Effects of preweaning milk allowance on long-term metabolism in Holstein heifers.

Suboptimal preweaning nutrition of dairy calves has been causally associated with impaired adult metabolic health and lactation performance. However, the biological mechanisms linking early life nutrient supply and future performance remain insufficiently understood. Thus, the objective of this study was to characterize growth, reproductive performance, glucose metabolism, and the metabolic profile of growing heifers fed a restricted (RES) or an elevated (ELE) milk supply preweaning. Heifer calves (n = 86) born from a single herd of ∼120 dairy cows were blocked in pairs by the dam's parity and birth date. Within block, calves were fed an identical colostrum supply and randomly assigned to a milk replacer (MR) allowance level treatment of either 5.41 Mcal of ME in 8 L of MR/d (ELE) or 2.71 Mcal of ME in 4 L of MR/d (RES). The MR (150 g/L), containing 24% crude protein, 18% crude fat, and 45% lactose, was fed from d 2 after birth until calves were stepped down by 50% at d 49 and fully weaned at d 56. All calves were kept in individual hutches until wk 10 and had ad libitum access to fresh pelleted calf starter, chopped wheat straw, and water. Starting from wk 8, heifers from both treatments were fed and managed in the same way, and preweaning treatments were blind to caretakers. Blood samples for metabolomics analysis were collected at 330 d of age, and an insulin-modified intravenous glucose tolerance test was conducted at 370 ± 12 d of age. Heifers fed the ELE diet exhibited higher average daily gain in the preweaning period, leading to higher body weight at 70 d of age (+ 9 kg). At 330 d of age, growth advantages were no longer significant, and preweaning nutrition had no effect on age at first service, first service conception rates, age at conception, or number of services per conception. The metabolomic serum data sampled at 330 d of age revealed that carnitine, glycerolipid, and purine metabolism were predicted to be significantly affected by preweaning nutrient supply, reflecting long-term metabolic programming. At 370 d of age, during the first 20 min following the glucose infusion, blood insulin levels were greater (10.3 ng/mL vs. 7.7 ng/mL), the area under the curve for insulin tended to be greater, and insulin sensitivity was lower in RES heifers. Increasing the amount of MR fed to calves preweaning had a sustained impact on metabolic processes, but long-term differences could not be detected in growth or reproductive performance, potentially due to the low number of animals.