De La Cruz Colin, Lino

Swan, Andrew

Walkom, Samuel

2023-06-09

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<p>The success to implement and conduct a breeding program necessarily requires a good design and a definition of a breeding objective. In addition, accurate pedigree, data quality and performance recording are essential to strengthen the accuracy of the estimated breeding values to establish an effective selection program. The overall objective of this dissertation was to develop strategies to design a breeding program to improve productivity and profitability in the Mexican sheep industry. Data sets from Hampshire, Katahdin and Pelibuey sheep breeds were used. Genetic parameters for early growth traits were estimated from a standard animal model, applying twelve statistical models (base models and sire by flock interaction) using Restricted Maximum Likelihood. The heritability for growth traits was higher in the base models than with sire by flock but reasonably consistent with estimates presented in a range of previous studies. Both direct genetic and phenotypic correlations for base models and sire by flock were positive and moderate to very high. The validation study showed reasonable predictability of sire EBVs, where it is better to fit sire by flock. Validation analyses showed that when using models accounting for sire by flock interaction, sire EBVs predicted progeny performance in line with expectation. Estimated genetic trends showed Mexican sheep breeders have made genetic progress even without a formal evaluation system. The impact of genotype by environment interaction (G by E) on breeding values across the diverse Mexican regions for the Katahdin sheep resulted in an average genetic correlation across regions and traits of 0.55, which could also be managed in a genetic evaluation model by fitting sire by flock interactions. In reproduction analyses for Katahdin sheep, litter size was shown to be heritable (0.05), with small to moderate correlations with body weight traits (0.15 – 0.33). An economic model to derive breeding objectives was developed and applied in selection indexes combining growth, reproduction and carcass traits to predict genetic responses in 10 years relevant to the commercial production system in the Hampshire and Katahdin breeds. The highest influence among the traits included in the selection index was for litter size, followed by growth traits, carcass and adult weight (which had a negative economic value due to the importance of feed costs in the breeding ewe flock). In conclusion, the Mexican sheep industry has the potential and the basic structure to implement these results to increase productivity and profitability. The industry could move in a favourable direction by implementing the results of this study in a modern genetic evaluation system.</p>

https://hdl.handle.net/1959.11/55613

en

University of New England

A genetic improvement program for the Mexican sheep industry

Thesis Doctoral

Publication