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Registro Completo |
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Biblioteca(s): |
Embrapa Meio-Norte. |
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Data corrente: |
17/10/1997 |
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Data da última atualização: |
17/10/1997 |
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Autoria: |
YOUNG, G. B. |
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Título: |
Population dynamics of the dexter breed of cattle. |
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Ano de publicação: |
1953 |
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Fonte/Imprenta: |
Journal of Agricultural Science, v. 43, p. 369-374, 1953. |
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Idioma: |
Inglês |
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Conteúdo: |
It is possiple for a breed of cattle to persist and to expand slowly, despite the existence of a genetic defect which prevents 50% of the calves born being used for breeding. Moreover, it is possible to exert a certain amount of selection in such a breed. The Dexter breed provides an example. Before 1924, about 64% of entrants to the breed were from inspected animaals. Between 1924 and 1939 the breed contracted. From 1940 to 1947 the breed expanded. During the period of decline almost every Dexter-type female born was registered and raised. The wastage rate and age distribution of the cows are similar in Dexters to those of other breeds. There would appear to have been comparatively little breeding from Kerry types. The average registered reproductive rate of Dexter-type females was about 0.8. While it was not possible to examine the breed structure in the period of expansion, this was probably accomplished by lengthening the average productive life of the female, and possibly also by breeding from Kerry types. The possibility of exercising selection in Dexters is shown to exist. Only about 13% of the females registered are used for producing registered bulls. Of the total bull crop, only about 7% are used to produce registered females, but the bulls selected have different numbers of offspring. The use of bulls selected after progeny testing is hardly feasible in Dexters. The increased numbers of females necessary in order to produce an adequate number of heifers, renders this technique almost impossible. There has been little inbreeding in Dexters. This is possibly due to deliberate policy, as some of the breeders associate inbreeding with the production of monstrous calves. It would, therefore, appear that the damaging effect of a lethal in a breed could be overemphasized. MenosIt is possiple for a breed of cattle to persist and to expand slowly, despite the existence of a genetic defect which prevents 50% of the calves born being used for breeding. Moreover, it is possible to exert a certain amount of selection in such a breed. The Dexter breed provides an example. Before 1924, about 64% of entrants to the breed were from inspected animaals. Between 1924 and 1939 the breed contracted. From 1940 to 1947 the breed expanded. During the period of decline almost every Dexter-type female born was registered and raised. The wastage rate and age distribution of the cows are similar in Dexters to those of other breeds. There would appear to have been comparatively little breeding from Kerry types. The average registered reproductive rate of Dexter-type females was about 0.8. While it was not possible to examine the breed structure in the period of expansion, this was probably accomplished by lengthening the average productive life of the female, and possibly also by breeding from Kerry types. The possibility of exercising selection in Dexters is shown to exist. Only about 13% of the females registered are used for producing registered bulls. Of the total bull crop, only about 7% are used to produce registered females, but the bulls selected have different numbers of offspring. The use of bulls selected after progeny testing is hardly feasible in Dexters. The increased numbers of females necessary in order to produce an adequate number of heifers, renders ... Mostrar Tudo |
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Palavras-Chave: |
Breed. |
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Thesagro: |
Bovino. |
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Thesaurus Nal: |
cattle; Dexter. |
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Categoria do assunto: |
-- |
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Marc: |
LEADER 02228naa a2200169 a 4500
001 1054875
005 1997-10-17
008 1953 bl --- 0-- u #d
100 1 $aYOUNG, G. B.
245 $aPopulation dynamics of the dexter breed of cattle.
260 $c1953
520 $aIt is possiple for a breed of cattle to persist and to expand slowly, despite the existence of a genetic defect which prevents 50% of the calves born being used for breeding. Moreover, it is possible to exert a certain amount of selection in such a breed. The Dexter breed provides an example. Before 1924, about 64% of entrants to the breed were from inspected animaals. Between 1924 and 1939 the breed contracted. From 1940 to 1947 the breed expanded. During the period of decline almost every Dexter-type female born was registered and raised. The wastage rate and age distribution of the cows are similar in Dexters to those of other breeds. There would appear to have been comparatively little breeding from Kerry types. The average registered reproductive rate of Dexter-type females was about 0.8. While it was not possible to examine the breed structure in the period of expansion, this was probably accomplished by lengthening the average productive life of the female, and possibly also by breeding from Kerry types. The possibility of exercising selection in Dexters is shown to exist. Only about 13% of the females registered are used for producing registered bulls. Of the total bull crop, only about 7% are used to produce registered females, but the bulls selected have different numbers of offspring. The use of bulls selected after progeny testing is hardly feasible in Dexters. The increased numbers of females necessary in order to produce an adequate number of heifers, renders this technique almost impossible. There has been little inbreeding in Dexters. This is possibly due to deliberate policy, as some of the breeders associate inbreeding with the production of monstrous calves. It would, therefore, appear that the damaging effect of a lethal in a breed could be overemphasized.
650 $acattle
650 $aDexter
650 $aBovino
653 $aBreed
773 $tJournal of Agricultural Science$gv. 43, p. 369-374, 1953.
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Embrapa Meio-Norte (CPAMN) |
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