Mink Dam Weight Changes During the Lactation Period: II. Energy Consumption and Plasma Concentrations of Thyroid Hormones and Insulin
Consumption of metabolizable energy (ME) and plasma concentrations of triiodothyronine (T3) and thyroxine (T4) were studied in lactating scanblack mink in the period from 1991 to 1994. In 1994, the plasma concentrations of insulin were also investigated. The objectives of the study were to describe the daily ME consumption and the plasma concentrations of T3, T4 and insulin during lactation and to evaluate the factors that influence ME consumption, and the concentrations of T3, T4 and insulin. The factors included were dam age, dam body weight, litter size and litter weight. The daily consumption was recorded from 72 dams in 85 lactations. Blood samples were collected at weekly intervals. Dam body weights were recorded before blood sampling and at days 14, 28, and 42 post partum. Kit body weights were recorded at parturition, and at days 14, 28, and 42 post partum. Between the first and the fourth weeks post partum, there was a steady increase in daily ME consumption from 1095 kJ to 1796 kJ. During the fifth week of lactation, the concentrations of T3 and T4 and insulin were low. In adult dams, ME consumption and concentration of T3 were lower than in yearlings. Litter weight had a greater influence on dam ME consumption than the number of kits. The results imply that in the lactation period a heavy demand is put on the mink dam. Despite the increase in ME consumption during lactation, the body weight loss of the dams indicates that they mobilize body reserves, especially in the final part of lactation. During the fourth week of lactation, the dams reach an upper limit for feed consumption. Insufficient feed consumption, and the increased milk production were associated with low concentrations of T3, T4 and insulin.