Amaury Apolonio de Oliveira

Genetic factors of sheep affecting gastrointestinal parasite infections in the Distrito Federal, Brazil

Three sheep farms were used in the Distrito Federal, Central Brazil, to study the occurrence of parasites in the feces. A total of 1798 collections were taken over the period of a year. A total of 1205 were taken in Santa Inês breed (SI) in all three farms, 323 in Bergamasca (Berg), 54 in Ile de France, 49 in IlexSI, 103 in Morada Nova (MN) and 64 in TexelxSI, these last five groups being on a single farm. The animals were drenched soon after weaning and feces collected every 3 weeks to calculate fecal egg count (FEC), at least on two occasions on each animal. In some cases, blood was collected to determine packed cell volume (PCV) at fecal collection. Fixed effects included farm, breed/genetic group within farm, animal age (months), birth type (simple, twin) and sex. (Co)variance components were estimated for Santa Inês sheep using restricted maximum likelihood under an animal model. FECs were affected by month and farm showing that climate and management are important sources of variation for the parasites studied. While age and birth type of the lambs did not affect infection level, their genetic group was important, showing that breeding strategies can help control these parasites. Heritabilities for infection level in the sheep varied between 0.09 for Strongyloides and 0.31 for Moniezia expansa. Genetic selection strategies for sheep aimed at reducing these infections should result in more resistant animals.

Parâmetros genéticos de características estimadas da curva de crescimento de ovinos da raça Santa Inês

Este trabalho foi realizado com os objetivos de estudar o ajuste das funcoes de Richards, Brody, Gompertz, Von Bertalanffy e Logistica sobre a curva de crescimento de ovinos Santa Ines e estimar parâmetros geneticos para caracteristicas calculadas a partir da funcao de melhor ajuste. Foram utilizadas apenas informacoes de femeas controladas entre os anos de 1993 e 2004, na Embrapa Tabuleiros Costeiros, e entre 1981 e 2004, na Embrapa Caprinos. Para o ajuste das curvas, as analises foram realizadas separadamente para cada rebanho, utilizando-se o procedimento NLIN do software Statistical Analysis System (SAS), por meio do metodo de GAUSS. Para determinar a funcao que melhor ajustava os dados, foram utilizados os criterios de coeficiente de determinacao (R2), de quadrado medio residual (QMR) e o erro de predicao medio (EM). No rebanho da Embrapa Tabuleiros Costeiros, todas as funcoes subestimaram os pesos, a excecao da curva de Richards. Diferentemente, todas as funcoes superestimaram o peso predito para o rebanho da Embrapa Caprinos. A curva de Richards foi a que promoveu melhor ajuste nos dois rebanhos. Os valores do peso adulto e da taxa de maturacao estimados pela funcao de Richards foram de 54,38 kg e 0,00144/dia, respectivamente, para o rebanho da Embrapa Tabuleiros Costeiros, e 42,74 kg e 0,00260/dia, respectivamente, para o da Embrapa Caprinos. A funcao de Richards foi utilizada para estimar curvas individuais de crescimento dos animais. A partir destas curvas, foram estimadas varias caracteristicas de interesse economico. Os parâmetros geneticos e os componentes de (co) variância para estas caracteristicas foram estimados pelo metodo da Maxima Verossimilhanca Restrita Livre de Derivadas (DFREML), utilizando-se o software MTDFREML. As estimativas de herdabilidades direta e materna variaram, respectivamente, de 0,01 a 0,99 e de 0,00 a 0,13. E possivel alterar o padrao da curva de crescimento destes animais por meio de selecao.

Genetic parameters for faecal egg count, packed-cell volume and body-weight in Santa Inês lambs

Worm infection is one of the main factors responsible for economic losses in sheep breeding in Brazil. Random regression analysis was used to estimate genetic parameters for the factors faecal egg-count (FEC), packed-cell volume (PCV) and body weight (BW) in Santa Inês lambs. Data from 119 female, offspring of nine rams, were collected between December, 2005 and December, 2006, from the experimental flock of Embrapa Tabuleiros Costeiros, the Brazilian Agricultural Research Corporation located in Frei Paulo, SE, Brazil. After weaning, females were drenched until the faecal egg count had dropped to zero. Two natural challenges were undertaken. FEC heritability was extremely variable, this increasing from 0.04 to 0.27 in the first challenge and from 0.01 to 0.52 during the second. PCV heritability peaks were 0.31 and 0.12 in the first and second challenges, respectively. In the second challenge, BW heritability was close to 0.90. The genetic correlations among these traits did not differ from zero. There is the possibility of increasing parasite resistance in Santa Inês by selecting those animals with lower FEC. Selection to increase resistance will not adversely affect lamb-growth, although lambs with a slow growth-rate may be more susceptible to infection.