Effect of feeding level of pregnant dairy heifers sired by one bull on maternal metabolism, placental parameters and birth weight of their female calves.

This study aimed to evaluate the effect of different phases of feed restriction on the metabolism and placental indices of growing heifers inseminated with sexed semen of one bull and on the birth weights of their calves. Red-Holstein heifers were randomly divided into three groups. C-group animals (N=17) daily received recommended energy and crude protein (standard diet). ER-Group animals (N=14) were fed 60% of recommended energy and crude protein for the first two pregnancy months followed by the standard diet. LR-group animals (N=13) were provided with the standard diet throughout the first seven months and with 60% energy and crude protein for the last two months of pregnancy. Blood metabolites and weights of dams were assessed regularly during pregnancy. Placenta weight, area of placentomes and calves' birth weights were examined directly after birth. The physiological levels of blood metabolites varied in C-group animals during the different pregnancy stages. Both restriction periods resulted in reduced weight gain of the dams. ER-group animals showed a marked compensatory growth during mid-pregnancy. Serum glucose, cholesterol and beta-hydroxybutyrate were lower in ER-group animals compared with C-group animals during early restriction. During late restriction, only non-esterified fatty acids increased in LR-group animals. Placental parameter and calves' birth weights did not differ between groups. Results indicate only minor effects of a 40% energy and protein restriction during early or late pregnancy in growing heifers on maternal metabolic and placental indices as well as on foetal development, but further studies might show long-term consequences of offspring.