The influence of milk replacer plane of nutrition on the performance, innate immune responses and pathophysiological response to a sub-clinical Salmonella typhimurium
The objectives were to determine the influence of plane of nutrition during the pre- and post-weaning periods on performance and innate immune activity of Jersey calves. Forty-six (3 ± 1 d of age) calves were randomly assigned to 2 treatments. Treatments were a low (LP; n=23) and high Plane of nutrition (HP; n=23). Calves in LP treatment were fed 409 g/d DM of a 20% protein and 20% fat milk replacer; whereas calves in HP treatment were fed 610 and 735 g/d DM of a 28% protein and 25% fat milk replacer during the 1st wk and wk 2-6, respectively. Weaning was initiated on d 42 by removing the PM feeding and calves were completely weaned when they were consuming 600 g of a calf starter ration after d 49. Calves on the HP on nutrition were fed a calf starter with 20% CP and 18% ADF while the LP nutrition calves were fed a calf starter with 18% CP and 14.5% ADF. Calves were fed their respective calf starter diets through the entire study. Peripheral blood samples were collected on d 0, 7, 21, 28, 42 and 77 for biochemical analyses. Blood samples collected on d 7, 21, 42, and 77 were also analyzed for ex vivo innate immune responses. Twenty bull calves (HP n=9 and LP n=11) on d 77 were orally challenged with 1.5 x 107 colony forming units of Salmonella typhimurium (ATCC14028). Indwelling rectal thermometers collected a measurement every 5 min. and peripheral blood samples were collected daily at 0800 throughout the study and . plasma analytes and innate immune responses were determined. As expected, metabolizable energy intake, crude protein intake, and average daily gain were greater (P<0.001) for HP calves when compared to LP calves. There were treatment x time interactions (P<0.001) for plasma concentrations of glucose and urea nitrogen. Glucose concentrations were greater (P<0.01) on d 21, 28, 42 and tended to be greater (P<0.10) on d 77 among HP calves, when compared to LP calves. Urea nitrogen concentrations tended to be greater (P<0.10) on d 7 among HP calves, when compared to LP calves, but were less (P<0.01) than LP calves on d 42 and 77. Secretion of TNF-α from diluted whole blood when co-cultured with lipopolysaccharide was higher (P<0.05) among HP calves on d 7, when compared to LP calves. In contrast, neutrophil expression of L-selectin was greater (P<0.05) among LP calves on d 7, 21, and 42, when compared to HP calves. No treatment or treatment x time differences (P=0.798) were observed for neutrophil oxidative burst capacities during the study. Following the Salmonella typhi. challenge, the percentage of neutrophils producing an oxidative burst was greater (P<0.05) among HP calves from d 1 – 5 after the challenge. Similarly, the intensity of the oxidative burst tended to be greater (P<0.10) among HP calves on d 2 and 3 after the challenge. In addition, the secretion of tumor necrosis factor-α tended (P<0.10) to be greater on d 1 and was greater (P<0.05) on d 5 and 6 after the challenge among HP calves. Median ranks of haptoglobin concentrations were lower (P<0.05) among HP calves throughout the challenge; however, there was no difference (P=0.99) between LP and HP calves on rectal temperatures. These data indicate that LP calves have activated innate immune responses during the pre-weaning period, but HP calves have a more aggressive innate immune response to an oral Salmonella typhimurium challenge, which may improve resistance to disease.