Consecutive unilateral recording of the two eyes affects dark-adapted ERG responses, when compared to simultaneous bilateral recording.

PURPOSE: Our aim was to compare the electroretinographic (ERG) responses of two eyes obtained by consecutive unilateral recordings to those obtained by a simultaneous bilateral recording in sheep. METHODS: Eight sheep underwent two full-field ERG recordings, using two recording strategies of the standard ISCEV protocol: consecutive unilateral recordings of one eye after the other, and simultaneous bilateral recording of both eyes. The order of recording strategy within an animal (unilateral/bilateral), eye recording sequence in the unilateral session (OD/OS), and amplifier channel assignment for each eye were all randomized. To test whether duration of dark adaptation and/or anesthesia affect the results, the ISCEV protocol was recorded bilaterally in six additional eyes following 38 min of patched dark adaptation, as was done for the second eye recorded in the consecutive unilateral recordings. RESULTS: The second recorded eye in the unilateral session had significantly higher scotopic b-wave amplitudes compared to the first recorded eye and to the bilaterally recorded eyes. A-wave amplitudes of the dark-adapted mixed rod-cone responses to a high-intensity flash were also significantly higher in the second eye compared to the first eye recorded unilaterally and to the bilaterally recorded eyes. Light-adapted responses were unaffected by the recording strategy. When the ISCEV protocol was recorded after 38 min of dark adaptation, the scotopic responses were higher than in the first eyes, and similar to those of the second eyes recorded unilaterally, suggesting that indeed the longer duration of anesthesia and dark adaptation are responsible for the increased scotopic responses of the second eye. CONCLUSIONS: Consecutive unilateral ERG recordings of two eyes result in higher amplitudes of the dark-adapted responses of the eye recorded second, compared to the eye recorded first and to bilaterally recorded eyes. The differences in scotopic responses can be attributed to different duration of dark adaptation and/or anesthesia of the two consecutively recorded eyes. Photopic responses are not affected. Therefore, simultaneous bilateral ERG responses should be recorded when possible, especially for evaluation of scotopic responses.

Unveiling genomic regions that underlie differences between Afec-Assaf sheep and its parental Awassi breed.

BACKGROUND: Sheep production in Israel has improved by crossing the fat-tailed local Awassi breed with the East Friesian and later, with the Booroola Merino breed, which led to the formation of the highly prolific Afec-Assaf strain. This strain differs from its parental Awassi breed in morphological traits such as tail and horn size, coat pigmentation and wool characteristics, as well as in production, reproductive and health traits. To identify major genes associated with the formation of the Afec-Assaf strain, we genotyped 41 Awassi and 141 Afec-Assaf sheep using the Illumina Ovine SNP50 BeadChip array, and analyzed the results with PLINK and EMMAX software. The detected variable genomic regions that differed between Awassi and Afec-Assaf sheep (variable genomic regions; VGR) were compared to selection signatures that were reported in 48 published genome-wide association studies in sheep. Because the Afec-Assaf strain, but not the Awassi breed, carries the Booroola mutation, association analysis of BMPR1B used as the test gene was performed to evaluate the ability of this study to identify a VGR that includes such a major gene. RESULTS: Of the 20 detected VGR, 12 were novel to this study. A ~7-Mb VGR was identified on Ovies aries chromosome OAR6 where the Booroola mutation is located. Similar to other studies, the most significant VGR was detected on OAR10, in a region that contains candidate genes affecting horn type (RXFP2), climate adaptation (ALOX5AP), fiber diameter (KATNAl1), coat pigmentation (FRY) and genes associated with fat distribution. The VGR on OAR2 included BNC2, which is also involved in controlling coat pigmentation in sheep. Six other VGR contained genes that were shown to be involved in coat pigmentation by analyzing their mammalian orthologues. Genes associated with fat distribution in humans, including GRB14 and COBLL1, were located in additional VGR. Sequencing DNA from Awassi and Afec-Assaf individuals revealed non-synonymous mutations in some of these candidate genes. CONCLUSIONS: Our results highlight VGR that differentiate the Awassi breed from the Afec-Assaf strain, some of which may include genes that confer an advantage to Afec-Assaf and Assaf over Awassi sheep with respect to intensive sheep production under Mediterranean conditions.

Gene Augmentation Therapy Restores Retinal Function and Visual Behavior in a Sheep Model of CNGA3 Achromatopsia.

Achromatopsia is a hereditary form of day blindness caused by cone photoreceptor dysfunction. Affected patients suffer from congenital color blindness, photosensitivity, and low visual acuity. Mutations in the CNGA3 gene are a major cause of achromatopsia, and a sheep model of this disease was recently characterized by our group. Here, we report that unilateral subretinal delivery of an adeno-associated virus serotype 5 (AAV5) vector carrying either the mouse or the human intact CNGA3 gene under the control of the red/green opsin promoter results in long-term recovery of visual function in CNGA3-mutant sheep. Treated animals demonstrated shorter maze passage times and a reduced number of collisions with obstacles compared with their pretreatment status, with values close to those of unaffected sheep. This effect was abolished when the treated eye was patched. Electroretinography (ERG) showed marked improvement in cone function. Retinal expression of the transfected human and mouse CNGA3 genes at the mRNA level was shown by polymerase chain reaction (PCR), and cone-specific expression of CNGA3 protein was demonstrated by immunohistochemisrty. The rescue effect has so far been maintained for over 3 years in the first-treated animals, with no obvious ocular or systemic side effects. The results support future application of subretinal AAV5-mediated gene-augmentation therapy in CNGA3 achromatopsia patients.

Flicker cone function in normal and day blind sheep: a large animal model for human achromatopsia caused by CNGA3 mutation.

PURPOSE: Recently we reported on day blindness in sheep caused by a mutation in the CNGA3 gene, thus making affected sheep a naturally occurring large animal model for therapeutic intervention in CNGA3 achromatopsia patients. The purpose of this study was to characterize flicker cone function in normal and day blind sheep, with the aim of generating a normative data base for ongoing gene therapy studies. METHODS: Electoretinographic (ERG) cone responses were evoked with full-field conditions in 10 normal, 6 heterozygous carriers and 36 day blind sheep. Following light adaptation (10 min, 30 cd/m(2)), responses were recorded at four increasing light intensities (1, 2.5, 5 and 10 cd s/m(2)). At each of these intensities, a single photopic flash response followed by 8 cone flicker responses (10-80 Hz) was recorded. Results were used to generate a normative data base for the three groups. Differences between day blind and normal control animals were tested in two age-matched groups (n = 10 per group). RESULTS: The normal sheep cone ERG wave is bipartite in nature, with critical flicker fusion frequency (CFF) >80 Hz. In all four flash intensities, the single photopic flash a-wave and b-wave amplitudes were significantly lower (p < 0.005), and implicit times significantly delayed (p < 0.0001), in day blind animals. In all four flash intensities, CFF values were significantly lower (p < 0.0001) in day blind sheep. CONCLUSIONS: Cone function is severely depressed in day blind sheep. Our results will provide a normative data base for ongoing gene therapy studies.

Biochemical and in vitro biological significance of natural sequence variation in the ovine leptin gene.

The hormone leptin is involved in diverse biological processes, including regulation of food intake, body-weight homeostasis and energy balance. Sequence variation in the bovine leptin gene has been found to be associated with variations in carcass fat content and average daily gain, as well as in milk yield, milk somatic cell count and several traits governing reproduction. We sequenced genomic DNA and cDNA samples of individuals from three divergent sheep breeds and revealed synonymous as well as novel non-synonymous allelic variation at the third exon of the ovine leptin gene (oLEP) as compared to the sequence published at Accession No. U84247 (reference sequence). In addition, two alternatively spliced oLEP transcripts were found in the abdominal fat tissue. The biochemical and the in vitro biological significance of the sequence variation in the oLEP was examined by generating recombinant oLEP-protein variants namely: p.Q28del, p.N78S, p.R84Q, p.P99Q, p.V123L and p.R138Q, carrying the corresponding sequence variation. Surface plasmon resonance experiments revealed, in most cases, reduced affinity of the oLEP protein variants examined, to human leptin-binding domain (hLBD), relative to the reference variant, being 0.75, 0.60, 0.60, 0.89, 0.92 and 1.03, respectively. In competitive binding assays between biotinylated oLEP and the recombinant leptin protein variants, p.N78S and p.R84Q variants exhibited the lowest affinity to hLBD (0.18 and 0.41, respectively) as compared to the reference hormone. We then tested the protein variants' ability to induce proliferation in Baf-3 cells stably expressing the long form of the human leptin receptor: significant differences in proliferative activity were only found for p.N78S (1.8-fold higher) and p.R138Q (4.2-fold lower) relative to the reference oLEP variant.

A mutation in gene CNGA3 is associated with day blindness in sheep.

Lambs with congenital day blindness show diminished cone function, which is characteristic of achromatopsia, a congenital disorder described in humans and dogs. To identify gene(s) associated with sheep day blindness, we investigated mutations in the CNGA3, CNGB3, and GNAT2 genes which have been associated with achromatopsia. Sequencing the coding regions of those genes from four affected and eight non-affected lambs showed that all affected lambs were homozygous for a mutation in the CNGA3 gene that changes amino acid R236 to a stop codon. By PCR-RFLP-based testing, homozygosity for the stop codon mutation was detected in another 19 affected lambs. Non-affected individuals (n=386) were non-carriers or heterozygous for the mutation. While a selection program has been launched to eradicate the day blindness mutation from Improved Awassi flocks, a breeding nucleus of day-blind sheep has been established to serve as animal models for studying human achromatopsia.

Mini review: breeding Awassi and Assaf sheep for diverse management conditions.

The Local Awassi, a triple-purpose breed for meat, milk, and carpet-wool production, is a low-prolific, hardy breed that is well adapted to the unfavorable conditions of the Middle East, where it is managed under traditionally extensive to semi-extensive conditions. Breeding work with the Awassi has included within-breed selection, crossbreeding, and gene introgression. Those efforts resulted in a variety of Awassi-derived genotypes that successfully occupy semi-intensive as well as intensive production systems. Thus, within-breed selection resulted in development of the "Improved Awassi"-a dairy-type Awassi strain which, under intensive management, produces over 500 l milk/ewe annually; crossbreeding with the East Friesian breed led to the development of the Assaf dairy breed, which exceeds the Improved Awassi in prolificacy and in year-round breeding activity, and introgression of the B allele of the FecB locus into the Awassi and Assaf breeds resulted in the formation of the prolific Afec Awassi and Afec Assaf strains, with prolificacies of 1.9 and 2.5 lambs born per ewe lambing, respectively. Advanced molecular genetics tools have enabled a better understanding of how the Awassi breed was formed during domestication and have uncovered differences in its genetic structure compared to other breeds. Implementing large-scale selection schemes that implement emerging new information on the sheep genome, overcoming threats of inbreeding depression, and further breeding for high uterine capacity are the new breeding goals for the Awassi, Assaf, and their derivatives.

Effect of supplementation of unprotected or protected arginine to prolific ewes on maternal amino acids profile, lamb survival at birth, and pre- and post-weaning lamb growth.

This research determined the effects of dietary supplementation with rumen-protected arginine (Pro-Arg) on metabolites and amino acids in maternal plasma and lamb survival rate at birth (LSRAB) in prolific Afec-Assaf ewes. The hypothesis was that Pro-Arg, the precursor for nitric oxide and polyamines, would increase placental development and vascularity, uteroplacental blood flow, and nutrient transport and reduce oxidative stress to increase LSRAB. Ewes were fed either their basal diet, basal diet with Pro-Arg, or basal diet with unprotected arginine (Unp-Arg; 18 g/head/d). The supplemental arginine was about 1% of the dry matter intake from day 40 or 60 of gestation until parturition. Ninety-two of 98 ewes produced live lambs. Ewes fed Pro-Arg had greater (P = 0.002) concentrations of arginine and other amino acids in plasma, whereas Unp-Arg did not affect concentrations of arginine, but decreased (P < 0.05) concentrations of some amino acids. There was no effect of treatments on gestation length (144 ± 2 d), prolificacy (2.65 lambs born per ewe), LSRAB (0.80), body weight (88.8 ± 10.8 kg), and body condition score (2.8 ± 0.6) of ewes, or birth weight and crown-rump length of lambs. The GI (BW/CRL1.5) was affected by sex of lamb (P = 0.008), parity of ewe (P = 0.002), litter size (P = 0.0001), and lamb status (P = 0.003). Of 229 lambs born, 32 were dead and 16 died before 5 mo of age, leaving 181 lambs with records on weights at birth and 5 mo of age. Interestingly, lambs born to ewes fed the Unp-Arg and Pro-Arg weighed 3.6 kg less at postnatal day 150 than lambs from control ewes.

Evaluation of Photoreceptor Transduction Efficacy of Capsid-Modified Adeno-Associated Viral Vectors Following Intravitreal and Subretinal Delivery in Sheep.

Gene augmentation therapy based on subretinal delivery of adeno-associated viral (AAV) vectors is proving to be highly efficient in treating several inherited retinal degenerations. However, due to potential complications and drawbacks posed by subretinal injections, there is a great impetus to find alternative methods of delivering the desired genetic inserts to the retina. One such method is an intravitreal delivery of the vector. Our aim was to evaluate the efficacy of two capsid-modified vectors that are less susceptible to cellular degradation, AAV8 (doubleY-F) and AAV2 (quadY-F+T-V), as well as a third, chimeric vector AAV[max], to transduce photoreceptor cells following intravitreal injection in sheep. We further tested whether saturation of inner limiting membrane (ILM) viral binding sites using a nonmodified vector, before the intravitreal injection, would enhance the efficacy of photoreceptor transduction. Only AAV[max] resulted in moderate photoreceptor transduction following intravitreal injection. Intravitreal injection of the two other vectors did not result in photoreceptor transduction nor did the saturation of the ILM before the intravitreal injection. However, two of the vectors efficiently transduced photoreceptor cells following subretinal injection in positive control eyes. Previous trials with the same vectors in both murine and canine models resulted in robust and moderate transduction efficacy, respectively, of photoreceptors following intravitreal delivery, demonstrating the importance of utilizing as many animal models as possible when evaluating new strategies for retinal gene therapy. The successful photoreceptor transduction of AAV[max] injected intravitreally makes it a potential candidate for intravitreal delivery, but further trials are warranted to determine whether the transduction efficacy is sufficient for a clinical outcome.

Naturally-occurring myopia and loss of cone function in a sheep model of achromatopsia.

Achromatopsia is an inherited retinal disease characterized by loss of cone photoreceptor function. Day blind CNGA3 mutant Improved Awassi sheep provide a large animal model for achromatopsia. This study measured refractive error and axial length parameters of the eye in this model and evaluated chromatic pupillary light reflex (cPLR) testing as a potential screening test for loss of cone function. Twenty-one CNGA3 mutant, Improved Awassi, 12 control Afec-Assaf and 12 control breed-matched wild-type (WT) Awassi sheep were examined using streak retinoscopy and B-mode ocular ultrasonography. Four CNGA3 mutant and four Afec-Assaf control sheep underwent cPLR testing. Statistical tests showed that day-blind sheep are significantly more myopic than both Afec-Assaf and WT Awassi controls. Day-blind sheep had significantly longer vitreous axial length compared to WT Awassi (1.43 ± 0.13 and 1.23 ± 0.06 cm, respectively, p < 0.0002) and no response to bright red light compared to both controls. Lack of response to bright red light is consistent with cone dysfunction, demonstrating that cPLR can be used to diagnose day blindness in sheep. Day-blind sheep were found to exhibit myopia and increased vitreous chamber depth, providing a naturally occurring large animal model of myopia.

Five ovine mitochondrial lineages identified from sheep breeds of the near East.

Archaeozoological evidence indicates that sheep were first domesticated in the Fertile Crescent. To search for DNA sequence diversity arising from previously undetected domestication events, this survey examined nine breeds of sheep from modern-day Turkey and Israel. A total of 2027 bp of mitochondrial DNA (mtDNA) sequence from 197 sheep revealed a total of 85 haplotypes and a high level of genetic diversity. Six individuals carried three haplotypes, which clustered separately from the known ovine mtDNA lineages A, B, and C. Analysis of genetic distance, mismatch distribution, and comparisons with wild sheep confirmed that these represent two additional mtDNA lineages denoted D and E. The two haplogroup E sequences were found to link the previously identified groups A and C. The single haplogroup D sequence branched with the eastern mouflon (Ovis orientalis), urial (O. vignei), and argali (O. ammon) sheep. High sequence diversity (K = 1.86%, haplogroup D and O. orientalis) indicates that the wild progenitor of this domestic lineage remains unresolved. The identification in this study of evidence for additional domestication events adds to the emerging view that sheep were recruited from wild populations multiple times in the same way as for other livestock species such as goat, cattle, and pig.

Six Years and Counting: Restoration of Photopic Retinal Function and Visual Behavior Following Gene Augmentation Therapy in a Sheep Model of CNGA3 Achromatopsia.

Achromatopsia causes severely reduced visual acuity, photoaversion, and inability to discern colors due to cone photoreceptor dysfunction. In 2010, we reported on day-blindness in sheep caused by a stop-codon mutation of the ovine CNGA3 gene and began gene augmentation therapy trials in this naturally occurring large animal model of CNGA3 achromatopsia. The purpose of this study was to evaluate long-term efficacy and safety results of treatment, findings that hold great relevance for clinical trials that started recently in CNGA3 achromatopsia patients. Nine day-blind sheep were available for long-term follow up. The right eye of each sheep was treated with a single subretinal injection of an Adeno-Associated Virus Type 5 (AAV5) vector carrying either a mouse (n = 4) or a human (n = 5) CNGA3 transgene under control of the 2.1-Kb red/green opsin promoter. The efficacy of treatment was assessed periodically with photopic maze tests and electroretinographic (ERG) recordings for as long as 74 months postoperatively. Safety was assessed by repeated ophthalmic examinations and scotopic ERG recordings. The retinas of three animals that died of unrelated causes >5 years post-treatment were studied histologically and immunohistochemically using anti-hCNGA3 and anti-red/green cone opsin antibodies. Passage time and number of collisions of treated sheep in the photopic maze test were significantly lower at all follow-up examinations as compared with pretreatment values (p = 0.0025 and p < 0.001, respectively). ERG Critical Flicker Fusion Frequency and flicker amplitudes at 30 and 40 Hz showed significant improvement following treatment (p < 0.0001) throughout the study. Ophthalmic examinations and rod ERG recordings showed no abnormalities in the treated eyes. Immunohistochemistry revealed the presence of CNGA3 protein in red/green opsin-positive cells (cones) of the treated eyes. Our results show significant, long-term improvement in cone function, demonstrating a robust rescue effect up to six years following a single treatment with a viral vector that provides episomal delivery of the transgene. This unique follow-up duration confirms the safe and stable nature of AAV5 gene therapy in the ovine achromatopsia model.

Sequence motifs capable of forming DNA stem-loop structures act as a replication diode.

Calculating peak-height ratios between single-nucleotide polymorphisms (SNP) alleles in sequencing chromatograms is a practical method for estimating their copy number proportions (CNPs). However, it is surprising that sequencing DNA from different directions might yield different results. We analyzed three adjacent SNPs within the ovine period circadian-clock 2 (PER2) gene that displayed such behavior. We compared Sanger and DNA-seq sequencing for this locus and applied high-resolution melt and MFOLD analyses to point to the DNA secondary structure that underlined this phenomenon. A synthetic system of oligonucleotides cloned into plasmids was used to further test the effect of such structures on sequencing. Our analyses indicated that a stem-loop structure capable of G-T pairing mediated the orientation bias by stabilizing this structure for specific alleles in heterozygous situations. We propose that this wobble-like pairing hinders DNA polymerase passage on one strand while, on the complementary strand, the nonpaired A-C nucleotide counterparts allow unobstructed replication. Experimentation with synthetic amplicons that form similar stem-loop structures supported our hypothesis. We coined the term 'replication diode' for this effect and demonstrated that we can minimize it by lowering DNA and salt concentration. We also demonstrated that common genomic palindromes might induce the replication diode effect by applying bidirectional sequencing to an amplicon containing the palindrome within the human miRNA 1-1 gene. Hence, to obtain reliable peak-height ratios, bidirectional sequencing should be practiced at the lowest possible ionic strength whenever estimating CNPs. Further research is needed to determine whether the observed variable stem-loop structures affect PER2 regulation in vivo.

Safety and Efficacy Evaluation of rAAV2tYF-PR1.7-hCNGA3 Vector Delivered by Subretinal Injection in CNGA3 Mutant Achromatopsia Sheep.

Applied Genetic Technologies Corporation (AGTC) is developing a recombinant adeno-associated virus (rAAV) vector expressing the human CNGA3 gene designated AGTC-402 (rAAV2tYF-PR1.7-hCNGA3) for the treatment of achromatopsia, an inherited retinal disorder characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. The results are herein reported of a study evaluating safety and efficacy of AGTC-402 in CNGA3-deficient sheep. Thirteen day-blind sheep divided into three groups of four or five animals each received a subretinal injection of an AAV vector expressing a CNGA3 gene in a volume of 500 µL in the right eye. Two groups (n = 9) received either a lower or higher dose of the AGTC-402 vector, and one efficacy control group (n = 4) received a vector similar in design to one previously shown to rescue cone photoreceptor responses in the day-blind sheep model (rAAV5-PR2.1-hCNGA3). The left eye of each animal received a subretinal injection of 500 µL of vehicle (n = 4) or was untreated (n = 9). Subretinal injections were generally well tolerated and not associated with systemic toxicity. Most animals had mild to moderate conjunctival hyperemia, chemosis, and subconjunctival hemorrhage immediately after surgery that generally resolved by postoperative day 7. Two animals treated with the higher dose of AGTC-402 and three of the efficacy control group animals had microscopic findings of outer retinal atrophy with or without inflammatory cells in the retina and choroid that were procedural and/or test-article related. All vector-treated eyes showed improved cone-mediated electroretinography responses with no change in rod-mediated electroretinography responses. Behavioral maze testing under photopic conditions showed significantly improved navigation times and reduced numbers of obstacle collisions in all vector-treated eyes compared to their contralateral control eyes or pre-dose results in the treated eyes. These results support the use of AGTC-402 in clinical studies in patients with achromatopsia caused by CNGA3 mutations, with careful evaluation for possible inflammatory and/or toxic effects.

Gene Augmentation Therapy for a Missense Substitution in the cGMP-Binding Domain of Ovine CNGA3 Gene Restores Vision in Day-Blind Sheep.

Purpose: Applying CNGA3 gene augmentation therapy to cure a novel causative mutation underlying achromatopsia (ACHM) in sheep. Methods: Impaired vision that spontaneously appeared in newborn lambs was characterized by behavioral, electroretinographic (ERG), and histologic techniques. Deep-sequencing reads of an affected lamb and an unaffected lamb were compared within conserved genomic regions orthologous to human genes involved in similar visual impairment. Observed nonsynonymous amino acid substitutions were classified by their deleteriousness score. The putative causative mutation was assessed by producing compound CNGA3 heterozygotes and applying gene augmentation therapy using the orthologous human cDNA. Results: Behavioral assessment revealed day blindness, and subsequent ERG examination showed attenuated photopic responses. Histologic and immunohistochemical examination of affected sheep eyes did not reveal degeneration, and cone photoreceptors expressing CNGA3 were present. Bioinformatics and sequencing analyses suggested a c.1618G>A, p.Gly540Ser substitution in the GMP-binding domain of CNGA3 as the causative mutation. This was confirmed by genetic concordance test and by genetic complementation experiment: All five compound CNGA3 heterozygotes, carrying both p.Arg236* and p.Gly540Ser mutations in CNGA3, were day-blind. Furthermore, subretinal delivery of the intact human CNGA3 gene using an adeno-associated viral vector (AAV) restored photopic vision in two affected p.Gly540Ser homozygous rams. Conclusions: The c.1618G>A, p.Gly540Ser substitution in CNGA3 was identified as the causative mutation for a novel form of ACHM in Awassi sheep. Gene augmentation therapy restored vision in the affected sheep. This novel mutation provides a large-animal model that is valid for most human CNGA3 ACHM patients; the majority of them carry missense rather than premature-termination mutations.

A novel day blindness in sheep: epidemiological, behavioural, electrophysiological and histopathological studies.

Four genetically related Improved Awassi sheep flocks had sporadic births of lambs with congenital visual impairments that differed from other known forms of sheep blindness. Pedigree analysis suggested an autosomal recessive mode of inheritance. Behavioural studies of 4-month old affected lambs showed that their day vision (but not night vision) was impaired. Electrophysiological results at this age demonstrated diminished function of cones but not rods. Histopathological and immunohistochemical evaluation of affected retinas from 5-month old lambs revealed both red-green and blue cones, suggesting that the behavioural day blindness and reduced cone electroretinograms reflect cone dysfunction rather than severe cone photoreceptor loss. Awassi day blindness may be a form of achromatopsia.

Prolificacy and lamb survival at birth in Awassi and Assaf sheep carrying the FecB (Booroola) mutation.

Prolificacy up to the fifth parity and lamb survival at birth were investigated in >or=31/32 Awassi and >or=31/32 Assaf sheep belonging to the ++, B+ and BB genotypes at the FecB locus. In the Awassi, prolificacy of ++, B+ and BB ewes was 1.28, 1.90 and 1.92 lambs born/lambing (LB/L), respectively. In the Assaf, prolificacy of ++, B+ and BB ewes was 1.68, 2.40 and 2.55LB/L, respectively. Lamb survival at birth in the ++ Awassi and the ++ Assaf averaged 0.98 and 0.94, respectively. It declined to 0.93 and 0.86, and 0.85 and 0.78 in the B+ and BB Awassi and B+ and BB Assaf, respectively. For singles, twins, triplets, quadruplets and quintuplets, lamb survival rate at birth was 0.98, 0.92, 0.86, 0.78 and 0.65, respectively. FecB genotype-litter size interactions were not significant (P<0.05). A compilation of study results in which prolificacy of the ++ and B+ genotypes at the FecB locus were investigated in a range of breed-environment combinations revealed that the B allele has a multiplicative effect on prolificacy as B+ prolificacy was significantly (P<0.05) linearly associated with ++ prolificacy.