Epsilon Archive for Student Projects

Abstract

The ability of dairy cows to survive and the economic importance of this have been in-creasing in dairy cattle breeding lately. Increased longevity contribute to an increased pro-portion of cows that produce milk in more productive lactations and reduces the replace-ment costs together with a good health and fertility. Unfortunately it is often argued that longevity has been decreasing due to a strong selection for production traits in dairy cattle.
The aims of this study were to find correlations between different longevity evaluations and between different estimates on longevity and other traits in the Nordic Total Merit (NTM) breeding value. The aim was also to compare different traits for cows of two differ-ent longevity groups.
The data were Predicted Breeding Values (PBV) from Nordic HOL and SR bulls and records from Holstein (HOL) and Swedish Red (SR) cows estimated by the Swedish Dairy Association.
The three Swedish longevity indexes were very highly correlated (>0.89) and the corre-lations between the Swedish official longevity index and the five Nordic Cattle Genetic Evaluation (NAV) longevity indexes varied between 0.73-0.83.
In the sire evaluation part, the traits most negatively correlated with longevity for HOL were dairyness, protein and fat index. In SR, milk, protein, and fat index only had slightly positive correlations with longevity. The traits most strongly positively correlated with longevity for SR were different fertility traits, udder health, leg and hoof treatments and other diseases. These traits also had high positive correlations to longevity for HOL togeth-er with metabolic treatments and different calving and udder traits. Some traits were found to have intermediate optima in the correlation to longevity and the correlations have also been varying during the past 20 years. It was also found that the Swedish official longevity index has been increasing during these 20 years.
In the cow record part all production traits in first lactation were significant positive re-lated to longevity together with udder traits, milking speed and temperament. They should also have posty and parallel legs with a steep foot angle and a fine bone and hock quality. A HOL cow should be shorter, shallower and narrower and have a strong top line, low pins and a coarse dairyness. SR should instead be deeper and more angular. Fertility problems were the most common culling reasons for first lactation cows and udder health traits were the most common culling reason for older cows. Herds decreasing in size had a higher amount of cows that were culled after one lactation than stable or increasing herds. Heifers were also found to live longer in loose housing barns and in organic systems. Heifers born or having their first calf during summer or autumn were more likely to live longer than cows born or having their first calf during winter or spring.