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143 results on '"Hickey, S. M."'

2. Can we have our steak and eat it: The impact of breeding for lowered environmental impact on yield and meat quality in sheep

Author

Rowe, S. J., primary, Hickey, S. M., additional, Bain, W. E., additional, Greer, G. J., additional, Johnson, P. L., additional, Elmes, S., additional, Pinares-Patiño, C. S., additional, Young, E. A., additional, Dodds, K. G., additional, Knowler, K., additional, Pickering, N. K., additional, Jonker, A., additional, and McEwan, J. C., additional

Published
2022
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10. Heritability of ram mating success in multi-sire breeding situations.

Author

Juengel, J. L., Hickey, S. M., Clarke, S. M., Cullen, N. G., McEwan, J. C., and Dodds, K. G.

Abstract

Multi-sire mating of a mob of ewes is commonly used in commercial sheep production systems. However, ram mating success (defined as the number of lambs sired by an individual) can vary between rams in the mating group. If this trait was repeatable and heritable, selection of rams capable of siring larger numbers of lambs could reduce the number of rams required for mating and ultimately lead to increased genetic gain. However, genetic correlations with other productive traits, such as growth and female fertility, could influence the potential for ram mating success to be used as a selection trait. In order to investigate this trait, parentage records (including accuracy of sire assignment) from 15 commercial ram breeding flocks of various breeds were utilised to examine the repeatability and heritability of ram mating success in multi-sire mating groups. In addition, genetic and phenotypic correlations with growth and female fertility traits were estimated using ASReml. The final model used for the ram mating success traits included age of the ram and mating group as fixed effects. Older rams (3+years old) had 15% to 20% greater mating success than younger rams (1 or 2 years of age). Increasing the stringency of the criteria for inclusion of both an individual lamb, based on accuracy of sire assignment, or a whole mating group, based on how many lambs had an assigned sire, increased repeatability and heritability estimates of the ram mating success traits examined. With the most stringent criteria employed, where assignment of sire accuracy was >0.95 and the total number of lambs in the progeny group that failed to have a sire assigned was<0.05, repeatability and heritability for loge(number of lambs) was 0.40±0.09 and 0.26±0.12, respectively. For proportion of lambs sired, repeatability and heritability were both 0.30±0.09. The two ram mating traits (loge(nlamb) and proportion) were highly correlated, both phenotypically and genetically (0.88±0.01 and 0.94±0.06, respectively). Both phenotypic and genetic correlations between ram mating success and growth and other female fertility traits were low and non-significant. In conclusion, there is scope to select rams capable of producing high numbers of progeny and thus increase selection pressure on rams to increase genetic gain. [ABSTRACT FROM AUTHOR]

Published
2019
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42. Responses of prolactin and hair growth to selection for age at puberty in Angus cattle.

Author

Morris, C. A., Amyes, N. C., and Hickey, S. M.

Subjects
ABERDEEN-Angus cattle, CATTLE genetics, CATTLE growth, PROLACTIN, HAIR, PUBERTY, MAXIMUM likelihood statistics, ANIMAL models in research
Abstract

A trial was carried out over a 7-year period (1999 to 2005 calf crops) to compare indicators of seasonality in Angus cattle, which were part of a long-term genetic selection experiment. Divergent selection was applied for early (‘AGE−’) or late (‘AGE+’) age at puberty (AP) in heifers, and selection lines differed over the 7-year period by 62 days (15% of the mean). The primary measures of seasonality studied in 629 heifer progeny (59 sire groups) were serum concentration of prolactin (PRL), and winter and summer hair growth. Serial samples were obtained for PRL from 11 to 18 months of age, and data were analysed with adjustment for cortisol concentration. Using restricted maximum likelihood procedures with an animal model, heritability estimates were: AP, 0.26 ± 0.03; logePRL concentration, 0.23 ± 0.07; logecortisol concentration, 0.22 ± 0.07; hair weight, 0.21 ± 0.04; and hair length, 0.09 ± 0.05. Corresponding repeatability estimates for the last four traits were 0.49 ± 0.03, 0.38 ± 0.03, 0.21 ± 0.04, and 0.64 ± 0.02, respectively. The genetic correlation between AP and logePRL concentration was estimated at −0.29 ± 0.13 (P < 0.05). PRL concentration in the AGE− line after passing through puberty was 11 ± 5% lower than in the AGE+ line (P < 0.05). Line effects were not significant for hair weight or hair length. It was concluded that divergent selection for AP changed PRL concentration, which may partly reflect sensitivity to changing day length. [ABSTRACT FROM AUTHOR]

Published
2010
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50. Genetic studies of carotenoid concentration in the plasma and milk of New Zealand dairy cattle

Author

Morris, C. A., Knight, T. W., Newman, S. -A. N., Hickey, S. M., Death, A. F., O'Neill, K. T., and Ridland, M.

Abstract

Blood and milk samples were collected in 1992/93 from 2-year-old heifers in the Livestock Improvement Corporation's Sire Proving Scheme, for analysis of carotenoid concentration (CC). The trial comprised heifers in 127 spring-calving North Island dairy herds, where blood samples were taken from a total of 2744 heifers (Holstein-Friesians (F), Jerseys (J), and their crosses) in early/mid lactation (spring), and from a sub-group of the same animals in autumn. These heifers were the daughters of 157 young F and J sires, and 15 older sires. Whole-lactation yields of milk, fat, and protein, and fat% and protein% were also obtained. Sire-model restricted maximum likelihood (REML) analyses were carried out to estimate genetic and phenotypic parameters. Purebred F and J breed means for plasma CC in spring were 14.1 and 17.9 μg ml-1 (P < 0.001), respectively, and for milk CC 5.24 and 7.50 μg g-1 fat (P < 0.001), and corresponding heritabilities for the two traits were 0.46 ± 0.08 and 0.11 ± 0.10. The repeatability of plasma CC across seasons was 0.64 ± 0.02. The genetic correlation between spring plasma CC and milk CC g-1 fat was 0.66 ± 0.22, whereas genetic correlation estimates for spring plasma and milk CC g-1 fat with other traits were: with milk volume -0.01 ± 0.16 and 0.41 ± 0.35, with fat yield 0.06 ± 0.22 and 0.29 ± 0.54, and with fat% 0.03 ± 0.13 and -0.26 ± 0.29. It was concluded that plasma CC was a repeatable and heritable trait, whereas milk CC g-1 fat was lowly inherited; plasma CC was essentially uncorrelated with the standard milk production traits; if bulls were selected for lower plasma CC, there would be reduced CC in both the plasma and milk of their daughters.

Published
2002
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