RESUMEN
The objective was to assess the effect of sire breed on birth weight, average daily gain from birth to weaning, and actual weaning weight of calves. The calves were produced by AI using semen of five Akaushi (Wagyu), six Angus, and six Brahman bulls. Dams of calves were Beefmaster (n = 60) and Brown Swiss x Zebu (n = 21). The three sire breeds were used on both dam genetic types to produce the calves (45 males and 36 females). Each dam genetic type was raised in two ranches; therefore, all calves were born in four ranches, in the same calendar year. Average age at weaning weight m easurement was 186 days. The traits were analyzed with the MIXED procedure of SAS. The statistical model included the fixed effects of sire breed, dam genetic type, calf sex, ranch, and birth season within sire breed-ranch; sire within breed of sire was included as a random effect (except for weaning weight; P > 0.05). In addition, the model for weaning weight included calf age at weaning as a covariate. Birth weights and average daily gains of Akaushi-, Angus- and Brahman-sired calves were similar (P > 0.05). In contrast, Angus-sired calves were heavier (P < 0.05) at weaning than Akaushi- and Brahman-sired calves. Calves out of Brown Swiss x Zebu dams had higher (P < 0.05) pre-weaning average daily gains than calves out of Beefmaster dams. Angus-sired calves performed better at weaning.
Asunto(s)
Parto , Clima Tropical , Embarazo , Femenino , Animales , Bovinos/genética , Masculino , Destete , Fenotipo , Peso al Nacer , Cruzamientos GenéticosRESUMEN
Pedigree and reproductive records of 151 Brown Swiss cows were analyzed with the objective of estimating the heritability (h²) and the repeatability (r) for different measures of fertility. Cows were daughters of 49 sires and 102 dams. The study was carried out at Las Margaritas research station located in Puebla, Mexico. The pedigree was the same for all traits; it consisted of 287 individuals, and included dams without records and sires. Genetic parameters were estimated for conception rate at first service (CR), days to first registered heat after calving (DH), days to first registered service after calving (DS), days open (DO), and calving interval (CI). Estimations were made independently for each trait with a repeatability animal model, which included the direct additive genetic effect, as well as the permanent environmental effect of the cow. Genetic parameters were estimated with restricted maximum likelihood. In general, estimates of permanent environmental variance were greater than estimates of additive genetic variance, so that r was mainly determined by permanent environmental effects. Estimates of h² and r were: 0.02 ± 0.06 and 0.16, 0.00 ± 0.05 and 0.15, 0.03 ± 0.03 and 0.03, 0.00 ± 0.03 and 0.14, and 0.03 ± 0.07 and 0.12 for DH, DS, CR, DO and CI. Artificial selection as a tool to induce genetic change in measures of fertility studied would be slightly effective because additive genetic variance is scarce.
Se analizaron los registros genealógicos y reproductivos de 151 vacas de la raza Suizo Pardo para estimar la heredabilidad (h²) y el índice de constancia (r) de diferentes indicadores de fertilidad. Las vacas fueron hijas de 49 sementales y 102 madres. El estudio se realizó en el sitio experimental Las Margaritas, en Puebla, México. El pedigrí fue el mismo para todas las características, consistió de 287 animales e incluyó madres sin registros y padres. Los parámetros genéticos fueron estimados para tasa de gestación a primer servicio (TG), días al primer calor registrado después del parto (DC), días al primer servicio registrado después del parto (DS), días abiertos (DA) e intervalo entre partos (IEP). Las estimaciones se hicieron en forma independiente para cada característica, con un modelo de repetibilidad que incluyó el efecto genético aditivo individual, así como el efecto ambiental permanente de la vaca. Los parámetros genéticos fueron estimados por medio de máxima verosimilitud restringida. Los estimadores de la varianza del ambiente permanente, en general, fueron mayores que los de la varianza genética aditiva, por lo que r estuvo determinado principalmente por el ambiente permanente. Los estimadores de h² y r fueron: 0.02 ± 0.06 y 0.16, 0.00 ± 0.05 y 0.15, 0.03 ± 0.03 y 0.03, 0.00 ± 0.03 y 0.14, y 0.03 ± 0.07 y 0.12 para DC, DS, TG, DA e IEP, respectivamente. La selección artificial como una herramienta para inducir cambio genético en las diferentes mediciones de fertilidad sería poco efectiva, ya que la variación genética es escasa.
