Consequences of dry period length and dietary energy source on physiological health variables in dairy cows and calves

Abstract

During the transition period, dairy cows experience a negative energy balance (NEB) caused by the high energy requirement for milk yield, while feed intake is limited. Severity of the NEB has been associated with an increased incidence of metabolic disorders and infectious diseases, inflammation, immunosuppression and oxidative stress. It is known that shortening or omitting the dry period or feeding a glucogenic ration improves the energy balance (EB) in dairy cows in early lactation. It can be expected that an improvement of the EB due to shortening or omitting the dry period results in reduced inflammation, immunosuppression and less oxidative stress in dairy cows in early lactation. The first objective of this thesis was to study the effects of dry period length and dietary energy source on immune competence, inflammatory biomarkers and oxidative stress in dairy cows over 2 subsequent lactations. The second objective was to study the consequences of maternal dry period length on colostrum immunoglobulin content and immune competence of calves in the first 12 weeks of life. In the current study, 167 cows were assigned to 3 dry period lengths (0, 30, or 60 d) and 2 early lactation rations (glucogenic or lipogenic). Cows were planned to have the same dry period length and ration over 2 subsequent lactations. Omitting the dry period reduced plasma bilirubin levels compared with a conventional dry period, which is line with the better EB in cows with a 0-d dry period. Effects of dry period length on inflammatory biomarkers, oxidative stress variables and natural antibodies (NAb) titers were, however, less consistent. Omitting the dry period increased not only negative acute phase proteins (APP) in plasma, but also positive APP, oxidative stress variables in plasma, and NAb in milk. Shortening the dry period to 30-d did not influence inflammatory biomarkers and oxidative stress compared with a conventional dry period of 60-d. Occurrence of clinical health problems did not differ between cows with different dry period lengths. In the current study, changes in positive APP and oxidative stress variables in plasma and NAb in milk could be explained by the occurrence of clinical health problems related to inflammation (clinical mastitis, fever, metritis and retained placenta), rather than a better EB due to a shorter or no dry period. Moreover, a higher titer of IgG binding lipopolysaccharide in plasma was associated with decreased odds of high somatic cell count and occurrence of clinical mastitis. In the first lactation after implementation of dry period length and dietary treatments, feeding a glucogenic ration in early lactation increased NAb titers in milk compared with a lipogenic ration, which could be explained partly by a better EB. In the second lactation after implementation of dry period length and dietary treatments, feeding a lipogenic ration in early lactation increased cholesterol levels in plasma compared with a glucogenic ration, which could be related to the high fat content in this ration. Cows with...