Effects of Varying Creep Feed Duration on Pre-weaning and Post-weaning Performance and Behavior of Piglet and Sow

32 sows (Landrace×Yorkshire) and their litters were used to evaluate the effects of varying creep feed duration on pre-weaning, post-weaning performance of piglets and sows. Sows were randomly assigned with 1, 2 or 3+ parities into 1 of 4 treatments. Creep feeding was initiated at day 5, 10 and 15 from birth for treatment 1 (TRT1), 2 (TRT2) and (TRT3), respectively, with a control group provided no creep feed. In this study, TRT1 and TRT2 diets had reduced (p<0.05) the post-weaning diarrhea scores in piglets and the weaning-to-estrus interval and cortisol concentration in sows at weaning time compared with other treatments. Dietary TRT1 led to a higher (p<0.05) epinephrine and norepinephrine concentrations than other treatments. No differences (p>0.05) were noted in suckling, sleeping, fighting frequency and mortality in piglet and eating, standing times, backfat and body weight loss in sows. In conclusion, creep feed initiated from day 5 and 10 reduce diarrhea scores in piglets and benefit the estrus interval in sows compared with those initiated from day 15 and no-creep feeding diets, indicating creep feeding could improve the pigs and sows performance, especially those initiated from day 5 and 10. (


INTRODUCTION
Piglets are given creep feed to fill the gap between their increasing nutrients requirement and nutrients supplied by the lactating sow because of the declining milk production, which may be insufficient to meet the steadily increasing demands from growing piglet.Generally, commercial recommendations on when to initiate creep feeding as early as 2 to 3 day of age to induce piglets to consume solid feed and achieve greater total creep feed consumption throughout lactation.Various studies have demonstrated the beneficial effect of creep feed on post-weaning performance, which is highly dependent on the absolute amount of creep feed consumption (Pajor et al., 1991;Carstensen et al., 2005).However, evidence on the effect of creep feeding duration on feed consumption and growth performance has been limited, and only Klindt (2003) showed that creep feeding from 5 day of age resulted in greater pre-weaning daily gains than creep feeding from 2 day prior to weaning.Recently, Sulabo et al. (2010) suggested creep feeding duration for 13 day (lactation period = 21 d) produced 10% unit more eaters than litters fed creep feed for 6 and 2 day.Bruininx et al. (2002) reported that eaters had more visits to the feeder and concomitantly had a greater rate of feed intake than non-eaters.Therefore, the duration of creep feeding could be an important factor in stimulating more pigs to consume more creep feed and subsequently greater daily gains.
The behavior and reproductive performance of sows is known to be influenced by the metabolic state of the sow and the suckling stimulus of the piglets (Foxcroft, 1992).A variety of factors could influence the behavior, including environmental quality, food quality and piglet behavior in some species (Berger, 1979;Hauser and Fairbanks, 1988).Pajor et al. (2002) also demonstrated that creep feeding cause piglets to consume more solid food and hence vocalize less when nursing frequency declines, which weakens the sow's responses to such calls (Weary et al., 1999).They also suggested that creep feeding can reduce the nutritional load, lactation BW loss and the weaning-toestrus interval.Therefore, the effects of creep feed duration on sows performance was also investigated, in consideration of its potential influence on piglet behavior and nursing-associated vocalization.
Collectively, the objectives of this study were i) to determine the effects of varying duration of creep feeding on the pre-weaning and post-weaning growth performance and behavior of piglets and ii) to determine the effects of varying duration of creep feeding on performance and behavior of sows.

MATERIALS AND METHODS
The experimental protocols employed in this study were approved by the Animal Care and Use Committee of Dankook University.

Animals and housing
A total of 32 sows (Landrace×Yorkshire) and their litters were used in this study.Sows were assigned randomly to 1 of 4 creep feeding groups, with parities of 1, 2 or 3+.At day 107 of gestation, the sows were moved to farrowing crates in an environmentally regulated farrowing house.The mean parity of the sows was 2.6±0.4.Sows were fed on a commercial gestation (2.5 kg) and lactation feed (programmed increased to 7 kg) (Table 1), divided into 2 daily meals.Creep feed (DE: 4,000 kcal/kg; CP: 22%; Lys 1.74%; Met: 0.70%; Ca: 0.81.P: 1.00) was given initiated at day 5, 10 and 15 (weaned at d 21) from birth for treatment 1, 2 and 3, with a control group (TRT 4) provided no creep feed (Table 2).Sows and their offspring were individually housed in farrowing crates (2.4×1.8 m), which were constructed of 1.95 m 2 of solid floor and 2.37 m 2 of slatted floor.This space included a piglet nest equipped with an infrared lamp (500 W), a piglet drinking nipple, and a piglet feeder placed on a dimpled rubber matting to collect any spillage from the feed.The temperature in the farrowing house was maintained at a minimum of 20°C.Drinking nipples provided water ad libitum to both sows the piglets.Litter size at birth varied from 7 to 14 piglets, and was standardized to 10 piglets per litter within 2 day after birth by cross-fostering within each treatment.All piglets received injections of 1 ml of iron dextran and the males were castrated 2 day after birth.At weaning, the sows were relocated to a mating room, with the piglets remaining in the pen for 1 week (weanling pigs), the number of weaning  piglets were recorded.

Measurements
Individual piglet BW was obtained on day 0, 5, 10, 15, and 21 (weaning), and day 7 after weaning to calculate the average daily gain (ADG).Creep feed residuals and general health was checked daily.Sow body weights were checked within a few hours after farrowing and on the day of weaning (21 day), after which the backfat thickness of the sows (6 cm off the midline at the 10 th rib) was measured using a real-time ultrasound instrument (Piglot 105, SFK Technology, Herlev, Denmark).The incidence of diarrhea in piglets was observed and recorded 3 times per day throughout the study.In order to assess the severity of diarrhea, feces from each pig were scored by estimating the moisture content according to the method described by Hart and Dobb (1988).In brief, the scores were as follows: 0, normal, firm feces; 1, possible slight diarrhea; 2, definitely unformed, moderately fluid feces; or 3, very watery and frothy diarrhea.A cumulative diarrhea score per diet and day was then calculated (Montagne et al., 2004).
To assess blood characteristics, the sows were bled via puncture of the vena cava prior to feeding at day 107 of gestation and at weaning (day 21) to determine the concentrations of epinephrine, norepinephrine, and cortisol.Blood samples were collected into non-heparinized tubes (Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ, USA) to obtain serum, which was separated via 30 min of centrifugation at 4,000×g at 4°C, the aliquot was stored at -4°C.The serum was removed and stored at -20°C until being used in cortisol, Norepinephrine (NE) and epinephrine (EPI) analysis.Serum concentrations of cortisol were determined with a standardized solid phase radioimmunoassay kit (Diagnostic Products Corporation, Los Angeles, CA).The NE and EPI were assayed using an ion-exchange purification procedure followed by liquid chromatography with electrochemical detection, as described previously by Hay and Mormède (1997).In brief, the samples were loaded onto cationic columns, and the catecholamines were eluted with boric acid.The eluates were assayed via HPLC with electrochemical detection with an oxidizing potential of +0.65V.The intra-and inter-assay CV were 7.0% and 7.1% for NE and 6.5% and 11.6% for EPI, respectively.
Detection of estrus was conducted twice per day from weaning onward, at 0830 and 1600 every day.A sow was considered to be in estrus when exhibiting a standing response induced by a back pressure test when in the presence of a boar.
Activity in the farrowing crates was recorded by 24 h time-lapse video recording.The video camera was positioned to provide a view of the entire farrowing crate.Behavior was recorded from the commencement of partition to weaning.All behavior of the litter was continuously recorded to determine the time spent by piglets at the creep feeder, sleeping and fighting during lactation.The time spent by sows on eating, and standing was also determined.Nursing was considered to have begun with the sow lying in the nursing posture with at least 80% of the litter in contact with the udder.Nursing was classified as unsuccessful if it was followed by a second nursing episode within 20 min.

Statistical analysis
All data in this experiment were analyzed in accordance with a completely randomized design using the GLM procedure (SAS Inst.Inc. Cary, NC).The individual sow or litter of piglets was used as the experimental unit.For the blood profile data, the initial data was used as a covariate.Differences among treatment means were determined via Duncan's multiple range test, and a probability level of p<0.05 was regarded as statistically significant.

Effect of creep feed duration in piglets
In this study, varying the duration of creep feed had no effect on the pre-weaning and post-weaning piglet growth performance in the current study (Table 3).Pigs fed different creep feeding duration exhibited no differences in suckling, sleeping and fighting frequency and mortality (Table 5).Creep feeding initiated from day 5 and 10 reduced (p<0.05) the post-weaning diarrhea scores compared with the other treatments (Table 3).Moreover, increasing creep feed consumption was observed with the increasing creep feeding duration (Table 4), indicating that the longer duration of creep feeding stimulated more pigs to consume more feed.Previously, Alger et al. (1990) observed that small piglets with low milk intake could consume more creep feed as a consequence of compensatory increase in foraging behavior.Pajor et al. (1991) proposed that exploratory investigation and social activity might be key factors in the initiation of creep feeding.Therefore, the duration of creep feeding may stimulate more eaters and subsequently the total feed consumption.Supportably, Sulabo et al. (2008) suggested that litters creep fed for 13 days produced 10% unit more creep feed eaters than litters fed creep diet for both 2 and 6 day.Moreover, ingestion of solid food during lactation can speed up the induction of amylase and protease enzymes (De Passille et al., 1989) and stimulate acid production (Cranwell et al., 1976, Sohn andMaxwell, 1995).Thus, higher creep feed consumption may result in greater growth performance, which is in agreement with Klindt (2003), who showed that creep feeding from 5 day of age resulted in greater pre-weaning daily gains than creep feeding from 2 day prior to weaning.However in the current study, varying creep feeding duration did not affect the growth performance throughout this study in spite of the increased feed consumption.Similarly, Sulabo et al. (2008) found no difference among varying creep feeding duration (2, 6 and 13 day) on pre-weaning gains and weaning weights (day 20).The reason for this lack of significant difference is unknown; it may have occurred due to the small feed intake of piglet may not enough to improve preweaning performance or the large variation among litters or as a result of replication and other systematic experimental errors.Moreover, our results revealed that creep feeding led to a lower diarrhea score than those provided no creep feeding post-weaning, which to some extent suggested that creep feed may have influenced positively gut maturity.Similarly, English (1981) proposed that creep feeding results in gut maturity and minimizes post-weaning scores.It was previously suggested that ingestion of solid food during lactation could modify the gut flora.Liu et al. (2008) indicated that diarrhea is always related to gut health and the intestinal microfloral population.Therefore, our study suggested that the negative effects associated with weaning pressure and the transition from milk to solid food may be impaired with creep feeding, because of the better capacity and maturation of gut health.

Effect of creep feeding duration in sows
Creep feeding initiated from day 5 and 10 significantly reduced (p<0.05) the weaning-to-estrus interval and cortisol concentration in sows compared with other treatments (Table 6).Creep feeding initiated from day 5 increased (p<0.05) the concentrations of epinephrine and norepinephrine in comparison to the piglets subjected to other treatments.No difference was noted in nursing, eating, standing times (Table 7), backfat loss and body weight loss (Table 6) during lactation in this study.Previously, it is well suggested that social stress activate the hypothalamicpituitary-adrenal axis and the sympathetic-adrenalmedullary axis, and inducing an elevation of catecholamines in the peripheral blood (Axelrod and Reisine, 1984;Ehrhart-Bornstein and Borstein, 2008).Several studies have reported that increased cortisol secretion and higher basal levels of NE and EPI is a valid indicator of stress in pigs (Becker et al., 1985;Smulders et al., 2006).Pajor et al. (2002) have demonstrated that creep feed cause piglets to consume more solid food and hence vocalize less when nursing frequency declines, which weakens the sow's responses to such calls.Tsuma et al. (1995) also noted that suckling and weaning induced increases in the concentrations of peripheral plasma cortisol  and endorphins.Therefore, the decreased EP, NPI and cortisol observed could be considered as a reflection of the reduced stressful effects of the suckling stimulus during lactation, owing to the relationship between the creep feed intake and the suckling time (suckling stimulus).Kuller et al. (2004) may provide support to this hypothesis, wherein they suggested that decreased suckling increased creep feed intake during lactation by an average of 218%.Additionally, Pajor et al. (2002) have suggested that creep feeding can reduce the nutritional load, the lactation BW loss and the weaning-to-estrus interval of sows.Our study revealed that creep feeding initiated from day 5 and 10 reduced the estrus interval compared with the other treatments, indicating the reproductive performance of sow is affected by the different creep feeding duration.It is well accepted that sustained elevations of plasma cortisol concentration impaired the LH surge, estrus and ovulation in female pigs, and also inhibited the secretion of LH in ovariectomized gilts (Turner et al., 1999a, b).Dobson and Smith (2000) and Foxcroft (1992) documented that stress (suckling) stimulates the adrenal axis and, in severe cases, inhibits LH secretion, which ultimately lead to an-ovulation and infertility.Therefore, the reason for the reduced estrus interval and EP, NPI and cortisol levels in blood are likely to be the decreased suckling stimulus.However, to the best of our knowledge, studies concerning the effects of creep feeding on sow performance are somewhat limited.There are no available studies with results that would allow for a clear comparison to the results of this study; therefore, further study will clearly be required to determine with more accuracy the effects of piglet stimulation on sows.

CONCLUSION
In conclusion, creep feed initiated from day 5 and 10 reduce diarrhea scores in piglets and benefit the estrus interval in sows compared with those initiated from day 15 and no-creep feeding diet, indicating creep feeding could improve the pigs and sow performance, especially those initiated from day 5 and 10.

Table 3 .
Effects of varying creep feeding duration on piglet performance and blood characteristics ,b,c Within a row, means with different superscripts differ (p<0.05).3Diarrhea score: 0, normal, firm feces; 1, possible slight diarrhea; 2, definitely unformed, moderately fluid feces; or 3, very watery and frothy diarrhea; Data were measured by average total diarrhea score during 7 day post-weaning. a

Table 4 .
Effects of varying creep feeding duration on piglet feed intake

Table 6 .
Effect of varying creep feeding duration on lactating sow performance

Table 5 .
Effects of varying creep feeding duration on pre-weaning piglet behavior

Table 7 .
Effect of varying creep feeding duration on lactating sow behavior