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In this study, 6 dietary DL-methionine (Met) levels (2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 g/kg) were tested to estimate the dietary Met requirements of Longyan ducks from 19 to 46 weeks of age, and to investigate its effect on the glutathione redox system. In total, 1080 Longyan ducks aged 19 weeks were allocated randomly to the 6 dietary treatments, where each treatment comprised 6 replicate pens with 30 ducks per pen. Met had no effects on egg production, yolk weight, yolk colour or the glutathione redox system, but the egg weight, egg mass and feed conversion ratio (FCR) were improved significantly by dietary Met supplementation. As the dietary Met concentration increased, the eggshell thickness and breaking strength decreased significantly, whereas the albumen weight increased significantly. According to broken-line regression analysis, the optimum Met requirements for egg weight, egg mass, FCR and albumen weight are 686, 661, 658 and 731 mg/bird/d, respectively, with a dietary crude protein level of 170 g/kg.

ABSTRACT. RFamide-related peptide (RFRP) gene is a crucial gene of the hypothalamo-pituitary-gonadal axis and plays an important role in reproduction regulation. This study aimed to clone and characterize the pig RFRP gene. We obtained a 645-bp cDNA of pig RFRP gene comprising a 546-bp open reading frame, which encoded a peptide of 188 amino acids. The pig RFRP coding sequences have the identities of 81, 68.8, and 76.1% with their counterparts in humans, mice, and rats, respectively. Real-time polymerase chain reaction showed that the pig RFRP gene was expressed predominantly in the stomach and testis of males, and large intestine and uterus of females. It was also found to be abundantly expressed in the cerebrum and liver tissues of both male and female pigs. The pig RFRP gene is 4.6 kb long and contains 3 exons and 2 introns. We further identified a total of 25 single nucleotide polymorphisms and 2 insertion/deletion (indel) polymorphisms across the whole RFRP gene, and 9 of them were in the exons. Marker trait association analysis in Yorkshire and Landrace populations showed that g.45859759C>T was significantly associated with the total number born of second parity (TBA2; P < 0.05). In conclusion, the pig RFRP gene was cloned and characterized in this study, and its polymorphism g.45859759C>T showed significant associations with reproductive traits.

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