Determination of metabolic alterations, inflammatory response and oxidative stress status in dairy cows and their calves exposed to heat stress in the dry period

This doctoral thesis investigated oxidative stress, alterations in metabolic and inflammatory parameters, health status, and milk yield in dairy cows, which were exposed to heat stress during the dry period, and their newborn calves. The study material comprised 53 healthy Holstein cows, including animals that were exposed to heat stress during the dry period (summer; n=25) and animals housed under normal climate conditions (winter; n=28), all of which had a lactation number of 2-5 and a body condition score of 3.0-3.5. Blood samples were collected into sterile dry vacutainers from cows 21 days before the expected date of parturition and at the time of parturition, and from their newborn calves immediately after birth (before colostrum intake) and at 24 h after birth. All cows were sampled for the colostrum from the first milking after calving. Sera were extracted by the centrifugation of the blood samples at 3500 rpm. The serum samples of the cows and calves were tested for inflammatory parameters (interleukin (IL)-17A, IL-10, IL-6, IL-1β, tumor necrosis factor-alpha (TNF-α), interferon gamma (IFN-γ), haptoglobin), oxidative stress indicators (nitric oxide (NO), paraoxanase (PON), total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), glutathione peroxidase (GSH-Px), catalase, superoxide dismutase (SOD), malondialdehyde (MDA)), and metabolic parameters (total protein (TP), albumin, creatinine, cholesterol, bilirubin, alkaline phosphatase (ALP)). The colostrum samples were tested for both lactoferrin and immunoglobulin G (IgG) concentrations, whilst blood samples taken from the calves at 24 h after birth were tested for IgG concentration. The respiratory rate, rectal temperature, gestation period, calf birth weight, colostrum quantity and quality (Brix percentage), postpartum health problems, and milk yield were recorded for each dairy cow. Statistical differences in the investigated parameters were assessed with two-way analysis of variance. The comparison of the cows, which were exposed to heat stress and housed under normal climate conditions, for respiratory rate (70.8+13.3 and 42.4+6.8, respectively) and rectal temperature (39.6+0.4 °C and 39.0+0.3 °C, respectively) demonstrated that both parameters had significantly increased with exposure to heat stress. Furthermore, the comparison of the study groups for gestation period (270.21±6.69 days and 277.44±4.26 days, respectively) and colostral IgG concentration (154.17±56.96 mg/dl and 224.51±91.10 mg/dl, respectively) demonstrated that exposure to heat stress had led to an average 7-day shortening of the gestation period and a decrease in colostral IgG content. Moreover, the prevalence of metritis/clinic endometritis was observed to be higher in the cows that were exposed to heat stress. The cows, which were exposed to heat stress, displayed significantly decreased serum ALP, cholesterol, IL-10, TNF-α, OSI and catalase levels, and significantly increased serum TP, MDA, NO, SOD and GSH-Px levels. The calves born to the cows that were exposed to heat stress presented with significantly decreased serum ALP activity and significantly increased serum NO, MDA, catalase, IL-6, IL-17A, IL-1β, IL-10, and haptoglobin levels. In conclusion, it was determined that exposure to heat stress during the dry period: 1) induced oxidative stress and disrupted metabolic processes in dairy cows; 2) induced oxidative stress and inflammatory reactions in calves exposed to heat stress during intrauterine life; 3) increased the incidence of postpartum health problems and yield losses in cows.