Maternal factors affecting early pregnancy in sheep

Embryonic mortality imposes a severe limitation to reproductive efficiency in the domestic species. In sheep, 20% to 30% of conceptions are not represented by lambs at birth. Attempts to improve embryonic survival by alterations to nutritional regimes and by control of other environmental factors have achieved only limited success. It has been suggested that some embryos may die because of an inappropriate uterine environment.The experiments described in this thesis investigated physiological mechanisms occurring during early pregnancy in the ewe. Knowledge of such factors may elucidate some causes of embryonic wastage and highlight potential means of improving embryonic survival. This thesis examined two aspects of maternal function during early pregnancy; luteal function, and the relationship between the developing embryo and the uterus.An association between the progesterone profile after mating and embryonic survival was observed. Pregnancies during which all embryos survived had higher progesterone concentrations from the day after mating, relative to pregnancies associated with embryonic mortality. This experiment also revealed complex inter-relationships between several factors known to affect embryonic loss. Reduced fertility late in the breeding season could be explained entirely by differences in progesterone concentration.The progesterone profile was highly variable both between ewes, and within ewes during successive pregnancies. The repeatability estimates for pre-luteal and luteal-phase progesterone concentrations suggested that the response to selection for a particular progesterone profile would be low.Luteal-phase progesterone secretion was pharmacologically suppressed in order to mimic the changes in progesterone concentration which may occur following environmental stress. Treatments which lowered progesterone levels also reduced embryonic survival.The composition of uterine fluids was investigated in cyclic and pregnant ewes, and in ovariectomised ewes receiving exogenous steroids. Concentrations of several enzymes varied throughout the oestrous cycle. These changes were considered to reflect ovarian steroid concentrations. Differences in the levels of uterine proteins were observed between pregnant and non-pregnant ewes, and between the gravid and non-gravid horn of unilaterally pregnant ewes. Variations in the schedule of steroid administration to ovariectomised ewes affected the relative concentrations of several uterine components. The potential mechanisms by which such differences may arise were discussed.The experiments described in this thesis have revealed associations between maternal factors and embryonic survival. Potential means of improving embryonic survival arising from these observations were described

A PARTIAL EQUILIBRIUM MODEL OF THE LINKAGES BETWEEN ANIMAL WELFARE, TRADE AND THE ENVIRONMENT IN SCOTLAND

This research analyses the impacts of a scientific advance that improves animal welfare, upon the environment and trade in Scotland using partial equilibrium (PE) modelling. The science improves pig neonatal survival through improved (high fibre) sow diets used before mating. Our model simulates the effects of animal welfare changes on the pig production systems (pig meat) and further on trade flows (trade in pig meat) and environment (water and air pollution). We consider two animal welfare simulation scenarios, namely the status quo – no animal welfare change as regards pig neonatal mortality (baseline scenario) and the case of improving pig neonatal survival (alternative scenario) and compare the impacts on trade and environment between the two scenarios during the simulation horizon 2008-2015. The results show that the increase in animal welfare has a lower impact on the environment in the alternative scenario compared to the baseline scenario (by about 6% at the end of the simulation horizon) and a positive impact on net trade in the alternative scenario compared to the baseline scenario (by about 13% at the end of the simulation horizon).Pig Welfare, Trade, Environment, Scotland, Partial Equilibrium Model., Agricultural and Food Policy, Environmental Economics and Policy, Research Methods/ Statistical Methods, Q18, Q50,

Associations between maternal vitamin D status and porcine litter characteristics throughout gestation

Emerging evidence suggests an important role of vitamin D in the establishment and maintenance of pregnancy, and the regulation of foetal growth across mammalian species. However, the temporal changes in maternal vitamin D status throughout gestation in the pig and the relationship between maternal vitamin D status and litter characteristics of interest across gestation remain poorly understood and under-investigated. The abundance of 25(OH)D in maternal plasma was quantified by HPLC–MS/MS at gestational days (GD) 18, 30, 45, 60 and 90 (n = 5–11 gilts/GD). Maternal plasma 25(OH)D concentrations significantly increased between GD18 and GD30 (P < 0.05). The relationship between maternal vitamin D metabolite concentrations and litter characteristics of interest including gilt weight, ovulation rate, mean litter weight, number of live foetuses, percentage prenatal survival, and sex ratio of the litter was assessed. Maternal 25(OH)D (P = 0.059) concentrations tended to be positively associated with percentage prenatal survival on GD60. On GD90, maternal 25(OH)D (P < 0.05) concentrations were inversely associated with gilt weight. Maternal plasma 25(OH)D concentrations were inversely associated with the percentage of male foetuses in the litter on GD90 (P < 0.05). This study has provided novel insights into temporal changes in maternal vitamin D status throughout gestation and the relationship between maternal vitamin D status and the economically important litter characteristics of gilt weight, percentage prenatal survival and percentage of male foetuses in the litter. Improving the understanding of the role of vitamin D across important developmental timepoints in relation to foetal growth is essential to improve reproductive success in livestock species. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40104-022-00760-w

Associations between testicular development and fetal size in the pig

BACKGROUND: Impaired reproductive performance is the largest contributing factor for the removal of boars from commercial systems. Intrauterine growth restricted piglets represent 25% of the total number of piglets born and have impaired reproductive performance. This study aimed to improve the understanding of temporal changes in testicular gene expression during testes development in fetuses of different size. The lightest and closest to mean litter weight (CTMLW) male Large White × Landrace littermates were collected at gestational days (GD) 45, 60 and 90 (n = 5–6 litters/GD). RESULTS: Testes weight and testes weight as a percentage of fetal weight were not associated with fetal size at GD60 or 90. Fetal plasma testosterone was not associated with fetal size at GD90. There was no association between fetal size and seminiferous tubule area and number, number of germ or Sertoli cells per tubule. The lightest fetuses tended to have wider seminiferous tubules compared to the CTMLW fetuses at GD90 (P = 0.077). The testicular expression of KI67 (P ≤ 0.01) and BAX:BCL2 ratio (P = 0.058) mRNAs decreased as gestation progressed. Greater SPP1 mRNA expression was observed at GD60 when compared with GD45 and 90 (P ≤ 0.05). Lower expression of DMRT1 and SPP1 (P < 0.01) mRNAs was observed in testes associated with the lightest fetuses compared to the CTMLW fetuses at GD90. CONCLUSIONS: These findings provide novel insights into the expression profiles of genes associated with testicular development and function. Further, these data suggest that programming of reproductive potential in IUGR boars occurs late in gestation, providing a platform for further mechanistic investigation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40104-022-00678-3

Efficiency of genomic selection using Bayesian multi-marker models for traits selected to reflect a wide range of heritabilities and frequencies of detected quantitative traits loci in mice

BACKGROUND: Genomic selection uses dense single nucleotide polymorphisms (SNP) markers to predict breeding values, as compared to conventional evaluations which estimate polygenic effects based on phenotypic records and pedigree information. The objective of this study was to compare polygenic, genomic and combined polygenic-genomic models, including mixture models (labelled according to the percentage of genotyped SNP markers considered to have a substantial effect, ranging from 2.5% to 100%). The data consisted of phenotypes and SNP genotypes (10,946 SNPs) of 2,188 mice. Various growth, behavioural and physiological traits were selected for the analysis to reflect a wide range of heritabilities (0.10 to 0.74) and numbers of detected quantitative traits loci (QTL) (1 to 20) affecting those traits. The analysis included estimation of variance components and cross-validation within and between families. RESULTS: Genomic selection showed a high predictive ability (PA) in comparison to traditional polygenic selection, especially for traits of moderate heritability and when cross-validation was between families. This occurred although the proportion of genomic variance of traits using genomic models was 22 to 33% smaller than using polygenic models. Using a 2.5% mixture genomic model, the proportion of genomic variance was 79% smaller relative to the polygenic model. Although the proportion of variance explained by the markers was reduced further when a smaller number of SNPs was assumed to have a substantial effect on the trait, PA of genomic selection for most traits was little affected. These low mixture percentages resulted in improved estimates of single SNP effects. Genomic models implemented for traits with fewer QTLs showed even lower PA than the polygenic models. CONCLUSIONS: Genomic selection generally performed better than traditional polygenic selection, especially in the context of between family cross-validation. Reducing the number of markers considered to affect the trait did not significantly change PA for most traits, particularly in the case of within family cross-validation, but increased the number of markers found to be associated with QTLs. The underlying number of QTLs affecting the trait has an effect on PA, with a smaller number of QTLs resulting in lower PA using the genomic model compared to the polygenic model