Weaning of piglets causes stress due to environmental, behavioral, and nutritional stressors and can lead to postweaning diarrhea and impaired gut development. The diet changes experienced during weaning require extensive adaptation of the digestive system. A well-developed piglet that had creep-feed experience before weaning performs better after weaning. In the current study, the effect of providing sow-fed piglets with a supplemental nutrient-dense complex milk replacer (NDM) on gut development and growth performance was studied. Litters of sows with similar parities (3.6 ± 0.8) and similar numbers of live born piglets (13.5 ± 0.3) were assigned to 1 of 2 groups: 1 group of piglets had ad libitum access to NDM from Day 2 through 21 after birth, whereas the other group was used as controls. Nutrient-dense complex milk replacer-fed piglets were shown to be significantly heavier after 21 d of supplementation compared with the control piglets. At Day 21, 3 piglets from each litter were euthanized for morphological and functional analyses of the intestinal tract. The small intestines of NDM-fed piglets had significantly higher weights (g) as well as significantly higher relative weight:length ratios (g//cm) compared with the small intestines of control piglets ( < 0.05). Morphometric analysis demonstrated that villi length and numbers of goblet cells did not differ between groups. However, NDM-fed piglets had deeper crypts ( < 0.001) and an increased expression of the cell-proliferation marker proliferating cell nuclear antigen in crypts ( < 0.05), suggesting higher cell-proliferation rates. The gene encoding IGF-1 showed a tendency to higher gene expression in the jejunum from NDM-fed piglets ( = 0.07) compared with the jejunum from control piglets, suggesting that IGF-1 might be involved in the regulation of cell proliferation and intestinal growth. Finally, as a result of dietary fiber in NDM, piglets showed significantly increased concentrations of metabolic fermentation products. This suggests differences in metabolic activity in the colon between treatment groups. In conclusion, providing sow-fed piglets with NDM before weaning stimulates intestinal proliferation, leading to increased circular growth. Nutrient-dense complex milk replacer supplementation might, therefore, help piglets through the transition period at weaning by increased BW and increased capacity for uptake of nutrients.

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In general, female zebrafish,Brachydanio rerio, ovulate only in the presence of males. The stimulant must be pheromonal as even male holding water is capable of inducing ovulation. After ovulation the mating phase begins. During this phase the male follows the female and oviposition as well as fertilization takes place. Both the ovulation and the mating are controlled by pheromones synthesized by the gonads. Ovulation can be induced by testicular homogenates. After the lipid material has been extracted from the testicular homogenates, the remaining aqueous phase can still induce ovulation. However, when the aqueous phase is treated with the enzymeβ-glucuronidase, it loses the ability to induce ovulation. This is an indication that glucuronides, probably steroid glucuronides, are the compounds responsible.During the mating phase, ovulated female zebrafish become attractive to males. It was found that, after ovulation, ovarian extracts contain the compounds responsible for attracting males. The attractant consists of a mixture of steroid glucuronides.After incubation of the gonads with(3)H-precursors seven steroid glucuronides have been identified in the testis and five in the ovary.Under fish culture conditions the African catfish,Clarias gariepinus, can produce postivitellogenic oocytes throughout the year. However, in capitivity neither males nor females spawn. In female catfish maturation and ovulation can be induced by treatment with gonadotropins. It might be possible that, analogous to the zebrafish, some reproductive processes in the catfish have to be induced by pheromones. It has been demonstrated that pheromonal compounds released by the seminal vesicles are involved in the attraction of female conspecifics. The steroid glucuronide synthesizing capability of the testes and the seminal vesicles of the male catfish are examined, as well as that of the ovary before and after ovulation of the female catfish. Both testes and seminal vesicles appear to be capable of steroid biosynthesis but only the latter synthesizes steroid glucuronides. Six of these conjugates have been isolated and identified. In the female catfish the ovaries are capable of synthesizing seven steroid glucuronides, but only after ovulation.

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Male zebrafish, Brachydanio rerio, have paired testes and no additional reproduction glands. Incubation experiments with 3H-labeled steroid precursors showed the capacity of testes to synthesize seven steroid glucuronides. Enzyme histochemical studies demonstrated interstitial (Leydig) cells as steroid and steroid glucuronide producing sites. Male holding water, testis homogenates, and testis fractions containing steroid glucuronides were able to induce ovulation in female zebrafish. Deglucuronidation of these fractions led to a loss of ovulation inducing potency, indicating steroid glucuronides as ovulation inducers. The chemical substances are perceived by the recipients by means of olfaction, as anosmic females do not have a n ovulatory response after administration of male holding water. In African catfish, Clarias gariepinus, the male reproductive organ system consists of two paired structures, the testis and the seminal vesicle. Histochemical enzyme investigations pointed to interstitial cells as sites of steroid and steroid glucuronide production both in testis and seminal vesicle. Glucuronidation of steroids may also take place in the epithelium lining and seminal vesicle tubules. Biochemical studies showed the seminal vesicle as the main source of steroid glucuronides. Eight conjugated steroids were identified. Electrophysiological studies demonstrated that these compounds, especially 5P-pregnane-3a,l7au-dio1-20-oneglucuronide are olfactory stimulants in female conspecifics. Males with enlarged seminal vesicles, caused by compensatory growth after castration, were more attractive to ovulated female catfish in a two-choice test, using a U-shaped tank. Males lacking seminal vesicles were less attractive. The steroid glucuronide fraction of seminal vesicle fluid appeared to be responsible for the attraction effect. A synthetic mixture of steroid glucuronides resulted in a dose dependent attraction effect. The data are indicative of a pheromonal function for steroid glucuronides that are produced by the reproductive organ system of male zebrafish and African catfish.