Date of Award
Doctor of Philosophy (PhD)
Animal and Veterinary Sciences
Susan K. Duckett, Committee Chair
Fescue Toxicosis is a prevalent problem in the Southeastern, United States causing an estimated loss of one billion dollars per year to the livestock industry (Roberts & Andrae, 2010). There has been much research aimed at understanding the grass itself, the endophyte and the ergot alkaloids it produces, as well as its relationship and impacts on consuming animals. Many mitigation plans have been established and have been shown to control the amount of alkaloids subsequent animals are ingesting; however, research is at the tipping point of needing a genetic approach to fescue toxicosis. This research looked into the bovine genome to apply the previously identified Single Nucleotide Polymorphism (SNP) found by Campbell et al. (2014) in the Dopamine (DRD2) gene (rs41749780) to a cow/ calf production setting in order to determine if genotype provided advantages for cows (N=74) consuming toxic fescue during late gestation and the effects on their calves until weaning. Furthermore, the Ovine genome was screened for SNP’s in the DRD2 gene in sheep (N= 57, N=61;, N=22) in a series of experiments and associations of the SNP and grazing toxic tall fescue were analyzed. Since fescue toxicosis can affect all ruminant species, the ovine genome was screened for possible SNP sites in the DRD2 gene, and one SNP (g270a) was located and identified. The objectives of this study presented in Chapter 2, were 1) identify a SNP in the DRD2 gene, and 2) determine if there are any genotypic associations with fescue toxicosis. Results indicated ewes of a particular genotype (G|G) had heavier fetal weights and were able to manipulate circulating hormonal levels during pregnancy. This study warranted further investigation, presented in Chapter 3, concluding a genotypic difference in lamb weight and growth with no associations with the dietary treatment of the ewe through gestation. Therefore, a follow up study was designed to further determine if there is an outperforming genotype when ewes were on the same plain of nutrition in the production setting. Conclusions can be made that the G|G genotyped ewes had no production benefits at birth (P=.180) but lambs tended to be heavier by weaning (P=.059) . These lambs tended to have greater average daily gain (ADG) (P=0.079) when compared to lambs from A|A ewes. It appears the G|G genotype has production advantage for lambs from birth to weaning. Furthermore, Chapter 4 applies SNP rs41749780 to cow/calf pairs during late gestation to weaning consuming E- or E+ forages. Seventy-four Angus-based cows were genotyped for the DRD2 SNP with the objective of investigating the effects of dopamine 2 receptor (DRD2) single nucleotide polymorphism (SNP; rs41749780) and fescue treatment during the last trimester on cow and calf performance. Dam weight, serum prolactin, body condition scores (BCS) and hair coat scores (HCS) were collected every 30 d during the last trimester of gestation. Cows with G|G genotype had greater (P =0.012) amount of rump fat deposition compared to A|A cows. Cows with DRD2 genotype of G|G tended to have lower (P = 0.07) prolactin levels at d 0 and 90 of grazing. Adjusted calf birth and weaning weights did not differ (P>0.23) by fescue pasture type or cow genotype. Milk production was estimated using weigh-suckle-weigh at d 30 post-calving. Fescue pasture type and cow genotype did not alter (P > 0.40) milk production. In evaluation of calf sire, there tended to be an interaction (P = 0.07) between fescue pasture type and cow genotype in calves that were sired by natural service. Results concluded grazing toxic tall fescue during late gestation reduced dam BW, rump fat deposition, and serum prolactin levels but did not alter adjusted birth or weaning weights of all calves born. However when evaluated by calf sire, adjusted birth and weaning weight for natural service sired calves showed that response to grazing E+ fescue during late gestation depended on cow DRD2 genotype. The collection of these studies show the potential for a production advantage for G|G genotypes in sheep flocks. In cattle, it appears there may be a genotypic advantage for calves born to dams of A|A genotypes, however due to a variety of other influences a second year study is warranted in order to develop a deeper understanding.
Wilbanks, Sarah Adams, "Association of DRD2 Single Nucleotide Polymorphism and Fescue Toxicosis in Ruminants" (2018). All Dissertations. 2286.