Investigation of genetic and non-genetic factors influencing ewe reproductive performance in a Scottish hill flock
Hill sheep farming is the backbone of the Scottish sheep farming industry. Due to the low productivity of hill sheep breeds and the changes in EU subsidy support system, the number of breeding ewes declined significantly between 2000 and 2018. This has affected the social, economic and environmental sustainability of rural areas. Introduction of lowland/upland prolific sheep breeds, such as the Lleyn, into hill farming systems might improve productivity of hill enterprises. However, the harsh hill weather conditions and poor nutritional supply in the hill environment might compromise the performance and the health of less adapted breeds, such as the Lleyn. The aim of this PhD project was to investigate the performance of Lleyn ewes farmed in a Scottish hill farm environment, comparing their performance with genetically unimproved Scottish Blackface (UBF) ewes and genetically improved Scottish Blackface (IBF) ewes farmed together in the same flock. The study was conducted between November 2012 and October 2017 in two phases. In the first phase (between November 2012 and October 2015; the flock was comprised of approximately 300 ewes per genetic line), Lleyn ewes achieved significantly higher litter sizes at pregnancy scanning, lambing and weaning than UBF and IBF ewes, and had heavier average lamb birth weight than, and comparable average lamb weaning weight to, UBF and IBF ewes. In the second phase (between November 2015 and October 2017; the flock was comprised of approximately 200 ewes per genetic line), the three genetic lines of ewes were further challenged, with half of the flock being farmed under more extensive conditions. In this phase, based on the whole flock performance, Lleyn ewes achieved comparable litter sizes at pregnancy scanning, lambing and weaning to UBF and IBF ewes. They also achieved heavier average lamb birth weights and heavier weaned litter weights than UBF and IBF ewes. Further investigations were performed to discover the possible reasons that led to performance differences among the three genetic lines. Firstly, Lleyn ewes were found to have higher pre-mating serum concentrations of vitamin D (25(OH)D3 in particular) than UBF and IBF ewes, and these vitamin D parameters were positively associated with lamb birth weight in the following lambing season. Additionally, pre-lambing metabolic profiles of twin-bearing ewes showed that they were well nourished in late pregnancy, with Lleyn twin-bearing ewes having higher magnesium concentrations than UBF and IBF ewes, which suggested that these Lleyns had higher feed intake. These outcomes could potentially assist Lleyn ewes to give birth to lambs with relatively heavier birth weight, which enhances lamb survival. The quality of colostrum secreted by Lleyn twin-bearing ewes, measured as Brix percentage, was as good as colostrum secreted by UBF and IBF twin-bearing ewes, and this is important for providing passive immunity and energy for neonates to survive. The post mortem examinations of the majority of dead lambs in three lambing seasons (2015-2017) showed that dystocia was the main cause of neonatal lamb death, with more IBF lambs dying as a consequence of this cause, compared to UBF and Lleyn lambs. Lleyn ewes had narrower external pelvic widths than UBF and IBF ewes, although no relationship between this measurement and lambing difficulty was found. Summer grazing behavioural observations showed that the number of ewes observed in different grazing sectors did not differ among the three genetic lines, suggesting no obvious differences in grazing behaviour. Overall, this thesis showed that Lleyn ewes have adapted well to the hill environment, and outperformed/equalled production levels of their UBF and IBF flockmates. Therefore, this lowland/upland sheep breed could be a good candidate for improving the productivity of hill sheep farming enterprises.