Selection response in New Zealand Romney sheep

Blair, Hugh T.; Garrick, Dorian J.; Rae, A. L.; Wickham, G. A.

doi:10.1080/00288233.1984.10430632

Cited by 8 publications

(1 citation statement)

References 12 publications

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“…These lines were established from a common base population in 1956 and have been subjected to single-trait selection on greasy fleece weight (FW) or have been randomly bred (C). Details of the lines are provided by Blair et al (1984) and Blair (1986). Greasy wool production is c. 25% greater in the FW than the C line with marked differences in the seasonal pattern of wool growth (McClelland et al 1987).…”

Section: Introductionmentioning

confidence: 99%

Physiological responses to selection for greasy fleeceweight in Romney sheep

Clark

Mackenzie

McCutcheon

et al. 1989

New Zealand Journal of Agricultural Research

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Two studies were conducted using rams from the Massey University fleeceweight-selected (FW) and control (C) lines ofRomnJY sheep. In the first study, conducted from April to July, nine ram hoggets from each line (mean liveweight 42.1 kg) were fed 1000 g/day protein-extract~d lucerne meal for 6 weeks before being blood-sampled by jugular venipuncture. They were then assigned to one of three groups receiving 0, 30, or 60 g/day formaldehyde-protected casein in addition to the basal diet. Blood sampling was repeated after 4 weeks of casein supplementation. During the pre-casein period, FW rams exhibited lower concentrations of urea (6.1 versus 7.2 mM, SE=0.3, P < 0.05) and thyroxine (3.3 versus 4.3 J.Lg/dl, SE = 0.5, P < 0.10) than Crams. During the period of casein supplementation, intakes of nitrogen (N) in the form oflucerne meal increased with dose of casein (from 24.8 to 26.1 g/day) but were not different between the lines. Casein supplementation also increased plasma urea concentration in a dose-responsive manner with no evidence of a casein level X selection line interaction. Plasma concentrations of the enzymes alanine aminotransferase and aspartate aminotransferase were not different between the lines at any time. In the second study, five rams from each line (mean 60.9 kg liveweight) were fed 110% maintenance as lucerne chaff for 30 days. Mean intakes ofN as lucerne chaff were 32.3 g/day and were not influenced by line. The rams then received intravenous infusions of saline or methionine (25.7 mg/kg liveweight per day) in a switchback design during July-August. FW rams maintained lower plasma urea concentrations (by 1 mM) than C rams during the saline infusions and this difference was halved during methionine infusion. In addition, FW rams had lower concentrations of creatinine and thyroxine in plasma (P < 0.01) but neither difference was influenced by methionine treatment. Erythrocyte reduced glutathione concentrations were not different between the lines but were elevated by methionine infusion. It is concluded that selection for greasy fleeceweight in these lines has been accompanied by changes in plasma concentrations of urea, creatinine, and thyroxine. Differences in plasma urea concentration between the lines appear to reflect differences in the efficiency with which amino acids are used for production, and differences in kidney function. The physiological basis of differences in circulating thyroxine is not known. Although these differences are unlikely to be useful as predictors of genetic merit in the field (as they are influenced by non-genetic factors such as nutrition), an understanding of their physiology may help in the development of genetic markers.

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Section: Introductionmentioning

confidence: 99%

Physiological responses to selection for greasy fleeceweight in Romney sheep

Clark

Mackenzie

McCutcheon

et al. 1989

New Zealand Journal of Agricultural Research

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The effect of selection for fleece weight upon urea metabolism and digestive function in Romney sheep

Thompson¹,

Dellow²,

Barry³

1989

Aust. J. Agric. Res.

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The effect of 30 years genetic selection for greasy fleece weight upon rumen metabolism, apparent digestibility and nitrogen metabolism was investigated in Romney sheep.Fleece weight (Fwt) animals had a 1 mM lower plasma urea concentration than control (C) animals when fed on both diets given, but there was no difference in plasma urea IRL, urinary urea excretion or urea recycling to the digestive tract between the Fwt and C sheep when fed either diet. Relative to the C shccp, the Fwt animals had a higher creatinine clearance rate when fed the meadow hay diet, and a higher urea clearance rate when fed both diets.When fed the meadow hay diet there were no differences between the Fwt and C animals in voluntary feed intake (VFI) or apparent DM digestibility. However, when fed on the lucerne chaff diet the Fwt animals had a higher VFI than the C animals and a lower apparent DM digestibility. These changes were associated with an increase in the rumen fractional outflow rate (FOR) of lignin in the Fwt sheep, and a higher molar proportion of acetate and a lower proportion of propionate in rumen fluid.The differences in urea and creatinine clearance rates suggest that selection for fleece production may have altered kidney function, with expression of this and rumen FOR being related to nutritional level. A factor contributing to the superior wool production of the Fwt sheep is suggested.

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Wool sulfur concentration and output in fleeceweight-selected and control Romney rams

Antram¹,

McCutcheon²,

Ht³

et al. 1991

Aust. J. Agric. Res.

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Wool sulfur concentration and output of Romney sheep from fleeceweight-selected and control lines were measured with a view to determining their potential use as genetic markers for fleeceweight. Midside wool samples were collected at 28 day intervals from 4 to 14 months of age from 35 fleeceweight-selected and 30 control rams. Clean wool growth during each sampling period was calculated. Wool samples were digested using an open wet digestion method and the wool sulfur concentration was determined by plasma emission spectrometry. Fleeceweight-selected rams had significantly greater midside wool growth than the control animals throughout the trial except on day 56. Average wool sulfur concentration in both lines increased over the sampling period to a peak at day 308. The wool sulfur concentration of control rams was significantly higher than that of fleeceweight-selected rams only on days 28 and 280. Total sulfur output (the product of midside wool growth rate and sulfur concentration) was significantly higher in the fleeceweight-selected than in the control rams on days 84-140 (March-May) and 196-308 (June-October). It is concluded that midside wool sulfur concentration and output of 4 to 14 month-old-Romney hoggets are unlikely to be useful genetic markers for fleece production.

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Selection response in New Zealand Romney sheep

Cited by 8 publications

References 12 publications

Physiological responses to selection for greasy fleeceweight in Romney sheep

Physiological responses to selection for greasy fleeceweight in Romney sheep

The effect of selection for fleece weight upon urea metabolism and digestive function in Romney sheep

Wool sulfur concentration and output in fleeceweight-selected and control Romney rams

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