The objectives of this study were to compare innate immune responses of calves weaned early (EW; n=23; weaned at 23.7 ± 2.3 d of age) with those of conventionally weaned calves (CW; n=22; weaned at 44.7 ± 2.3 d of age). All calves were fed 3.8L of colostrum within 12h of birth and were subsequently fed milk replacer twice daily. The weaning process began by withdrawal of the afternoon milk-replacer feeding. Milk was fully withdrawn, and the calf was considered completely weaned when it consumed 900 g of calf starter as-fed for 2 consecutive days. Blood samples were collected from all calves at 24, 27, 31, 45, 48, 52, and 66 ± 2.3 d of age. Early weaned calves took a variable amount of time to completely wean from milk replacer; therefore, data were also analyzed by comparing calves grouped by latency to completely weaned (fast=1 to 5 d; intermediate=6 to 8 d; slow=15 to 17 d). Slow-EW calves weighed less than either the fast- or intermediate-EW calves before initiating weaning. At 27 d of age, circulating neutrophils were greater among EW calves than CW calves. Moreover, fast-EW calves had lower neutrophil:mononuclear cell ratios at 45 d of age than other EW calves. Slow-EW calves had lower TNF-α concentrations from whole blood stimulated with endotoxin at 27 and 31 d of age compared with fast- and intermediate-EW calves. All EW calves had decreased neutrophil L-selectin at d 27 and increased neutrophil L-selectin at 31 d of age. At 31 d of age, neutrophil β(2)-integrin was the greatest among the fast-EW calves. All EW calves had decreased neutrophil oxidative burst at 27 and 31 d of age. Three days after CW calves were weaned they had higher neutrophils, hematocrit percentages, and circulating cortisol than EW calves. In addition, 3 d after CW calves were weaned they had decreased neutrophil oxidative burst responses to Escherichia coli. Weaning, irrespective of age, suppressed many innate immune responses. In addition, early weaning transiently suppressed L-selectin expression on neutrophils; however, the immunological significance in the context of the resistance to disease is unknown because EW calves likely had greater protection from passively derived immunoglobulins when they were weaned. Finally, calves with lower BW around 24 d of age may not be suitable for early weaning programs as evident in the suppressed secretion of TNF-α from whole blood cultures during the week following the initiation of weaning.

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Two experiments were conducted to determine the influence of plane of nutrition during (1) the pre- and immediate postweaning periods and (2) the grower phase on the performance and leukocyte responses of Holstein calves. In experiment 1, 39 (2 ± 1 d old) colostrum-fed heifer calves were randomly assigned to 2 planes of nutrition, a low (LPN; n = 19) and a high plane of nutrition (HPN; n = 20). Calves in the LPN treatment were offered 418 g/d of dry matter (DM) of a 20% crude protein (CP)/20% fat milk replacer, whereas calves in the HPN treatment were offered 747 and 1,010 g/d of DM of a 28% CP/20% fat milk replacer during wk 1 and wk 2 to 6, respectively. Calves were offered ad libitum access to a calf starter until the end of the study. Peripheral blood samples were collected on d 3, 10, 21, 45, 47, 53, and 91 for many ex vivo leukocyte responses and biochemical analyses. A nutrition × time interaction was present for average daily gain and feed efficiency (feed:gain ratio). A nutrition × time interaction existed for plasma glucose concentration. Neutrophil L-selectin expression was greater in calves fed the LPN than HPN on d 3 and 21. The percentage of neutrophils producing an oxidative burst (OB) when cocultured with Escherichia coli tended to be greater and was greater in calves fed the LPN than HPN on d 10 and 21, respectively. In addition, neutrophils from calves fed the LPN had greater OB intensity throughout the neonatal period (0 to 21 d). However, plasma haptoglobin was not different between the 2 planes of nutrition throughout the study. In experiment 2, 50 heifer calves that were all previously fed a HPN similar to that described for experiment 1 were randomly assigned to 2 planes of nutrition (HPN and LPN) during the grower phase (5 pens/treatment; 5 calves/pen). Calves fed the HPN during the grower phase were fed 4.1 kg of concentrate DM (pellets; 22.4% CP, DM basis) per head per day, whereas calves on the LPN during the grower phase were fed 1.6 kg of DM of the same concentrate per head per day. All calves were fed alfalfa hay (16.2% CP; DM basis) ad libitum. Overall, average daily gain was greater in HPN calves than LPN calves. No differences were noticed for concentrations of plasma urea nitrogen, glucose, neutrophil L-selectin expression, percentage of neutrophils producing OB, and plasma haptoglobin concentration between the 2 planes of nutrition. In summary, intake and performance were improved in calves fed the HPN than calves fed the LPN in both experiments. The neutrophil responses of calves fed an LPN were more active during the preweaning period than calves fed an HPN; however, this response was not observed during the immediate postweaning period or the grower phase.

The objectives of this study were to determine the effects of switching Holstein calves to once-daily feeding during the fourth week of life (24 ± 2.3 d of age; once-fed n=22; twice-fed n=22) on innate immune responses, and to evaluate whether carry-over effects occurred when the calves were weaned during the seventh week of life. Peripheral blood samples were taken immediately before the change in feeding strategy (24 d of age) and at 27, 31, 45, 48, 52, and 66 d of age and were analyzed for circulating cortisol, haptoglobin, total leukocyte counts, neutrophil:mononuclear cells, and hematocrit percentage. Heparinized whole blood was also stimulated with lipopolysaccharide (LPS) for 24h and the concentration of tumor necrosis factor-α (TNF-α) in the supernatant was analyzed. Neutrophil L-selectin and β(2)-integrin expression were analyzed by flow cytometry. Simultaneous neutrophil phagocytic and oxidative burst responses to a heat-killed Escherichia coli were quantified by dual-color flow-cytometry. Treatment (once-daily or twice daily feeding) had no effect on pre- or postweaning performance. Once-fed calves tended to have more circulating neutrophils at 27 d of age, greater expression of L-selectin on neutrophils at 31 and 45 d of age, and greater intensity of phagocytosis at 45 d of age. Once-fed calves secreted less TNF-α in LPS-stimulated whole blood cultures at 45 d of age compared with twice-fed calves and this tended to persist through the immediate postweaning period. None of the other immune parameters differed after weaning between the preweaning feeding strategies. Consolidating calf milk replacer into one feeding during the fourth week of life was likely a mild and acute stressor, as evidenced by transient neutrophilia in the absence of suppressed functional capacities of neutrophils. Future research should address the mechanism and immunological significance of the persistent decreased TNF-α response in once-fed calves.

The objective was to determine if outdoor group housing of Holstein calves influences metabolic status, leukocyte responses, and behavior compared with individually housed calves. Forty-nine Holstein heifer calves (2 ± 1 d of age) were randomly assigned to 1 of 2 treatments: individually housed (G1; n = 22) or group housed [3 calves per pen (G3); n = 27]. The space allowances per calf were 4.8 and 7.0m(2) for G1 and G3, respectively. All calves were offered an identical plane of milk replacer nutrition (747 and 1,010 g of DM/d of a 28% CP:20% fat milk replacer from wk 1 to 2 and wk 3 to 6, respectively). Weaning was initiated during wk 7 by removing the p.m. feeding and calves were completely weaned when they consumed 900 g of calf starter/d (as fed) for 2 consecutive days after d 54. At d 90, calves were commingled into random outdoor groups of 5 calves per pen. Peripheral blood was collected during the neonatal (d 3, 10, and 21), weaning (d 46, 48, and 54), and commingling periods (d 90, 93, and 98) and was analyzed for neutrophil oxidative burst (OB) capacity when cocultured with Escherichia coli, neutrophil surface L-selectin protein expression, and whole-blood secretion of tumor necrosis factor-α when cocultured with lipopolysaccharide. Starter intake was greater for G3 during the postweaning period (wk 8 to 12). Average daily gain was greater for G3 than G1 from d 54 to 68 and tended to be greater after commingling from d 113 to 133. During the neonatal period, G3 calves had more activated neutrophils, as evidenced by increased neutrophil L-selectin protein expression and a tendency for increased percentage of neutrophils producing an OB than G1 calves. During weaning, G3 calves continued to have more activated neutrophils with increased L-selectin expression on d 46 and 48 and a greater OB intensity throughout the period. No differences were observed among leukocyte responses between treatments at d 93 and 98. Outdoor group-housed Holstein calves had improved performance and heightened neutrophil responses compared with individually housed calves.