Factors that affect fertility in a feral population of sheep

Feral livestock offer an excellent opportunity lo study factors affecting fertility as the physiology of their husbanded relatives is well known and social and environmental influences can be studied free of man's interference. This is so in the population of about 1250 sheep of the primitive Soay breed on the islands of St Kilda, Scotland. There is a high coincidence of oestrus amongst the ewes in mid November, and the breeding season is constant within a few days, from year to year. The breeding season in other British breeds of sheep demonstrates a strong correlation with latitude. On St Kilda, mortality rates in male sheep are higher than in females so that the ratio of rams to ewes at mating time is about 1:5. Competition amongst rams is intense. The optimal time for mating and the place of ram lambs in the social system are discussed.     

Hybridization studies of Haemonchus contortus (rudolphi, 1803) and H. placei (place, 1893) (Nematoda: Trichostrongylidae)

Hybridization experiments between Haemonchus contortus from sheep and H. placei from cattle indicate that the H. placei vulvar morph type and the inability of the eggs to hatch and develop at 11°C were inherited as dominant traits in the hybrids. The size of the third stage larvae was similar to H. placei in hybrids from the mating of male H. placei × female H. contortus while larvae from the reciprocal mating were intermediate in size. Hybrids produced by the mating of thiabendazole resistant female H. contortus × non-resistant male H. placei were also resistant. The F₁ males of the mating between male H. contortus and female H. placei were sterile. Male sterility did not occur in the reciprocal cross until the F₂ generation. Female hybrids from these generations had a low level of fertility when backcrossed to males of either parent species. Cytological studies of the hybrid males indicated that sterility was due to several kinds of meiotic disturbance and that spermatogenesis stopped during metaphase I. The chromosomes in eggs of unfertilized females did not undergo meiosis and polar body formation; instead they increased in number by a process of endomitosis. Unfertilized eggs in the faeces were characterized by uneven cytoplasmic division and abnormal shape. It is proposed that hybrid sterility can lead to the local eradication of one species of Haemonchus by the other. Furthermore, the outcome of which species is eradicated can be influenced by such variables as initial population sizes, climate, and the local ratio of sheep to cattle.     

Net methane emissions from grazing sheep

Methane emissions from ruminant livestock are responsible for 45 % of New Zealand’s combined CO₂-equivalent greenhouse gas inventory, and arise principally from sheep. Using a flock of 6-month old sheep (20 ha^–1) grazing abundant pasture, we compare micrometeorological measurements of net methane emission rates with measurements from individual sheep based on a sulphur-hexafluoride tracer technique. Individual sheep emission rates were highly variable and averaged 19.5 ± 4.8 (SD) g CH₄ sheep^–1 d^–1, or 39 ± 9.6 mg CH₄ m^–2 d^–1 on an areal basis. Emission rates were poorly correlated with animal live weight or dry matter intake but represented an average dietary energy loss of 3.6%. Methane fluxes from the surface were determined as half hourly averages by a flux-gradient technique using temperature and methane gradients. Soil methane consumption was measured using chambers and found to be negligible (< 0.09 mg CH₄ m^–2 d^–1) in comparison with the animal contribution. Daily net emission rates averaged 46 mg m^–2 d^–1 and exhibited a broad peak in the early afternoon which corresponded with animal activity patterns. On average, net emisssion rates were 40% higher during the day than at night. Stable nocturnal conditions led to a separation of the micrometeorological measurements from the methane source and hence highly variable results. Based on two corroborating techniques, the average net methane emission rate was c. 43 mg CH₄ m^–2 d^–1 or 155 kg CH₄ ha^–1 y^–1.     

Anisakis simplex: the activity of larval products on the complement system

The effects of the larval products (crude extract and excretory-secretory) of Anisakis simplex on the classical and alternative pathways of human complement system were investigated. This could constitute a mechanism to evade host defences, similarly than in other parasitic diseases. The larval products showed a stronger effect on the classical pathway than on the alternative pathway. The most pronounced modulating effects were found for the excretory-secretory products. Chelation of bivalent cations (Ca(2+) or Mg(2+)) by these larval products may be responsible for their mode of action on the alternative pathway, whereas the chelation is not likely to be particularly involved in the anticomplementary activity found on the classical pathway. Detailed studies revealed that the larval products of A. simplex act at the level of the C3 and other complement components. Heating the crude parasite extract led to a notable loss of haemolysis inhibition activity, and the addition of PMSF (a serine protease inhibitor) also cause variation in the activity of the crude extract.     

Mitochondrial diversity and the origin of Iberian sheep

Mitochondrial DNA diversity was analysed in 19 Iberian and six foreign sheep breeds. Three mtDNA lineages (B, A and C) were found in the Iberian sheep, with type B clearly predominating over the others. The results were analysed for each of the morphologically determined breed groups in Iberian sheep: Merino, Entrefino, Churro and Iberian trunks. MtDNA lineage C was found only in the Iberian trunk composed of Montesina and Ojalada. These two populations had high mtDNA variability, and in the Iberian sheep only Merino Branco had more variation. The other three Merino types studied showed moderate variability, including the most authentic Merino, the Spanish Merino. These three Merinos clustered closely in a multidimensional scaling representation of distances, while the fourth breed (Merino Branco) showed a clear separation. As for the other two trunks, breeds from the Churro group showed greater maternal uniformity while results for populations included in the so-called Entrefino trunk seemed to have a more heterogeneous maternal origin. The results obtained are discussed with available data from nuclear markers and with morphological classifications, and all this information is analysed in relation to the origin of the different Iberian sheep breeds.     

Quantitative trait loci linked to PRNP gene controlling health and production traits in INRA 401 sheep

In this study, the potential association of PrP genotypes with health and productive traits was investigated. Data were recorded on animals of the INRA 401 breed from the Bourges-La Sapinière INRA experimental farm. The population consisted of 30 rams and 852 ewes, which produced 1310 lambs. The animals were categorized into three PrP genotype classes: ARR homozygous, ARR heterozygous, and animals without any ARR allele. Two analyses differing in the approach considered were carried out. Firstly, the potential association of the PrP genotype with disease (Salmonella resistance) and production (wool and carcass) traits was studied. The data used included 1042, 1043 and 1013 genotyped animals for the Salmonella resistance, wool and carcass traits, respectively. The different traits were analyzed using an animal model, where the PrP genotype effect was included as a fixed effect. Association analyses do not indicate any evidence of an effect of PrP genotypes on traits studied in this breed. Secondly, a quantitative trait loci (QTL) detection approach using the PRNP gene as a marker was applied on ovine chromosome 13. Interval mapping was used. Evidence for one QTL affecting mean fiber diameter was found at 25 cM from the PRNP gene. However, a linkage between PRNP and this QTL does not imply unfavorable linkage disequilibrium for PRNP selection purposes.     

Association between PrP genotypes and performance traits in a Welsh Mountain flock

The UK national scrapie plan (NSP) for sheep is based on selection for the resistant ARR/ARR genotype and elimination of susceptible types of the ovine prion protein (PrP) gene. The aim of this study was to estimate the possible association of the PrP genotype and performance traits by using data from the CAMDA Welsh Mountain flock. Four alleles (ARH, ARQ, ARR and VRQ) and 10 genotypes covering all five NSP risk groups were present in the CAMDA flock. Overall, the most common allele was ARR (35.2%), and VRQ was the least common (5.4%). The commonest genotypes were ARR/ARQ (23.7%) and ARR/AHQ (23.1%). The most resistant genotype, ARR/ARR, and the most susceptible genotype, VRQ/VRQ, were found in 10.2% and 0.3%, respectively, of the population tested. The associations of PrP genotypes with weight and ultrasonically scanned traits were investigated in three analyses, the first using genotypes, the second using risk categories and the third using number of alleles. These associations were evaluated by univariate analysis of each trait using an animal model with maternal effects where appropriate, and PrP was included as a fixed effect. Selection for scrapie resistance will not adversely affect progress in the traits considered and is consistent with improvements in muscle depth.     

Nutritional status of adult ewes during early and mid-pregnancy. 1. Effects of plane of nutrition on ewe reproduction and offspring performance to weaning

The objective of this study was to determine the effects of plane of nutrition during early and mid-pregnancy on the performance of mature ewes and their offspring. From day 0 to day 39 post mating (early pregnancy, EP), 82 multiparous ewes were fed to provide either 60% (low, L), 100% (medium, M) or 200% (high, H) of predicted metabolisable energy (ME) requirements for maintenance, following a synchronised mating. From day 40 to day 90 (mid-pregnancy, MP), ewes were provided with either 80% (M) or 140% (H) of ME requirements. After 90 days of gestation, all ewes were fed to meet requirements for late pregnancy. During EP, mean live weight (LW) and body condition score (BCS) change of ewes were -6.3, -0.8 and +6.0 kg and -0.02, +0.10 and +0.22 units in the L-, M- and H-EP treatments, respectively. During MP, mean LW and BCS change were -0.8 and +4.9 kg and -0.09 and +0.09 units in the M- and H-MP treatments, respectively (P < 0.001). Treatments had no effect (P > 0.05) on conception rate, although there tended to be an inverse relationship (P = 0.085) between plane of nutrition in EP and plasma progesterone concentrations at day 42 of gestation. EP nutrition influenced foetal development with lambs from ewes offered diet L-EP being smaller (P < 0.01) at day 56 than M- or H-EP lambs. However, at parturition L-EP lambs were heavier (P < 0.05) and tended to have higher (P = 0.056) immunoglobulin status 24 h after birth. Mortality rates at weaning were reduced (P < 0.05) for lambs born from ewes offered diet L-EP compared with M- or H-EP lambs. Diet M during mid-pregnancy resulted in larger (P < 0.05) foetuses at day 80 of gestation. At parturition, these lambs had longer head and crown-rump lengths than H-MP lambs (P < 0.05). Lambs born to ewes offered diet M-MP tended to progress faster to attempting to suckle than H-MP lambs (P = 0.089). There was an interaction between plane of nutrition in early and mid-pregnancy, whereby the highest number of lambs weaned was a result of diet L-EP followed by diet M-MP. These results indicate that in adult ewes, temporary nutrient restriction during early pregnancy results in better lamb survival; and mild nutrient restriction in mid-pregnancy tends to improve neonatal behaviour and results in lambs with longer skeletal size.