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  • The Effect of Selection on Gene and Genotypic Frequencies

    Selecting animals for breeding is a process by which those deemed ‘best’ are allowed to be parents, and those deemed not, aren’t. The next generation is similarly assessed, and the next, and the next, with the population expected to improve incrementally each time. This gradual improvement over time is due to the frequency of desirable genes increasing in the population and the frequency of undesirable genes decreasing in the population. This results in a group of animals with increased breeding value, as they have a higher concentration of ‘best’ genes more likely to be passed onto the next generation. That next generation, with its higher concentration of ‘best’ genes will perform* at a higher level than earlier generations did. (* ‘Performance’ here is a breeding term that doesn’t necessarily refer to athletic performance such as speed. Rather, it refers to the resulting phenotype, as determined by the genotype. ‘Performance’ could be how fine a sheep’s wool is, for example.) Gene frequencies, breeding values and performance are all intertwined. Increasing breeding values and performance in a population increases the frequencies of desirable genes. Increasing the frequencies of desirable genes increases breeding values and performance. more »
  • Effect of Selection for Wool Growth on Seasonal Patterns of Yield, Fibre Diameter, and Colour in Romney Lines

    Seasonal wool growth and associated wool characteristics were measured in a Romney line selected for high fleece weight and an unselected control line in 1990 and 1991. Both had a significant (P < 0.01) decline in wool growth rate in winter compared with summer. The wool growth rate advantage (P < 0.001) of the selected line over the control averaged 19 and 33% for ewes, and 24 and 36% for hoggets, in summer and winter, respectively. Staple strength, yield, and fibre diameter differences were closely associated with wool growth. Colour analysis showed no difference between lines in either brightness (Y) or yellowness (Y - Z). However, both the Y and Z values were lower in spring and summer, while Y - Z was highest in summer. The results suggest that selection for high fleece weight also improves major wool characteristics and reduces the relative winter wool growth decline in Romneys. more »
  • Selecting Rams - Using Australian Sheep Breeding Values (ASBVs)

    When selecting rams for a commercial enterprise the first step is to set your breeding objective. Spend a few minutes to write down precisely what you are aiming for, including the levels of performance and by when you want to achieve it. Find more information on setting a breeding objective. Because the most effective way to select for a trait or characteristic is to directly measure or assess that characteristic, you should buy rams from a stud that objectively measures or collects scores (using a standardized system) for the traits you wish to improve. For instance, staple strength can be selected with much higher accuracy if the stud directly measures staple strength on its rams, rather than just having the ASBV calculated from related measurements such as fibre diameter coefficient of variation. However, the ram’s own performance is only part of the picture. What you see in the ram isn’t necessarily what you will get in the progeny because much of the ram’s performance is a result of the ‘environment’. Nutritional differences between animals are a key environmental element and not only come from what they eat, but whether they were born or reared as a twin or their mother was a maiden ewe—giving them less nutrition during pregnancy and lactation than for a single lamb and/or from a mature ewe. Also, climate, disease and management differences will affect how they perform. If you know these environmental factors for each individual, and if you have been able to inspect all of the animal’s relatives and see their performance data, you’d be able to predict very accurately, how the progeny will look and perform. However, this is not practical for you to do, so studs that provide you with Australian Sheep Breeding Values (ASBVs) already have this information taken into account. Pedigree information, management groups, data from relatives and relationships to rams used in the stud and elsewhere are all accounted for and very important when calculating Australian Sheep Breeding Values. Importantly, you can accurately compare rams from different studs (whether at opposite sides of the country or having had quite different management) if they both provide ASBVs for the same trait. more »
  • Sources of Variation in Fibre Diameter Attributes of Australian Alpacas and Implications for Fleece Evaluation and Animal Selection

    Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection were investigated using data collected in the years 1994–97, from 6 properties in southern Australia. Data were analysed using REML (multiple regression analysis) to determine the effect on mean fibre diameter (MFD) and coefficient of variation of MFD (CV(FD)) of age, origin (property), sex (entire male, female), breed (Huacaya, Suri), liveweight, fibre colour, individual, and interactions of these effects. The mean (n = 100) age (range) was 4.2 years (0.1–11.9), liveweight 72.0 kg (12.0–134 kg), MFD 29.1 μm (17.7–46.6 μm), CV(FD) 24.33% (15.0–36.7%). A number of variables affected MFD and CV(FD). MFD increased to 7.5 years of age, and correlations between MFD at 1.5 and 2 years of age with the MFD at older ages were much higher than correlations at younger ages. Fibre diameter 'blowout' (increase with age) was positively correlated with the actual MFD at ages 2 years and older. There were important effects of farm, and these effects differed with year and shearing age. Suris were coarser than Huacayas with the effect reducing with increased liveweight; there was no effect of sex. Fleeces of light shade were 1 μm finer than dark fleeces. CV(FD) declined rapidly between birth and 2 years of age, reaching a minimum at about 4 years of age and then increasing; however, CV(FD) measurements on young animals were very poor predictors of CV(FD) at older ages, and the response of CV(FD) to age differed with farm and year. Suris had a higher CV(FD) than Huacayas on most properties, and MFD, liveweight, and sex did not affect CV(FD). Fleeces of dark shade had higher CV(FD) than fleeces of light shade in 2 of the years. It is concluded that there are large opportunities to improve the MFD and CV(FD) of alpaca fibre through selection and breeding. The potential benefit is greatest from reducing the MFD and CV(FD) of fibre from older alpacas, through reducing the between-animal variation in MFD and CV(FD). Sampling alpacas at ages more »
  • Can Selection for Skin Traits Increase the Rate Of Genetic Progress in Merino Breeding Programs?

    There is widespread interest in the use of skin properties for the selection of superior Merino genotypes. This is despite the fact that no selection experiments to date have demonstrated beneficial effects on production traits from selection based solely on skin traits. Two studies have examined whether the inclusion of skin traits in a realistic selection program improves the rate of genetic progress towards a breeding objective emphasising fleece weight and fibre diameter. Both indicated little benefit from including the skin traits. However the impact of the skin traits will depend on their heritabilities and their genetic associations with one another and with the traits in the breeding objective. There is increasing evidence that the genetic parameters differ between the Merino strains so results from one strain cannot be extrapolated to another. In this paper we examine the effects of including classer assessed skin quality and two objectively measured skin characters, skin biopsy weight and follicle density, on the genetic and economic gain made over and above that made using a standard selection index in South Australian Strongwool Merinos. The results indicate that substantial additional genetic gain can be made by including the skin traits. This was particularly true at low micron premiums where addition of all three skin traits increased the economic gain by 25%. The genetic improvement in adult clean fleece weight by including all three skin traits at this premium, was increased from 0.9% per annum to 1.4% per annum with a corresponding slight reduction in the decrease in mean fibre diameter. At higher micron premiums the benefit of including the skin traits was substantially less, again reflecting the tendency for skin trait inclusion to influence fleece weight to a larger extent than fibre diameter. Inclusion of the skin traits had little impact on coefficient of variation of fibre diameter, staple strength and staple length. Our results suggest that consideration of some skin traits may lead to moderate genetic gains and be worthwhile including in breeding programs for Strongwool Merinos, but they do not lend support to notions that consideration of skin traits will produce dramatic increases in fleece weights with concomitant large decreases in fibre diameter. more »
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