Change in molasses consumption in Holstein calves as an indicator of HPA axis activation

Clair Sophia Wilcox, Purdue University

Abstract

Phlorizin increases glucose demand by temporarily blocking renal absorption of glucose. The objective of the preliminary study was to determine whether a phlorizin-induced increase in glucose demand would be reflected in exogenous glucose consumption. In a completely randomized block design with two treatment, 3-wk-old male calves (n = 6), maintained on milk replacer at 10% of body wt were allowed free access to molasses during a 7-d adjustment period as well as 24 h after treatment. On d 8, calves designated for treatment received subcutaneously 0.045 mg/kg BW of phlorizin in 3 mL of saline. Mean molasses consumption increased for the 24 h after injection for the phlorizin treated calves compared to the control calves (P = 0.02) and compared to baseline consumption (P = 0.02) established prior to treatment. Total urinary output (P = 0.026) and urinary glucose concentration (P < 0.001) for the 8-h test period also increased in the phlorizin treated calves compared to the control calves. The second study also used 3-wk old male calves. Twenty calves were transported for 3h, randomly sorted into 5 groups of 4 calves each, and fitted with a jugular catheter. Treated calves (n=16) were subjected to 5 cycles of 24 h of isolation followed by regrouping and 48 h in the group pen. The calves were then subjected to an ACTH challenge (0.1 IU/kg body weight) after the 5th cycle. Both group and isolation pens provided visual and physical isolation. Blood samples were collected via a jugular catheter 15 and 0 min prior to the calves being moved either from the isolation to the group pen or from the group to the isolation pen. Fecal samples were collected before and after each move, behavior observations were recorded in the group pens from 0600 h to 1800 h, and molasses consumption was measured. As in the preliminary study, all data were normalized and analyzed using a mixed model procedure and Tukey adjustment in SAS. After d 2, stress treated calves showed a decreased (P = 0.10) area under the curve, as calculated from the cortisol concentration found in the 9 blood samples from each calf on each move. After d 3, peak cortisol concentration of the stress-treated calves decreased (P < 0.001). Fecal shedding of Enterobacteriaceae, particularly Salmonella also decreased with each move. After the first move, 56.25% of treated calves and 50% of control calves changed from negative to positive for shedding. After the third move, 18.75% of treated calves and no control calves changed from negative to positive for shedding of Salmonella. Within the treated group, differences in fecal shedding of Enterobacteriaceae from samples taken before and after moving the calves on d 6 was less than on d 2, d 3 and d 5 (P < 0.05). However, latency to lie after eating increased as the study progressed, requiring more time on d 12 than on d 3, d 5 and d 8 (P < 0.05). Treated calves stood more than control calves in the 4-h afternoon period on d 3, d 4, d 6, and d 14 (P < 0.05) based upon 10-min instantaneous scan sample observations. However, on d 14 (ACTH challenge) control calves stood more (P < 0.05) during the morning observations. On d 6, neutrophil percentages were greater than on d 2, and d 5 ( P < 0.01), and on d 9 neutrophil percentage was less than on d 12 and d 14 (P < 0.05). Molasses consumption was greater for treated calves on d 2, d 8 and d 11 (P < 0.05). This study was designed to investigate whether molasses consumption changed as a result of increased glucose demand and whether this change in consumption is evident under the condition of mild chronic stress. This study implemented repeated intermittent applications of isolation and regrouping, over a period of 14 d to create chronic mild stress in dairy calves. Although it is unclear that this model achieved chronic stress as characterized by adrenal fatigue or hyperplasia, molasses consumption increased in the stress treated calves. This study indicates that change in the consumption of molasses can be used as an indicator of acute stress. (Abstract shortened by UMI.)

Degree

M.S.

Advisors

Schutz, Purdue University.

Subject Area

Animal sciences

COinS