The present study was designed to determine the interrelationships between sex, weaning age, and weaning weight on aspects of physiological and gastrointestinal development in pigs. Forty-eight Large White × Landrace pigs were used in a factorial arrangement with the respective factors being: age at weaning (14 or 28 days), weight at weaning (heavy or light), sex (boar or gilt), and time after weaning (1, 7, and 14 days). At weaning, 48 pigs were removed from the sow: 16 pigs were then fasted for 24 h before euthanasia for determination of organ weights, gut histology, and enzymology, and 32 pigs were offered a high quality pelleted weaner diet ad libitum for subsequent assessment of organ weights, histology, and enzymology at 7 and 14 d after weaning. On Day 6 and 13 after weaning, 2 pigs from each group had their feed removed, and 24 h later were euthanased and similar measurements were taken. In general, the data highlighted the overall gastrointestinal underdevelopment of pigs weaned at 2 weeks of age and of pigs weaned light-for-age at either 2 or 4 weeks. Heavier body organs, gastrointestinal organs, and accessory digestive organs observed after weaning, except for the spleen, presumably reflected the increase in substrates available for cellular growth as feed intake increased after weaning, and the development of organs required to process this feed. Interestingly, the relative weights (% of liveweight) of the stomach and small intestine and, to a lesser extent, the caecum and colon, were greater in the light, 14-day-old weaned pigs, but these differences diminished with increasing time after weaning. Consistent effects due to age, weight, and sex were not observed for villous height and crypt depth, or for the specific activities of the brush-border and pancreatic enzymes measured. However, increases (P < 0.001) in the activities of maltase (P�<�0.001), glucoamylase (P < 0.001), and sucrase (P = 0.020) (all expressed per gram of mucosa), and that of trypsin (per gram of pancreas), occurred by 14 days after weaning. This most likely reflected the inducible nature of these enzymes in response to the increasing intake of substrates provided in the diet. In contrast, the specific activity of lactase declined (P = 0.012) in the first 14 days after weaning. These data suggest that pigs weaned at 2 weeks of age and pigs weaned light-for-age at either 2 or 4 weeks have a less developed gastrointestinal tract, and that its development after weaning might proceed differently to that of pigs weaned older and heavier.

Pigs from 154 litters (n = 1132, 19 ± 3 days of age, 4.9 ± 1.1 kg of bodyweight) were used in a 3 × 2 factorial design to evaluate two raw materials with nutraceutical properties being used in feeds, spray-dried porcine plasma (SDPP) and a yeast protein meal, and their effects on growth performance, immune parameters and gastrointestinal adaption of piglets to weaning. Factors included dietary treatments being (1) 5% SDPP (PLA), (2) 3.5% yeast protein meal (NUP) and (3) medicated control (TMC) and parity (primiparous versus multiparous). The treatment groups were imposed from Day 19 through to weaning at Day 27. Selected pigs (n = 720, 28 ± 3 days of age, 7.4 ± 1.0 kg of bodyweight) were weaned and remained on their respective diets from Day 28 to Day 34. From Day 35 to Day 48 all group-housed pigs were offered a commercial weaner 1 diet, and from Day 49 to Day 68 pigs were offered a commercial weaner 2 diet. Growth performance, survival, and serum immunoglobulin G were monitored throughout the nursery phase (Day 28 to Day 68). Adaptation of the gastrointestinal tract in the acute post-weaning phase (Day 28 to Day 34) was assessed in 36 individually housed male weaners, with the effects of feed on structural, digestive, microbial and immune parameters along the gastrointestinal tract determined at Day 34. Pre-weaning feed disappearance was greater (P < 0.01) in multiparous litters independent of diet. In the commercial nursery, total removals (mortality and morbidity) were highest (P < 0.01) in primiparous sow progeny, with pigs offered NUP having greater (P ≤ 0.05) total removals. Pigs offered PLA had superior average daily gain, average daily feed intake and feed conversion ratio from Day 28 to Day 34 (P < 0.05). Pigs offered NUP tended to (P = 0.07) have superior average daily gain from Day 35 to Day 49. Pigs offered NUP had higher (P < 0.05) serum immunoglobulin G concentrations at Day 68 compared with pigs offered TMC, with the effect most pronounced in primiparous sow progeny. Individually housed weaners offered PLA consumed more (P < 0.05) feed on Day 30 to Day 31, had shorter relative intestine length (P < 0.05), greater villous height in the medial jejunum (P < 0.10) and lower immuno-pathology scores along the intestine. Pigs offered PLA also tended (P < 0.10) to have increased pancreatic-specific lipase and amylase activity compared with pigs offered NUP. Pigs offered NUP had a higher ratio of E. coli : coliforms in the colon (P < 0.01) and more counts of β-haemolytic bacteria in the medial jejunum (P < 0.05) and colon (P < 0.10). Diets containing either SDPP or NUP offered pigs benefits beyond nutrition relative to the medicated control diet. The benefits of SDPP were highly effective but transient, while the yeast derived protein had a successive or accumulative effect which was more pronounced in primiparous sow progeny.

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