Breeding objectives for sheep should be customised depending on variation in pasture growth across years

Abstract

Breeding programmes for livestock require economic weights for traits that reflect the most profitable animal in a given production system, which affect the response in each trait after selection. The profitability of sheep production systems is affected by changes in pasture growth as well as grain, meat and wool prices between seasons and across years. Annual pasture growth varies between regions within Australia's Mediterranean climate zone from low growth with long periods of drought to high growth with shorter periods of drought. Therefore, the objective of this study was to assess whether breeding objectives need to be adapted for regions, depending on how reliable the pasture growth is across years. We modelled farms with Merino sheep bred for wool and meat in 10 regions in Western Australia. Across these 10 regions, mean annual pasture growth decreased, and the CV of annual pasture growth increased as pasture growth for regions became less reliable. We calculated economic values for nine traits, optimising management across 11 years, including variation for pasture growth and wool, meat and grain prices between and within years from 2002 to 2012. These economic values were used to calculate responses to selection for each trait for the 10 regions. We identified two potential breeding objectives, one for regions with low or high reliability and the other for regions with medium reliability of pasture growth. Breeding objectives for high or low pasture growth reliability had more emphasis on live weight traits and number of lambs weaned. Breeding objectives for medium reliability of pasture growth had more emphasis on decreasing fibre diameter. Relative economic weights for fleece weight did not change across the regions. Regions with low or high pasture reliability had similar breeding objectives and response to selection, because the relationship between the economic values and CV of pasture growth were not linear for live weight traits and the number of lambs weaned. This non-linearity was caused by differences in distribution of pasture growth between regions, particularly during summer and autumn, when ewes were pregnant, with increases in energy requirements affecting the value of lambs weaned. In addition, increasing live weight increased the intake capacity of sheep, which meant that more poor quality pasture could be consumed during summer and autumn, which had more value in regions with low and high pasture reliability. We concluded that breeding values for sheep production systems should be customised depending on the reliability of pasture growth between years.

Matching breeding goals with farming systems to enhance the sustainability of fish farming

“…Given the climatic conditions, the western and eastern part of the Mediterranean could require a separate breeding program. This is comparable to the conclusion of Rose et al (2015) who demonstrated that sheep breeding programs in Australia should be region specific, depending on 97 pasture growth. For sea bass in Europe, most breeding programs include several traits in the breeding objective Janssen et al, In Press).…”

“…Therefore, it was valuable to decrease FCR whilst increasing TGC, which is easy to achieve when there are negative correlations between the two traits. The differences observed in genetic gain based on different EV have been shown to exist in terrestrial production systems Spelman and Garrick (1997) or Rose et al (2015). As expected, Differences in genetic gain across quota also generated differences in economic gains, suggesting that each quota would need a specific breeding program to maximize economic return for farmers and that using only one breeding goal with one set of EVs for all quotas would not be profitable for all farmers.…”

“…For sea bass in Europe, most breeding programs include several traits in the breeding objective Janssen et al, In Press). Therefore, to confirm the hypothesis that different breeding programs between eastern and western Mediterranean are needed, the economic values of all the traits in the breeding objectives and the correlation between breeding objectives from both regions should be estimated (Rose et al, 2015). When multiple traits are included in a breeding objective the response to selection is the response in the aggregate genotype.…”

“…These values weigh the traits of a breeding goal according to their impacts on farm profit. They are specific to production systems according to the quota applied or the environmental conditions (Rose et al, 2015). When EVs differ from one production system to another, a single breeding program may not be enough to maximize economic response in all production systems (Rose et al, 2015).…”

“…Consequently, genetic gain in each of these quotas is expected to differ if fish were to be produced from a single breeding program. In sheep, Rose et al (2015) found that genetic gain from a single breeding program varied across different climatic regions in Australia, due to differences in relative economic values of traits. They also demonstrated that different breeding goals were needed to maximize economic response in each climatic region.…”