The effect of transporting, scoring and roping on cortisol concentrations in acclimated roping calves

Abstract

This study evaluated the effect of transportation, scoring and roping activities on cortisol concentration in acclimated calves. A total of 16 cross-bred Longhorn calves between 4 and 6 months old and ranging in weight between 104 and 136 kg were used. These calves were preconditioned to roping for 6 weeks prior to study and were randomly allotted to treatments based on a Latin Square experimental design with treatments as follows; remaining at farm (farm), transport to arena (transport), twice passing through roping chute but not being roped (score) and twice being roped and tied (rope). Blood samples were collected via jugular vena puncture, received respective treatment and then second blood samples were collected. This experiment was replicated twice (n = 8 calves, per year), and calves were roped twice per day for 3 days per week during the study. The data was analysed by replicate and by pooled data. The mean±SE pre-event and change in serum cortisol concentrations (µg/dL) were: farm (n = 16), 4.5±0.9, −0.9±0.6; transport (n = 16), 5.1±0.6, −0.9±0.8; score (n = 16), 5.0±0.5, −1.6±0.4; rope (n = 15) 4.9±0.6, −0.5±0.6. The cortisol concentration was elevated for pre-event samples during week 2 compared with week 4 and this suggests possibly a change in routine may have affected cortisol. However, treatment did not affect (P<0.05) change in cortisol concentration among calves; farm (−0.9±0.6), transport (−0.5±0.6), score (−1.7±0.4), farm (−0.9±0.8). Also, calves weight gain was not different (P>0.05) between groups and averaged 0.32 kg/day, for year 2. These data indicate roping does not increase cortisol concentrations in acclimated calves.

Keywords:

• cortisol
• rodeo
• stress
• roping calves

1. Introduction

A current and increasing problem among animal production and animal-based sports is anthropomorphism which projects human characteristics onto non-human animals. A human's and animal's reality is based on perception and many farm procedures and events in animal-based sports appear to be stressful to humans. But few scientific studies have been performed to determine if these production schemes or activities created chronic stress for the animals. One such animal-based sport that creates much controversy is American rodeo and especially the calf roping event.

The scientific inquiry into physiological stress in response to psychological and physical events would be welcomed among animal producers as this would be harmful from either an animal welfare or economic perspective (Grandin 1999). The most common psychological event to affect physiological stress is fear and anxiety with novelty probably being the greatest stimulator of fear and anxiety (Grandin 1997).

Measuring the stress of fear and anxiety can be difficult as there are many measures of stress; however one of the most common measures has been cortisol concentrations (Schwartzkopf-Genswein et al. 1997). Samples to measure cortisol concentrations to determine stress levels can be collected from urine, feces, or saliva (Sconberg et al. 1993). But due to timely changes in circulating cortisol levels blood samples are probably more precise even though the act of collecting blood may induce stress. In cattle, cortisol concentrations can reach peak values within 30 minutes to 1 hour of the stressor (Lay et al. 1992a; Mears and Brown 1997) and can remain elevated for 3–6 hours post-stress or even 7 days post-surgery (Fisher et al. 1996).

The purpose of this study was to determine the effects of transporting, scoring and roping on plasma cortisol concentrations and weight gain in acclimated roping calves.

2. Materials and methods

2.1. Animals

A total of 16 cross-bred Longhorn calves ranging in weight from 104 to 136 kg and 4 to 6 months in age belonging to the McNeese State University (MSU) Rodeo Team, were used for both replicates of this experiment. All animals were treated in accordance with guidelines set forth by the animal care and use committee of MSU. Additionally, calves were vaccinated for blackleg and respiratory diseases twice a year, and dewormed with a rotation of Safeguard (Intervet Inc., Millsboro, DE, 19966) and Ivermectin Plus (Merial, Duluth, Georgia, 30096) every 6 weeks. These calves were maintained on pasture and supplemented with hay and Purina Preconditioning/Receiving Chow (PRECON, Gray Summit, MO).

2.2. Preconditioning of calves

All calves in this study were weaned between 90 and 120 days of age, transported to auction, sold, transported to the university farm, and allowed a 3-week recovery period. Then all calves (both replicates) were roped twice a day for three consecutive days per week (Mon, Tue and Wed) for six weeks prior to initiation of in this study. During this acclimation process, on Monday, calves were transported to the arena for practice from the MSU Farm were roped as described above following practice on Wednesday calves transported back to the MSU farm.

2.3. Experimental design

This experiment was conducted, in the spring, twice in a 2-year period at the MSU Farm in Lake Charles, Calcasieu Arena in Sulphur, La (Replicate 1), and Burton Coliseum in Lake Charles, La (Replicate 2). The experimental design was based on a Latin Square where each calf received each treatment and was conducted with eight calves per replicate. At the beginning of each replicate two calves were randomly allocated for one of the four treatments, (1) remaining at the farm in pairs (farm), (2) traveling to arena and kept in pairs in pens adjacent to calves to be scored or roped (transport), (3) twice being loaded into the roping chute with horse and rider ready but the calf is released without being roped (score) and (4) twice passing through roping chute and being chased by horse and rider, roped around the neck and having three legs tied together for 5 sec (rope). The two calves allocated to each treatment each week were rotated between different treatment groups in the following order; farm to transport to score to rope. During the experiment, calves were transported to arena on Monday, roped twice and returned to farm for blood collection. These calves were returned to the practice arena Tuesday and remained there until completion of Wednesday practice when they were transported back to the farm for the remainder of the week.

During Replicate 1, rodeo practice was conducted at the West Cal Arena in Sulphur, Louisiana. The trailer ride from the MSU Farm to the West-Cal Arena was 23 km one way which lasted ~18–20 minutes, passing through traffic in Lake Charles before following the interstate the remainder of the route to the arena. During Replicate 2, rodeo practice was conducted at the Burton Coliseum's Western Arena in Lake Charles, Louisiana. The trailer ride from the MSU Farm to the Burton Coliseum was ~9 km requiring ~8–15 minute passing through traffic the entire route due to road construction along the route. The only difference in transportation between replicates was ~10 minutes of additional transportation time during Replicate 1 and encountering more stops and starts than experienced during Replicate 2.

2.4. Weight, blood collection and RIA

Each Monday of the study, calves were restrained in hydraulic squeeze chute with head and neck immobilisation and blood samples were collected via jugular vena puncture. Initial weights were recorded for all calves at beginning of each replicate, however, only calves in Replicate 2 were weighed weekly (immediately prior to immobilisation). Calves assigned to farm treatment were placed in holding pens immediately adjacent to hydraulic chute and working corrals and all other calves were loaded on trailer and transported to roping practice, immediately following blood collection.

Blood samples were collected in sodium heparinised vacutainer tubes and labeled according to each calf's ID number, date, and time. Following practice (treatments), calves were transported back to MSU Farm and placed in a squeeze chute and jugular blood samples were collected again. In both replicates, Calves were returned to the farm following treatment for the post-event blood collection. This was to avoid blood collection, in calves at the rodeo arena, without proper and safe restraint. The increased travel was elected over increased stress or physical harm as a result of attempting to restrain these animals without use of a chute. The collected blood samples were stored on ice until they were centrifuged at 300 x g for 15 min, then the plasma was extracted and lastly stored in a freezer (−4°C) until radioimmunoassay (RIA) was performed. The time lapse from the first blood collection to each event and second blood collection is described in Figure 1. Cortisol was measured, in an independent laboratory at Louisiana State University, using a commercially available RIA kit Pantex I-125 Direct Cortisol (Pantex, Santa Monica, CA) with extraction via acetone. The sensitivity of the assay was 0.2 µg/dL, and the intra-assay and inter-assay coefficients were 5.6 and 8.7%, respectively.

Figure 1.  Time from each event to time of blood collection.

The purpose of only two blood samples to determine differences in cortisol was to reduce the amount of stress induced in animals via blood collection. Additionally, the use of catheters was not prudent in this experiment as the risk of injury to blood vessels from the catheter in response to the physical jerking of the animal during roping. Due to this inability to catheterised all calves for all treatments two blood collections via head restraint was determined the least stressful of possibilities to measure circulating cortisol concentrations.

2.5. Statistical analysis

Statistical analysis was performed using a general linear model (Mixed Model; Proc Mixed) with repeated measures in SAS (SAS Institute, Inc., Gary, NC). The change in cortisol concentration was calculated by subtracting the pre-event concentration from the post-event concentration. Differences between pre-event and post-event cortisol concentrations between replicates, changes in cortisol between weeks or treatments from pooled data, and the per cent of animals experiencing a positive change in cortisol by weeks or treatment were determined using repeated measures of analysis of variance (ANOVA) with a Tukey's post-hoc test (Duncan). Any differences among the pre-event, post-event or change in cortisol concentration between treatments and replicate interaction or by week and replicate interaction were determined using repeated ANOVA with a LSmeans post-hoc test.

Table 1. The mean±SE pre-event, post-event and change in plasma cortisol concentrations among roping calves by treatment and by year.

			Plasma cortisol concentrations (µg/dL)
			Pre-event	Post-event	Change
Treatment	n	Replicate	mean±SE	mean±SE	mean±SE
Farm	8	1	4.7±1.7	4.2±0.9	−0.5±0.9^a,b
	8	2	4.3±0.9	3.0±0.6	−1.2±0.8^a,b
Transport	8	1	5.9±1.0	4.3±0.7	−1.6±1.0^a,b
	8	2	4.0±0.5	4.5±0.2	0.6±0.5^b
Score	8	1	5.1±0.8	3.7±0.5	−1.4± 0.6^a,b
	8	2	4.9±0.7	3.0±0.4	−2.0± 0.5^a
Rope	7^1	1	5.0±0.9	3.2±0.9	−1.8±1.8^a
	8	2	5.1±0.8	5.0±0.8	−0.2±1.4^a,b
Note: Values with differing superscript letters within a column are significantly different (P<0.05).
^1One post-treatment sample from this group was missing therefore observation for that one calf was removed from this treatment group.

3. Results

The mean±SE plasma cortisol concentrations (µg/dL) for pre-event, post-event and the change in cortisol were not different for Replicate 1 (5.2±0.6, 3.9±0.4 and −1.3±0.4) compared with Replicate 2 (4.6±0.4, 3.9±0.3 and −0.7±0.5), respectively. There were no differences between the pre-event and post-event samples among years therefore the data were pooled. There was a treatment by year interaction the change in cortisol being more positive (P<0.05) for the transported group in Replicate 2 compared with the Replicate 2 scored group and Replicate 1 roped group (Table 1). Additionally, there was a decrease in cortisol following all treatments except the Replicate 2 transported group; however, the transported group was not different from other treatments in pooled data analysis (Table 2).

Table 2. The mean±SE pre-event, post-event and change in plasma cortisol concentrations among roping calves by pooled totals.

			Plasma cortisol concentrations (µg/dL)
			Pre-event	Post-event	Change
Treatment	n	Replicate	mean±SE	mean±SE	mean±SE
Farm	16	Pooled	4.5±0.9	3.6±0.6	−0.9±0.6^a
Transport	16	Pooled	4.9±0.6	4.4±0.4	−0.5±0.6^a
Score	16	Pooled	5.0±0.5	3.4±0.3	−1.7±0.4^a
Rope	15^1	Pooled	5.1±0.6	4.1±0.6	−0.9±0.8^a
Note: Values with differing superscript letters within a column are significantly different (P < 0.05).
^1One post-treatment sample from this group was missing therefore observation for that one calf was removed from this treatment group.

Tables 3 and 4 and Figure 2 illustrates a decrease (P<0.06) in pre-event cortisol during week 4 (Replicate 2 and pooled data) compared with week 2 (both replicates and pooled data). There were no differences in post-event cortisol; however the change in cortisol was greater (P<0.05) during week 2 (Replicate 2) compared with week 4 (Replicate 2).

Figure 2.  The mean±SE pre-event and post-event plasma cortisol concentration for each week of the replicate.

There was an increase (P<0.05) in the percentage of animals with a positive change in cortisol concentration among the transport group (8/16, 50%) compared with the score group (2/16, 12.5%), but not different from the farm (6/16, 37.5%), and rope groups (3/15, 20%). During the Replicate 2, the average weekly weight gain was 2.25 kg and the average daily gain was 0.32 kg.

Table 3. The mean±SE pre-event, post-event and change in plasma cortisol concentrations among roping calves by week and by year (replicate).

			Plasma cortisol concentrations (µg/dL)
			Pre-event	Post-event	Change
Week	n	Replicate	mean±SE	mean±SE	mean±SE
1	7^1	1	5.1±0.9^ab	3.8±0.7	−1.3±1.0^ab
	8	2	4.0±0.6^ab	3.2±0.5	−0.8±0.7^ab
2	8	1	6.1±1.5^ac	4.5±0.8	−1.5±1.0^ab
	8	2	6.1±0.9^ac	3.8±0.4	−2.3±0.8^a
3	8	1	5.6±1.2^ab	4.0±0.9	−1.64±0.8^ab
	8	2	4.6±0.7^ab	4.4±0.7	−0.2±1.0^ab
4	8	1	4.0±0.9^ab	3.2±0.7	−0.7±0.3^ab
	8	2	3.6±0.4^b	4.1±0.8	0.5±0.9^b
Note: Values with differing superscript letters within a column are significantly different (P < 0.06).
^1One post-treatment sample from this group was missing therefore observation for that one calf was removed from this treatment group.

4. Discussion

Despite early weaning, exposure to sale barn cattle, 6 weeks of two round trips greater than 1 hour per week, being roped twice a day 3 days and a 4-week study period with a changed routine including blood collection and 2 additional round trips from farm to arena, 50% of these calves had post-event plasma cortisol concentrations < 4 µg/dL and 75% had < 5 µg/dL. Grandin (1997) reported that baseline cortisol levels in calves was from 0.2 to 0.9 µg/dL, and cattle subjected to headgate restraint ranged from 1.3 to 6.3 µg/dL (Mitchell et al. 1988; Zavy et al. 1992; Lay et al. 1992b). Theses roping calves were subjected to many events in a short period time period and still possessed circulating cortisol levels that remained within the range for cattle subjected to only headgate restraint, which they also experienced twice in a 3–5-hour time period.

Table 4. The mean±SE pre-event, post-event and change in plasma cortisol concentrations among roping calves by week for pooled data.

			Plasma cortisol concentrations (µg/dL)
			Pre-event	Post-event	Change
Week	n	Replicate	mean±SE	mean±SE	mean±SE
1	15^1	Pooled	4.5±0.5^de	3.5±0.4	−1.0±0.6^d
2	16	Pooled	6.1±0.8^d	4.2±0.5	−1.9±0.6^d
3	16	Pooled	5.2±0.7^de	4.3±0.5	−0.9±0.6^d
4	16	Pooled	3.8±0.5^ef	3.6±0.5	−0.1±0.5^d
Note: Values with differing superscript letters within a column are significantly different (P<0.05).
^1One post-treatment sample from this group was missing therefore observation for that one calf was removed from this treatment group.

Additionally, the transport, score and rope treatments did not stimulate an increase in cortisol, as the post-treatment values declined and were not different than calves that stayed at the farm. These results demonstrate that even though experiencing multiple transportations and being roped around the neck and tied down twice a day from 2 to 3 days a week may appear stressful to a human this activity failed to stimulate an increase in plasma cortisol concentration. These calves being roped experienced multiple stressors in rapid succession would have been believed to elevated cortisol concentrations for a longer period of time. As animals transported for longer time periods have elevated cortisol concentrations compared with compared with other animals transported a shorter time period which have elevated cortisol for shorter time periods (Schmidt et al. 2010).

One factor that produced a statistical increase in cortisol was transportation during Replicate 2 which involved travel over a shorter time period but resulting in more stops and starts during the trip. However, the transportation group in Replicate 2 had a greater increase in cortisol than the score group from Replicate 2 which experienced the same travel experience as the transport group. It is unknown at this time why a difference in plasma cortisol concentration occurred between these two groups; further investigation may lead to a better understanding of why these two groups were different.

Additionally, fear of the unknown may have produced a significant increase in pre-event cortisol during week 2 which was significantly higher compared with week 4 pre-event cortisol concentrations. These pre-event samples represent the normal cortisol concentration following routine penning from pasture and can reflect any physical or psychological perturbations experienced during this process. Additionally, these samples should account for any stress-related cortisol increases resulting from a disruption in the calf's normal routine as experienced the week prior to this sample. The pre-event sample from week 4 should account for normal penning experiences and may reflect the calf's ability to expect the same novel routine they have followed for the past three weeks. Even though these roping calves have considerable experience adapting to novelty, novelty can still affect cortisol concentration as reported in other farm animals (Grandin 1997; Van Reenen et al. 2005).

The significant increase in the number of calves with a positive increase in the transport group compared with the score group reinforces the difference between these two groups in Replicate 2, in regard to change in cortisol concentrations and the possibility of difficult travel preconditioning animals to respond to novelty more stressfully.

During this study only calves on Replicate 2 were weighed weekly and had a positive average daily gain (ADG) of 0.32 kg/d. The positive weight gain, lack of significant increase in cortisol concentrations provide evidence that these calves were not experiencing chronic stress or fear as based on weekly cortisol concentrations. This may also be attributed to at the 6-week acclimation period and the consistent routine these calves were previously exposed to which enabled them to accurately predict their future activities.

Although, anthropomorphism would speculate that roping is stressful to calves, in conditioned calves this event fails to stimulate a significant increase in cortisol. Future studies should evaluate cortisol levels and behavioural scores of calves during the acclimation process to gain further understanding of how these animals perceive their world and their physiological and psychological responses.