Delayed separation I: The effects of transition milk feeding with and without cow-calf contact until 5 days of age on the health and growth of preweaning Holstein and crossbred calves.

Physiological effects of delaying cow-calf separation until a few days after birth are of increasing interest as access to the dam makes the rich profile of immunological, nutritive, and bioactive factors of transition milk (TM) available for postnatal development of the calf. Scientific inquiry into opportunities for cow-calf contact may also inform the current cow-calf contact debate. Our objective was to compare preweaning health and growth of calves with access to TM, with or without extended dam contact. Singleton Holstein and Holstein x Limousin male and female calves (n = 81) and their primiparous and multiparous Holstein dams were enrolled at birth in a randomized block design from d 0 to 5 of life to (1) delayed separation until 5 d with unrestricted suckling of TM (URS, n = 26), (2) immediate separation after birth and offered their dam's TM (n = 27) twice daily (up to 10% BW/feeding), or (3) immediate separation and offered unpasteurized whole milk (WM, n = 28) twice daily (up to 10% BW/feeding). All calves received a single meal of maternal colostrum (8% of BW) within 4 h of calving. All calves were moved to a designated calf area on d 5, while cows remained in the experimental stalls until d 7 after which they returned to the herd. Calves were blood sampled, weighed, and assigned health scores according to a rubric (adapted from the Wisconsin Calf Health Scorer) before each morning feeding. On d 0 and 7, calf height was measured at the withers and hips. Calves that were retained as Holstein replacement heifers (n = 38) were raised according to herd protocols after d 7, and were weighed, withers and hip height measured, and health scores assessed once per week until weaning at d 63. Serum IgG concentrations were quantified by radial immunodiffusion and packed cell volume (PCV) by centrifugation. Data analysis was conducted using mixed effects models, or Pearson's chi-squared test as appropriate. Data are reported as LSM ± SEM. Serum IgG concentrations (g/L) 1 d after colostrum feeding (URS: 42.1 ± 2.0; TM: 44.6 ± 1.9; WM: 41.9 ± 1.9) were not different between groups and declined by a similar percentage from d 1 to 7 (22.7 ± 0.6%), whereas PCV (%) was different between groups (URS: 38.3 ± 1.4; TM: 38.7 ± 1.5; WM: 41.5 ± 1.4). There was no difference between groups in BW, ADG, or withers and hip heights through the first 63 d, but BW interacted with group such that URS calves had greater weight during the suckling phase only. There was no association of treatment with fever or diarrhea events from d 1 to 7, or d 7 to 63. Feeding of TM, with and without cow-calf contact, did not result in meaningful differences in growth or health indicators compared with WM feeding, however, the benefits of TM may not be fully explained by serum IgG concentration and short-term growth indicators.