Size In Sheep Research Articles

Response to dietary tannin challenges in view of the browser/grazer dichotomy in an Ethiopian setting: Bonga sheep versus Kaffa goats.

It has been suggested that goats (typical browser) are better adapted to digest tannin-rich diets than sheep (typical grazer). To evaluate this, Bonga sheep and Kaffa goats were used in a 2 × 3 randomized crossover design with two species, three diets, and three periods (15-day adaptation + 7-day collection). The dietary treatments consisted of grass-based hay only (tannin-free diet = FT), a high-tannin diet (36 % Albizia schimperiana (AS) + 9 % Ficus elastica (FE) + 55 % FT (HT)), and HT + polyethylene glycol 6000 (PEG). Animals were individually fed at 50 g dry matter (DM)/kg body weight (BW) and had free access to clean drinking water and mineralized salt licks. Nutrient intake, apparent nutrient digestibility, nutrient conversion ratios, and live weight changes were determined. Condensed tannin concentrations in AS and FE were 110 and 191 g/kg DM, respectively. Both sheep and goats ate 47 % more of HT than FT, and dry matter intake further increased by 9 % when PEG was added, with clear difference in effect size between goats and sheep (P < 0.001). The effects of the tannin-rich diet and PEG addition were similarly positive for DM digestibility between sheep and goats, but crude protein (CP) digestibility was higher in HT + PEG-fed goats than in sheep fed the same diet. However, PEG addition induced a larger improvement in growth performance and feed efficiency ratio in sheep than in goat (P < 0.001). The addition of PEG as a tannin binder improved digestion and performance in both species, but with the highest effect size in sheep.

Mutations and sequence variants in GDF9, BMP15, and BMPR1B genes in Maremmana cattle breed with single and twin births

The families of TGF-β (transforming growth factor-β) proteins are the most important growth factors in the ovary, and three related oocyte-derived members, namely GDF9 (growth differentiation factor 9), BMP15 (bone morphogenetic protein 15), and BMPR1B (bone morphogenetic protein receptor 1B), have been shown to be essential for follicular growth and ovulation. Although the essential role of these genes in determining litter size in sheep and mouse and in controlling folliculogenesis in human has been demonstrated, there is limited information on their action in other species, especially in bovine. Bovine is a monotocous specie, as humans, with one or sometimes two newborns per birth. The twinning is a complex trait determined by both genetic and environmental factors. This study aimed at investigating the nucleotide sequences of different fragments of GDF9, BMP15, and BMPR1B genes in Maremmana cows reared in Castelporziano Presidential Estate (Rome). In this herd, in the period between 1996 and 2008, a twinning rate of 12 % (on average) was observed. We identified nine single-nucleotide polymorphisms (SNPs), five in the coding region, and four in the noncoding region: Two polymorphisms caused non-synonymous mutations, g.6045 G>A (V202I) in the BMP15 gene, and g.231 T>C (L66S) in GDF9 gene. The mutation L66S was found only in cows with double birth. In the literature, there are different evidences that mutations in proregion of GDF9 protein could affect its correct function. A relationship between mutations in this region of protein and granulosa cells proliferation and oocyte development was hypothesized.

Molecular characterization, expression profiles of the ovine FSHR gene and its association with litter size.

Follicle-stimulating hormone receptor (FSHR) is a glycoprotein family member of G proteins coupled receptor super-family, and plays important roles in animal follicular development. In this study, we cloned the 5' flanking region of ovine FSHR gene and analyzed its genomic structure. One special domain named the LRRNT (Leucine rich repeat N-terminal domain) was found in the prediction amino acid sequence of ovine FSHR. RT-qPCR showed that ovine FSHR was expressed widely in detected tissues and was significantly higher in sexual gland (testicle and ovary) than in other tissues (heart, liver, spleen, lung, kidney, rumen, duodenum, muscle, fat, hypothalamus and pituitary) (P < 0.05). In addition, synonymous mutation g.-47C > T of the FSHR gene was detected and confirmed to be significantly associated with the litter size (P < 0.01), the genotype of CC had 0.42 (P < 0.01) and 0.53 (P < 0.01) lambs more than TC and TT genotype, respectively. Our results indicated the association of ovine FSHR with the litter size in sheep and FSHR could be used as a candidate gene for improving reproductive traits in industrial sheep breeding.

Feeding behaviour of artificially reared Romane lambs

A consequence of increasing litter size in sheep is that a portion of the lambs have to be reared artificially. Detailed information about the pattern of milk consumption of artificially reared lambs would help improve their management. The purpose of this study is to describe the individual and group feeding behaviour of 94 Romane artificially reared lambs from 5 to 28 days of age using an electronic automatic lamb feeder. Animals were located in four pens of 8 to 15 lambs of similar age with one teat per pen. They were fed ad libitum. In our experimental situation (group rearing, continuous lightning) on average a lamb made 1.4±0.7 visits to the teat per meal and 9.5±3 meals per day. Mean meal duration was 247±158 s and the mean daily time spent feeding was 38±25 min. The mean quantity of milk intake was 176±132 ml per meal and 1.68±0.8 l per day. With age, the number of daily meals and their duration decreased while the quantity of milk consumed per meal and per day increased. Females tended to make more visits to the teat per meal and perform more meals per day but their milk consumption per meal was lower. The feed conversion ratio was 1.36±0.2. Synchrony in feeding (group meal) was estimated as the percentage of lambs that wanted to access the teat within the same short period (relative group meal size). On average 65% of lambs in the pen wanted to access the teat within the same period, but for 35% of group meals the relative group meal size was >90%. There was no consistency in the order in which lambs accessed the teat during a group meal. Our evaluation suggested that electronic automatic lamb feeders are tools that can provide, on a large scale, data describing the feeding behaviour of artificially reared lambs. It is then possible to study factors influencing these traits in order to improve the outcome of artificially reared lambs.

A missense mutation in growth differentiation factor 9 (GDF9) is strongly associated with litter size in sheep

BackgroundA genome wide association study for litter size in Norwegian White Sheep (NWS) was conducted using the recently developed ovine 50K SNP chip from Illumina. After genotyping 378 progeny tested artificial insemination (AI) rams, a GWAS analysis was performed on estimated breeding values (EBVs) for litter size.ResultsA QTL-region was identified on sheep chromosome 5, close to the growth differentiation factor 9 (GDF9), which is known to be a strong candidate gene for increased ovulation rate/litter size. Sequencing of the GDF9 coding region in the most extreme sires (high and low BLUP values) revealed a single nucleotide polymorphism (c.1111G>A), responsible for a Val→Met substitution at position 371 (V371M). This polymorphism has previously been identified in Belclare and Cambridge sheep, but was not found to be associated with fertility. In our NWS-population the c.1111G>A SNP showed stronger association with litter size than any other single SNP on the Illumina 50K ovine SNP chip. Based on the estimated breeding values, daughters of AI rams homozygous for c.1111A will produce minimum 0.46 - 0.57 additional lambs compared to daughters of wild-type rams.ConclusionWe have identified a missense mutation in the bioactive part of the GDF9 protein that shows strong association with litter size in NWS. Based on the NWS breeding history and the marked increase in the c.1111A allele frequency in the AI ram population since 1983, we hypothesize that c.1111A allele originate from Finnish landrace imported to Norway around 1970. Because of the widespread use of Finnish landrace and the fact that the ewes homozygous for the c.1111A allele are reported to be fertile, we expect the commercial impact of this mutation to be high.

Genetic improvement of reproductive efficiency of sheep and goats

Sheep and goats are produced in a wide range of production systems and climatic conditions and possess great genetic diversity in reproductive potentials. Mean litter sizes range from near 1 to 3 or more, and patterns of seasonal reproduction are often strongly synchronised to local conditions. Thus, optimisation, rather than maximisation, of reproductive potentials is required, and optimum reproductive rates are often well below those which could be achieved. However, changing employment patterns, increasing urbanisation, and emergence of new markets provide corresponding opportunities for sustainable intensification of small ruminant production, potentially requiring enhancements in reproductive potentials. Heritabilities for most reproductive traits are less than those for many other traits, usually ranging from 0.05 to 0.15, and opportunities for within-breed selection are therefore limited. Substantial changes in litter size or major changes in seasonal breeding patterns are thus best achieved by crossing of divergent breeds to rapidly reset genetic potentials for these traits, followed by within-breed selection to optimise reproductive potentials. Various mutations influencing ovulation rate and litter size in sheep provide additional opportunities to rapidly adjust genetic potentials, but require careful breeding management. Comparable major genes have not yet been found in goats or for traits associated with breeding season.

Association between polymorphism of GPR54 gene and litter size in Small Tail Han sheep

A DNA fragment (4262 bp) of sheep GPR54 gene was obtained through PCR and DNA sequencing methods. One nucleotide transition mutation (A125G) and one 5 bp deletion/insertion (TTCTT) mutation at the 163–167 locus in 5´-regulatory region of sheep GPR54 gene were identified by sequence alignment between Small Tail Han and Corriedale sheep. The distributions of these two mutations were determined in high prolificacy breeds (Small Tail Han and Hu sheep) and low prolificacy breeds (Chinese Merino and Corriedale sheep) and their effects on litter size in Small Tail Han sheep were also evaluated. The results showed that the two mutations existed in all four sheep breeds tested. In Small Tail Han sheep, genotype frequency of AA, AG and GG was 0.250, 0.500 and 0.250, respectively. The differences of litter size between three genotypes were not significant in Small Tail Han sheep ( P > 0.05). Genotype frequency of CC, CD and DD was 0.175, 0.125 and 0.700, respectively. Small Tail Han sheep ewes with genotype CC had 0.66 ( P < 0.05) or 0.49 ( P < 0.05) lambs more than those with genotype DD or CD, respectively. The ewes with hap3/hap3 or hap2/hap3 had the most litter size in Small Tail Han sheep. And the inserted/deleted mutation may influence the binding of the transcription factor deltaE. These preliminary results indicated that allele C at the 163–167 locus in GPR54 gene may be a potential marker for improving litter size in sheep.

Observations on the ultrastructure of equatorial scleral collagen fibrils in sheep eyes

To investigate collagen fibrils of the equatorial sclera in relation to the age-related changes in eye size in sheep. Lambs and outbred ewes. Sheep eyes (three lamb and three from adult outbred ewes), presumed disease-free, were processed for transmission electron microscopy (TEM) immediately postmortem. Tissue blocks from the equatorial region were sectioned across fibril bundles orientated along the equator. Micrographs including at least 500 fibrils were projected at 22,000× magnification for measures of fibril diameters (FDs). Lamb eyes were smaller than those of adult ewes but equatorial scleral thickness was only marginally less at 0.232±0.013 vs. 0.254±0.012 mm (P value not significant). Scleral tissue was composed of compacted bundles of collagen fibers that tended to be rounder in outer compared to being flatter in inner regions. In typical (normal) appearing regions, FDs were distinctly larger (68-410 nm) in outer sclera compared to inner sclera (63-281 nm). Outer sclera FDs were bimodal averaging 192±58 nm, compared to unimodal distributions at inner locations averaging 156±48 nm (P<0.001). Some atypical regions, especially at outer-mid sclera locations, were also noted where the FD distribution was bimodal but also included numerous microfibrils (<50 nm diameter), with similar appearances being found for both lamb and adult ewe eyes. The equatorial sclera is a mixture of rounder versus flatter collagen fiber bundles, the former being more likely to be made up of a mixture of both smaller and larger fibrils, as compared to slightly smaller fibrils.

Polymorphisms of KiSS-1 and GPR54 genes and their relationships with litter size in sheep

The KiSS-1 and GPR54 genes were studied as candidate genes for the prolificacy in sheep. Four pairs of primers were designed to detect single nucleotide polymorphisms of exon 1 of KiSS-1 gene and exon 1, exon 2 and partial exon 5 of GPR54 gene in high fecundity breeds (Small Tail Han and Hu sheep) and low fecundity breeds (Dorset, Texel and Corriedale sheep) by PCR-SSCP. Polymorphisms in exon 1 of KiSS-1 gene were detected in prolific Small Tail Han sheep (AA, AB and BB genotypes) and Hu sheep (AA and CC genotypes), no polymorphism was found in low fecundity sheep breeds (only AA genotype). Polymorphisms in exon 2 of GPR54 gene were detected in prolific Hu sheep (DD and EE genotypes) and no polymorphism was found in prolific Small Tail Han sheep and low fecundity sheep breeds (only DD genotype). No polymorphism was detected in exon 1 and partial exon 5 of GPR54 gene in five sheep breeds. The polymorphic genotypes were sequenced. While compared the BB genotype with the AA genotype, one nucleotide mutation (G1035A) was detected, which resulted in amino acid change, Val25Met. Five nucleotide mutations were detected from AA to CC genotype (C981T, C996T, T997C, C1034G, C1039T), and among them four caused amino acid changes, that is, Arg7Trp, Phe12Leu, Asn24Lys, Ala26Val. While compared the EE genotype with the DD genotype, two nucleotide mutations (T2360C, A2411C) were detected, which gave rise to amino acid changes, Met90Thr and Asp107Ala, respectively. Genotype frequencies of AA, BB and AB were 0.62, 0.05 and 0.33 in Small Tail Han sheep, respectively. The Small Tail Han sheep ewes with genotype BB or AB had 0.88 (P < 0.05) or 0.51 (P < 0.05) lambs more than those with genotype AA; the Small Tail Han sheep ewes with genotype BB had 0.37 (P > 0.05) lambs more than those with genotype AB. These results preliminarily indicated that the KiSS-1 gene may have some association with prolificacy in sheep.

Predictive potential of microsatellite markers on heterosis of fecundity in crossbred sheep

Small Tail Han (STH) sheep is a famous Chinese local breed and has perfect prolificacy performance, but it is inferior to imported mutton sheep breeds on meat production. In this study, six imported male sheep populations (White Suffolk, Black Suffolk, Texel, Dorper, South African Mutton Merino and East Friesian) were crossbred with STH female sheep respectively. The heterosis values of litter size, average daily gain (ADG) and feed conversion ratio (FCR) of crossbred sheep were analyzed for seeking the optimal cross. Meanwhile 28 microsatellite markers were used to measure the genetic distance between imported populations and STH population. Regression between the genetic distance and heterosis was analyzed for evaluating potential of microsatellite on predicting heterosis. Results showed a significant positive linear correlation (r = 0.892, P < 0.05) between heterosis of litter size and genetic distance D (A) of six crosses. This implied that these microsatellite markers had moderate potential to forecast heterosis of litter size in sheep. Results of this study also indicated that South African Mutton Merino and East Friesian sheep would be the optimal sire breeds for the litter size and might bring the greatest economic benefit in six imported populations; Suffolk sheep could be prior consideration as sire breeds when breeding objective focused on ADG. Finally these results provided valuable information for Chinese sheep industry.

Polymorphisms of coding region of BMPR-IB gene and their relationship with litter size in sheep

The bone morphogenetic protein receptor IB (BMPR-IB) was studied as a candidate gene for the prolificacy of sheep. Nine pairs of primers (P1-P9) were designed to detect single nucleotide polymorphisms (SNPs) of exons 1-4 and 6-10 of the BMPR-IB gene in both high (Small Tail Han and Hu sheep) and low prolificacy breeds (Texel and Chinese Merino sheep) by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP). Only the products amplified by primers P2, P5, P6, P7, P8 and P9 displayed polymorphisms. The present study identified 22 SNPs in partial coding regions of ovine BMPR-IB, in which 20 SNPs were reported for the first time. In total of the 22 mutations, 18 DNA variations were originated from the Hu breed, three were found in the Small Tail Han breed (two of them were found in other sheep breeds), three in the Chinese Merino breed, and none in the Texel breed. These results preliminarily demonstrated that BMPR-IB is a major gene affecting the hyperprolificacy in Small Tail Han and Hu sheep, and could be used as a molecular genetic marker for early auxiliary selection for hyperprolificacy in sheep.

Polymorphism of inhibin βB gene and its relationship with litter size in sheep

The inhibin β(B) (INHBB) gene was studied as a candidate gene for the prolificacy of Small Tail Han and Hu sheep. According to the sequence of exon 1 and 2 of bovine INHBB gene, six pairs of primers were designed to detect single nucleotide polymorphisms of exon 1 and 2 of INHBB gene in both high (Small Tail Han and Hu sheep) and low prolificacy breeds (Dorset, Texel and German Mutton Merino sheep) by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). Three pairs of primers (primers 1-1, 1-2 and 1-3) were used to amplify the exon 1, and others (primers 2-1, 2-2 and 2-3) to the exon 2. Only the products amplified by primer 2-3 displayed polymorphism. For primer 2-3, three genotypes (AA, AB and BB) were detected in Hu sheep and only AA genotype in other breeds. In Hu sheep, frequency of AA, AB and BB genotypes was 0.636, 0.046 and 0.318, respectively. Sequencing revealed 276A > G mutation (based on the amplification region of primer 2-3) which did not cause any amino acid change because it lay in the 3' untranslated region. The ewes with genotype BB had 0.58 (P < 0.01) lambs more than those with AA in Hu sheep.

Comparison of repeatability and multiple trait threshold models for litter size in sheep using observed and simulated data in Bayesian analyses

Bayesian analyses were used to estimate genetic parameters on 5580 records of litter size in the first four parities from 1758 Mule ewes. To examine the appropriateness of fitting repeatability (RM) or multiple trait threshold models (MTM) to litter size of different parities, both models were used to estimate genetic parameters on the observed data and were thereafter compared in a simulation study. Posterior means of the heritabilities of litter size in different parities using a MTM ranged from 0.12 to 0.18 and were higher than the heritability based on the RM (0.08). Posterior means of the genetic correlations between litter sizes of different parities were positive and ranged from 0.24 to 0.71. Data sets were simulated based on the same pedigree structure and genetic parameters of the Mule ewe population obtained from both models. The simulation showed that the relative loss in accuracy and increase in mean squared error (MSE) was substantially higher when using the RM, given that the parameters estimated from the observed data using the opposite model are the true parameters. In contrast, Bayesian information criterion (BIC) selected the RM as most appropriate model given the data because of substantial penalty for the higher number of parameters to be estimated in the MTM model. In conclusion, when the relative change in accuracy and MSE is of main interest for estimation of breeding values of litter size of different parities, the MTM is recommended for the given population. When reduction in risk of using the wrong model is the main aim, the BIC suggest that the RM is the most appropriate model.

Estimation of sensitivity and flock-sensitivity of pooled faecal culture for Mycobacterium avium subsp. paratuberculosis in sheep

Pooled faecal culture (PFC) is a widely used test in ovine Johne's disease (OJD) control programmes in Australia but information about its characteristics is limited. We conducted this study to estimate sensitivity and flock-sensitivity of PFC in sheep with different OJD histopathological lesions in simulated flocks with a range of infection prevalence levels. Initially, a known quantity of faeces from sheep with pauci- or multibacillary lesions was pooled with uncontaminated faeces from confirmed non-infected sheep and cultured using PFC technique. PFC sensitivity, calculated as a proportion of the pools of a particular size that tested positive, was determined to be 90% in sheep with the multibacillary form of the disease but varied with pool size in sheep with the paucibacillary form of OJD. Subsequently, probabilistic models were developed to estimate overall pool-sensitivity achieved in a flock (Sek) and flock-sensitivity of PFC (FSe) in various simulated scenarios. In flocks with a given ratio of multi- to paucibacillary sheep and with low to moderate infection prevalence level, Sek decreased with increase in pool size, but increased with pool size in flocks with ≥10% prevalence. FSe, in contrast, increased with pool size in all the tested scenarios. Both Sek and FSe increased with infection prevalence, ratio of multi- to paucibacillary sheep and the number of pools sourced from flocks. Sensitivity analyses indicated that the estimates and trends were robust to moderate changes in input parameters. The results suggest that the current testing of seven pools of size 50 is adequate for most scenarios, however, for very low prevalence flocks, a gain in FSe can be made by increasing the number of pools tested and a higher Sek can be achieved by reducing pool sizes.

DNA polymorphism of 5′ flanking region of prolactin gene and its association with litter size in sheep

A single nucleotide polymorphism of 5' flanking region of the prolactin gene was investigated in both high prolificacy breeds (Small Tail Han and Hu sheep) and low prolificacy breeds (Dorset and Suffolk sheep) using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP). The results indicated that two genotypes (AA and AB) were detected in Small Tail Han sheep (n = 239), only one genotype (AA) was detected in Hu (n = 40), Dorset (n = 50) and Suffolk sheep (n = 39). The mutant homozygous genotype (BB) was not detected in four sheep breeds. In Small Tail Han sheep (n = 239), the frequency of genotypes AA and AB was 0.91 and 0.09, the frequency of the A and B alleles was 0.95 and 0.05, respectively. The fitness tests showed that the Small Tail Han sheep population was in Hardy-Weinberg equilibrium. Sequencing revealed a mutation (G-->T) at the position 63 bp of the 5' flanking region of prolactin gene in AB genotype compared with AA genotype in Small Tail Han sheep. The Small Tail Han ewes with AB genotype had 0.83 (p < 0.05) lambs more than those with AA genotype. These results preliminarily showed that the prolactin locus is either a major gene that influences the high prolificacy in Small Tail Han sheep or is in close linkage with such a gene.

Kangaroos and greenhouse gases: Response to Russell

We used 50 kg as the average weight for kangaroos and not 19 kg as in table 2. This is an error in the table but not in our calculations. Published kangaroo weights range widely, perhaps because there is marked sexual and species dimorphism and because kangaroos, especially males, grow throughout most of their lives (Dawson 1995). In settling on a 50 kg average we referred to the following weight ranges for the larger, harvested species of kangaroos; for males 90–60 kg (Dawson 1995) and 78–28 kg (Wilson & Read 2003); and for females 40–23 kg (Dawson 1995), 27–16 kg (Wilson & Read 2003), and 23–19 kg (Kempton et al. 1976). Even if a 50-kg weight is high, overestimating it does not affect the conclusions. This is because the model manages the population during the transition to 2020 to take a high proportion of males, which will increase the average weight of harvested kangaroos and allow a greater proportion to be harvested. There is also scope for discussion about the size of sheep and cattle carcasses from the rangelands, the amount of meat they produce and its value. All are subject to environmental and market variation. Regardless, we stand by the estimate of an average 33 kg carcass from a 50-kg live kangaroo and the comparisons between cattle and kangaroos carcass weights as a proportion of live weight. We had decided that the personal communication of 19 kg average weight reported by Grigg (2002) was too low. Russell (1999) himself refers to kangaroo weights of 65 (male) and 25 (female) kg, giving an average of 45 kg. In concluding that 120 kangaroo carcasses equal one beef carcass, Russell (2008) asserts that the carcass yield of useable meat is higher for cattle than kangaroos. Our article does not discuss the relative boning-out percentages; however, studies on carcass composition and kangaroo anatomy reveal the opposite. Hopwood (1976) found that kangaroo carcasses yield approximately 79% muscle, which is higher than the 60–70% for beef quoted by Russell (2008). Hopwood et al. (1976) compared kangaroos and sheep and concluded that the “body composition of a kangaroo is a highly desirable one for a meat animal. Carcass fat is negligible and muscle mass is concentrated in the region of the loin, rump, and thigh increasing the percentage of high value muscle in the carcass.” Further, Russell (2008) refers to Kelly's (2005)“1.5 kg each of prime cuts;” this means that Russell discards all but the premium cuts from kangaroos; however, he does not do the same for cattle. He classifies all other kangaroo meat as “processed meat” whereas for cattle he uses the phrase “cuts or mince” to combine prime and processed meat from cattle. Russell (2008) notes that sheep numbers declined since 1990 but kangaroo numbers did not increase. However, he omits to refer to the rise in cattle. From 1990 to 2006, cattle have increased from 23.1 to 28.8 million (ABS 1992; 2008), while Australian sheep and lamb populations declined over that period from 170.3 to 92.7 million (ABS 1992; 2008). Using the same dry sheep equivalents (DSE) that were used in Wilson & Edwards (2008), the reduction of sheep creates 78 million DSE. The rise in cattle takes up 88% of this DSE and so accounts for much of the pasture made available from the decline in sheep. The decline in sheep numbers was a result of a reduction in the profitability of the wool industry. Many wool farmers adjusted by expanding other sectors such as cattle and cropping. So the decline in sheep numbers does not mean that pastures were made available to kangaroos. The expansion of other sectors may even have reduced kangaroo's access to pasture. Editor : Dr. Corey Bradshaw

Vaccine Adjuvants Revisited

A huge amount of evidence has been made available on various as immunological auxiliaries. Very few of them, however, have made it into commercial vaccines. Their defining properties and uses are discussed in the fol- lowing mini-review. WHAT IS AN ADJUVANT? In Freund's words (1) an adjuvant should evoke very abundant serum antibody sustained for an unex- pectedly long time. In other words, it is something very practical. It must work in animals at least the size of sheep and of course in both veterinary and human vaccination. To this end it must be thoroughly biocompatible, easy to handle and to store, sterile, safe, acceptable for registration as an auxiliary in vaccination and, last but not least, must have an affordable price. Abundant serum antibody production moreover always seems to go hand-in-hand with a host of other beneficial cel- lular immunostimulatory effects. WHAT IS NOT AN ADJUVANT? The following are not adjuvants: Any soluble or insolu- ble substance producing antibodies only in mice (which then have to take the blame for lying), and also immunopoten- tiators (showing saturation doses) or immunomodulators (showing dose optimum and even inhibition at the high end). Examples are: water soluble muramyl peptides, saponins, liposaccharides, hormones. These one might characterize as adjuvants for adjuvants, or, in a word, pseudo-adjuvant. Undoubtedly they are important in special cases, but their usefulness is more remote.

Prolactin Receptor as a Candidate Gene for Prolificacy of Small Tail Han Sheep

DNA polymorphism of the ovine prolactin receptor gene (PRLR) was investigated and used to study its effect on litter size in sheep. By means of PRLR gene sequence homology between sheep and human, three primer pairs were designed for polymerase chain reaction (PCR) amplification within intron 1 and exon 10 of the PRLR gene in sheep. In these parts of the gene the single nucleotide polymorphisms were detected by PCR-single strand conformation polymorphism (SSCP) in 314 Small Tail Han ewes. These poly-morphisms were used to study the associations with litter size. The results indicated that there were three genotypes (AA, AB and BB) detected by three primer pairs. For three primer pairs the frequency of allele A was 0.96, 0.79, 0.68; and the frequency of allele B was 0.04, 0.21, 0.32, respectively. The frequency of genotype AA was 0.93, 0.62, 0.51; the frequency of genotype AB was 0.06, 0.34, 0.34; the frequency of genotype BB was 0.01, 0.04, 0.15, respectively. The Small Tail Han ewes with genotype BB or AB had 0.64–0.76 or 0.44–0.54 more lambs than those with genotype AA, respectively. These results preliminarily showed that the prolactin receptor locus is either a major gene that influences the prolificacy in Small Tail Han sheep or is in close linkage with such a gene.

Is there a relationship between prion protein genotype and ovulation rate and litter size in sheep?

The identification of an association between polymorphisms of the prion protein (PrP) gene and susceptibility to scrapie has enabled the development of breeding programmes to increase natural resistance to scrapie. It is, however, imperative to identify if such selection would affect important reproduction and production traits. The objective of this study was to determine if there is a relationship between polymorphisms at codons 136, 154 and 171 of the PrP gene and ovulation rate or litter size in sheep. Data were collected from a mixed-aged flock of Belclare ewes, over a 9-year period. Ovulation rate was determined annually using laparoscopy by counting the number of corpora lutea at each of two consecutive oestrous cycles, one immediately before and one after mating (2418 records from 366 ewes). Litter size was recorded at parturition (875 records from 353 ewes). The five common PrP alleles were present in the population and 14 PrP genotypes were represented among the animals studied. There was no significant overall effect of PrP genotype on ovulation rate or litter size and pairwise comparisons among genotypes did not reveal any significant differences for either trait. These data suggest that breeding programmes based on selection for specific polymorphisms of the PrP gene will not influence ovulation rate or litter size, at least in the breed studied.

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.