Growth and metabolism of calves in a dairy cow-calf contact system with gradual weaning and separation.

In dairy cow-calf contact (CCC) systems, cows and calves stay together for a prolonged period, allowing for more suckling and strengthening of the maternal bond compared with the early separation of cow and calf in conventional dairy systems. Extended suckling in CCC systems is related to greater calf growth, although knowledge on consequences of extended suckling for body condition and metabolic and inflammatory variables of calves is limited. This study aimed to evaluate growth, backfat thickness, energy metabolism, and inflammatory status of calves with minimum 12 wk of CCC followed by gradual weaning and separation compared with calves separated from their dam 13.5 h after birth. In 2 experimental batches, treatment group allocation was balanced for cow parity and breed (Swedish Holstein or Swedish Red) and for calf sex and breed (dairy or beef-on-dairy crossbred). Calves were allowed full contact with dams (FC, n = 21) until the start of the 10-d fence-line weaning with gradually reduced suckling opportunities at average 12.5 wk of age. Conventionally reared calves with no contact with dams (NC, n = 22) received 8 L whole milk/d from teat buckets and were first individually housed for 1 wk followed by group housing. The NC calves were gradually weaned over 10 d when 12.2 wk old. In addition, both FC and NC calves had ad libitum access to concentrates and roughage. Preweaning growth was greater in FC than NC calves (1.4 vs. 1.1 ± 0.06 kg/d; LSM ± SEM). During the preweaning period, serum glucose, insulin, IGF-1, and haptoglobin concentration did not differ between treatment groups, but nonesterified fatty acids (NEFA) concentration was greater in FC than NC calves. After weaning, serum glucose, insulin, and NEFA concentration decreased for both FC and NC calves. Serum IGF-1 concentration decreased after weaning for FC calves but not for NC calves. Postweaning, the FC calves retained their BW advantage and higher backfat thickness compared with NC calves despite having lower postweaning growth than NC calves in batch 1 (1.1 ± 0.06 kg/d vs. 1.4 ± 0.06 kg/d) but not in batch 2 (1.1 ± 0.09 kg/d vs. 1.0 ± 0.06 kg/d). In conclusion, prolonged full CCC led to heavier calves with higher preweaning growth and a lower postweaning growth than calves separated from the dam shortly after birth. Consequences of CCC for metabolic and inflammatory variables were limited, except for a greater serum NEFA concentration and a decline in serum IGF-1 concentration from pre- to postweaning for the FC calves.