Litter Size In Sheep Research Articles

Analysis of litter size and days to lambing in the Ripollesa ewe. II. Estimation of variance components and response to phenotypic selection on litter size1

A performance data set from 376 Ripollesa purebred ewes of the experimental flock of the Universitat Autònoma of Barcelona was analyzed using a bivariate Bayesian threshold-linear model. The data set contained 1,598 litter size records and 1,699 days-to-lambing records. The model included the additive genetic effect of each animal and 3 nongenetic sources of variation: ewe age, year of lambing, and the permanent environmental effect characterized by the ewe. The flock was phenotypically selected for litter size since 1986, and replacement ewes and rams were selected from the progeny of the more prolific ewes, which had at least 3 deliveries recorded. The phenotypic trend for litter size was positive, whereas days to lambing followed an unclear pattern. Both traits had low heritabilities; 0.13 for litter size and 0.11 for days to lambing. Response to selection was evaluated through (a) the average breeding value of the ewe lambs chosen annually, and (b) the average breeding value of the overall flock. The first measurement suggested a positive trend for litter size, although it showed important oscillations. On the other hand, the average breeding value for the overall flock showed a stable positive tendency after yr 4 of selection, with estimates clearly different from zero after yr 11 of selection. A significant increase in the incidence of multiple births was observed, with a mode of approximately 10%. The correlated response in days to lambing did not show a significant trend. The effect of year of lambing also positively influenced both litter size and days to lambing, although important oscillations were observed between years. Results indicated that litter size in sheep can be effectively improved through phenotypic selection, even in small flocks; moreover, days to lambing could also be genetically improved, given the estimate obtained for its heritability.

Mutations in BMPR-IB and BMP-15 genes are associated with litter size in Small Tailed Han sheep (Ovis aries)1

The Small Tailed Han is a prolific local sheep breed in China. The bone morphogenetic protein receptor IB (BMPR-IB) gene, which affects the fecundity of Booroola Merino sheep, and the bone morphogenetic protein 15 (BMP-15) gene, which affects the fecundity of Inverdale, Hanna, Belclare, Cambridge, and Lacaune sheep, were studied as candidate genes associated with the prolificacy of Small Tailed Han sheep. Single nucleotide polymorphisms of BMPR-IB and BMP-15 genes were detected in Small Tailed Han ewes (n = 188) by PCR-RFLP. The combined effect of the 2 genes on the prolificacy of Small Tailed Han sheep was studied. The results indicated that the same FecB mutation (Q249R) occurred in the BMPR-IB gene in Small Tailed Han ewes as found in Booroola Merino ewes. The Small Tailed Han ewes with genotypes FecB(B)/FecB(B) and FecB(B)/FecB(+) had 1.40 (P < 0.01) and 1.11 (P < 0.01) more lambs, respectively, than those with genotype FecB(+)/FecB(+). The same FecX(G) mutation (Q239Ter) of the BMP-15 gene was found in Small Tailed Han ewes as in Belclare and Cambridge ewes. The Small Tailed Han ewes with the heterozygous mutant FecX(G)/FecX(+) had 0.55 (P < 0.01) more lambs than those with the wild-type FecX(+)/FecX(+). The Small Tailed Han ewes carrying mutations in both BMPR-IB and BMP-15 genes had greater litter size than those with either mutation alone. In view of our results, marker-assisted selection using both BMPR-IB and BMP-15 genes is warranted to increase litter size in sheep and will be of considerable economic value to sheep producers.

Analysis of litter size and days to lambing in the Ripollesa ewe. I. Comparison of models with linear and threshold approaches1

The analysis focused on model fitting of 2 ewe reproductive traits, litter size, and days to lambing (interval between the introduction of the ram into the flock and the subsequent parturition of the ewes). The experimental data set of the Universitat Autònoma of Barcelona flock was used, including 1,598 records of litter size and 1,699 records of days to lambing from 376 Ripollesa ewes between 1986 and 2005. Univariate and bivariate models were considered as beginning points with linear or threshold approximation for litter size. Model fitting was evaluated in terms of goodness-of-fit and predictive ability, using the mean square error and the correlation between phenotypic and predicted records (rho(y,ŷ)) as reference parameters. The bivariate model was preferable for both variables, minimizing mean square error and maximizing rho(y,ŷ). A threshold approximation for litter size was preferable over a linear approximation. Models were also compared with a simulation study, comparing the correlation coefficient between simulated and predicted breeding values (rho(a,â)). The bivariate threshold model was favored, with a rho(y,ŷ) of 0.677 and 0.834 for litter size and days to lambing, respectively. Correlation coefficients between simulated and predicted breeding values in the bivariate linear model were reduced slightly to 0.651 and 0.831, respectively, and they were lowest with linear univariate models (0.642 and 0.802). Although the bivariate models for ewe litter size and days to lambing were more accurate than the univariate models, the threshold approaches showed a greater advantage under the bivariate model. For the purpose of genetic evaluation of litter size in sheep, use of the threshold-linear model seems justified. In the Ripollesa breed, the evaluation of litter size can benefit from recording birth weight.

A Novel Mutation in the Bone Morphogenetic Protein 15 Gene Causing Defective Protein Secretion Is Associated with Both Increased Ovulation Rate and Sterility in Lacaune Sheep

Genetic mutations with major effects on ovulation rate and litter size in sheep were recently identified in three genes belonging to the TGFbeta superfamily pathway: the bone morphogenetic protein 15 (BMP15, also known as GDF9b), growth differentiation factor 9 (GDF9), and BMP receptor type IB (also known as activin-like kinase 6). Homozygous BMP15 or GDF9 mutations raise female sterility due to a failure of normal ovarian follicle development, whereas heterozygous animals for BMP15 or GDF9 as well as heterozygous and homozygous animals for BMP receptor type IB show increased ovulation rates. In the present work, a new naturally occurring mutation in the BMP15 gene in the high prolific Lacaune sheep breed is described. The identified variant is a C53Y missense nonconservative substitution leading to the aminoacidic change of a cysteine with a tyrosine in the mature peptide of the protein. As for other mutations found in the same gene, this is associated with an increased ovulation rate and sterility in heterozygous and homozygous animals, respectively. Further in vitro studies showed that the C53Y mutation was responsible for the impairment of the maturation process of the BMP15 protein, resulting in a defective secretion of both the precursor and mature peptide. Overall, our findings confirm the essential role of the BMP15 factor in the ovarian folliculogenesis and control of ovulation rate in sheep.

Bone morphogenetic protein receptor IB as a candidate gene for prolificacy in Small Tail Han and Hu ewes

AbstractThe bone morphogenetic protein receptor IB (BMPR-IB) gene, which controls the fecundity of Booroola Merino ewes, was studied as a candidate gene for the prolificacy of Small Tail Han and Hu ewes. A single nucleotide polymorphism of the BMPR-IB gene was detected in both high (Small Tail Han and Hu) and low (Suffolk and Dorset) fecundity sheep breeds by polymerase chain reaction–single-strand conformation polymorphism (PCR-SSCP) analysis. The results indicated the presence of the same mutation (A746G) of the BMPR-IB gene in both Small Tail Han and Hu ewes and in Booroola Merino ewes, but not in both Suffolk and Dorset ewes. In Small Tail Han ewes, frequencies of BB, B+ and ++ genotypes were 0.524, 0.383 and 0.093, respectively. In Hu ewes, these frequencies were 0.882, 0.118 and 0.000. The BMPR-IB genotype distributions were significantly different (P&lt;0.001) among high- and low-fecundity sheep breeds. Small Tail Han ewes with genotype BB had 0.92 (P&lt;0.01) and 1.02 (P&lt;0.01) lambs more than those with genotype ++ in the first and second parity, respectively. These results demonstrated that the BMPR-IB gene is a major gene affecting the prolificacy in both Small Tail Han and Hu ewes, and could be used as a molecular genetic marker to select the litter size in sheep.

Association Between PCR-SSCP of Growth Differentiation Factor 9 Gene and High Prolificacy in Small Tail Han Sheep#

Small Tail Han sheep that has significant characteristics of high prolificacy and nonseasonal ovulatory activity is an excellent local sheep breed in P.R. China. The lambing percentage averaged 260% in Small Tail Han sheep. Growth differentiation factor 9 (GDF9) gene, which was essential for growth and differentiation of early ovarian follicles, was considered as a possible candidate gene for litter size in Small Tail Han sheep. The genetic polymorphism of a part of the GDF9 gene was detected in 130 ewes of Small Tail Han sheep by PCR-SSCP. The results indicated that there were two genotypes (AA and AB) detected by two primer pairs. In both exon 1 and exon 2 of the GDF9 gene in Small Tail Han sheep, frequencies of AA genotype were 0.846 and 0.908, frequencies of AB genotype were 0.154 and 0.092, frequencies of A allele were 0.923 and 0.954, and frequencies of B allele were 0.077 and 0.046, respectively. The results of χ 2 fitness test indicated that both exon 1 and exon 2 of the GDF9 gene were in Hardy-Weinberg equilibrium (p > 0.05) in Small Tail Han sheep. Least squares means of litter size in the first and the second parity for genotype AA were 0.30 (p < 0.05) and 0.77 (p < 0.0001) more than those for genotype AB detected in exon 1 of the GDF9 gene in Small Tail Han sheep, respectively. Fragments detected in exon 2 of the GDF9 gene had no significant effect (p > 0.05) on litter size in both the first and the second parity in Small Tail Han sheep. Litter size in sheep is lowly heritable, expressed only in females, and manifested relatively late in life. Access to genetic markers would thus be advantageous in selection programs. #Supported by National Natural Science Foundation of China (30300248 and 30140004) and National High Technology Research and Development Program of China (2002AA211081).

Are BMP-15 and GDF-9 primary determinants of ovulation quota in mammals?

How do mammals control the number of eggs that are ovulated during the estrous and menstrual cycles? Our understanding of this fundamental process has grown in recent years as a result of intense efforts to identify and characterize the genes that control the ovulation quota. An increasing body of evidence shows that two oocyte-specific factors, bone morphogenetic protein-15 (BMP-15) and growth and differentiation factor-9 (GDF-9), play crucial roles in determining folliculogenesis, ovulation rate and litter size in sheep and mice. In this article, we review recent advances on the physiological, cellular and molecular roles of BMP-15 and GDF-9, which, potentially, link these oocyte-secreted factors to the species-specific determination of ovulation quota and litter size in mammals.

Multitrait and repeatability estimates of random effects on litter size in sheep

AbstractFive data sets with records of first, second and third lambings of the White Alpine sheep (WAS1, WAS2), the Brown-Headed Meat sheep (BFS), the Black-Brown Mountain sheep (SBS) and the Valais Black-Nose sheep (SNS) of Switzerland were used to estimate phenotypic and genetic parameters for litter size using a multitrait and a repeatability model by the REML method. The sets contained litter information from 26 274, 25 165, 18 913, 14 953 and 21 726 ewes, respectively. Average numbers of litters per ewe were between 2·09 and 2·31. Average litter sizes at birth were between 1·36 and 1·57 lambs in first, between 1·52 and 1·75 in second and, between 1·56 and 1·86 in third parities. Multitrait estimates of heritability for size of first litters were 0·164, 0·157, 0·117, 0·223 and 0·116 for the WAS1, WAS2, BFS, SBS and SNS data, respectively. The corresponding estimates were 0·176, 0·165, 0·140, 0·208 and 0·134 for second and, 0·141, 0·155, 0·121, 0·145 and 0·107 for third litters. The systematic increase in phenotypic variances from first to third litter within data sets favoured the multivariate over the repeatability approach. Genetic correlations between size of the first three litters were, with one exception, above 0·927. Random flock ✕ year and sire of litter effects contributed between 2·2% and 13·2% and between 0·7% and 4·7% to the phenotypic variance of the traits, respectively. Residuals contributed between 70·6% and 84·2% to this parameter, estimates for the third litter were always highest. Heritability estimates from the repeatability model were smaller than the smallest multivariate estimates. Expected genetic gain in litter size from selection on the multitrait model was equal to the achieved response from the repeatability approach.

Suitability of microsatellites BM1329 and OarAElOl as markers for the introgression of the Fec&amp;lt;sup&amp;gt;B&amp;lt;/sup&amp;gt; locus into different sheep breeds

Abstract. Litter size in sheep can be improved by introgression of the FecB gene. Genetic markers closely linked to the FecB locus can be used to detect gene carriers. The efficiency of introgression can be increased by using marker assisted selection. Individuals of the prolific breeds Tyrolean Mountain sheep (n = 41), Romanov (n = 43), East Friesian Milksheep (n = 35) and Merinoland sheep (n = 265) were genotyped with the microsatellite markers OarAElOl and BMI 329 linked to the FecB gene to estimate allele frequencies of both microsatellites in these breeds. The frequencies of the microsatellite alleles linked to the FecB gene in Merinoland sheep were 0.07 and 0.1 respectively. The alleles occured also in the other breeds (Tyrolean Mountain sheep, Romanov and East Friesian Milksheep) but with mostly higher frequencies. Furthermore the segregation of the microsatellite alleles was studied in families produced by mating Merinoland sheep ewes (Fec+/Fec+) with two heterozygous Booroola Merino rams (Fec+/FecB) in order to use these markers within an indirect gene test. The recombination rate between BM 1329 and OarAElOl was 13 cM (LOD score 14.6).

Estimation of genetic parameters for litter size in sheep: a comparison of a repeatability and a multivariate model

AbstractGenetic parameters were estimated for litter size in two prolific sheep breeds, i.e. the Zwartbles and the synthetic breed Swifter. Genetic parameters and breeding values for litter size in different parities were estimated using both a repeatability and a multivariate animal model. The estimated heritability from the repeatability model was 0·10 for the Zwartbles and 0·12 for the Swifter. For the multivariate model, heritability of litter size in first, second and third parity was 0·05, 0·07 and 0·10 for the Zwartbles and 0·09, 0·12 and 0·09 for the Swifter. Genetic correlation for litter size in Swifter was 0·81 between parity 1 and 2 and 0·99 between parity 2 and 3. For the Zwartbles genetic correlations were all very close to unity. Environmental correlations between litter size in subsequent parities were not constant over parities. Phenotypic variance in litter size in both breeds was 0·309 in first parity and was almost 50% higher in later parities. Based on the results it is recommended to apply a multiple trait model.

Genetic improvement of litter size in sheep. A comparison of selection methods

Genetic improvement of litter size in sheep. A comparison of selection methods

Genetic improvement of litter size in sheep. A comparison of selection methods

Cet article discute l'interet du taux d'ovulation (OR) pour accroitre le progres genetique sur la taille de portee (LS) et etudie a cet effet divers criteres de selection combinant OR et le taux de survie embryonnaire (ES). On a examine par simulation les reponses a la selection en 5 generations dans une population de 20 et 600 reproducteurs mâles et femelles avec 50 replications par methode. On a considere 2 races, de prolificite faible (Merinos) et moyenne (Lacaune). Les performances ont ete generees a partir d'un modele bicaractere a seuils. Les heritabilities d'OR et ES ont ete supposees constantes sur l'echelle sous-jacente dans les 2 races et prises egales respectivement a 0,35 et 0,11 avec une correlation genetique entre ces 2 caracteres de −0,40. Quatre methodes d'evaluation genetiques ont ete comparees: i) Blup unicaractere base sur LS (b-LS); ii) Blup unicaractere base sur OR (b-OR); iii) Blup bicaractere base sur OR et LS (b-ORLS); iv) Predicteur du maximum a posteriori bicaractere d'un modele lineaire generalise ou OR est traite comme un caractere continu et ES comme un caractere a seuils (t-ORES). Les reponses observees etaient tres voisines avec b-LS, b-ORLS et t-ORES, alors que b-OR donne une reponse significativement inferieure. La reponse sur OR etait maximum avec b-OR et minimum avec b-LS, tandis que la reponse sur ES etait maximum avec b-LS. Cette etude pose la question de savoir pourquoi la selection basee sur des indices combinant OR et ES ne donne pas de resultats significativement superieurs a la selection sur LS

Active immunisation against inhibin promotes a recurrent increase in litter size in sheep.

Active immunisation against inhibin promotes a recurrent increase in litter size in sheep.

Inhibin as a fecundity vaccine

Inhibin acts as a negative feedback regulator of follicle stimulating hormone (FSH), therefore, attenuation of its biological activity through immunisation should lead to an increase in the circulating concentrations of FSH. In turn, this should result in increased ovulation rates and a consequent increase in litter size. In this article, we review work on the structure and function of inhibin which ultimately led to the development of inhibin-based fecundity vaccines. These vaccines have been shown to cause increases in ovulation rate and litter size in sheep and increases in ovulation rate in cattle and pigs. The data establish a basis for using inhibin vaccines to increase fecundity in animals of economic importance.

Physiology and molecular genetics of mutations that increase ovulation rate in sheep.

I. Introduction VARIATION in litter size in sheep is controlled by both genetic and environmental factors. Most breeds of domestic sheep have one or two lambs at each lambing, although a small number of breeds, including the Booroola Merino, Cambridge, D'Man, Finnish Landrace, and Romanov, consistently have litter sizes of three or more (see Ref. 1). Attempts to increase litter size by selection within a breed result in slow progress because the heritability of litter size is low (2). Therefore, the discovery of major genes (or mutations) with large effects on ovulation rate, and thus litter size, has generated considerable interest among sheep breeders and scientists. The major gene (FecB) in the Booroola Merino breed was first postulated in 1980 (3). Since then, the search for other mutations influencing reproduction in sheep has intensified, and a number have been proposed (4–8). As an alternative to the slow progress achieved by selection for litter size, these mutations allow more rapid progress by i...

Increased ovulation and twin-calving rates in heifers immunized against bovine inhibin peptides

Inhibin is a dimeric protein hormone composed of two dissimilar, disulphide-linked subunits (termed α and β) involved in the negative feedback regulation of gonadotrophin secretion, preferentially FSH. Interfering with this negative feedback by active immunization against inhibin has resulted in a consistent increase in ovulation rate and litter size in sheep. However, similar results have not been achieved in cattle. This paper describes the effect of active immunization of heifers against either of 3 synthetic peptide sequences from the bovine inhibin α-subunit on inhibin antibody titres, ovulation rate, calving rate and twin-calving rate.Three peptide sequences from the bovine inhibin a-subunit were identified as likely immunological epitopes by computer analysis. These peptides (P1: bl-α-[YG] (18-30); P2: bl-α-(63-72)[GY]; P3: bl-α-[CG](107-122) were synthesized by solid phase methods and tyrosyl or cystenyl residues, linked through a glycine spacer where appropriate, were added during synthesis in order to facilitate iodination and conjugation respectively.

Reproductive technology in animal production

Research into physiology and embryology has provided a basis for the development of technologies that increase productivity of farm animals through enhanced control of reproductive function. Progestagens, alone or in combination with luteolysins, are used to control the time of oestrus in cattle, sheep and pigs, thus permitting better use of artificial insemination, providing synchronised recipients for embryos and facilitating management strategies. Treatment with progestagens and pregnant mare serum gonadotrophin (PMSG) or with gonadotrophin releasing hormone induces breeding activity in sheep and goats before the commencement of the breeding season and reduces the duration of postpartum anoestrus in cattle. In pigs, gonadotrophins are used to hasten puberty in gilts, control the time of oestrus in sows and gilts and reduce the interval between farrowing and oestrus. Implants of melatonin hasten the onset of the breeding season in sheep and goats. Success in increasing litter size in sheep and cattle with PMSG has been limited because of the large variation in response between animals. Likewise, immunisation against steroids has not given consistent results. Immunisation against inhibin appears to offer the possibility of increasing farm animal fecundity. Induction of twinning in cattle by embryo transfer is practicable, and recent developments suggest that in vitro fertilisation may provide a source of embryos for this purpose. Real-time ultrasonic scanning has proved to be a reliable method for diagnosing pregnancy in small ruminants and pigs. The identification of pregnancy-specific proteins in cattle and sheep may provide a cheap and practical serological test for pregnancy in these species. Partial segregation of spermatozoa into X- and Y-bearing components has been reported, but the method is not yet practicable for use in conventional artificial insemination of farm animals. The sex of bovine and ovine embryos can be determined reliably by DNA probes specific for the Y chromosome. Monozygous twins can be produced in all farm animal species by microsurgical bisection of embryos and techniques for cloning from embryonic cells are rapidly being developed. There is a need to devise strategies to utilise these clones to best advantage in genetic programmes. Chimeric animals can be produced in the common farm animal species and will play an important role in genetic engineering, particularly when embryonic stem cell lines are produced in these species.

Effect of selection for increased litter size on ovulation rate and embryo survival in sheep

Variation in litter size in sheep is essentially attributable to variation in ovulation rate and embryo survival. Genetic variation in litter size, both among and within breeds, is largely attributable to variation in ovulation rate. While there is evidence for genetic differences among breeds in embryo survival the contribution of this component to within breed variation appears to be minor (Hanrahan, 1982). The impact of selection based on litter size on its component traits should reflect the relative contribution of these components to within breed variation. Data from two lines of Galway sheep, a Control line and one selected for increased prolificacy (Hanrahan and Timon, 1978), have been used to provide evidence on this point.Details relating to the selection experiment which provided the data for the present study are in Hanrahan (1984). Briefly a flock of Galway sheep was assembled from industry sources (both pedigree and non-pedigree) between 1963 and 1965.

Methods of estimation of genetic effects from two breeds crossing system with an application to litter size in sheep1

Methods of estimation of genetic effects from two breeds crossing system with an application to litter size in sheep¹

The evaluation of selection in a crossing ram breed to improve litter size in sheep.

Five genotypes were compared as sires of crossbred ewes from Scottish Blackface dams. These included Border Leicester (BL), New Zealand Romney (R) (from two group breeding schemes where selection had emphasized litter size), and three lines from the composite A.B.R.O. Damline (DL). Selection of the male and female lambs in the purebred DL flock was: a)for an average of 5.5 years on a Ewe Index of eight week litter weight (Martin and Smith, 1980).b)for an average of 3.5 years on a Testis index, combining testis size (adjusted for body weight) and Ewe Index of eight week litter weight both components receiving approximately equal weight andc)a random bred control.These five genotypes (two rams per genotype per year for five years) were group mated (sires of individual ewes were not known) with Scottish Blackface ewes on an upland farm in Ayrshire.