Validation of qPCR reference genes in the endangered annual killifish Austrolebias charrua considering different tissues, gender and environmental conditions

The annual killifish Austrolebias charrua is an endangered species, endemic to the southern region of South America, which inhabits temporary ponds that emerges in the rainy season. The main anthropogenic threat driving the extinction of A. charrua stems from extensive agriculture, primarily due to the widrespread use of glyphosate-based herbicides near their habitats. Annual killifishes have been used as models for ecotoxicological studies but, up to now, there are no studies about reference genes in any Austrolebias species. This represents an obstacle to the use of qPCR-based technologies, the standard method for gene expression quantification. The present study aimed to select and validate potential reference genes for qPCR normalization in the annual killifish Austrolebias charrua considering different tissues, gender and environmental conditions. The candidate reference genes 18 s, actb, gapdh, ef1a, shox, eif3g, and the control gene atp1a1 were evaluated in male and female individuals in three different tissues (brain, liver, and gills) under two experimental conditions (control and acute exposition to Roundup Transorb®). The collected tissues were submitted to RNA extraction, followed by cDNA synthesis, cloning, sequencing, and qPCR. Overall, 18 s was the most stable reference gene, and 18 s and ef1a were the most stable combination. Otherwise, considering all variables, gapdh and shox were the least stable candidate genes. Foremost, suitable reference genes were validated in A. charrua, facilitating accurate mRNA quantification in this species, which might be useful for developing molecular tools of ecotoxicological assessment based on gene expression analysis for environmental monitoring of annual killifish.

Butyrate supplementation in the liquid diet of dairy calves leads to a rapid recovery from diarrhea and reduces its occurrence and relapses in the preweaning period

The present study aimed to evaluate the effect of continuous butyrate administration in dairy calves' liquid diet considering diarrhea, metabolic profile, gastrointestinal development, and corporal growth. Immediately after birth, calves were randomly allocated into 2 groups of 62 calves (50 females and 12 males), with access to water and a solid feed ad libitum. The butyrate group (BG) received 4 g/d of sodium butyrate (Admix Easy, Adisseo) diluted in the whole milk, and the control group (CG) received whole milk with no supplementation. Sodium butyrate was administered from d 1 of life until the weaning at 90 d. Feces consistency was assessed daily for the first 30 d of life and characterized by scores from 0 to 4 (0 and 1 for normal, and 2, 3, and 4 for abnormal feces). Diarrhea was diagnosed when the animals had abnormal feces and fever. Morbidity, recurrence, mortality, and lethality data were recorded and compared between the groups. Average daily gain (ADG) and corporal growth (body weight, thoracic perimeter, height at the withers, and croup width) were evaluated weekly, from the first day to d 30, and later at 45, 60, and 90 d of life. Blood samples were taken weekly for up to 30 d to determine the circulating levels of total calcium, phosphorus, chloride, bicarbonate, glucose, β-hydroxybutyrate, and nonesterified fatty acids. The males were euthanized at 15 (n = 6 per group) and 30 d (n = 6 per group) for morphometric, histological, and gene expression analysis of the gastrointestinal tract. The results showed that the BG had a lower rate of morbidity (BG = 30% vs. CG = 50%) and recurrence (BG = 26.7% vs. CG = 60%) of diarrhea than the CG. In addition, the BG had abnormal feces for a shorter period (BG = 4.64 ± 0.47 d vs. CG = 8.6 ± 0.65 d). The ADG tended to be higher in BG than CG up to 30 and 60 d. Metabolic evaluations showed the lowest levels of glucose and highest levels of nonesterified fatty acids in BG. On d 30 of life, rumen papillae length, papilla area, duodenum villus length, and crypt depth were higher in BG than in CG. The duodenal gene expression at 30 d showed that animals with diarrhea episodes that did not receive butyrate had the highest levels of transcripts for the LCT and GLP2 genes. In addition, in different ways, both butyrate and neonatal diarrhea affected the gene expression of IGF1, SLC5A1, and AQP3. These results allow us to conclude that continuous supplementation with sodium butyrate improves gastrointestinal development, reduces the occurrence of diarrhea, and makes clinical conditions milder with faster recovery, favoring a higher ADG in the first 30 and 60 d of life. Based on these results, we conclude that sodium butyrate can be indicated for liquid diet supplementation to accelerate gastrointestinal tract development and prevent severe cases of neonatal diarrhea, tending to improve average daily gain until weaning.