Fat Content and Composition of Animal Products Proceedings of a Symposium (1976) / Chapter Skim
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Genetics of Fat Content in Animal Products
Genetics of Fat Content in Animal Products
Pages 85-100
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From page 85... ...
The first is to describe the kind and the relative amount of genetic variation available in domestic species that can be used to change the fat content of animal products.
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From page 86... ...
These include genetic defects and undesirable genetic correlations with other traits of economic import. The third is to define breeding programs based on available genetic knowledge-programs that, when implemented, can achieve genetic change in the fat content of animal products.
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From page 87... ...
The study of the response of domestic animal populations to inbreeding and crossbreeding provides the population geneticist with knowledge concerning the relative importance of gene pair effects or of nonadditive genetic variation to the total. The ability to synthesize and deposit fat, from an evolutionary point of view, is of value to the population and the individual by serving as a homeostatic mechanism Werner, 1954)
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From page 88... ...
Current research that most clearly illustrates this point for fat deposition is that from the Meat Animal Research Center, U.S. Department of Agriculture, where many newly introduced breeds of cattle belonging to several biological types are being evaluated for the economical traits of beef production (Agricultural Research Service, 19741.
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From page 89... ...
The increase in the frequency of the Holstein breed in the United States has helped milk production remain relatively constant while the number of dairy cows has decreased. Within breeds, consideration of fat deposition leads to an accumulation of data in most of the domestic species, suggesting that fat differences among animals treated alike are highly heritable.
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From page 90... ...
Heritability estimates are of use in the design of breeding programs, since the heritability of a trait is the criterion of what selection method will make the most rapid genetic change. Since fat deposition is highly heritable, simple selec TABLE 3 Realized Heritability Estimates from Selection Responses Expressed as Deviations from Controls ~ Line Generation Breed of Selection High Fat Low Fat Duroc 0-5 48 73 5-10 29 30 0-10 47 48 Yorkshire 0-4 13 64 4-8 60 46 ~8 38 43 a SOURCE: Hetzer and Harvey (1965)
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From page 91... ...
Such evidence leads to the conclusion that the kind of genetic variation available for making genetic change in fat deposition is additive primarily and can be used in a selection program both among breeds that differ in fat deposition and within breeds. Further, the additive genetic variance in measures of fat deposition among animals treated alike accounts for about 50% of the phenotypic variance.
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From page 92... ...
The general conclusions to be drawn from the research evidence concerning the kind and relative amount of genetic variation available to change the fat content of animal products are as follows: · Fat deposition among animals treated alike is highly heritable. Major breed differences exist in rate of maturity and fat deposition.
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From page 93... ...
Heterosis and inbreeding depression results suggest a moderate amount of nonadditive genetic variance for milk and fat production; however, this has not been exploited economically because of the superiority of one breed for milk production and because of the management system that controls calf production where heterosis could be beneficial. Evidence suggests that a genetic trend of about 1 percent of the mean for milk production exists, indicating that sire selection in conjunction with artificial insemination is effective in increasing production both of fat and of solids-not-fat.
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From page 94... ...
Meat Animal Research Center, demonstrated this. Work on the selection study with swine suggests that there is no clear indication of a consistent decline in reproductive fitness due to selection for backfat thickness (Hetzer and Miller, 19701.
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From page 95... ...
The prospects of selecting for less fat secretion in animal products, produced to nurture the young, appear to be limited. Reduction in fat deposition by breeding could theoretically result in lean meat entirely devoid of fat content; however, before this stage is reached, production limits under current management systems, as well as natural selection, will end selection progress.
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From page 96... ...
Traits in the reproduction class include calf crop percentage and calving difficulty. The production class involves both maternal traits, such as maternal performance and milk production, and market traits, such as average daily gain and feed efficiency.
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From page 97... ...
Selection on this basis can aid in developing a maternal line of cows and in producing a market steer with just enough fat deposition to meet current grading standards and demand top price. The heritability of the production and product traits is high enough that breeding stock herds producing germ plasm for the commercial producer can select for improvement in these two classes of traits and pass this improvement directly to the producer through superior breeding stock.
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From page 98... ...
SUMMARY This chapter described the kind and relative amount of genetic variation available that can be used to change the fat content of animal products,
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From page 99... ...
Large breed differences exist, but small hybrid vigor or inbreeding depression effects suggest primarily additive genetic variance for the ability to deposit fat. The heritability of fat secretion in milk and eggs is moderate to low, with large positive genetic correlations existing among the constituents of the product, suggesting that total amount or percentage can be improved but that the relative amount of the constituents cannot be altered readily.
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From page 100... ...
1973. Selection for high and low fatness in swine: correlated responses of various carcass traits.
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