Evaluation of barley to replace milk by-product in weaning pig’s diet

All experimental procedures involving animals were conducted in accordance with the Animal Experimental Guidelines provided by the Seoul National University Institutional Animal Care and Use Committee (SNU-IACUC; SNU-160513-2).

A total of 112 crossbred ([Yorkshire × Landrace] × Duroc) piglets were allotted to 4 treatments in a randomized complete block (RCB) design. Each treatment had 7 replications with 4 pigs per pen and four diets containing 0% (B0), 10% (B10), 20% (B20), or 30% (B30) barley were fed to weaning pigs. The diets were formulated to contain 3,350, 3,307, 3,277 kcal of ME/kg for phase I, II and III, respectively. For phase I and phase II, milk products were decreased by 39%–26%–13%–0% and 15%–10%–5%–0%, respectively, as the barley level increase from 0% to 30%. All other nutrients were met or exceeded the nutrient requirements of NRC [12]. The experimental diets and chemical composition were presented in Table 1, 2, and 3.

Animals were housed in a 1.2 × 3.6 m² plastic floor, equipped with a feeder and a nipple drinker to allow freely access to feed and water during the experimental period. The ambient temperature in the weaning house was maintained at 31°C, and then gradually fallen to 26°C at the end of the experiment. Individual body weight (BW) and feed intake were recorded at 0, 2, 4, and 6 weeks to calculate the average daily gain (ADG), average daily feed intake (ADFI) and gain-to-feed ratio (G:F ratio).

Blood samples were taken from the jugular vein of each pig for measuring blood urea nitrogen (BUN) concentration and blood glucose level (BGL) at 0, 2, 4, and 6 weeks. Collected blood samples were centrifuged for 15 min at 700 × g on 4°C (Eppendorf centrifuge 5810R, Germany). The serum was carefully transferred to 1.5 mL plastic tubes and stored at −20°C until further analysis. The BUN concentration was analyzed by kinetic UV assay (Modular analytics, Hitachi, Japan) and the BGL was analyzed by enzymatic kinetic assay with hexokinase (Modular analytics, Hitachi, Japan).

Digestibility trial was conducted in completely randomized design (CRD) with 6 replicates to evaluate the nutrient digestibility and nitrogen relation. Experimental diets for phase II were provided to each treatment animals. A total of 24 crossbred (YLD) barrows, averaging 11.74 ± 0.72 kg BW, were individually allotted to each treatment and housed in a metabolic crate. Total collection method was utilized for the apparent total tract digestibility. During the digestibility trial, water was provided ad libitum and experimental diet was provided twice a day at 0700 and 1900 by three times of the maintenance energy requirement (106 kcal of ME/kg of BW^0.75, [13]). After 5 days of adaptation period, then 5 days of collection period was followed. To determine the first and last day of collections, 0.1% of ferric oxide and chromium oxide were added in experimental diets as a selection marker. Feces and urine were collected daily and stored −20°C until analysis. Collected fecal samples were pooled and dried in an air-forced drying oven at 60°C for 72 h, and ground into 1 mm particles in a Wiley mill for chemical analyses include moisture, crude protein (CP), crude fat, and crude ash contents. Total urine was collected daily in a plastic container containing 50 mL of 4N H₂SO₄ and frozen during the 5 day collection period for nitrogen retention analysis.

Observation of diarrhea incidence was conducted at 0800 during the whole period of feeding trial. Data was recorded by each pen and divided into 3 phases to assess the general pattern (Phase I: 0–2 week, Phase II: 3–4 week, Phase III: 5–6 week). The score of diarrhea incidence was given into 5 numbers (0 = No evidence of watery diarrhea, 1 = 1 pig shows evidence of watery diarrhea, 2 = 2 pigs, 3 = 3 pigs, and 4 = All pigs show evidence watery diarrhea in the pen) by counting pigs with evidence of watery diarrhea [14]. After recording data, evidence of watery diarrhea was cleaned away every time to separate from the next day.

Economic analysis was conducted to compare the feed cost per 1 kg weight gain of pigs fed the diets containing different milk products and barley levels. Calculation of feed cost per 1 kg weight gain as follows.

Experimental diet and excreta were analyzed for contents of dry matter (DM, procedure 967.03; [15]), crude ash (procedure 923.03; [15]), nitrogen (N) by using the Kjeldahl procedure with Kjeltec (KjeltecTM 2200, Foss Tecator, Sweden) and CP content (N × 6.25; procedure 981.10; [15]). Nitrogen of urine was determined by the Kjeldahl procedure.

Statistical analysis was carried out by least squares mean comparisons using PDIFF option of General Linear Model (GLM) procedure of SAS (SAS Institute Inc., Cary, NC, USA). For data on growth performance, a pen was considered the experimental unit, while individual pig was used as the experimental unit for data on blood profiles, nutrient digestibility, diarrhea incidence, and economic analysis. The effects of increasing levels of barley were analyzed as linear and quadratic responses by orthogonal polynomial contrasts. Differences were declared significant at p < 0.05 and highly significant at p < 0.01.

Table 4 showed the influence of barley supplementation on growth performance in weaning pigs. During the phase I, BW, ADG, and G:F ratio was declined as the supplementation level of barley increased, resulting in linear response (linear, p < 0.01). However, there was no significant difference in the parameters of growth performance in phase II and III.

Numerous swine researchers and nutritionists have been demonstrated the positive effects of milk products in young pig. Most of studies [16–19] showed the using milk products in combination with cereal grains and soybean meal has resulted in superior postweaning weight gains compared with simple grain and soybean meal mixture diet. Mahan [20] reported increased growth performance of weaning pigs fed diets containing dried whey from 0% to 35% in the early postweaning period and the results of the current study were agreed with those suggested, resulting in increased growth performance in phase I. Although little information about the effects of barley inclusion levels in weaning pig’s diet is available, supplementation of barley, which contained high NSP and β-glucan, reduced ADG during 0–10 days in weaned pigs [11]. In addition, there were some findings which suggested added fiber may reduce the effect of lactose supplementation on weaning pigs [21–23]. Touchette et al. [24] also reported that lactase activity is higher than amylase activity at three weeks of age and this trend was maintained from day 0 to 14 postweaning, but the response was inconsistent in late phase because lactase activity was decreased relative to amylase activity [25]. In the current study, ADG and G:F ratio was affected by the supplementation level of barley and milk by-product in phase I, but this trend was changed in late phase in agreement with that of Stephas et al. [25], resulting in no significant difference of ADG, ADFI, and G:F ration during the whole experimental period. Some studies reported that β-glucan within barley was degraded in the small intestine of pigs due to hydrolysis by endogenous β-glucanase and the microflora colonizing the small intestine of pigs [26–28]. It should be noted that the activity of enzymes can change depending on the pig age and diet composition. Thus, no difference in growth performance of weaning pigs during phase II and III among treatments could have been due to barley and milk by-product availability depending on enzyme activities.

The response of barley supplementation on nutrient digestibility was shown in Table 5. Barley supplementation up to 30% did not affect nutrient digestibility of DM, CP, and crude fat. However, a linear increase of crude fat digestibility was observed as addition level of barley increased, resulting in linear response (linear, p < 0.01). In the result of nitrogen retention, there was no significant difference among all parameters supporting this observation of CP digestibility.

The negative effects of fiber diets on energy and nutrient utilization of pigs were reported many times [22,23,29]. In barley, barley β-glucans have been shown to be 70% soluble and 30% insoluble fiber [30]. For the high soluble fiber composition, it can cause an increase in digesta viscosity, preventing interaction between nutrients and digestive enzymes [31] and reducing nutrient digestibility in pigs [32]. The digestible energy and CP contents of barley decrease as the percentage of hulls in the barley increases, as a result of the high fiber content [33,34]. Moreover, apparent total tract digestibility of nutrients such as DM, CP, crude fat, crude fiber, NDF, ADF, and energy was decreased by high fiber or β-glucan contents of barley-based diet [35,36]. Although barley contained higher dietary fiber relative to other carbohydrate sources, it also contained a high level of free sugar and there was a study suggesting no detectable difference on DM, organic matter, nitrogen, NDF, and gross energy digestibility between barley and other carbohydrate diets [36]. Also, supplementation of two different barley-based diets with different NSP and β-glucan contents had no difference in apparent digestibility of NSP and amino acids [11], and nitrogen [28]. In the present study, the piglets fed high barley diets showed similar digestibility with those fed barley 0% diet and these might be explained by the high sugar content and the supplementation level.

Increased feed efficiency and fat digestibility by the addition of fat sources have been reported many times in weaned pigs [37–40]. The ability of weaned pigs to digest fat was associated with fat sources and improves as age increased [41]. In the present study, the digestibility trial was conducted in early phase and increased fat digestibility by fat inclusion level was detected with an agreement of the results in growth performance.

Table 6 showed the effects of barley supplementation on blood profiles in weaning pigs. The significant differences by the addition of barley on BUN and BGL were not observed during the whole experimental period except BUN concentration in phase III. The pigs fed diets containing a high level of barley showed lower BUN concentration relative to those fed diets containing a low level of barley in phase III, resulting in linear response (linear, p < 0.01).

Although little information is available about the effects of barley supplementation on BGL, the high BGL in pigs fed barley diet was expected because of the high sugar content of barley. However, there was no response of barley supplementation with an agreement of Qureshi [42] who found that BGL was not changed by barley supplementation when inclusion level was relatively low. Kornegay [43] found the negative correlation between the inclusion level of dietary fiber and nutrient digestibility and there were researches reporting decreased DM and energy digestibility in pigs fed a diet containing high level of barley [44,45]. In the previous findings, the piglets were weaned before day 21, but piglets in the present study were weaned at day 28.

In general, BUN was the indicator for determination of amino acid utilization by pigs and it was directly related to intake of protein and protein quality [46]. Thus, the high level of BUN indicated that excessive amino acids were metabolized and circulated in the blood. In the current study, the BUN concentration of weaning pigs at 2 week and 4 week did not affected by dietary treatments. The result of BUN in the current study was similar to the result of Yoo et al. [47] that milk by-products level in weaning pig’s diet had no influence on the BUN in weaning pigs. However, the BUN concentration in 6 week decreased linearly as barley supplementation level increased. Considering the diet formulation of phase III diets, there were no milk by-products and barley inclusion level increased by corn and SBM decreased. It should be noted that the BUN concentration can vary depending on the excessive nitrogen or amino acids and amino acid imbalance. Thus, the linear decrease of BUN at 6 week could be due to the improvement of the amino balance for weaning pigs fed barley in corn-SBM based diet.

The effect of barley supplementation on diarrhea incidence in weaning pigs was shown in Table 7. In all phases, diarrhea incidence was decreased linearly as the inclusion level of barley increased, resulting in linear response (linear, p < 0.01).

Schulman [48] demonstrated that weaning could cause gastric changes increasing counts of E. coli, resulting in severe diarrhea and growth depth. However, many researchers indicated that these negative effects of weaning on gastric condition could be decreased by the supplementation of fiber sources and prebiotics [49–51]. Soluble fiber, highly included in barley, improves the volume and bulk of intestinal contents and it may cause increased water-holding capacity and viscosity causing low moisture content of feces [52]. Moreover, the supplementation of fiber source as prebiotics was associated with inhibiting harmful bacterial activity [53]. Fermented barley β-glucans increased short-chain fatty acids and low digesta pH, thus it helps to the production of beneficial bacteria at the expense of acid-sensitive Enterobacteria spp. [32] and killed Salmonella and E. coli bacteria in the gastrointestinal tract [54]. The β-glucans in barley have been shown to have prebiotic properties [32] and it could affected positively the diarrhea incidence of weaned pigs. In the present study, although the diarrhea incidence was improved by barley supplementation in phase I, ADG was decreased linearly. It should be noted that the growth rate of pigs within 7 days postweaning can vary depending on weaning weight, weaning stress, nutrient digestibility or availability, and diarrhea. Thus, this result could partly be attributed that the positive effect for high digestible milk by-product intake affect strongly to the growth rate of phase I than the negative effect for the diarrhea incidence.

To evaluate the effects of barley supplementation on the cost of feed and productivity, the economic analyses were conducted at end of growth trial (Table 8). The feed cost/1 kg BW was reduced significantly as the inclusion level of barley increased in phase I and II. Although there was no significant difference, feed cost / 1 kg BW in phase III was also improved numerically in pigs fed the diet containing a high level of barley and low level of milk by-product.

Consequently, there were no detrimental effects of barley supplementation up to 30% replace to milk by-product on growth performance, nutrient digestibility, and blood profiles. Feed cost per weight gain and diarrhea incidence were im-proved clearly when the pigs fed the diet containing a high level of barley.