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An investigation of Dairy Cow Response to Stimulation by a cattle immobilizer

The Company Farmfreund

Objective


To examine plasma cortisol levels in response to stimulation of dairy cows with an cattle immobilizer

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Objective

To examine plasma cortisol levels in response to stimulation of dairy cows with an cattle immobilizer



Method

Twelve lactating dairy cows of predominantly Holstein-Friesian breed were selected. Following morning milking the cows were grazed in a pasture for four hours and were then loaded side by side in a herringbone race for the duration of experimental period (approximately 2 hours). Measurements were made on two treatment days with an interval of three days between treatment days.

Cows were assigned randomly to the treatment groups in a crossover design such that they received two of the three possible stimulation treatments using a cattle immobilizer during the course of the project (n=8 cows per treatment over the two treatment days). Stimulation was applied for a sustained period of two minutes. This duration was selected as being the period required for most examinations and minor manipulations to be carried out. The levels of stimulation chosen were at Setting 2 and 4 on the device dial. Thus the three treatments consisted of:

Setting 2 – probe inserted into the rectum and stimulation applied at level 2 for two minutes (mils stimulation).

Setting 4 – probe inserted into the rectum and stimulation applied at level 4 for two minutes (moderate stimulation).

Control treatment – probe which was unconnected to any electrical box inserted into the rectum for two minutes.

Coccygeal blood samples were taken before the device was applied and again at 2, 15, 30 and 60 minutes after the end of the stimulation period. Blood samples were collected into heparinised vacutainers and immediately placed into ice water. They were centrifuged at 1800g and 4°C for 12 minutes within 90 minutes of collection. Plasma was then aspirated and stored at -20°C until analysed. Plasma cortisol concentrations were measured by radio-immune assay in a single assay run. This assay has previously been described by Fisher et al (2001) and has a minimum detectable level of 1,1ng/ml. Samples were analysed in duplicate. Within assay coefficients of variation were 11.7%, 9.6% and 8.2% for reference samples or 5.6, 25.7 and 52.3ng/ml, respectively.

Data were analysed using a REML variance components analysis (GenStat9.1) with raw and log transformed data. Pre-treatment plasma cortisol concentration was initially analysed as a covariate but found to be significant only at the 2-minute post-treatment sample.

Pre-treatment cortisol levels as a covariate were therefore omitted from further analysis. Day of treatment was a non-significant factor in all analysis and so was treated as a fixed effect in the model.



Results

Data for plasma cortisol concentrations at each sample are given in Table 1 and are presented graphically using values calculated as fitted splines of raw data in Figure 2. Results are reported mean ± standard errors of differences (sed).

 

Setting 2

Setting 4

Control

SED

P Value

-2 minutes

9.6

15.3

12.3

 

 

2 minutes

13.1

18.1

15.6

2.4

 

15 minutes

13.8

22.8**

14.6

2.7

** Treatment P<0.01

30 minutes

13.6

18.3

17.5

3.1

 

60 minutes

12.4

13.9

15.1

4.3

 

Table 1:

Mean plasma cortisol concentrations; mean standard errors of difference and P values for significant differences (n=8 cows per treatment) on each sampling occasion for each treatment. Treatments were stimulation with the Pacifier device at Setting 2 and 4 for two minutes and a control treatment, which consisted of insertion of a non-electrified device for two minutes.

Mean Plasma cortisol concentration did not differ between treatments in the samples taken at -2, 2, 30 and 60 minutes for both Settings. For 15-minute sample, plasma cortisol concentration did not differ for Setting 2, however for the treatment at Setting 4 was higher (P<0,01) than for the other two treatments.

No direct behavioral responses were observed in any of the cows during the treatment periods. All animals were able to maintain normal patterns of breathing and all though in general they remained still during the period of stimulation, they were not paralysed.

 

Figure 2:

Mean Plasma cortisol concentrations (ng/ml) for each treatment group (n=8 per treatment). Treatments were stimulation with the pacifier device at Settings 2 and 4 for two minutes and a Control treatment, which consisted of insertion of a non-electrified device for two minutes. Samples were taken 2 minutes before stimulation and at 2, 15, 30 and 60 minutes following treatment. The pattern of change in plasma cortisol concentrations showed marked individual variation. At level 4 only half of the cows showed a reaction. Examples of three individual cows are given in Figure 3. For example, cow 4047 had similar plasma cortisol concentrations when given both Control and Setting 4 treatment. While cow 0540 showed a greater response to the Control treatment than to the stimulation.

 

Image1.gif

Figure 3:

Plasma cortisol concentrations (mg/ml) in three individual cows during their respective treatments on each of the treatment days. The x-axis represents the time in minutes and the treatment was applied for a two minute period represented by the y-axis of the graph.



Discussion

There was no significant change in plasma cortisol concentrations during the period of observation for either the control treatment of following stimulation with the Pacifier device at Setting 2. Stimulation with the cattle immobilizer at Setting 4 for a period of two minutes produced an increase in plasma cortisol concentration of approximately on third of pre-treatment levels in the samples taken 15 minutes later. While concentrations were tending upwards at the two-minute sample in all treatment groups, the effect of stimulation at Setting 4 was not significant until the 15-minute sample. By 30 minutes following stimulation, levels were again indistinguishable from those of the control treatment or stimulation at Setting 2. Furthermore the changes in plasma cortisol concentrations were only mild and transient even with the higher level of stimulation tested i.e. towards the maximum that the marketers of the product recommend for restraint in dairy cows for routine husbandry procedures of front and hind feet.

There was marked level of individual variation in response such that although the overall average was indicative of low noxiousness. Only half the cows react at Level 4, and then only 2 had plasma cortisol concentrations that exceeded 30ng/ml. Some individuals were more sensitive to the stimulation e.g. Cow 3215. This observation is consistent with reports from the human literature where marked individual variation in the effectiveness of TENS treatment for various conditions is observed (Bergmann, 2007=. This may be an important observation when using the device as it suggests that not all animals will react in the same manner. Thus there is a responsibility on the part of the operator to be aware of the individual animal response and modify treatment accordingly.

Changes in plasma cortisol concentrations have been used in many situations as measure of pain and distress induced by husbandry procedures. These changes are perception of a range of noxious and stressful stimuli will result in activation of higher neuro-endocrine centres in the brain activate the hypothalamus to release corticotrophin releasing hormone. This produces a cascade of hormonal response, first by the anterior pituitary gland , which releases adren corticotrophin hormone (ACTH) into circulation, and the cortisol release from the adrenal gland, situated near the kidney. Information gained from studying these changing hormone levels, in particular cortisol, has been used to develop recommendations for pain relief and improved methodologies for castration of lambs and calves, docking lambs, disbudding and dehorning of calves, velvetting of deer and welfare during transport. (Stafford et al, 2002).

Routine husbandry procedures of calves, which result in tissue damage and subsequent pain, have been shown to result in marked elevation of plasma cortisol concentration. Dehorning using a surgical scoop dehorner is generally considered to be noxious experience for calves. Plasma cortisol levels during the first hour after calves were subjected to scoop dehorning without anaesthetic were elevated eight times above pre-treatment levels. This inclusion of local anaesthetic and non-steroidal anti-inflammatory treatments constrained these increases to be not significantly different to the control treatments of handling and drug treatment only (Stafford et al., 2003)

Castration of three-month old calves using rubber rings, tight latex bands, Burdizzo device or surgery (pull method) all resulted in increases in plasma cortisol concentration during the hour following the manipulation with peak levels of 76, 101, 64 and 68 ng/ml, respectively, with the period of elevation above pre-treatment level being between 1.5 to 3 hours (Stafford and Mellor, 2005).

The changes in plasma cortisol concentration reported in this study are of small magnitude and transient compared to those reported for painful husbandry procedure. Further observations, by the author of plasma cortisol concentrations during physical restraint for procedures such as jugular catheterisation have shown at least two-fold elevation above basal levels. Most studies of this nature have includes manipulations with greater levels of restraint and so elements of discomfort and pain. There is little information available about the impact of restraint alone of adult cattle (e.g. in a cattle crush or head lock gate) on plasma cortisol concentration. In the literature, levels op plasma cortisol for control treatments are relatively constant suggesting that the impact of handling for sampling is benign; however as much of the reported work has been with young animals and most protocols include pre-trial handling to condition the animals for restraint, a response would be expected.

The first electro-immobilisation device introduced into New Zealand was the Stockstill. This was developed in Australia in the 1970s to assist farmers with robotic shearing. It consists of a unit that connects electrodes applied to the mouth and the tail and works by causing contraction of all skeletal muscles. The instructions for use indicate that it should not be used at such intensity that breathing is prevented. The manufacturers claim savings in time and labour costs as well as well as minimising the chance of self-injury and wound contamination conferring and welfare advantage. The effect of this device on plasma cortisol concentrations was investigated by Jephcott et al.(1988). Sheep were immobilised with three different levels of current and plasma cortisol concentrations measured. Peak concentration occurred 20 minutes after the end of the treatment and were com (P<0.01) with current level. At the highest level of stimulation peak cortisol was two-fold higher than the levels unstimulated controls.

The noxiousness of an unspecified electro-immobiliser device was reported in a pilot study of 10 cows (Pascoe and McDonell, 1986) and then in a larger study of 20 adult Holstein cows (Pascoe, 1986).The description and time of these investigations suggested that this device was similar to the Stockstill. In the latter study the cows were trained to recognise a conditioning stimulus and they receive either a high or low exposure to the electro-immobiliser stimulation or an intramuscular injection of saline. Heart rate responses and the time taken to enter the station where treatment had been applied were measured following condition training (10 treatments) with an extinction period (10 session without treatment). Cows that had received both the high and the low stimulus in training period were significantly more reluctant to enter the station, reacted physically, and had higher heart rates than either control cows that were given the intra muscular injections (which showed intermediate levels of response). These authors conclude that electro-immobilisation was a noxious experience for the cows, and that they became strongly conditioned to avoid the stimulus.

The study reported here has examined the response of dairy cows in terms of activation of the hypothalamic pituitary adrenal axis alone. It has not attempted to examine either activation of the sympathetic system, or in depth cognitive behaviours associated with the manipulation e.g. would the animals express aversion to treatment. A full and complete judgement of the noxiousness of the device would require additional work of this manner. Given that similar devices have attracted the attention of international animal welfare proponents (CIWF, 2007) additional studies of this nature may be required if public pressure were brought to bear on use of the device for routine husbandry procedures.



Conclusion

Given that plasma cortisol levels reported when animals were exposed to Setting 2 stimulation for two minutes were similar to those seen in the control treatment, the lower level of stimulation with the cattle immobilizer would appear to represent an experience for the animal that is not sufficiently noxious to activate the hypothalamic pituitary adrenal axis. At Setting 4 there was a mild response, but even then it was significantly less than that seen during interventions. It is reasonable to conclude therefore that when used carefully and at lower settings the cattle immobilizer is not particularly noxious. Safety when handling larger animals is a major issue for occupational safety and health on New Zealand farms, and often animals are injured during restraint procedures for example, by falling when leg is roped for hoof treatment. Judicious use of the cattle immobilizer  may help to overcome some of these issues and improve safety both the farmer and the animal.

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