@conference {41980,
	title = {Responses to selection in ryegrass staggers lines of sheep},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {67},
	year = {2007},
	month = {Jan},
	pages = {204-208},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Wanaka},
	abstract = {Ryegrass Staggers (RGS) is predominantly a summer/autumn metabolic disorder in ruminants, caused by ingestion of the lolitrem-B toxin from endophyte-infected perennial ryegrass, and it is common in New Zealand. It causes lack of neuromuscular co-ordination in susceptible animals under stress, e.g. when mustered by sheep dogs. It is of welfare concern, and it is costly to farmers because it severely compromises grazing management. A flock was established at AgResearch in 1993, with two lines bred for resistance (RGS-R) or susceptibility (RGS-S) to RGS. Lambs are scored for susceptibility each year, when grazing on high endophyte pastures, and mustered by sheep dogs. In 2005 and 2006, 94\% and 91\% of lambs respectively in the RGS-S line showed clinical staggers, when grazing together with the RGS-R line which had 2\% and 6.5\% of clinical cases, respectively (P < 0.001). Using the latest standardised RGS scoring system, the heritability estimate of resistance/susceptibility to RGS was 0.36 {\textpm} 0.04. To understand more about why and how the RGS lines differ, blood samples were taken from the breeding-ewe flock (n = 126) in June 2005, outside the usual RGS and facial eczema season. Compared with the RGS-R line, the RGS-S line ewes had a 23\% higher activity (P < 0.001) of aspartate transaminase (AST), an enzyme indicating hepatic or muscular damage; there were similar findings inewes sampled four weeks apart (between-animal repeatability for AST = 0.85). In plasma samples from selection-line yearling females (two birth years; n = 95), the RGS-S line had 27\% and 37\% higher AST and alanine transaminase activities, respectively (both P < 0.001), and a 38\% higher creatine kinase activity (P < 0.05) than the RGS-R line. One explanation of these results is that, compared with the RGS-R line, selection in the RGS-S line may have changed two functions, a reduced ability to detoxify lolitrem-B, and an increased sensitivity to stress expressed as a tendency to show increased muscle tetany and damage.},
	issn = {1176-5283},
	author = {Morris CA and Amyes NC and Orchard RL}
}
