Abstract

Most dairy cows generally have a non-lactating, “dry period” prior to parturition. As the milk production of dairy cows has increased dramatically during the last decades, cows managed conventionally with a 12 to 13 month-calving interval are dried off (DO) while still producing significant quantities of milk. The DO period is probably one of the most physiologically demanding periods for the high-yielding dairy cow, and may negatively affect animal welfare, but few studies have been performed in this area. Therefore, the general aim of the present work was to investigate how different DO procedures and milk yield at DO affect metabolism and udder health of the dairy cow. Furthermore, the effects of different calving intervals and breed were also evaluated. Three studies are included in this thesis. In the first study cows were randomly assigned to two different feeding treatments. One group was fed straw ad libitum, while the other group was fed silage [4 kg dry matter (DM)] daily and straw ad libitum to evaluate metabolic changes and health during DO. In the second study, the effects of daily milk yield at DO, different calving intervals (12 and 15 months) and breed on metabolism and udder health were studied when feeding additional silage at DO. The third study was conducted on over 10 000 lactating cows and the association between daily milk yield prior to DO and veterinary-treated clinical mastitis (VTCM) from DO until early lactation was evaluated. The overall results of this thesis show that extensively restrictive feeding DO protocols may have negative effects on metabolism. The plasma concentration of non-esterified fatty acids (NEFA) was markedly elevated during DO as an effect of restrictive feeding. Furthermore, plasma NEFA was related to the milk yield prior to DO. Feeding straw only during DO affected the rumen environment as shown by increased pH, a reduced concentration of volatile fatty acids, urea, and lower number of protozoa. Restrictive feeding also increased the plasma cortisol, which indicates an elevated metabolic load in this group. In addition, high milk yield at DO increased the risk for VTCM and the number of open teat canals during the dry period. Swedish Holsteins were at higher risk for VTCM from DO until early lactation compared to Swedish Red and White cows. In conclusion, this thesis shows that the common DO procedure to feed straw only may give rise to metabolic disturbances. However, this might be avoided without any apparent negative effects on udder health if a limited amount of silage is added during DO. As high daily milk yields at DO increase the risk for mastitis, alternative ways to reduce the milk yield at DO should be considered.