Blood enzymatic activity in Saanen goats during different periods of the reproductive cycle and their association with the completion of pregnancy

Metabolic processes in milk-producing cows are substantially modified that is the main reason of different abnormalities in the reproductive function. At the same time the pattern of metabolic changes and its influence on the reproductive capacity in high-producing dairy goats ( Capra hircus ) are yet unknown. The aim of the present work was to study the activity of metabolic enzymes in the blood of Saanen goats depending on the period of the reproductive cycle and the competence for pregnancy maintenance. We analyzed for the first time alterations in the serum activity of enzymes, regulating the intensity of protein-carbohydrate and energy metabolism including integration of metabolic processes, at different stages of goat gestation as well as prior to the mating period in animals with the negative outcome of the subsequent pregnancy. The enzyme status of animals was assessed during the pre-mating period, the first half of pregnancy (1.5-2.5 months), and the second half of pregnancy (3.5-4.0 months). Goats were divided into two groups - with the completed reproductive cycle (the birth of viable offspring, n = 15) and with the interrupted reproductive cycle (abortions in the second half of pregnancy, n = 6). Samples of blood serum were tested to determine concentrations of total protein and activities of several enzymes: aspartate aminotransferase (AST, EC 2.6.1.1), alanine aminotransferase (ALT, EC 2.6.1.2 ), gamma glutamyltransferase (GGT, EC 2.3.2.2), creatine phosphokinase (CPK, EC 2.7.3.2), alkaline phosphatase (ALP, EC 3.1.3.1), lactate dehydrogenase (LDH, EC 1.1.1.27), and alpha hydroxybutyrate dehydrogenase (isoenzymes of LDH: LDH-1 and LDH-2). In goats with the completed reproductive cycle, the blood activity of AST in the second half of pregnancy was found to be 1.2 times lower (p < 0.05) than during the pre-mating period or the first half of pregnancy. The activity of ALT in the blood serum of the animals increased 1.3 times (p < 0.01) by 1.5-2.5 months of pregnancy as compared with the pre-mating period and then decreased 1.9 times (p < 0.001) by 3.5-4.0 months of pregnancy. Furthermore, there was a decline in the blood activities of GGT (1.3 times, p < 0.05), CPK (1.9 times, p < 0.01), and isoenzymes LDH-1 and LDH-2 (1.3 times, p < 0.05) and a rise in the activity of ALP (1.4 times, p < 0.05) between the first and the second half of pregnancy. During the pre-mating period, a lower activity of ALT and GGT was revealed in goats with the interrupted reproductive cycle as compared with animals retained pregnancy (14.4±2.9 vs. 20.1±0.7 U/l, p < 0.05 and 43.8±2.4 vs. 54.7±4.2 U/l, p < 0.05, respectively). The results of this research suggest a reduction in the intensity of some metabolic processes in the goats by the fourth month of pregnancy to maintain increased fetus demands. Analysis of the findings also indicates that the activity of enzymes, regulating the coupling of protein and carbohydrate metabolism, in the blood of goats during the pre-mating period may be related to their subsequent capacity for fetus bearing