Delayed separation II: The effects of cow-calf contact for 5 days postpartum on milk production, milk composition, and metabolic and inflammatory indicators of Holstein cows.

Loss of milk yield and alteration of milk components is a primary cow-focused concern for producers when considering cow-calf contact. This is further complicated by the heterogeneity of available studies and lack of evidence-based recommendations. Our objective was to determine whether delaying cow-calf separation and allowing unrestricted suckling by the calf until 5 DIM would result in altered short-term or long-term milk yield and composition, as well as differences in circulating metabolic and inflammatory markers. Primiparous and multiparous Holstein cows (n = 81) and their singleton Holstein and Holstein x Limousin male and female calves were enrolled at birth in a randomized block design from d 1 to 5 of life. Cows were either allowed full contact with suckling by the calf (URS, n = 26) or had calves removed immediately after birth (NS, n = 55). Cows were machine-milked in a custom box stall twice daily. Each stall was configured to either allow full cow-calf contact of a pair, or complete physical and visual separation of the dam and calf. All calves were moved to a designated calf area on d 5, while cows remained in the experimental stalls until their return to the herd on d 7. Calves were temporarily removed during milking procedures in URS. Milk weights were recorded for each milking and AM and PM milk composition determined on d 2, 4, and 6. Concentrations of circulating Ca, BHB, NEFA, glucose, and haptoglobin (Hp) were determined on d 0, 1, 3, 5, 7, and 14. Cows were milked 3 times per day after d 7, and daily milk yield and test day milk protein and fat results recorded until wk 13. Data analysis was conducted using mixed effects models. Data are reported as LSM ± SEM, unless otherwise stated. Milk yield for URS (21.1 ± 1.3 kg/d) was lower than in NS (27.0 ± 1.0 kg/d) during the observation period but was not different from NS by 12 h after separation. Milk yield differences between treatment groups were not observed after separation, and through the first 13 wk of lactation. Milk composition did not differ during the experimental period, or in the first 4 test days (∼120 DIM). Concentrations of plasma Ca (mmol/L) increased from d 1 to 7 in both groups and were marginally higher in NS (2.34 ± 0.02) than in URS (2.27 ± 0.02) over the observation period. Treatment group and day interacted for BHB (mmol/L) concentrations with peak concentrations on d 14 in NS (1.09 [95% CI: 0.94-1.28]) and on d 5 in URS (0.84 [95% CI: 0.68-1.04]). An interaction between treatment and day for Hp was found, with lower concentrations in URS-Primi (LSM [95%CI]: 0.82 mg/mL [0.61-1.11]) than all other groups on d 3 (URS - Multi: 1.03 mg/mL [0.76-1.39]; NS - Primi: 1.08 mg/mL [0.83-1.40]; NS - Multi: 1.19 mg/mL [0.92-1.52]. Delaying cow-calf separation until 5 DIM resulted in a temporary milk yield reduction, and small differences in metabolic and inflammatory markers. Long-term milk yield or composition were not affected.