Expression of seasonality in Merinos d'Arles ewes of different genotypes at the MT1 melatonin receptor gene

Genome-Wide Association Study Demonstrates the Role Played by the CD226 Gene in Rasa Aragonesa Sheep Reproductive Seasonality

Simple Summary

To elucidate the genetic basis of reproductive seasonality in Rasa Aragonesa sheep breed, we performed a genome-wide association study (GWAS) in order to detect single nucleotide polymorphisms (SNPs) or regions associated with traits related to ovarian function and behavioural signs of estrous. The GWAS included 205 ewes with genotypes for 583882 SNPs. Only one SNP overcame the genome-wide significance level. Nine potential SNPs overcame the chromosome-wise significance level (FDR 10%). Gene annotation demonstrated that CD226molecule (CD226) and neuropeptide Y (NPY) genes that could be involved in reproductive seasonality were close to the significant SNPs. To validate the results, we sequenced the entire coding region of the NPY gene and four exons of the CD226 gene to search for polymorphisms that could be involved in the phenotypes studied. Two synonymous and two nonsynonymous SNPs in the NPY and CD226 genes, respectively, were genotyped in the whole population. We demonstrated that the AA genotype of the SNP rs404360094 located in exon 3 of the CD226 gene was associated with higher and lower total days of anoestrus and oestrous cycling months, respectively. Therefore, this SNP could be utilized as a genetic marker for assisted selection marker to reduce seasonality.

Abstract

A genome-wide association study (GWAS) was used to identify genomic regions influencing seasonality reproduction traits in Rasa Aragonesa sheep. Three traits associated with either ovarian function based on blood progesterone levels (total days of anoestrus and progesterone cycling months) or behavioral signs of oestrous (oestrous cycling months) were studied. The GWAS included 205 ewes genotyped using the 50k and 680k Illumina Ovine Beadchips. Only one SNP associated with the progesterone cycling months overcame the genome-wide significance level (rs404991855). Nine SNPs exhibited significant associations at the chromosome level, being the SNPs rs404991855 and rs418191944, that are located in the CD226 molecule (CD226) gene, associated with the three traits. This gene is related to reproductive diseases. Two other SNPs were located close to the neuropeptide Y (NPY) gene, which is involved in circadian rhythms. To validate the GWAS, partial characterization of both genes by Sanger sequencing, and genotyping of two synonymous and two nonsynonymous SNPs in the NPY and CD226 genes, respectively, were performed. SNP association analysis showed that only SNP rs404360094 in the exon 3 of the CD226 gene, which produces an amino acid substitution from asparagine (uncharged polar) to aspartic acid (acidic), was associated with the three seasonality traits. Our results suggest that the CD226 gene may be involved in the reproductive seasonality in Rasa Aragonesa.

The LEPR Gene Is Associated with Reproductive Seasonality Traits in Rasa Aragonesa Sheep

The aim of this study was to characterize and identify causative polymorphisms in the leptin receptor (LEPR) gene responsible for the seasonal variation of reproductive traits in sheep. Three reproductive seasonality traits were studied: the total days of anoestrous (TDA), the progesterone cycling months (P4CM) and the oestrous cycling months (OCM). In total, 18 SNPs were detected in 33 ewes with extreme values for TDA and OCM. Six SNPs were non-synonymous substitutions and two of them were predicted in silico as deleterious: rs596133197 and rs403578195. These polymorphisms were then validated in 239 ewes. The SNP rs403578195, located in exon 8 and leading to a change of alanine to glycine (Ala284Gly) in the extracellular domain of the protein, was associated with the OCM trait, being the G allele associated with a decrease of 12 percent of the OCM trait. Haplotype analyses also suggested the involvement of other non-synonymous SNP located in exon 20 (rs405459906). This SNP also produces an amino acid change (Lys1069Glu) in the intracellular domain of the protein and segregates independently of rs403578195. These results confirm for the first time the role of the LEPR gene in sheep reproductive seasonality.

Short-, Medium- and Long-Term Metabolic Responses of Adult Meat Ewes Subjected to Nutritional and β-Adrenergic Challenges

Simple Summary

The ability of Merinos d’Arles ewes to quickly overcome undernutrition situations by efficiently using their body energy reserves was confirmed in this study. There is potential for a simplified ß-adrenergic challenge protocol helping to identify differences in adaptive capacity among individuals reared and fed under similar conditions in the same flock.

Abstract

Shortage and refeeding situations lead to switches in metabolic pathways induced by undernutrition and body energy reserve (BR) replenishment cycles. In a 122-d experiment, 36 adult Merinos d’Arles ewes were chosen and first accustomed to diet ingredients (i.e., wheat straw, pelleted alfalfa and sugar beet pulp) and the facility environment for 22 d. Then, ewes were randomly assigned to one of three “diet challenge” treatments during 50 d, (control, underfed and overfed; 12 ewes each) corresponding to 100%, 70% or 160% of energy requirements allowances, respectively. Then, a “refeeding challenge” was applied the last 50 d (i.e., diets adjusted with the same ingredients). An individual monitoring of body weight (BW), body condition score (BCS) and energy metabolism was carried out. The last day, a “ß-adrenergic challenge” was applied. Anabolic or catabolic responses were accompanied by synchronized metabolic regulations, leading to contrasting metabolic and BR profiles. Average BW and BCS were higher and lower in overfed and underfed ewes, respectively, which was proportional to lower and higher BR mobilization dynamics. Higher plasma free fatty acids (FFA) were accompanied by lower blood insulin, leptin and glucose levels. After refeeding, a rebound in BW and BCS were observed, and FFA were drastically reduced in underfed ewes. No differences were detected in plasma FFA at the end of the study, but the lipolytic activity was different and contrasted with the adipose tissue mass.

Genetic polymorphism in melatonin receptor 1A and arylalkylamine N-acetyltransferase and its impact on seasonal reproduction in Egyptian sheep breeds

This study was carried out to detect polymorphisms in the melatonin receptor 1A (MTNR1A) and arylalkylamine N-acetyltransferase (AA-NAT) genes and their association with reproductive traits. Blood samples of 126 animals from three Egyptian sheep breeds were collected. DNA was extracted and subjected to PCR restriction fragment length polymorphism (RFLP) analysis using the RsaI and SmaI enzymes. Two alleles (C and T) and three genotypes (CC, CT and TT) for MTNR1A and for AA-NAT (A and G; GG, GA and AA) were detected. The alleles C and A and the genotypes CT and GA showed the highest frequencies for the MTNR1A and AA-NAT genes, respectively. Association analysis of the MTNR1A single nucleotide polymorphism (SNP) with ewe reproductive traits revealed significant associations in the Ossimi and Rahmani breeds with age at first lambing, and the C allele seemed to be the favorable allele. The results for the AA-NAT SNP demonstrated significant correlations in Ossimi with age at first lambing and litter size and in Rahmani with lambing interval; the G allele seemed to be the desirable allele. In the first conception season, ewes carrying CT exhibited a significantly lower age of first lambing in the unfavorable season. Additionally, GG ewes exhibited a significantly lower age of first lambing in the early favorable season, followed by the unfavorable season. To the best of our knowledge, this is the first study of these associations in Egyptian sheep breeds. In conclusion, the polymorphisms revealed in this study could be used as genetic markers to improve reproductive efficiency during the unfavorable season, and the obtained desirable genotypes could be considered in new genetic selection schemes.

An automated method for the evaluation of ram libido in real mating conditions

We investigated if sexual behaviour of rams can be assessed with an electronic Alpha-Detector (AD) which automatically records mounts of mating rams. To evaluate the rams' libido (i.e. all sexual activities), we used six intact and six vasectomised rams in pen tests in three different seasons (late spring, autumn and early spring). The pen tests consisted of 30-min visual observations of each ram placed in a group of six Merino ewes (three ewes in oestrus and three ewes not in oestrus). In the pen tests, sexual behaviour was recorded and divided into two categories: pre-copulatory and copulatory. For validation purposes, during the pen tests the 12 rams were equipped with the AD and the number of times the 18 oestrous ewes were mounted were counted over a period of 3 days. Of the 1191 mounts visually identified in the six 30-min sessions, 1026 were recorded automatically by the AD (i.e. 94%). The paddock test is an automated method consisting of the same rams wearing an AD and placed in a flock of ~250 Merino ewes on two occasions (late spring (spring 1) and early spring of the following year (spring 2)), their copulatory activities were automatically recorded over a 5-day period. The results of the pen tests in the three seasons revealed no difference between the two types of rams (breeding v. detecting rams). Based on live observations high correlations (r=+0.81, P<0.003 for breeding and r=+0.76, P<0.02 for detecting rams) were found between pre-copulatory and copulatory behaviours. The libido of the two types of rams measured in pen tests showed high repeatability across the three seasons (83 and 75%, P<0.05 for copulatory and pre-copulatory behaviours, respectively). When measured automatically in paddock tests over two consecutive springs, even higher repeatability was observed in both breeding (94%; P<0.01) and detecting rams (97%; P<0.004) in the number of mounts. In addition, high correlations (+0.89<r<+0.94) between copulatory behaviours, as measured by live observations, and those measured by the AD were obtained. The automatic measurement of ram libido in paddock tests appears to be more reliable than pen tests and far less time consuming. We therefore recommend this automated method to estimate the libido of rams. In addition, this method can be used at any season of the year provided that ewes in oestrus are present in the flock.

Seasonal reproductive performance of crossbred ewes in intensive lamb-production systems

The lambing performance of 1179 crossbred ewes with 5540 joining records in three seasons (autumn, winter and spring) at two sites (Cowra and Wagga Wagga) was evaluated in three lamb-production systems (spring joining with autumn backup matings at both locations, with accelerated lambing at Cowra or annual autumn joining at Wagga Wagga) over 4 years. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural matings to Dorset, Suffolk or Hyfer rams. The following five traits were analysed separately at each site to evaluate ewe lambing performance: fertility, litter size, lambs born (per ewe joined), lambs weaned (per ewe joined) and weight of lamb weaned (per ewe joined). The mixed model included fixed effects for season of joining, ewe breed, ram group, ewe prejoining weight (spline) and their interactions, with ewe fitted as a random effect. The autumn (February) joinings had higher ewe fertility, litter size and overall lamb production than did joinings in spring (October and November), with winter (June) being intermediate. At the autumn joinings, the BLM ewes had higher fertility, lambs weaned and weight of lamb weaned than did the Hyfer ewes, although this was reversed at the spring joinings, causing significant season × ewe breed interactions. While litter size was larger in the autumn than in the spring for both breeds there was a much smaller seasonal effect among the Hyfer than BLM ewes. Prejoining ewe weight had a significant effect on all reproduction traits, with generally a curvilinear response with increasing weight. The interactions of weight with season × ewe breed were significant (P < 0.001) for all traits at Cowra and most traits at Wagga Wagga. Ram group was significant (P < 0.05) for most traits, with ewes joined to Hyfer rams having higher fertility than those joined to Suffolk. and with Dorset rams being intermediate. At Wagga Wagga, this was the case for spring joinings, but there was no difference between the ram groups in autumn, causing a significant ram × season interaction (P < 0.001). Ewe repeatability ranged from 0.15 to 0.25 for all traits. Using suitable breeds or genotypes, together with optimising management, could improve out-of-season lamb production.

Characterisation of the Melatonin Receptor 1A (MTNR1A) gene in the Rasa Aragonesa sheep breed: association with reproductive seasonality

The ovine Melatonin Receptor 1A (MTNR1A) gene was structurally characterised and association between its variants and the reproductive seasonality was examined in a daughter design comprising three families of Rasa Aragonesa sheep breed. Sequencing of six Rasa Aragonesa ewes with extreme values for seasonality trait revealed 28 polymorphisms: 11 SNPs in the coding region (all in Exon 2), and 17 SNPs in the promoter region MTNR1A. All the substitutions in the coding region were found most likely lacking any phenotypic effect, because they are conservative mutations or were not part of the transmembrane domain. The silent mutations, which had shown association with reproductive seasonality in other breeds, were also found and genotyped in Rasa Aragonesa. The T allele of SNP606/RsaI of MNTR1A gene was associated with a greater percentage of oestrous cyclic ewes in the Rasa Aragonesa breed, indicating that this SNP may be in linkage disequilibrium with a mutation responsible for this trait close to MTNR1A, or in regulatory sequences of the gene. In this sense, several SNPs affecting a binding element for some transcription factors have been identified in the promoter region. The SNPs at 422 and 527 positions could constitute a binding element for some transcription factors (TFs), located in an EF2 and SRY consensus sites in the promoter region, respectively. Haplotype h(5) showed significant differences with the h(2) haplotype (66% compared to 49.2%) on oestrous cyclicity, thus these results are consistent with genotypic associations for each SNP. Haplotype with T, A and T alleles for SNPs 422, 677 (promoter region) and 612 (Exon 2) showed an increase of the percentage of oestrous cyclic ewes. Although some of these mutations have been associated with seasonal reproduction, further studies with a more appropriate animal design as well as functional studies of TF binding activity are needed.