Effects of pellet diameter during and after lactation on feed intake of piglets pre- and postweaning 1

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1 Published December 12, 2014 Effects of pellet diameter during and after lactation on feed intake of piglets pre- and postweaning 1 H. van den Brand,* 2 D. Wamsteeker,* M. Oostindjer,* L. C. M. van Enckevort, A. F. B. van der Poel, B. Kemp,* and J. E. Bolhuis* *Adaptation Physiology Group, Department of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH, Wageningen, The Netherlands; Denkavit Nederland B.V., P.O. Box 5, 3780 BA, Voorthuizen, The Netherlands; and Animal Nutrition Group, Department of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH, Wageningen, The Netherlands ABSTRACT: Effects of 2 pellet diameters for piglets pre- and postweaning on feed intake, BW, and feedrelated behavior were studied in 3 experiments. In Exp. 1, 19 litters were provided with pellets of 2 and 12 mm in diameter in a choice-feeding setup from d 4 of lactation onward. From d 4 to 18, piglets preferred the 12-mm diameter pellet over the 2-mm diameter pellet (519 vs. 168 g/pen; P < 0.001). In Exp. 2, 39 litters were provided with creep feed of either 2- or 10-mm diameter pellets. Feed intake from d 3 to 17 was higher in litters provided the 10-mm diameter pellet than the 2-mm diameter pellet (1,752 vs. 1,101 g/pen; P < 0.001). Piglet BW at weaning did not differ between treatments. Treatment day of lactation interactions were found for time spent eating, interest in eating, and time spent suckling. Time spent eating and interest in eating increased with time. This increase was lower in the litters provided with the 10-mm diameter pellet. Time spent suckling remained the same in litters provided with 2-mm diameter pellets but decreased in time in litters provided the 10-mm diameter pellets. Experiment 3 was set up as a 2 2 factorial design with pellet diameter both pre- and postweaning as factors. During lactation, 18 litters were provided creep feed of either 2 or 12 mm in pellet diameter. At weaning, each litter was split into 2 comparable half litters and each half litter was provided with feed of 2 or 12 mm in diameter. Feed intake was higher in the 12-mm diameter pellet litters than in the 2-mm ones from d 4 to 11 of lactation (P < 0.01). Pellet diameter provided after weaning did not affect BW gain or feed intake. Piglets provided the 12-mm diameter pellet before weaning, however, had a higher BW gain (2,060 vs. 2,606 g/pig; P = 0.003) and feed intake (2,772 vs. 3,173 g/pig; P = 0.04) and a lower feed conversion ratio (P = 0.03) between d 0 and 10 after weaning than piglets provided the 2-mm diameter pellet before weaning. Postweaning pellet diameter had no effect on BW gain or feed intake. Behavior was not affected by pellet diameter pre- and postweaning. We conclude that young piglets (<18 d of age) prefer pellets with a large diameter compared to very small pellets, as currently used in practice. Feed intake and BW gain after weaning were higher in piglets provided with a large pellet diameter during lactation, possibly due to the higher creep feed intake in early lactation. Key words: creep feed, feed intake, lactation, pellet diameter, piglet, weaning 2014 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas The staff of the experimental farm of Wageningen University and Denkavit Nederland B.V. is acknowledged for taking animal care. Fleur Bartels, Meggie Habets, Monique Ooms, Elske de Haas, Anne Raats, Samantha Vos, and Esther van de Hoek are gratefully acknowledged for behavioral observations and technical assistance and Tamme Zandstra for analysis of pellet hardness and durability. 2 Corresponding author: Henry.vandenbrand@wur.nl Received November 20, Accepted June 11, INTRODUCTION Weaning is a stressful event for piglets, associated with a low nutrient intake (Bruininx et al., 2002) and a low and variable growth rate or even weight loss for several days (Pajor et al., 1991). A low postweaning feed intake is associated with impaired intestinal structure and function and increased susceptibility to enteric pathogens, resulting in the occurrence of digestive disorders (e.g., Van Beers-Schreurs, 1996).

2 4146 van den Brand et al. Several studies have demonstrated that creep feed intake of piglets during the suckling period is positively related with early postweaning feed intake and performance (Bruininx et al., 2002; Kuller et al., 2004). However, ingestion of creep feed is often low and varies considerably among and within litters (e.g., Appleby et al., 1991). In attempting to stimulate feed intake in young piglets, most studies focused on feed composition (e.g., Fraser et al., 1994; Pajor et al., 2002; Sulabo et al., 2010b), whereas much less is known about the potential effects of physical feed characteristics. Commercial pellet sizes for piglet creep feed are typically 3 mm or less, in line with the general opinion that smaller diameter pellets promote feed intake in young pigs (e.g., Edge et al., 2005). However, larger feed particles, as commonly ingested in nature, may be more attractive for piglets (A Ness et al., 1997; Edge et al., 2005). Both 5-mm diameter pellets (Edge et al., 2005) and feed in the form of large sow rolls (A Ness et al., 1997) resulted in more feeder-directed exploratory behavior compared to feed with a smaller size. However, preference of piglets during lactation for either small or large particles and effects on feed intake postweaning have not yet been investigated. Aim of this study was to investigate 1) the preference of piglets for large vs. small feed pellets and 2) effects of pellet diameter on feed intake, feed-related behaviors, and growth of piglets during and after lactation. We hypothesized that piglets would be more interested in feed with a larger pellet size, resulting in a higher creep feed intake during and after lactation. MATERIALS AND METHODS Three experiments were performed in which pellets differing in diameter were used. Experiment 1 investigated the preference of piglets for pellets differing in diameter during the lactation period. Experiment 2 investigated the effects of pellet diameter on litter creep feed intake and performance during lactation. Experiment 3 investigated the effects of pellet diameter during lactation and after weaning on postweaning performance. Pellet diameter of the large pellet in Exp. 1 and 3 was 12 mm and was 10 mm in Exp. 2. This diameter was chosen based on the diameter of acorns in nature, which has been shown to be ingested already by young piglets (Meynhardt, 1980), and furthermore on the maximum availability of the matrix by the feed manufacturer. The difference in pellet diameter between Exp. 1 and 3 on the one side and Exp. 2 on the other side was the result of a logistic situation in which in Exp. 2, the 12-mm matrix was not available to produce pellets with large diameter. Because of that we chose the 10-mm matrix. Protocols of experiments were approved by the Animal Use and Care Committee of Wageningen University, The Netherlands. Experiment 1 Experiment 1 was conducted at the experimental farm of Wageningen University, The Netherlands. Nineteen litters of Topigs-20 sows (parity 4 7) in 2 batches were used in a choice-feeding experiment. Within 2 d after birth, litters were standardized by cross-fostering to a litter size of 11 to 13 piglets, taking sex of the piglets into account. From d 4 of lactation onward, piglets were ad libitum provided with both 2- and 12-mm diameter pellets of creep feed, offered in 2 feeders, each having 5 feeding spaces, positioned each at one side of the pen. Feeders were placed on a solid concrete floor. The position of feeders containing the 2- and 12-mm diameter pellets was randomly assigned to each pen. A commercially available creep feed was mixed and pelleted by Research Diet Services (Wijk bij Duurstede, The Netherlands) and pellets from both diameters had the same nutritional composition (NE = 10.4 MJ/kg, CP = g/kg, and ileal digestible lysine = 11.1 g/kg). Pellet length for both the 2- and 12-mm diameter pellets was approximately 10 mm. Pellet hardness, measured with a Kahl hardness device (Thomas and van der Poel, 1996), was tested in 10 pellets per diameter, whereas pellet durability was tested per diameter in 2 batches of 100 g of pellets using a Holmen device (Thomas and van der Poel, 1996; pneumatic procedure; processing time was 0.5 and 2 min and diameter sieve was 1.25 and 10 mm for the 2- and 12- mm diameter pellets, respectively). Weight of the piglets was determined within 24 h after birth and at weaning. Weaning moment was fixed at 1 d per batch and due to variation in birth moment, weaning age varied between 25 and 28 d. Creep feed intake per pen per week per pellet diameter was determined at d 11, 18, and 25 and at weaning. At d 5, 12, and 19, feed-related behavior of individual piglets was scored using 4-min instantaneous scan sampling during 6 h/d. The ethogram is given in Table 1. To investigate interest in feed, the behaviors exploring feed trough, exploring spilled creep feed, eating, eating spilled feed (piglets + sow), exploring spilled feed of the sow, and nosing feed trough of the sow were combined; for interest in drinking, the behaviors drinking and nosing drinking nipple were combined. Experiment 2 Experiment 2 was performed at the experimental farm of Denkavit Nederland B.V., Voorthuizen, The Netherlands. Thirty-nine Topigs 30 sows (parity 1 11) were used in 4 batches. Litters were standardized to 11 to 13 piglets within 2 d after birth by cross-fostering. Piglets were provided creep feed ad libitum from d 3 onward in feeders, having 8 feeding places. Within each batch, litters were paired based on parity of the sow and thereafter 1 litter of each pair was assigned to a creep feed with a pellet diameter of

3 Pellet diameter for suckling piglets 4147 Table 1. Ethogram preweaning (Exp. 1 3) Behavior Description Feed related explorative behavior Exploring feed trough Sniffing or touching piglet feeder without sampling feed Exploring spilled creep feed Sniffing or touching spilled creep feed without sampling feed Exploring feed spilled by sow Sniffing or touching feed spilled by the sow without sampling feed Exploring feed trough sow Sniffing or touching feed trough sow without sampling feed Exploring drink nipple Touching drink nipple in pen Ingestive behavior Eating Eating from feed trough or chewing feed Eating feed spilled by piglets Eating feed spilled from the piglet feeder Eating feed spilled by sow Eating feed spilled by the sow Drinking Drinking from drink nipple in pen Suckling behavior Massaging udder Massaging udder with head/nose Suckling Suckling 2 mm and the other to a creep feed with a pellet diameter of 10 mm. The creep feeder was placed on a slatted iron floor, with a distance among slats of 8 mm. This meant that the 10-mm diameter pellets could not be wasted in the slurry pit, while this was possible for the 2-mm diameter pellets. A commercially available creep feed was mixed and pelleted by Research Diet Services (Wijk bij Duurstede, The Netherlands) and the 2- and 10-mm diameter pellets had the same composition (NE = 12.5 MJ/kg, CP = 200 g/kg, and ileal digestible lysine = 15.2 g/kg). Pellet length for both the 2- and 12-mm diameter pellets was approximately 10 mm. Pellet hardness was measured with a Kahl hardness device in 30 pellets per diameter, whereas pellet durability was tested per diameter in 3 batches of 100 g of pellets using a Holmen device (pneumatic procedure; processing time was 1 min and sieve was 1.25 and 7 mm for the 2- and 10-mm diameter pellets, respectively). Piglets were individually weighed within 24 h after birth and at weaning. Weaning moment was fixed at 1 d per batch and due to variation in birth moment, weaning age varied between 25 and 28 d. Creep feed intake per pen per week was determined at d 10, 17, and 24 and at weaning. At d 8, 15, and 22, behavior of individual piglets was scored using 4-min instantaneous scan sampling during 6 h/d using the same ethogram as in Exp. 1 (Table 1). Experiment 3 Experiment 3 was conducted at the experimental farm of Wageningen University, The Netherlands. Eighteen litters (parity 4 7) of Topigs 20 sows in 1 batch were used. Housing and standardization of the litters was the same as described for Exp. 1. The experiment was setup as a 2 2 factorial arrangement. Factors used were pellet diameter during lactation (2 vs. 12 mm) and pellet diameter after weaning (2 vs. 12 mm). Litters were paired based on parity of the sow and thereafter 1 litter of each pair was assigned to a creep feed with a pellet diameter of 2 mm and the other to a creep feed with a pellet diameter of 12 mm during lactation. Preweaning, weight of the piglets, creep feed intake, and behaviors of the piglets were assessed as described in Exp. 1. Weaning moment was fixed at 1 d and due to variation in birth moment, weaning age varied between 25 and 30 d. At weaning, each litter was split up in 2 comparable half litters, based on sex and BW of the piglets, and thereafter housed per half litter. After weaning, half of each litter received the 2-mm diameter pellets, whereas the other half of the litter received the 12-mm diameter pellets. The same creep feed as in Exp. 1 was used, both before and after weaning, and both feed and water were available ad libitum. Individual BW of the piglets was determined at weaning and at d 7 and 10 postweaning. Creep feed intake per pen was determined at d 2, 3, 4, 5, 7, and 10 postweaning. At d 2 and 8, postweaning behavior was observed for 6 h/d using 4-min instantaneous scan sampling (see Table 2 for ethogram). The prevalence of diarrhea (yes or no) for each individual piglet was examined daily by visual inspection of the area around the anus of the piglet by the same person from d 1 until d 10 after weaning. Any presence of yellow, grey, or watery brown feces around the anus was considered as diarrhea. The total number of days that a piglet suffered from diarrhea within the first 10 d after weaning was calculated and used for analysis (Oostindjer et al., 2010). Statistical Analyses Data of the experiments were averaged or summed per pen before analyses. Residuals were checked and variables were log-transformed if needed to obtain homogeneity of variance. Behavioral proportions were arcsine square root transformed if needed. All statistical analyses were performed with the statistical package SAS (version 9.2; SAS Inst. Inc., Cary, NC). Data are expressed as least square means ± SEM and differences were assumed to be significant at P In Exp. 1, feed intake and behavior were analyzed with a mixed model with pellet diameter, day of lactation, interaction between pellet diameter and week of lactation, and batch as fixed factors. Pen was used as a random effect with compound symmetry as covariance structure. In Exp. 2, litter variables and feed intake (per week and overall) and parity of the sow were analyzed with a GLM with pellet diameter, batch, and their interaction as class factors. Average birth weight per litter was used as a covariate analyzing BW at weaning. The interaction

4 4148 van den Brand et al. Table 2. Ethogram postweaning (Exp. 3) Behavior Description Nonfeed related explorative behavior Exploring floor or fixtures Sniffing, touching, or rooting floor or parts of the pen Chewing Chewing particles other than feed (e.g., feces) or vacuum chewing Play behavior Gamboling; running across the pen with at least 2 piglets Belly nosing Rubbing belly of a pen mate with up and down movements of the snout Manipulating others Nibbling, sucking, chewing, or biting ears tail or other body parts of a pen mate Mounting Placing both front hoofs on the back of a pen mate Aggression Ramming, pushing, or biting pen mate, including mutual fighting Feed related explorative behavior Exploring feed trough Sniffing or touching feeder without sampling feed Exploring spilled feed Nosing drink nipple Ingestive behavior Eating Eating spilled feed Drinking Sniffing or touching spilled feed without sampling feed Touching drink nipple in pen Eating from feed trough or chewing feed Eating feed spilled from the feeder Drinking from drink nipple in pen between pellet diameter and batch was not significant for any of the variables and was therefore removed from the model. Behavior was analyzed with a mixed model with pellet diameter, batch, day, and the interaction between pellet diameter and day as fixed factors. Pen nested within pellet diameter was used as repeated subject with compound symmetry as covariance structure. In Exp. 3, litter variables were analyzed with a GLM, with pellet diameter as class factor. Creep feed intake and behavior during lactation were analyzed with a mixed model with pellet diameter and week of lactation as fixed factors. Pen within pellet diameter was used as repeated subjected and compound symmetry as covariance structure. Postweaning, piglet BW and BW gain were analyzed with a GLM, using pellet diameter before weaning, pellet diameter after weaning, and their interaction as class factors. Because weaning weight differed between pellet diameters, weaning weight was added to the model as a covariate. Feed intake of the piglets after weaning and postweaning behavior were analyzed with a mixed model with pellet diameter before weaning, pellet diameter after weaning, their interaction, and day after weaning as fixed factors. Pen (containing a half litter) within pellet diameter was used as repeated subject and the compound symmetry as covariance structure. Figure 1. Experiment 1. Ratio between 2- and 12-mm diameter pellets during the different weeks of lactation. RESULTS Experiment 1 Hardness of the pellets was 0.8 for the 2-mm and 7.8 kg for the 12-mm diameter pellets (P < 0.001), whereas pellet durability was 94.5 and 88.8%, respectively (P = 0.08). Average (±SEM) birth weight of piglets was 1,366 ± 45 g, weaning weight was 7,645 ± 120 g, and weight gain was 6,179 ± 111 g. Piglets were weaned at d 25.8 ± 0.3 and preweaning mortality was 8.7 ± 3.6%. From d 4 to 18 of lactation, feed intake from 12-mm diameter pellets was higher than from 2-mm diameter pellets (Table 3; difference [Δ] = 53 g/pen from d 4 to 11; P < 0.001; and Δ = 318 g/pen from d 11 18; P < 0.001). Creep feed intake from d 18 to weaning did not differ between 2- and 12-mm diameter pellets. Overall, feed intake per litter during lactation did not differ between the 2- and 12-mm diameter pellet but was 561 g/litter higher for the 12-mm diameter pellets than for the 2-mm diameter pellets (P = 0.27). Ratio in creep feed intake between the 2- and 12-mm diameter pellets increased from 16:84 (d 4 to 11) to 49:51 (d 25 until weaning; Fig. 1). Ratio between 2- and 12-mm diameter pellets consumed during the whole lactation period was 40:60. No interactions between pellet diameter and day of lactation were found for behavioral data. Piglets tended to explore the feed trough containing the 12-mm diameter pellets more often than the feeder of the 2-mm diameter pellets (0.17 vs. 0.11% of time; P = 0.06). Time spent on eating increased with day of lactation (P < 0.001) but was not affected by pellet diameter. Experiment 2 Hardness of the pellets was 5.5 for the 2-mm and 13.9 kg for the 10-mm diameter pellets (P < 0.001), whereas pellet durability was 90.5 and 93.2%, respectively (P = 0.16).

5 Pellet diameter for suckling piglets 4149 Table 3. Effect of creep feed pellet diameter on feed intake during lactation using a choice-feeding setup (Exp. 1; Least square means) Pellet diameter Pooled Item 2 mm 12 mm SEM P-value Feed intake, g/pen d <0.001 d <0.001 d d 25 weaning d 4 weaning 1,187 1, Creep feed intake was significant higher in the first (Δ = 135 g/pen; P < 0.001) and second week (Δ = 516 g/ pen; P = 0.002) after the start of feeding (d 3) in litters provided the 10-mm diameter pellet compared to the litters provided the 2-mm diameter pellet (Table 4). Total creep feed intake per piglet during lactation did not differ between pellet diameters (Δ = 92 g; 15%; P = 0.20). Pellet diameter did not affect piglet weaning weight. Regarding feeding behavior, interactions between pellet diameter and day of lactation were found for eating (P < 0.001), interest in drinking (P < 0.001), interest in eating (P < 0.001), and massaging the udder (P < 0.001; Fig. 2). For these variables, time spent on these behaviors at d 8 of lactation was higher for the 10-mm diameter pellet than for the 2-mm diameter pellet, but the opposite was found at d 22 of lactation. Time spent on chewing and suckling was not affected by pellet diameter but increased (P < 0.001) and decreased (P < 0.001), respectively, by week of lactation (data not shown). Experiment 3 Piglet birth weight, weaning weight, mortality, and litter size at weaning did not differ between the 2- and 12- mm diameter pellet groups (Table 5; P > 0.42). Creep feed intake in the first week after the start of feeding was higher for litters provided with the 12-mm diameter pellet compared to those given the 2-mm diameter pellet (Δ = 90 g/ pen) but did not significantly differ between pellet diameters after d 10 of lactation. Total creep feed intake per piglet during lactation did not differ (Δ = 77 g; 33%; P = 0.23) between the 12-mm and the 2-mm diameter pellet. During lactation there was no interaction between pellet diameter and week of lactation nor was there an effect of pellet diameter on behavior. Time spent eating, chewing, and drinking increased with week of lactation (all P < 0.05), whereas time spent on suckling tended to decrease (P = 0.08) during that period (data not shown). Neither the interaction between pre- and postweaning pellet diameter nor the postweaning pellet diameter affected BW of the piglets or feed intake characteristics Table 4. Effect of creep feed pellet diameter during lactation on creep feed intake litter characteristics (Exp. 2; least square means) Pellet diameter Pooled Item 2 mm 10 mm SEM P-value Number of litters Parity of the sow Litter size after cross-fostering Birth weight piglets, g 1,559 1, Age at weaning, d Litter size at weaning Weaning weight, kg Creep feed intake, g/pen d <0.001 d , d ,358 3, d 24 weaning 2,311 2, d 3 weaning 6,770 8, d 3 weaning, g/weaned pig after weaning (Table 6). Pellet diameter before weaning, however, strongly affected postweaning BW gain. Body weight gain between d 0 and 10 after weaning was higher for piglets fed the 12-mm diameter pellet before weaning than for piglets fed the 2-mm diameter pellet before weaning (2,060 vs. 2,606 g; P = 0.003). This difference remained when weaning weight was used as a covariate (2,127 vs. 2,540 g; P = 0.002). Body weight at d 7 (9,391 vs. 10,195 g; P = 0.09) and 10 (9,992 vs. 10,936 g; P = 0.07) after weaning tended to be higher in piglets fed the 12-mm diameter pellet before weaning compared to piglets fed the 2-mm diameter pellet before weaning. Feed intake from d 0 to 4 after weaning was not affected by pellet diameter pre- and postweaning (Table 6). Feed intake from d 4 to 5 (288 vs. 354 g/piglet; P = 0.02) and from d 5 to 7 (614 vs. 788 g/piglet; P = 0.005) after weaning and total feed intake between d 0 and 10 after weaning (2,772 vs. 3,173 g/piglet; P = 0.04) was higher in piglets fed the 12-mm diameter pellet before weaning compared to piglets fed the 2-mm diameter pellet before weaning, irrespective of the pellet size offered after weaning. Feed conversion ratio (FCR; kg feed intake/kg weight gain) between d 0 and 10 after weaning was lower for piglets fed the 12-mm diameter pellet before weaning compared to piglets fed the 2-mm diameter pellet before weaning (1.24 vs. 1.36, respectively; P = 0.03). Diarrhea score was not affected by pre- or postweaning pellet diameter. Behavior of the piglets after weaning was not affected by pellet diameter pre- or postweaning. Feed exploration, drinking, and manipulation other piglets decreased between d 2 and 8 after weaning (all P < 0.05). Playing, belly nosing, and mounting increased (all P < 0.05) in the same period (data not shown).

6 4150 van den Brand et al. Figure 2. Experiment 2. Effect of pellet diameter during lactation on feeding and drinking behavior (least square means). A) Eating (pooled SEM = 0.23), B) interest in drinking (pooled SEM = 0.08), C) interest in eating (pooled SEM = 0.33), and D) massaging udder (pooled SEM = 0.53). = 2-mm diameter pellet; = 10-mm diameter pellet. Values indicated in the figures are P-values. Note: different y-axis scaling. DISCUSSION Experiment 1 demonstrated that in a choice-feeding setup, piglets during the first 2 wk of lactation prefer creep feed with a large diameter (12 mm) above feed identical in composition but with a small diameter (2 mm). Piglets provided with the larger pellet size creep feed showed more interest in the feeder (Exp. 2), in line with previous studies (A Ness et al., 1997; Edge et al., 2005), particularly in the first weeks of lactation. Moreover, in all 3 experiments, piglets ingested more of the large pellet size creep feed during the first 1 or 2 wk of lactation, in spite of the fact that the hardness of the larger pellets was considerably higher. Jensen and Becker (1965) and Van der Poel et al. (1998) suggested that pigs have a preference for relatively softer pellets compared to harder pellets. This suggests that even with a suboptimal hardness of the pellet, piglets prefer the larger pellet over the smaller pellet in early lactation. The 2-mm diameter pellets could easily pass the slats and get lost in the slurry pit, which was not the case for the larger pellets. Therefore, the higher intake of the larger pellets during early lactation is not due to a higher wastage and might even have been underestimated as the smaller pellets were more easily lost. Large pellets may have promoted an early onset of feed-related exploration and feeding for several reasons. First, as hypothesized by Edge et al. (2005), the large pellets may have stimulated exploratory behavior. The piglets could more easily manipulate the larger pellets on the floor, as these did not pass the slats. Indeed, during behavioral observations, young piglets were seen to move (dropped or spilled) large pellets around and pick them up from the floor by themselves or by another piglet. Under seminatural or natural conditions, wild and domestic piglets have been described to start exploring and ingesting solids early in life, long before the weaning process is fully terminated. For instance, piglets were reported to follow their mothers to feeding sites (Newberry and Wood-Gush, 1986, 1988) and to sample acorns and corn (Meynhardt, 1980) at around 10 to 14 d

7 Pellet diameter for suckling piglets 4151 of age. This early, playful exploration of potential food items could positively affect the onset of independent feeding. In line with this, Kuller et al. (2010) showed that an exploration stimulating feeder enhanced creep feed intake of piglets during lactation. Second, during the weaning process, changes in musculature, bones, and teeth occur that are required for piglets to adapt to independent feeding (Herring and Wineski, 1986; Tucker and Widowski, 2009). It can be speculated that the larger pellets might be easier to handle and ingest because of the immature jaw musculature and oral movements of young piglets (see Herring and Wineski, 1986; German et al., 2006; Popowics and Herring, 2006). Moreover, the chewing on the large pellets may have stimulated motor learning and potentially have facilitated teething. The eruption of premolars in young piglets may have profound effects on their feeding behavior and feed intake (Tucker et al., 2010). During the last 2 wk of lactation the preference for the large pellets disappeared. It seems that once piglets start eating, they can easily generalize using another feed type or size (Oostindjer et al., 2010) or that they, with increasing age, have developed jaw motoric movements enabling the handling and processing of the small pellets (see above). This is supported in the current study by the lack of a difference in feed intake between pellet sizes postweaning. Based on these findings, we conclude that large pellets particularly stimulate the ingestion of solid feed very early in life. Table 5. Effect of creep feed pellet diameter during lactation on feed intake and piglet BW (Exp. 3; Least square means) Pellet diameter Pooled Item 2 mm 12 mm SEM P-value Number of litters 9 9 Parity of the sow Birth weight piglets, g 1,345 1, Litter size after cross-fostering Weaning weight, g 7,909 8, Weaning weight, g 1 8,008 8, Growth, g 6,654 6, Age at weaning, d Litter size at weaning Creep feed intake, g/pen d d d ,383 1, d 25 weaning d 4 weaning 2,549 3, d 4 weaning, g/weaned pig Corrected for birth weight. Experiment 3 shows that the higher feed intake of the 12-mm diameter pellets in early life also positively affected postweaning performance. This can potentially be due to 1) a larger number of eaters in pens provided the larger pellets during lactation or 2) improved adaptation mechanisms in piglets fed the large pellets due to an earlier onset Table 6. Effect of creep feed pellet diameter during lactation and after weaning on feed intake and piglet BW after weaning (Exp. 3; Least square means) Pellet diameter preweaning 2 mm 12 mm Pellet diameter postweaning Pooled P-values 3 2 mm 12 mm 2 mm 12 mm SEM Pre Post Int. Number of half litters Weaning weight (d 0), g 7,869 7,993 8,265 8, Weight d 10, g 9,876 10,107 10,886 10, Weight gain d 0 10, g 2,007 2,114 2,621 2, Weight gain d 0 10, g 1 2,094 2,160 2,574 2, Feed intake, g/piglet d d d d d d , ,182 1, d ,769 2,775 3,230 3, FCR, 4 d Diarrhea score Corrected for weaning weight. 2 Number of days with diarrhea between d 1 and 10 after weaning. 3 Pre = pellet diameter preweaning; Post = pellet diameter postweaning; Int. = interaction between pellet diameter pre- and postweaning. 4 FCR = feed conversion ratio.

8 4152 van den Brand et al. of eating. Apart from stimulating behavioral and motor skills needed for independent feeding, ingestion of solid feed may influence the structure of the gastrointestinal tract and the activity of digestive enzymes (e.g., Appleby et al., 1992; Nabuurs et al., 1993). Experience with the ingestion of solid feed can also be important to increase the acceptance and intake of solid feed after weaning. After weaning, many piglets show a very low feed intake and, as a consequence, a depression in growth and increased incidence of diarrhea (Van Beers-Schreurs, 1996; Madec et al., 1998; King, 2003; King and Pluske, 2003; Vente- Spreeuwenberg and Beynen, 2003). Experience with eating solid feed during the suckling period will prepare the piglet, both behaviorally and physiologically, for the postweaning diet. It has indeed been demonstrated that a higher feed intake during lactation increases feed intake and growth rate postweaning (Bruininx et al., 2002, 2004; Kuller et al., 2004; Berkeveld et al., 2007; Sulabo et al., 2010a). Summed over the whole lactation period, however, feed intake was not significantly different between piglets provided the 2-mm or 10- or 12-mm diameter pellets. The larger pellet only promoted the feed intake very early in lactation (<d 18 of age) when feed intake was still low. Yet preweaning pellet size profoundly increased BW gain and feed intake postweaning and decreased FCR. This suggests that a very early onset of feeding, despite being low and probably nutritionally negligible, may be important to prepare piglets better to cope with the transition at weaning from mother s milk to a solid feed diet. We conclude from these 3 experiments that suckling piglets in early lactation prefer a feed with a large pellet diameter above a pellet with a very small diameter, which consequently results in a higher creep feed intake in early lactation. The pellet diameter provided after weaning did not affect feed intake or BW gain, but piglets fed the large pellet diameter during lactation had a higher feed intake and BW gain and a lower FCR than piglets fed the small pellet diameter during lactation. This suggests that creep feed provision should start early in lactation, not for its nutritive value but to stimulate early feed intake. This study also implies that larger pellets in early lactation supports this early feed intake. LITERATURE CITED A Ness, P. J. A., R. I. Horrell, and T. S. Chen The responsiveness of suckling piglets to solid food presented in different forms. In: J. M. Forbes, T. L. J. Lawrence, R. G. Rodway, and M. A. Varley, editors, Animal choices. 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