| The main focus of this research was to determine if prepartum exercise training of dairy cows causes physiological and metabolic changes in physical fitness, acid-base status, and energy metabolism that could facilitate adaptations transition to lactation. After 60 d of exercise training, pregnant and non-pregnant cows that exercised had greater physical fitness than non-exercised cows in that the time to end of treadmill tests were greater, and heart rate and plasma lactate concentrations at given workloads (during treadmill tests) were reduced. The reduction of plasma lactate concentrations (less metabolic acidosis and (or) anaerobic metabolism or increased lactate utilization) at given workloads also influenced the maintenance of blood acid-base status during acute exercise. As indicators of extracellular buffering capacity, the partial pressures of CO2 at given workloads were greater, whereas the concentrations of K+ were reduced for exercised compared with non-exercised cows. However, exercise training treatments did not greatly affect other mineral element concentrations (Cl- and ionized Ca2+), or acid-base status during rest. Related to energy metabolism, prepartum body weight gains at similar dry matter intakes (DMI) were reduced for exercised compared with non-exercised cows, regardless of pregnancy status. Additionally, postpartum DMI during the first 4 wk of lactation was slightly greater for cows exercised prepartum compared with non-exercised cows, whereas milk yields were similar among treatment groups. Furthermore, exercise training also influenced the endocrine control of circulating concentrations of glucose and fatty acids, and the storage of substrates in muscle and liver tissues. During acute exercise tests, plasma lactate, glucose and glucagon concentrations were reduced for exercised cows compared with non-exercised cows. Prepartum liver glycogen concentrations increased, whereas postpartum liver glycogen concentrations were lower for pregnant, exercised cows compared with non-exercised cows. Exercise training increased prepartum plasma concentrations of non-esterified fatty acids (NEFA) and muscle and liver triglycerides, but decreased plasma beta-hydroxy butyrate (BHBA) concentrations. (Abstract shortened by UMI.). |
