Model for fitting longitudinal traits subject to threshold response applied to genetic evaluation for heat tolerance

A semi-parametric non-linear longitudinal hierarchical model is presented. The model assumes that individual variation exists both in the degree of the linear change of performance (slope) beyond a particular threshold of the independent variable scale and in the magnitude of the threshold itself; these individual variations are attributed to genetic and environmental components. During implementation via a Bayesian MCMC approach, threshold levels were sampled using a Metropolis step because their fully conditional posterior distributions do not have a closed form. The model was tested by simulation following designs similar to previous studies on genetics of heat stress. Posterior means of parameters of interest, under all simulation scenarios, were close to their true values with the latter always being included in the uncertain regions, indicating an absence of bias. The proposed models provide flexible tools for studying genotype by environmental interaction as well as for fitting other longitudinal traits subject to abrupt changes in the performance at particular points on the independent variable scale

A Validated Genome Wide Association Study to Breed Cattle Adapted to an Environment Altered by Climate Change

Continued production of food in areas predicted to be most affected by climate change, such as dairy farming regions of Australia, will be a major challenge in coming decades. Along with rising temperatures and water shortages, scarcity of inputs such as high energy feeds is predicted. With the motivation of selecting cattle adapted to these changing environments, we conducted a genome wide association study to detect DNA markers (single nucleotide polymorphisms) associated with the sensitivity of milk production to environmental conditions. To do this we combined historical milk production and weather records with dense marker genotypes on dairy sires with many daughters milking across a wide range of production environments in Australia. Markers associated with sensitivity of milk production to feeding level and sensitivity of milk production to temperature humidity index on chromosome nine and twenty nine respectively were validated in two independent populations, one a different breed of cattle. As the extent of linkage disequilibrium across cattle breeds is limited, the underlying causative mutations have been mapped to a small genomic interval containing two promising candidate genes. The validated marker panels we have reported here will aid selection for high milk production under anticipated climate change scenarios, for example selection of sires whose daughters will be most productive at low levels of feeding

Studies on genetics of heat tolerance in Holsteins.

ABSTRACT.One of the limiting factors in dairy production in hot climates is heat stress (Costa et al., 2002). Under heat, animals produce less and have lower reproduction rates (Kadzere et al., 2002). Management devices that reduce the impact of high temperature and humidity on the animal are available, but they are not fully efficient and not all production systems can afford them. Higher heat tolerance can be achieved by selecting or crossbreeding more heat-tolerant animals. Crossbreds in dairy cattle have been successful under extensive, but not intensive, management because of much lower production levels than purebreds (McDowell et al., 1996). Therefore, the remaining option is to select more heat resistant purebreds, predominantly Holsteins

Índices de selección: economía y genética en perfecta sintonía.

Mediante un trabajo colaborativo, INIA y la Sociedad de Criadores de Hereford han desarrollado dos herramientas para la mejora genética bovina en sistemasganaderos comerciales: el ÍNDICE DE CICLO COMPLETO y el ÍNDICE DE CRÍA. Ambos índices aportan información objetiva al proceso de toma de decisionesdel productor, maximizando el retorno económico de los sistemas ganaderos de nuestro país

Longevity in genetic evaluation of Holstein cows in Uruguay.

ABSTRACT.- The objective of this study was to estimate variance components and to analyze the possibility of carrying out a genetic evaluation of the longevity trait in animals of the Uruguayan dairy production system of the Holstein breed. Longevity was defined as a binary trait with values of 1 and 0 whether or not the cow survived a lactation, respectively

Genetic relationships between faecal worm egg count and production traits in Merino sheep of Uruguay.

The purpose of this study is to estimate the genetic correlation between FEC and the main production traits for the Merino in Uruguay

Development of selection indexes for a beef cattle production system from available EPDs.

ABSTRACT.Due to the complexity of selection in beef cattle where numerous traits are involved, identification of breeding objectives and developing a selection index to improve a global goal is required. A selection index was developed to maximize genetic gain for a beef cattle operation system. Breeding objective includes calving rate, carcass weight, calving ease, feed intake, direct and maternal weaning weight. Indexes were constructed from traits which EPDs are available so it can be implement to make comparisons between animals with different genetic merit. Genetic responses obtained from the use of a propose index were compared with simpler indexes. Selection through the proposed index achieved higher genetic progress in the breeding objective and resulted in an increased economic return to the system. The lack of national genetic parameters for some of the most important traits is a limitation and some implications were discussed