Genomic analysis of inbreeding level, kinship and breed relationships in Creole cattle from South America.

The conservation of animal genetic resources refers to measures taken to prevent the loss of genetic diversity in livestock populations, including the protection of breeds from extinction. Creole cattle populations have suffered a drastic reduction in recent decades owing to absorbent crosses or replacement with commercial breeds of European or Indian origin. Genetic characterization can serve as a source of information for conservation strategies to maintain genetic variation. The objective of this work was to evaluate the levels of inbreeding and kinship through the use of genomic information. A total of 903 DNAs from 13 cattle populations from Argentina, Bolivia and Uruguay were genotyped using an SNP panel of 48 K. Also, a dataset of 76 K SNPs from Peruvian Creole was included. Two inbreeding indices (FROH and Fhat2) and kinship relationships were calculated. In addition, effective population size (Ne), linkage disequilibrium, population composition and phylogenetic relationships were estimated. In Creole cattle, FROH ranged from 0.14 to 0.03, and Fhat2 was close to zero. The inferred Ne trends exhibited a decline toward the present for all populations, whereas Creole cattle presented a lower magnitude of Ne than foreign breeds. Cluster analysis clearly differentiated the taurine and Zebu components (K2) and showed that Bolivian Creole cattle presented Zebu gene introgression. Despite the population reduction, Creole populations did not present extreme values of consanguinity and kinship and maintain high levels of genetic diversity. The information obtained in this work may be useful for planning conservation programmes for these valuable local animal genetic resources.

Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout oogenesis and influence of steroid hormones.

In rainbow trout, a variable in vivo pituitary sensitivity to GnRH has been previously observed, depending on the stage of oogenesis. The purpose of the present work was to study, in vitro, the role of oestradiol (E2) and 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha 20 beta P), respectively, involved in vitellogenesis and in oocyte maturation, upon this variability. The study was performed using primary cultures of whole pituitary cells from animals at different stages of oogenesis and subjected to increasing doses of salmon GnRH (sGnRH) after a 3-day pretreatment with control medium or medium supplemented with the steroid at levels corresponding to those circulating at the time of particular events of the sexual cycle (maturation and vitellogenesis). In control cultures, pituitary GtH responsiveness to sGnRH was maximal at ovulation, since at this time the gonadotrophs were able to respond to 10(-9) M sGnRH, whereas during vitellogenesis and preovulatory stages, the minimal effective dose of sGnRH ranged between 10(-6) and -8 M. We have demonstrated that 17 alpha 20 beta P has a positive or negative effect by acting directly on pituitary cell responsiveness to sGnRH, depending on the stages at which it is applied; its effect is positive during early vitellogenic and preovulatory stages whereas it is negative at the time of ovulation. E2 also increased pituitary responsiveness to sGnRH when applied during early vitellogenesis at low doses, corresponding to circulating levels at the time of ovulation; higher levels of E2, corresponding to circulating levels found during the last stages of vitellogenesis, did not modify pituitary responsiveness but increased cell GtH content.(ABSTRACT TRUNCATED AT 250 WORDS)

Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout spermatogenesis and influence of steroid hormones.

Using primary cultures of whole dispersed pituitary cells collected from rainbow trout at different stages of spermatogenesis, basal and GnRH-induced GtH release and cell GtH content were studied in control and steroid-pretreated cultures. Steroid pretreatments were performed for 3 days with 11-ketotestosterone (11KT) and 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha 20 beta p) at levels corresponding to those circulating at the time of spermiation (50 and 20 ng/ml, respectively). In control cultures, basal GtH release and cell GtH content increased with the stage of spermatogenesis in a characteristic pattern as predicted from in vivo results concerning plasma and pituitary GtH contents. The pituitary response to salmon GnRH (sGnRH) also varied as indicated by the decrease in the minimal effective dose of GnRH able to induce a significant GtH release with the advancement of spermatogenesis: 10(-7) M at the spermatocyte stage, 10(-9) M at prespermiation and spermiation. Steroid pretreatments were shown to have a direct effect on pituitary gonadotrophs and particularly on pituitary response to sGnRH, depending on the stage at which they are applied. At the beginning of spermatogenesis both of them induced an increase in GtH release and at prespermiation they have a slight negative effect, significant only with 17 alpha 20 beta P. At spermiation they have no effect except for 17 alpha 20 beta P which increased the response to 10(-8) M of sGnRH. Results are discussed in relation to hormonel changes (gonadotropin and steroid) observed by different authors during the sexual cycle.

The metabolic clearance rate of estradiol-17 beta in rainbow trout, Salmo gairdneri R., estimated by both single injection and constant infusion methods: increase during oocyte maturation.

A dual cannulation of free-swimming rainbow trout is used to estimate the metabolic clearance rate (MCR) of Estradiol-17 beta (E2-17 beta) by both single injection and constant infusion methods. It is shown that E2-17 beta MCR changes significantly during the progress of oogenesis, mainly at the end of the sexual cycle. The same changes in MCR and very similar values are found with both single injection and constant infusion methods: MCR is stable (28.8 ml/hr/kg) from the postovulation period (throughout endogenous vitellogenesis) to early exogenous vitellogenesis. It decreases significantly during advanced exogenous vitellogenesis (18.7 ml/hr/kg) and increases clearly at the onset of oocyte maturation (40.9 ml/hr/kg). A direct relationship between MCR and plasma E2-17 beta occurs: Plasma E2-17 beta levels increase (advanced exogenous vitellogenesis) when MCR decreases. Then estradiol decline takes place at the same time that MCR reaches its highest values (oocyte maturation). An increase in MCR is probably one event required to allow the establishment of an appropriate hormonal environment for oocyte maturation.

[Evolution of plasma levels of glycoproteic gonadotropins and of 17 alpha hydroxy-20 beta dihydroprogesterone during maturation and ovulation of rainbow trout, Salmo gairdnerii]. / Evolution des niveaux plasmatiques de la gonadotropine glycoprotéique et de la 17 alpha hydroxy-20 beta dihydroprogestérone au cours de la maturation et de l'ovulation chez la Truite arc-en-ciel. Salmo gairdnerii.

The plasma concentrations of the glycoproteic gonadotropin (GTH) and of the 17 alpha hydroxy-20 beta dihydroprogesterone (17 alpha 20 beta OHP) have been followed in the course of ovulation in 6 rainbow trout, using radioimmunoassays on samples taken every two days. A first slow and limited GTH increase (10 to 20 ng/ml) is detected before and during the ovulation, while the 17 alpha 20 beta OHP rises sharply (up to three to five hundreds nanogrammes per millilitre). Then the progestagen levels drop back to their previous values, for about three weeks after ovulation. At the same time, a second higher GTH increase (25 to 20 ng/ml) is taking place. The relations between these two hormones, maturation and ovulation are discussed.