Genetic analysis of lifetime productivity traits in goats
2021
Abstract. As part of the development of a breeding programme for dairy goats
to support sustainable production in organic farming, the overall aim of the
present study was to identify traits that can be used as selection criteria
for lifetime productivity. The breeding goal is high lifetime productivity
with a good milk composition and a good level of robustness in the animals,
especially within grazing systems. The lifetime productivity traits analysed in this study were the
length of the animal's productive life (LPL), the lifetime efficiency (LEF), and the animal's milk yield efficiency with respect the total number of lactating days (EDM); the average fat and protein content over the animal's lifetime, the
fat-to-protein ratio (FPR), and the urea content (UC) were also included as indirect health traits and
potential indicators of robustness in dairy goats. The traits' influencing
factors, phenotypic and genetic correlations, and heritability were
examined. Furthermore, factors influencing milk yield in the first 120 d of lactation during the animal's first lactation were analysed. The aim of investigating
milk yield during the first lactation was to consider a connection between early
performance recoding in the life of an animal and LPL, LEF, and EDM. In
total, lactation and pedigree data from 9192 dairy goats of the common German Fawn (GF) and German White (GW) dairy
breeds were used. Prerequisites were
that the investigated birth cohorts had to have definitively completed their
lifetime production, and a high proportion of goats had to have completed
extended lactation. The data analysis showed that breed did not
influence milk yield. The age at first kidding, the average number
of kids born during the animal's lifetime, and the lactation length did influence the milk yield.
This applies to the milk yield during the first 120 d of the first
lactation as well as over the lifetime of an animal. Considering the
influencing factors, the results showed that LPL was genetically and
positively correlated with LEF and EDM ( r g = 0.65 ± 0.06 and
0.29±0.07 respectively). The heritability of LPL, LEF, and EDM was
0.22±0.02 , 0.29±0.03 , and 0.44±0.03 respectively.
Regarding the lifetime milk composition, the heritability of protein and fat
content, FPR, and UC was 0.63±0.02 , 0.52±0.02 ,
0.32±0.03 , and 0.47±0.04 respectively. The heritability regarding the milk yield during
the first 120 d of the first lactation was 0.34±0.03 . We found that the milk yield during the first 120 d of the first
lactation showed a genetic correlation with LPL, LEF, and EDM of 0.30±0.08 , 0.82±0.04 , and 0.89±0.03 respectively. In summary,
LPL, LEF, and EDM are suitable traits to indicate lifetime productivity in
dairy goats. An additional indicator for lifetime productivity could be the
milk yield during the first 120 d of the first lactation. Moreover, FPR and UC appear to be promising indicator traits for the health and robustness of dairy
goats. The present study showed the importance of considering extended
lactation in selective breeding programmes as well as the importance of modelling extended lactation in the
breeding value estimation.
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