior pig of a physical encounter counted for aggressive behavior. In addition, fighting pigs, which were not obviously inferior or superior, counted for aggressive behavior. The inferior pig of a physical encounter, which evaded the aggressor without defending or which was pushed away by a superior pig, counted for displacement.

Lesions of the Integument
After each observation period, the same 2 persons, who were blind to the treatment groups, registered skin lesions in all pigs among the 20 pens observed. The head, belly, and the caudal part of the pig were assessed according to the presence of skin lesions (0 = no lesions; 1 = few lesions; 2 = several lesions; and 3 = many lesions; Svendsen et al., 1990).

Statistics
Statistical analyses were carried out using the PROC GLM and the PROC NPAR1WAY procedures, and verification of a normal distribution was made using the PROC UNIVARIATE procedure of SAS (SAS Inst. Inc., Cary, NC). Data that were collected with scan sampling were aggregated into daily means for each observation day and pen. Consequently, 60 data sets were available for statistical calculations. The GLM procedure was used for evaluating behavioral data, which were normally distributed. The statistical model included the effects of feeding frequency and growing-finishing stage as fixed factors, interactions between the 2, as well as the random effect of pen nested in feeding frequency. Tests of differences between feeding frequencies were carried out with the t-test, in which the mean square of the source pen nested in feeding frequency was used as an error term. These results are presented as least squares means with SE.

For analysis of the behavior of the focal pigs during the morning feeding period, 30,202 data points were available, which were aggregated into sums for each pig and each morning feeding (growing-finishing wk 4, 10, and 14). Thus, 84 data sets were available for statistical analysis. Active, lying, and feeding behaviors of the focal pigs were also analyzed using the GLM procedure. The statistical model considered the effect of feeding frequency and growing-finishing stage as fixed factors, interactions between the 2, as well as the random effect associated with individual pigs nested in feeding frequency. The influence of initial BW (small or large focal pig) on active, lying, and feeding behaviors was tested. Because no effect of BW was found, this was not considered in the model.

Data on additional activities (rooting, belly-nosing, being belly-nosed, aggressiveness, and displacement) was logarithmically transformed into a normal distribution and analyzed using the GLM procedure. The statistical model considered the effect of feeding frequency, growing-finishing stage, and BW as fixed factors, the feeding frequency x growing-finishing stage and feeding frequency x BW interactions, as well as the random effect associated with individual pigs nested in feeding frequency and BW.

Data on integument lesions were not normally distributed. With these data, statistical analyses were carried out using the NPAR1WAY procedure to consider the influence of feeding frequency, growing-finishing stage, and initial BW (Wilcoxon-Test). These results are presented as means and SD.

	RESULTS

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Diurnal Behavior
The behavior of pigs from 20 pens was analyzed over a 24-h period in wk 4, 9, and 14 of the growing-finishing period. In this study, pigs from both groups were sitting less than 1% of the daytime period. Therefore, the categories sitting and standing were subsumed under the single category of active. Compared with pigs in the reference group (active time: 2.7 h/d), pigs fed 9 times daily were more active (P = 0.021) with 3.0 h/d (Table 2). Feeding time means were only 3.7% per day (53 min/ d) for the reference group and 4.7%/d (68 min/d) for the experimental group. Pigs fed 9 times daily spent 15 min longer (P < 0.001) feeding compared with the pigs fed 3 times daily. Pigs from both groups spent the greatest amount of time each day in a lying position. Animals in the reference group lay 84.6% (20.3 h), and pigs in the experimental group lay 81.5% (19.6 h) of the day. By increasing feeding frequency from 3 to 9 times daily, the period when pigs were lying was reduced by 45 min. Lying was subdivided into 3 positions, of which only lying lateral tended to differ (P = 0.083) between the 2 groups. Pigs in the reference group lay 1 h longer on their side per day than pigs in the experimental group. An interaction between feeding frequency and growing-finishing period was only found for active behavior. In growing/finishing wk 4, pigs in the experimental group displayed more (P = 0.007) active behavior (4.5 h/day) compared with the pigs in the reference group (3.4 h/ d). In growing-finishing wk 10 and 14, no differences for active behavior were found between the 2 groups.

Other Behavior Exhibited by Focal Pigs
Feeding Frequency.
Rooting was the most frequently observed additional activity. During the morning feeding period, in growing-finishing wk 4, 10, and 14, pigs fed 9 times daily tended to spend more time rooting than those fed 3 times daily. Between both groups, no differences were found in growing-finishing wk 4, 10, and 14 for belly-nosing. In the experimental group, pigs tended to be belly-nosed longer by pen companions in growing-finishing wk 4 (P = 0.083) and wk 14 (P = 0.084; Table 4).

No differences were found between the 2 groups in relation to time budgets and frequency of displacements (Table 5). Moreover, groups did not differ with regard to the time budgets of aggressive acts, though the aggressive behavior of focal pigs in the experimental group tended to last longer in wk 4 of the growing period than that of focal pigs in the reference group (P = 0.076). Frequency for aggressive behavior only differed between the groups at the beginning of the growing period (P = 0.019).

Integument
In growing-finishing wk 4 and 10, skin lesions of the head and belly of pigs did not differ between the groups (Table 7). In both treatments groups, skin lesions of the caudal part of pigs were at a lower level compared with the head and belly, but pigs in the experimental group showed greater lesion scores in growing-finishing wk 4 (P = 0.048) and tended to do so in wk 10 (P = 0.058).

	DISCUSSION

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Restricted feeding of liquid diets is common in large, growing-finishing units. The advantage of liquid feeding is that whey and other liquid agricultural byproducts can be used as feed. In most cases, liquid feed is provided restrictedly to the pigs in a trough, which has enough eating places for all the pigs to eat simultaneously. However, more aggressive interactions were displayed when pigs were restricted-fed than when they had ad libitum access (Vargas Vargas et al., 1987). Nevertheless, in practice, in many pig facilities, it is not feasible to give pigs ad libitum access to feed during the entire growing-finishing period because of the lower carcass meat percentage and impaired feed conversion ratio (Leymaster and Mersmann, 1991). In the current study, pigs were fed liquid feed restrictedly; only feeding frequency differed between the reference and experimental groups.

By raising the feeding frequency from 3 to 9 times daily, active behavior (sitting and standing) increased in duration by 46 min/d in growing-finishing wk 4. Kracht et al. (1982) compared 2 feedings/d and 3 feedings/d for growing-finishing pigs fed liquid feed. They analyzed the behavior of pigs weighing about 60 and 100 kg and reported that raising the feeding frequency from 2 to 3 feeding/d led to an increase in active behavior and a reduction in rest periods of 60-kg pigs. As in the study presented here, Kracht et al. (1982) did not find differences in active and lying behavior of 100-kg pigs. In this study, pigs lay 1 h less on the side in the experimental group compared with the reference group. According to Van Putten (1978), different lying postures reflect different degrees of relaxation. The resting behavior of pigs begins with sternal lying, passes into inclined lying, and ends in lateral lying, in which the pigs show the greatest relaxation. The lower ratio of pigs lying lateral in the experimental group might be due to interruption of resting behavior brought about by a new feed serving, after the first and second meal, during each feeding period.

Results of the observation of behavior using scan sampling revealed that pigs fed 3 times daily spent 3.7% (53 min) and pigs fed 9 times daily spent 4.6% (66 min) of their time feeding each day. Continuous observation of focal pigs during the morning feeding period did not establish differences in feeding time between the 2 feeding regimes.

Both behavior analyses using scan sampling and continuous observation of focal pigs were always made on the same observation day. For a short-term behavior such as feeding, continuous observations are more precise than the time sampling method with a 5-min interval.

During each feeding period (morning, midday, evening), pigs from both feeding groups were fed the same amount of feed, but in the reference group, feed was dispensed once, whereas in the experimental group the feed was administered at 3 intervals. Neither of these treatments affected feeding time. In agreement with this finding, Kracht et al. (1982) found that changing feeding frequency from 2 to 3 times a day did not result in longer daily feeding periods. De Haer and Merks (1992) established different feed intake patterns among group-housed pigs compared with pigs kept individually. Group-housed pigs ate faster and had a greater feed intake per meal, but had fewer meals per day, less eating time per day, and a lower daily feed intake than pigs housed individually. In their view, social interactions are responsible for these results. The competition for feed causes pigs housed in groups to eat more quickly. Baxter (1986) found that 90% of all aggressive interactions between pigs occur during feeding. Aggression is caused by competition. Such behavior comprises fighting for both a rank in the group when feeding and for the limited pen area. When feeding space is limited, competition has the most disadvantageous effect for the smallest pigs (Botermans et al., 2000b). Georgsson and Svendsen (2002) reported that the smallest pigs showed a different feed-intake pattern with greater competition within the pen; they ate less and most of their daily intake was consumed during the night, which appeared to be the primary explanation for the greater variation in performance. In the current study, antagonistic behavior, which is associated with threats, attack, or defense, and includes features of behavior involving escape or passivity, as well as aggression (Fraser and Broom, 1997), was considered as aggression and displacement. Each pig had access to the trough at the same time, but antagonistic actions were still observed during feeding. Independent of feeding frequency, heavier pigs displayed more aggressive actions than small pigs. These actions appear to result from competition for food. Heavier pigs usually have a greater rank within a group (Jensen, 2002). During feeding, they display more aggressive behavior, to obtain the limited amount of feed. In this study, time budgets of antagonistic activities were the lowest at the end of the growing-finishing period. Compared with pigs of the reference group, pigs fed 9 times daily tended to show more antagonistic behavior during feeding in wk 4 of the growing-finishing period. According to Botermans and Svendsen (2000), competition for food leads to an increase in skin injuries. Botermans et al. (2000a) reported more skin injuries and more forced withdrawals from the feeder in a highly competitive environment. The greater injury score for the caudal part of pigs fed 9 times are also in accordance with this assumption. In this study, increasing feeding frequency seemed to increase the risk of skin injuries, especially with greater BW. Though time budgets for aggressive and displacement activities decreased at the end of the finishing period, skin injury scores increased in this period. Pigs used in this study were housed in identical pens. Therefore, the possibility can be excluded that differences in skin lesion scores are due to housing conditions. It is assumed that differences in skin lesion scores are the result of social interactions between pigs. The extent of skin lesions gives indirect information about the social behavior of pigs within 1 pen. Thus, feeding pigs 9 times daily seems to be a more competitive feeding environment, especially toward the end of the growing-finishing period. Surprisingly, antagonistic behavior was reduced during the 2-h morning feeding period at the end of the growing-finishing period, but this short observation time gives only a small time interval for the diurnal antagonistic behavior. Possibly, the antagonistic behavior observed does not reflect the antagonistic behavior of the pigs during the rest of the day. According to Van Putten (1978), pigs engage in more rooting activity after very short and restricted feeding. Rooting is a typical form of pigs’ feeding behavior and is closely linked to exploration behavior (Jensen, 2002). During morning feeding, pigs in the experimental group tended to spend more of the observation period in rooting on the floor. We hypothesize that the pigs were feeding, though no precise distinction between exploring and feeding can be made on the basis of video observations. Perhaps pigs belonging to the reference group showed more rooting behavior because they were still hungry after the first serving of feed and bridged the time gap until the next serving with rooting.

Belly-nosing is a behavior in which pigs perform rooting snout movements directed toward the belly of a pen-mate. This behavior is often interpreted as a sign of a strong motivation to perform suckling activity, and it may be harmful by causing injuries to the object of this behavior (Jensen, 2002). The sum of belly-nosing and being belly-nosed behavior of focal pigs was greater in the experimental group compared with the reference group. In the experimental group, each meal size was one-third as large as one serving to those in the reference group. It is assumed that feeding pigs smaller meal sizes could incite them to search for more food, which, in turn, would result in more rooting and belly-nosing behavior.

A greater frequency of feeding per day, in the case of pigs restricted to liquid feed, appears to be a condition resulting in greater competitive feeding than a lower feeding frequency.

This hypothesis is supported by the results of occurrence and prevalence of gastric lesions in the pigs used in the current study (Persson et al., 2003). In summary, they found that pigs fed 9 times daily had a lower BW gain and a greater score for gastric lesions.

More frequent feedings combined with restricted feeding among group-housed pigs does not seem to improve the well-being of growing-finishing pigs, as is indicated by elevated aggressive behavior and greater skin injury scores in pigs fed 9 times, caused by multiple incidents of competition for food.

	IMPLICATIONS

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A greater frequency of feeding per day, in the case of pigs restricted to liquid feed, appears to result in greater competitive feeding than for pigs on a lower feeding frequency. Increased feeding frequency did not positively affect behavior and the occurrence of skin lesions. Over the course of a day, different feeding frequencies hardly affected feeding time. As a result of the greater competitive feeding conditions provoked by smaller servings, more antagonistic behavior and greater scores for skin lesions were recorded, and more rooting and belly-nosing behaviors were evident. Increasing feeding frequency combined with restricted feeding among group-housed pigs is not appropriate for improving pig welfare. Further research should be carried out to look at possibilities of increasing the time spent feeding, to keep the pigs occupied for a longer period of time, without increasing competition for food.

	Footnotes

 
¹ This project is a part of FOOD 21 research project for sustainable food production, funded by MISTRA. The authors thank Rolf Grahm and Niklas Karlsson at the research station for taking good care of the animals and giving their support during the collection of data.

² Corresponding author: earkena{at}gwdg.de

Received for publication September 8, 2005. Accepted for publication January 25, 2006.

	LITERATURE CITED

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Andersson, K. 1985. SLU-normen en ny utfodringsnorm till slaktsvin. Allmänt 67, Konsulentavdelningen, SLU, Uppsala, Sweden. (in Swedish)

Baxter, M. R. 1986. The design of feeding environment for the pig. Ph. D. Thesis, Univ. Aberdeen, UK.

Botermans, J. A. M., L. Georgsson, B. R. Westström, A.-Ch. Olsson, and J. Svendsen. 2000a. Effect of feeding environment on performance, injuries, plasma cortisol and behaviour in growing-finishing pigs: Studies on individual pigs housed in groups. Acta Agric. Scand. 50:250–262.

Botermans, J. M. A., M. S. Hedemann, M. Sörhede-Vinzell, C.-H. Erlandsson-Albertsson, J. Svendsen, L. Evilevitch, and S. G. Pierzynowski. 2000b. The effect of feeding time (day versus night) and feeding frequency on pancreatic secretion in pigs. J. Anim. Physiol. Anim. Nutr. 83:24–35.

Botermans, J. A. M., and J. Svendsen. 2000. Effect of feeding environment on performance, injuries and behaviour in growing-finishing pigs. Acta Agric. Scand. 50:237–249.

De Haer, L. C. M., and A. G. De Vries. 1993. Feed intake patterns and feeding digestibility in growing pigs housed individually or in groups. Livest. Prod. Sci. 33:277–292.

De Haer, L. C. M., P. Luiting, and H. L. M. Aarts. 1993. Relations among individual (residual) feed intake, growth performance and feed intake pattern of growing pigs in group housing. Livest. Prod. Sci. 36:233–253.

De Haer, L. C. M., and J. W. M. Merks. 1992. Patterns of daily food intake in growing pigs. Anim. Prod. 54:95–104.

Fraser, A. F., and D. M. Broom. 1997. Glossary of terms relevant to farm animal behaviour and welfare. Pages 385–391 in Farm Animal Behavior and Welfare. 3rd ed. CAB Int., Oxon, UK.

Georgsson, L., and J. Svendsen. 2002. Degree of competition at feeding differentially affects behaviour and performance of group-housed growing-finishing pigs of different relative weights. J. Anim. Sci. 80:376–383.[Abstract/Free Full Text]

Jensen, P. 2002. Behaviour of pigs. Pages 159–172 in The Ethology of Domestic Animals. P. Jensen, ed. CAB Int., Oxon, UK.

Kracht, W., H.-O. Ohle, W. Matzke, and G. Bolduan. 1982. Untersuchungen zur Auswirkung der Fütterungsfrequenz auf die Mast-leistung und das Verhalten der Schweine. Tierzucht 36:276–279. (in German)

Leymaster, K. A., and H. J. Mersmann. 1991. Effect of limited feed intake on growth of subcutaneous adipose tissue layers and on carcass composition in swine. J. Anim. Sci. 69:2837–2843.[Abstract]

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Persson, E., M. Wülbers-Mindermann, C. Berg, and B. Algers. 2003. How does feeding frequency influence performance and prevalence of gastric lesions in fattening pigs? Pages 773–774 in Programme Book of the Joint Conference of ECPA—ECPLF. A. Werner, and A. Jarfe, ed. Wageningen Academic Publishers, Wageningen, The Netherlands.

Raemaekers, P. J. L. J, W. G. M. Swinkels, J. H. Huiskes, and M. W. A. Verstegen. 1999. Eating traits in relation to performance and carcass traits of restrictedly fed group-housed finishing pigs. Anim. Sci. 68:399–405.

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This Article Abstract Full Text (PDF) Erratum An erratum has been published Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hessel, E. F. Articles by Algers, B. Search for Related Content PubMed PubMed Citation Articles by Hessel, E. F. Articles by Algers, B.