With the increased availability of daily milk yield measurements, data exists for analyses of additional traits that could be related to health and fertility. The objective of this thesis was to determine if day-to-day variation in milk yield is heritable, how it is correlated with daily milk yield (dMY), and how it is correlated with commonly measured production, health, and fertility traits. 789,266 dMY records were retrieved from 5 to 305 days in milk (DIM) for 2,366 lactations among 1,184 Holsteins. dMY was merged with the previous days milk yield (pMY) to derive the absolute value of dMY - pMY (ABS), and relative change in milk yield (REL), which was ABS/pMY. The average REL, ABS and dMY for four lactation segments were calculated and included in a series of single-step genomic evaluations in ASReml. Three-trait models with lactation segments of 5 to 50 DIM, 51 to 100 DIM, and 101 to 200 DIM were fit separately for dMY, ABS, and REL; this was followed by a series of two-trait models of DIM 5 to 200 with one of 5 to 50 DIM, 51 to 100 DIM, or 101 to 200 DIM for dMY, ABS, and REL. Finally, a three-trait model of dMY, ABS, and REL from 5 to 200 DIM was fit. The fixed effects included lactation group (lactations 1, 2, 3), age at calving, and year-season of calving while the random effects included the genomic relationship effect, permanent environment, and residual error. The genomic relationship matrix was generated with PREGSF90 and included 7007 animals of which 516 had 40K SNP genotypes and phenotypic records. Genomic estimated breeding values (gEBV) for dMY, ABS, and REL from 642 cows with genotypes were merged with their official genomic predicted transmitting abilities (gPTA) for several traits from Council on Dairy Cattle Breeding national genetic evaluations. All traits were heritable across all segments with dMY generally having the highest heritability (23% for 5 to 200 DIM) and REL having the lowest (16% for 5 to 200 DIM). Genetic correlations within trait indicated that variable milk yield in early lactation was strongly correlated with variable day-to-day yield for the remainder of lactation. Variation defined as ABS was strongly correlated with both dMY (0.73 from 5 to 200 DIM) and REL (0.62 from 5 to 200 DIM), where dMY and REL were independent (-0.08 from 5 to 200 DIM). Higher gEBV for dMY, ABS, or REL was unfavorably correlated with gPTA for health and fertility traits such as daughter pregnancy rate or somatic cell score. In conclusion, daily milk yield variability was heritable, and REL was more independent of milk yield than ABS. Milk yield variability was also associated with unfavorable health and fertility outcomes. Genome wide association analysis suggests that milk yield variability is largely polygenic but with some influence from major genes.

Fitness and adaptation are fundamental characteristics of plant and animal species, enabling them to survive in their environment and to adapt to the inevitable changes in this environment. This is true for both the genetic resources of natural ecosystems as well as those used in agricultural production. Extensive genetic variation exists between varieties/breeds in a species and amongst individuals within breeds. This variation has developed over very long periods of time. A major ongoing challenge is how to best utilize this variation to meet short-term demands whilst also conserving it for longer-term possible use. Many animal breeding programs have led to increased performance for production traits but this has often been accompanied by reduced fitness. In addition, the global use of genetic resources prompts the question whether introduced genotypes are adapted to local production systems. Understanding the genetic nature of fitness and adaptation will enable us to better manage genetic resources allowing us to make efficient and sustainable decisions for the improvement or breeding of these resources. This book had an ambitious goal in bringing together a sample of the world’s leading scientists in animal breeding and evolutionary genetics to exchange knowledge to advance our understanding of these vital issues.

The past decade has revealed unfavourable trends in e.g. fertility, udder health and locomotion in some major dairy cattle breeds due to a large increase in production and insufficient consideration of functional traits in the breeding goals. Such unfavourable trends in some functional traits increase costs. Additionally, the enlargement of herds leads to less available labour time per individual cow. This asks for cows that are easy to handle. At the same time, society is demanding a higher welfare standard of animals. These contradicting developments have increased the desire for so called more robust animals. Robustness can be defined as 'the ability to maintain homeostasis in commonly accepted and sustainable herds of the near future'; or 'the ability of the cow to function well in the environment she lives in as well as in a wide range of climates and production systems'. This book contains a series of articles (26) dealing with the concept of robustness, including aspects like evolution, genetics, environment, animal health and welfare, and integrity. Besides the major functional traits also the links to energy balance, hot climatic conditions, and the attitude and input of stakeholders towards robustness as part of the breeding program are discussed. This book is the first attempt to summarise the available knowledge concerning this topic in cattle, making this book unique. The contributions are from authors of 16 countries from all over the world. However, the focus is presently on farm animal level, while in future robustness of the whole production system may also require additional attention.

Precision Livestock Farming (PLF) technology is a reality. PLF is a combination of developing animal sensing (sensors) tools and decision-making process at the farm level. It also has the potential to support animal feed suppliers, human-food retailers and other players along the supply chain to make better choices. The current challenge for PLF is the integration of the technology in the majority of the farms and not only to the pioneering farms. This book consist of full-length peer-reviewed papers combined with 'questions and answers' sections. It is the result of a joint session hosted by the European Association of Animal Production and brings together research focusing on real-time interpretation of the combination of sensor development, industry, animal genetics, animal nutrition, and animal health. Unique of this 'cross-disciplinary' approach is that 'animal-focused' scientists, engineers, companies as well as farmers' organizations have interacted and combined their strengths and views. 'Precision Livestock Farming Applications - Making sense of sensors to support farm management' provides an update on the state of the art of PLF in interaction with the other scientific and applicative expertise. It is of interest for researchers, students, professionals, farmers, and livestock industry concerned with livestock production management.