|Carroll, Jeffery - Jeff Carroll|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2011
Publication Date: 4/29/2011
Citation: Hulbert, L.E., Cobb, C., Carroll, J.A., Ballou, M. 2011. The effects of early weaning on innate immune responses of Holstein calves. Journal of Dairy Science. 94:2545-2556. Interpretive Summary: Pre-weaning growth is the most expensive growth that animal will undergo during its life. It is common practice within the dairy cattle industry to restrict the consumption of milk or milk replacer in order to stimulate an earlier consumption of calf starter, which accelerates rumen development and decreases the age at which calves can be completely weaned from milk. It is not known, however, whether age at weaning influences the innate immunological responses to weaning in dairy calves. It is conceivable that if weaning dairy calves does decrease innate immune defenses regardless of age, then weaning at an earlier age may provide better immunity to disease because passively derived humoral immunity will be greater. Therefore, a collaborative study among scientists from ARS' Livestock Issues Research Unit and Texas Tech University was conducted to determine the influence of weaning during either the 4th or 7th week of age on innate immune responses of Holstein calves. The results from this study demonstrated that weaning Holstein calves caused transient neutrophilia and suppressed neutrophil phagocytic and oxidative burst responses in all calves independent of age at weaning, but only early weaned calves had transiently decreased expression of L-selectin on neutrophils. The immunological significance of the additional suppression of L-selectin in early weaned calves in the context of the resistance to disease is not known because early weaned calves likely had greater protection from passively derived immunoglobulins when they were weaned. This information will be of interest to dairy producers and dairy cattle nutritionists who are seeking alternative weaning strategies for young dairy calves.
Technical Abstract: 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) to conventionally-weaned calves (CW; n = 22; weaned at 44.7 ± 2.3 d of age). All calves were fed 3.8 L of colostrum within 12 h 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 a calf consumed 900 g of calf starter as-fed for two consecutive d. 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 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 the either the Fast- or Intermediate-EW calves before initiating weaning. At 27 d of age, circulating neutrophils were greater among EW than CW calves. Moreover, Fast-EW calves had less neutrophils:mononuclear cell ratios at 45 d of age than other EW calves (P < 0.01). Slow-EW calves had lower TNF-alpha concentrations from whole blood stimulated with endotoxin at 27 and 31 d of age compared with Fast- and Intermediate-EW calves (P < 0.05). All EW calves had decreased neutrophil L-selectin at d 27 and increase neutrophil L-selectin at 31 d of age (P < 0.01). At 31 d of age, neutrophil Beta-integrin was the greatest among the Fast-EW calves (P < 0.05). All EW calves had decreased neutrophil oxidative burst 27 and 31 d of age (P < 0.01). Three days after CW calves were weaned they had higher neutrophils, hematocrit percentages and circulating cortisol than EW calves (P < 0.05). In addition, 3 d after CW calves were weaned they had decreased neutrophil and oxidative burst responses to E. coli (P < 0.05). Weaning, irrespective of age, suppresses 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 early weaned calves likely had greater protection from passively derived immunoglobulins when they were weaned. Finally, calves that are lighter in BW around 24 d of age may not be suitable early weaning programs as evident in the suppressed secretion of TNF-alpha from whole blood cultures during the week following the initiation of weaning.