Impact of fibre intake and fibre source on digestibility, gut development, retention time and growth performance of indigenous and exotic pigs

Effects of Varying Levels of Wheat Bran Dietary Fiber on Growth Performance, Fiber Digestibility and Gut Microbiota in Erhualian and Large White Pigs

To evaluate the tolerance of a high-fiber diet in Erhualian pigs (Er-HL), the present investigation systematically investigated the ramifications of varying wheat bran fiber levels, specified as total dietary fiber (TDF) values of 14.07%, 16.32%, 17.99%, and 18.85%, on growth performance, fiber digestibility and gut microbiota in Er-HL, large Large White pigs (L-LW, the same physiological stage as the Er-HL) and small Large White pigs (S-LW, the same body weight as the Er-HL). Our results revealed that fiber levels exerted no discernable impact on growth performance (average daily feed intake (ADFI), and average daily gain (ADG)) of Er-HL (p > 0.05). Conversely, L-LW exhibited a decrease in ADFI and ADG with increasing fiber levels (p < 0.05). Notably, the apparent total tract digestibility (ATTD) of various fiber components, including neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose, TDF and insoluble dietary fiber (IDF), in Er-HL were significantly higher than those in S-LW and L-LW irrespective of diets (p < 0.05). The ATTD of cellulose and hemicellulose in Er-HL significantly decreased with increasing fiber levels (p < 0.05), yet remained statistically indifferent when comparing the 7%-wheat-bran-replaced diet (7% WRB, TDF 16.32%) to the basal diet (TDF 14.07%) (p > 0.05). The cecal microbiota of Er-HL had higher richness estimators (Chao1 and ACE) than those of S-LW and L-LW irrespective of diets (p < 0.01). Breed serves as a pivotal determinant in shaping swine gut microbiota. Thirteen genera were selected as the key bacteria related to high fiber digestibility of Er-HL. Further functional examination of these key genera elucidated an enrichment of pathways pertinent to carbohydrate metabolism in Er-HL samples compared with S-LW and L-LW samples. In summary, Er-HL exhibited high-fiber tolerance both in terms of growth performance and fiber digestibility compared with Large White pigs. Specifically, the ATTD of NDF, ADF, hemicellulose, IDF and TDF were significantly higher in Er-HL compared with L-LW and S-LW, irrespective of diets. Fiber level exerted no discernable impact on growth performance (ADFI, ADG) and the ATTD of fiber (NDF, ADF, IDF and TDF) in Er-HL. The optimum fiber level of the Er-HL was identified as 7% WRB (TDF 16.32%). Thirteen genera were ascertained to significantly contribute to high fiber digestibility of Er-HL, correlating with an enhancement of carbohydrate metabolism pathways.

Review: Methods and biomarkers to investigate intestinal function and health in pigs

Society is becoming increasingly critical of animal husbandry due to its environmental impact and issues involving animal health and welfare including scientific experiments conducted on farm animals. This opens up two new fields of scientific research, the development of non- or minimally invasive (1) methods and techniques using faeces, urine, breath or saliva sampling to replace existing invasive models, and (2) biomarkers reflecting a disease or malfunction of an organ that may predict the future outcome of a pig's health, performance or sustainability. To date, there is a paucity of non- or minimally invasive methods and biomarkers investigating gastrointestinal function and health in pigs. This review describes recent literature pertaining to parameters that assess gastrointestinal functionality and health, tools currently used to investigate them, and the development or the potential to develop new non- and minimally invasive methods and/or biomarkers in pigs. Methods described within this review are those that characterise gastrointestinal mass such as the citrulline generation test, intestinal protein synthesis rate, first pass splanchnic nutrient uptake and techniques describing intestinal proliferation, barrier function and transit rate, and microbial composition and metabolism. An important consideration is gut health, and several molecules with the potential to act as biomarkers of compromised gut health in pigs are reported. Many of these methods to investigate gut functionality and health are considered 'gold standards' but are invasive. Thus, in pigs, there is a need to develop and validate non-invasive methods and biomarkers that meet the principles of the 3 R guidelines, which aim to reduce and refine animal experimentation and replace animals where possible.

Small Intestinal Digestive Functions and Feed Efficiency Differ in Different Pig Breeds

Small intestinal growth and health affect its digestion and absorption ability, while little information exists about the small intestinal morphology and function differences among the different pig breeds. Therefore, 90 healthy 35 days of age Taoyuan black (TB), Xiangcun black (XB), and Duroc (DR) pigs (30 pigs per breed) with similar body weight (BW) of the same breed were reared to 185 days of age to evaluate the potential relationship between feed efficiency and small intestinal morphology and function at 80, 125, and 185 days of age. The results show that the TB and XB pigs had lower initial and final BW, ADG, and ADFI and plasma CHO and LDL-C levels, whereas they had higher plasma LIP levels and jejunal trypsin, invertase, lactase, and maltase activities and higher DM, ADF, Tyr, Arg, and His digestibility at 80 days of age compared with the DR pigs. At 125 days of age, TB and XB pigs had lower apparent total tract digestibility and plasma CHO, HDL-C, LDL-C, and NH3 levels; XB pigs had lower DM and NDF digestibility, and TB pigs had higher jejunal lactase and maltase activities. At 185 days of age, TB and XB pigs had lower DM, EE, ADF, and GE digestibility, while having higher plasma ALT and UN levels; TB pigs had higher plasma AST level and jejunal chymase activity. Furthermore, the plasma free amino acid contents, small intestinal VH, and nutrient transporter expression levels differed at different ages. Therefore, the different pig breeds exhibited significantly different growth performance and small intestinal growth, mainly resulting from the differences in digestive enzymes and nutrient transporters in the small intestine.

Identification of Gut Microbiota Affecting Fiber Digestibility in Pigs

Dietary fiber plays an important role in porcine gut health and welfare. Fiber is degraded by microbial fermentation in the intestine, and most gut microbiota related to fiber digestibility in pigs are worth pursuing. The aim of this study was to identify gut microbiota associated with the apparent total tract digestibility (ATTD) of neutral detergent fiber (NDF) and of acid detergent fiber (ADF) in pigs. Large phenotypic variations in the ATTD of NDF and of ADF were separately found among 274 Suhuai pigs. Microbial community structures were significantly different between high and low fiber digestibility groups. Fourteen genera separately dominated the communities found in the high ATTD (H-AD) of NDF and ADF samples and were in very low abundance in the low ATTD (L-AD) of NDF and ADF samples. In conclusion, norank_f__Bacteroidales_S24-7_group (p < 0.05), Ruminococcaceae_UCG-005 (p < 0.05), unclassified_f__Lachnospiraceae (p < 0.05), Treponema_2 (p < 0.01), and Ruminococcaceae_NK4A214_group (p < 0.01) were the main genera of gut microbiota affecting the ATTD of NDF in pigs. Christensenellaceae_R-7_group (p < 0.01), Treponema_2 (p < 0.05), Ruminococcaceae_NK4A214_group (p < 0.05), Ruminococcaceae_UCG-002 (p < 0.05), and [Eubacterium]_coprostanoligenes_group (p < 0.05) were the main genera of gut microbiota affecting the ATTD of ADF in pigs. The most important functions of the above different potential biomarkers were: carbohydrate transport and metabolism, general function prediction only, amino acid transport and metabolism, cell wall/membrane/envelope biogenesis, translation, transcription, replication, energy production and conversion, signal transduction mechanisms, and inorganic ion transport and metabolism. The most important metabolic pathways of the above different potential biomarkers were: membrane transport, carbohydrate metabolism, amino acid metabolism, replication and repair, translation, cell motility, energy metabolism, poorly characterized, nucleotide metabolism, metabolism of cofactors and vitamins, and cellular processes and signaling.

Effect of Dietary Fructus mume and Scutellaria baicalensis Georgi on the Fecal Microbiota and Its Correlation with Apparent Nutrient Digestibility in Weaned Piglets

Traditional Chinese medicine (TCM) has long been demonstrated to exert a therapeutic effect on various diseases and has been used as a substitute for antibiotics in pig production. However, few studies have investigated the relationship between the intestinal microbiota and apparent nutrient digestibility when weaned piglet diets are supplemented with TCM. One hundred and sixty-two 25-day-old weaning piglets were housed in an environmentally controlled nursery facility and fed a basal diet (control group, n = 54) or a TCM complex (Fructus mume 1%, Scutellaria baicalensis Georgi 3%) (TCM group, n = 54), or a fermented diet with a complex of these two TCMs (F-TCM group, n = 54). Compared with the control group, in the TCM and F-TCM groups, the average daily gain (ADG) increased (p < 0.05), the F:G ratio and diarrhea rate decreased (p < 0.05), and the apparent digestibility of dry matter (DM) and ether extract (EE) of weaned piglets increased (p < 0.05). Bacteroidetes and Firmicutes were the predominant phyla, representing approximately 95% of all sequences. The abundance of four genera and 10 OTUs (belonging to Ruminococcaceae_UCG-014, Lachnoclostridium, Prevotellaceae_NK3B31 group, Prevotella_1) were negatively correlated with apparent EE digestibility (p < 0.05). The results suggest that weaned piglets fed with antibiotic-free diets supplemented with Fructus mume and Scutellaria baicalensis Georgi gained more weight and were healthier. When added to the diet, the complex of these two TCMs may have a direct impact on apparent EE digestibility by modifying the gut microbial composition, which favors the health of weaned piglets.

Nitrogen balance in slow-growing Windsnyer pigs fed on incremental levels of amarula (Sclerocarya birrea subsp. caffra) nut cake

Feeding-derived amarula cake to growing pigs can overcome a narrow range of ingredients challenges and improve productivity. The objective of the current study was to determine the response in nitrogen (N) balance in slow-growing pigs fed on incremental levels of amarula nut cake (ANC). Thirty clinically healthy male growing Windsnyer (30.7 kg ± 6.57) (mean ± standard deviation) were individually assigned to separate pens in a completely randomized design, with six pigs per dietary treatment. Iso-energetic experimental diets were formulated to contain 0, 50, 100, 150, and 200 g/kg dry matter (DM) of ANC using the summit and dilution technique. Pigs were given 10 days of dietary adaptation and a collection period of 5 consecutive days after 31 days of feeding. Nitrogen intake increased linearly with incremental levels of ANC (P < 0.01). As ANC inclusion increased, the nitrogen (N) absorption, apparent N digestibility, and N retention in pigs increased until it reached a maximum, then started to decrease (P < 0.05). Nitrogen utilization increased at the rate of 0.63 g for each 1 g increase in ANC (P < 0.01). There was a linear decrease (P < 0.01) in total nitrogen excretion through urine and faeces with ANC inclusion. Urinary pH levels decreased quadratically in response to graded levels of ANC (P < 0.01). The relationship between urinary pH and ANC inclusion was Y = 0.0115x² - 0.3491x + 4.872 (P < 0.01). The nitrogen balance responses were due to ANC inclusion in diets that were balanced for limiting amino acids. It can be concluded that ANC reduces N excretion, potentially minimizing ammonia volatilization, which makes it an alternative protein source for slow-growing pigs.

Response in digestibility, growth performance, and carcass quality of local Kandol pigs to incremental levels of fermented banana stems

Fermentation of banana stems is a novel method for increasing the digestibility of fibrous porcine rations in the tropics; however, optimal feeding rates have not been determined. An experiment was carried out to determine the response of digestibility, growth performance, and carcass quality in local Kandol pigs to incremental levels of FBS in rations. A total of 20 castrated male pigs were randomly allocated to five diets, containing 0, 400, 500, 600, and 700 g FBS of the ration. Daily feed on offer was provided as 4% of the body weight on a dry matter basis and offered three times per day. As result, the inclusion level of FBS was positively correlated with NR (p < 0.001, r = 0.68). The linear regression equation was y = 0.002x + 2.4276 (R² = 0.63). Furthermore, it was also correlated with ADG (p < 0.05, r = 0.46) and with FCR (p < 0.05, r = - 0.45). The regression equation was y = 0.0634x + 174.2 (R² = 0.43) and y = - 0.0009x + 4.6521 (R² = 0.62) for ADG and FCR, respectively. The correlation between inclusion level of FBS and large intestine weight was also observed (p < 0.05, r = - 0.61). The R² value was 63. However, there was no any correlation between the inclusion level of FBS and the percentages of hanging carcass, dressing carcass, pH, color score, marbling score of the meat, and WHC (p > 0.05). The economic benefit of using FBS to improve pig diets will depend on the availability of banana stems and the labor and processing costs.

Body size and gastrointestinal morphology of nutria (Myocastor coypus) reared on an extensive or intensive feeding regime

Although plasticity of growth rates is mainly associated with ectotherm species, it does occur in endotherms as well, but has not been documented systematically for many species. We compared the effect of 2 common types of feeding systems, differing in energetic value, on body size and gastrointestinal tract morphology in nutrias (Myocastor coypus). A total of 30 extensively (E) fed and 20 intensively (I) fed animals were used in the study. We noted significant effects of age, sex, and feeding regime on body weight and length, with 1-yr-old females attaining 3.7 ± 0.4 kg and 33.4 ± 1.5 cm on E and 4.9 ± 0.3 kg and 36.1 ± 2.3 cm on I. A significant treatment-sex interaction indicated that treatment had a greater effect on the length growth in males (1-yr-old males attaining 4.0 ± 0.2 kg and 34.7 ± 1.2 cm on E and 5.4 ± 0.4 kg and 41.0 ± 1.4 cm on I). The differences matched individual literature reports of free-ranging or intensively fed nutrias. The majority of gastrointestinal tract measurement results were only related to body weight, without additional effect of the diet regime, except for a higher small intestinal tissue weight on I (79 ± 14 g vs. 61 ± 7 g on E). In contrast, the wet content weight of the stomach, caecum, and the total gastrotinestinal tract was higher on E (196 ± 34 g vs. 164 ± 51 g on I). Overall, we observed strong influence of dietary regime on body development but not on digestive anatomy, indicating a distinct phenotypic flexibility in growth rates in nutrias.

In growing pigs, nutritive value and nutrient digestibility of distillers' by-products obtained from two varieties of rice

In South-East Asia, rice distillers' by-product (RDP) is a widely abundant feedstuff whose adequate incorporation into pig diets is still questionable. Especially, effects of RDP on nutrient digestibility of growing pigs fed corn-soybean meal-based diet are lacking. The objective of this study was to determine nutrient digestibility and energy value of ordinary (ORDP) and glutinous (GRDP) rice distillers' by-product in growing pigs. Two groups of 12 castrated crossbred barrows (Duroc × Landrace × Yorkshire), about 3 months old, 38 ± 1.04-kg initial body weight, were each allocated to a 15-day experiment in which pigs were divided into three isonitrogenous diet-groups. The animals were housed individually in metabolism cages for separated collection of feces and urine. Each diet-group was provided either a control corn-soybean meal diet or a diet in which corn and soybean meal were partly replaced by ORDP or GRDP at 15 or 30% on diet dry matter basis. Glutinous by-product especially showed higher levels in crude protein, neutral/acid detergent fiber, total branched-chain amino acids, and butyric acid. When compared to the control diet, ORDP tented to increase DM intake (P = 0.054) but decreased energy (P < 0.001) and crude protein (P < 0.04) digestibility, while GRDP decreased DM intake (P < 0.001). Both GRDP and ORDP products negatively affected digestibility of ether extract. The average digestible and metabolizable energy of ORDP and GRDP were 17.0 and 16.6, and 17.7, and 17.1 MJ/kg DM, respectively. In conclusion, these results show that both RDP, and especially GRDP, are highly valuable protein and energy sources for pig production.

Characteristics of Gut Microbiota in Sows and Their Relationship with Apparent Nutrient Digestibility

The gut microbiota plays important roles in animal health and nutrient digestibility. The characteristics of gut microbiota population in grower pigs and their correlation with apparent nutrient digestibility were assessed in previous study. Here we studied characteristics of intestinal microbiota of sows and analyzed their relationships with apparent nutrient (ether extract (EE), crude protein (CP), crude fiber (CF), neutral detergent fiber (NDF) and acid detergent fiber (ADF)) digestibility. Firmicutes and Bacteroidetes were the most dominant phyla, approximately 73% of the total sequences. Treponema, Oscillibacter and Lactobacillus were the most dominant generas, more than 49% of the total sequences. The microbiota of sows clustered separately from the microbiota of grower pigs at the age of D28 D60, D90 and D150. The abundance of Clostridium and Turicibacter was positively correlated with apparent EE digestibility. The abundance of Anaerofustis and Robinsoniella in sow fecal samples was positively correlated with apparent CF digestibility. The abundance of Collinsella and Sutterella was positively correlated with apparent NDF digestibility. The abundance of Clostridium, Collinsella, Robinsoniella and Turicibacter was positively correlated with apparent ADF digestibility. Sows have their unique gut microbial structure compared with grower pigs and some of them participate in the digestive process of different nutrients.

Nutrient utilisation in grower pigs fed a protein concentrate blended with sweet potato roots either boiled or ensiled with or without vines

Blending sweet potato (Ipomoea batatas L. (Lam)) with a protein concentrate for pig feed is a common strategy used by small-scale livestock farmers across Africa, Asia and the Pacific. However, high dietary fibre in sweet potato (SP) forage may reduce nutrient utilisation and energy metabolism and reduce the growth rate of young pigs. A 32-day metabolic trial with grower pigs using a 4 × 4 Latin square design tested the hypothesis that there would be no difference in apparent total tract digestibility (ATTD) of nutrients, energy and nitrogen (N) balance in 25 kg grower pigs (Large White × Landrace × Duroc) fed diets based on a blend of 43–40% protein supplement with 57–60% of DM as SP roots either boiled (BR43) or ensiled alone (ER43) or ensiled with vines (ERV40). Blended SP diets provided ~14–15% crude protein (CP), 16.1–16.3 MJ digestible energy (DE)/kg DM and 0.54–0.58 g lysine/MJ DE. The control diet (STD) contained 16.5% CP, 14.8 MJ DE/kg DM, 0.58 g lysine/MJ DE. The major findings were as follows: (1) DM intake was higher (P &lt; 0.05) for BR43 than ER43, ERV40 and STD diets, which were similar; (2) DM ATTD and energy utilisation were higher (P &lt; 0.05) in pigs fed SP diets; (3) carbohydrate (N-free extracts) ATTD was higher (P &lt; 0.05) in pigs fed BR43 and ER43 diets, while CP ATTD of both these diets was similar to that of STD and higher than that of ERV40; (4) ATTD of fats (ether extracts), CP, carbohydrates (N-free extracts) and total phosphorus was lower (P &lt; 0.05) on ERV40, but fibre ATTD was higher; (5) N intake and N retained were similar (P &gt; 0.05) for pigs fed BR43, ER43 and STD diets but lower for ERV40 (P &lt; 0.05). Boiled or ensiled SP roots provided high nutrient and energy utilisation in growing pigs, but the inclusion of SP vines lowered ATTD, energy utilisation and N retained from the mixed diet (ERV40). It is concluded that boiled or ensiled SP root are equally valuable as blended feed for grower pigs. However, at 30%DM, ensiled SP vine in blended feed led to reduced grower-pig performance.

Nutritive value of three tropical forage legumes and their influence on growth performance, carcass traits and organ weights of pigs

The effects of tropical forage legumes on feed intake, growth performance and carcass traits were investigated in 16 groups of two Large White × Duroc pigs. The diets consisted of a commercial corn-soybean meal diet as the basal diet and three forage-supplemented diets. Four groups of control pigs received daily 4 % of body weight of the basal diet, and 12 groups of experimental pigs were fed the basal diet at 3.2 % of body weight completed with fresh leaves of one of the three forage legumes (Psophocarpus scandens, Stylosanthes guianensis and Vigna unguiculata) ad libitum. The study lasted 90 days. The in vitro digestion and fermentation of the forage legumes were also determined. The in vitro digestible energy content of the legumes was between 0.72 and 0.77 that of the basal diet (14.4 MJ/kg dry matter (DM)). V . unguiculata was the most digestible forage legume expected for crude protein digestibility. Feeding forage legumes lowered the dry matter intake by 4.5 to 9.6 % (P < 0.05), final body weight (P = 0.013), slaughter weight, average daily gain and hot carcass weight (P < 0.05) without affecting the feed conversion ratio (FCR), dressing percentage and back fat thickness. In conclusion, using forage to feed pig could be interesting in pig smallholder production with limited access to concentrate, as FCR was not significantly affected.

Characterization of smallholder pig breeding practices within a rural commune of North Central Vietnam

This case study focused on a pig production system in a rural area of North Central Vietnam, with a focus on describing household pig breeding practices and estimating herd demographic parameters, particularly on reproduction. One hundred five households undertaking small-scale piglet production were surveyed, with information gathered on 3268 individual pigs. Pig keeping contributed variably to the overall household livelihood portfolio, with female household members as the main decision makers, contributors to labor, and beneficiaries of income from the pig enterprise. All households kept between one and four young or adult sows, with 69% of these sows of a local breed type (predominantly Mong Cai), 28% a cross between a local sow and an exotic sow (predominantly Large White), and the remainder (3%) as exotic sows. Eighty-eight percent of the piglets produced were cross-bred, while 12% were local breed. No adult males were kept by the surveyed households, reflecting the common use of artificial insemination for mating purposes. The most common breeding system practiced-the keeping of Mong Cai females and production of cross-bred piglets-capitalizes on the small body size and high fecundity of the sows and the fast growth rate and leanness of the cross-bred piglets. The survey tool used, which was based on farmer recall of events over the preceding 12-month period, appeared to give reasonable results although some recall bias could be detected. This case study will serve as an entry point to planned broader scale characterization and development of pig breeding systems in North Central Vietnam.

Dynamic distribution of the gut microbiota and the relationship with apparent crude fiber digestibility and growth stages in pigs

The gut microbiota plays an important role in nutrient digestibility in animals. To examine changes in the pig gut microbiota across growth stages and its effects on nutrient digestion, the gut microbiota population in pigs at 28 days (before weaning), and 60, 90, and 150 days of age was assessed by 16S rDNA gene sequencing. The apparent digestibility of crude fiber (CF), neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP) and ether extract (EE) was also assessed in these pigs. A total of 19,875 operational taxonomic units (OTUs) were identified from all samples. Both bacterial abundance and diversity increased with age. A total of 22 phyla and 249 genera were identified from all fecal samples; Firmicutes and Bacteroidetes were the most dominant phyla in all samples. With increasing age, the proportion of TM7 and Tenericutes increased, whereas the proportion of Lentisphaerae and Synergistetes decreased. The abundance of 36 genera varied with age, and the apparent digestibility of CF increased with age. Three phyla, Proteobacteria, Tenericutes and TM7, and 11 genera, including Anaeroplasma, Campylobacter, and Clostridium, were correlated with apparent CF digestibility.

Effects of corn gluten feed inclusion at graded levels in a corn-soybean diet on the ileal and fecal digestibility of growing pigs

BACKGROUND

This study aimed to determine the effect of the inclusion of corn gluten feed (CGF) on the apparent and standardized ileal digestibility of protein and amino acids and the apparent ileal and total tract digestibility of energy in growing pigs. The study was performed using 16 barrows (weight, 45.3 ± 4.5 kg) that were fitted with a T cannula at the terminal ileum. There were four treatments: a corn-soybean diet without CGF and three corn-soybean diets containing increasing levels of CGF (65, 130, and 195 g/kg). Data were analyzed according to a randomized complete block design, four blocks with four pigs each (one pig per treatment). The trend of the response (linear or quadratic) was determined using orthogonal contrasts, and when a linear effect was determined, a linear equation was obtained.

RESULTS

The results showed that the inclusion up to 195 g/kg of CGF in the corn-soybean diet did not diminish the ileal digestibility (apparent and standardized) of protein and amino acids (P > 0.05), except that of phenylalanine, cystine, and proline. A linear decrease (P < 0.05) per gram of CGF added to the diet in the apparent and standardized ileal digestibility of phenylalanine (0.011 and 0.015 percentage units, respectively), cystine (0.048 and 0.043 percentage units, respectively), and proline (0.045 and 0.047 percentage units, respectively) was noted. Similarly, ileal digestibility of dry matter and energy were adversely affected (reduced by 0.028 and 0.025 percentage units, respectively, per gram of CGF increment in the diet). A significant (P < 0.05) linear reduction in total tract digestibility with increase in CGF amount in the diet was observed for energy (0.027 percentage units), dry matter (0.027 percentage units), crude protein (0.020 percentage units), and neutral detergent fiber (0.041 percentage units) per gram of CGF added to the diet.

CONCLUSION

CGF did not affect the ileal digestibility of protein and most amino acids but reduced the ileal and total tract digestibility of energy.

Forage plants as an alternative feed resource for sustainable pig production in the tropics: a review

Globally, pressure on concentrate feed resources is increasing, especially in the tropics where many countries are net importers of food. Forage plants are a possible alternative, but their use as feed ingredients for pigs raises several issues related to their higher fibre and plant secondary metabolites contents as well as their lower nutritive value. In this paper, the nutritive value of several forage species and the parameters that influence this nutritive value in relationship to the plant family, the physiological stage, the plant part and the preservation method (fresh, hay and silage) are reviewed. The influence of the breed and the physiological status of the animal on animal voluntary intake of fibre-rich ingredients, digestibility as related to gastrointestinal volume and transit time and growth performances are also discussed. The final section highlights the advantages and drawbacks of forage plants in pig diets and stresses the need for proper economic evaluation to conclude on the benefits of the use of forage plants in pig feed.

Fiber effects in nutrition and gut health in pigs

Dietary fiber is associated with impaired nutrient utilization and reduced net energy values. However, fiber has to be included in the diet to maintain normal physiological functions in the digestive tract. Moreover, the negative impact of dietary fiber will be determined by the fiber properties and may differ considerably between fiber sources. Various techniques can be applied to enhance nutritional value and utilization of available feed resources. In addition, the extent of fiber utilization is affected by the age of the pig and the pig breed. The use of potential prebiotic effects of dietary fiber is an attractive way to stimulate gut health and thereby minimize the use of anti-microbial growth promoters. Inclusion of soluble non-starch polysaccharides (NSP) in the diet can stimulate the growth of commensal gut microbes. Inclusion of NSP from chicory results in changes in gut micro-environment and gut morphology of pigs, while growth performance remains unaffected and digestibility was only marginally reduced. The fermentation products and pH in digesta responded to diet type and were correlated with shifts in the microbiota. Interestingly, fiber intake will have an impact on the expression of intestinal epithelial heat-shock proteins in the pig. Heat-shock proteins have an important physiological role in the gut and carry out crucial housekeeping functions in order to maintain the mucosal barrier integrity. Thus, there are increasing evidence showing that fiber can have prebiotic effects in pigs due to interactions with the gut micro-environment and the gut associated immune system.