Grooming in horses

Issue 26, April 2003

In many social animals grooming is an important activity, in removing ectoparasites for example. Sometimes an animal will groom itself but sometimes one animal grooms another. In France, a study of grooming in horses was carried out, see Figures 1 and 2.

Figure 1. Two Camargue horses grooming

Figure 2. The areas that were groomed: each other at the preferred site at the base black - the preferred grooming site of the neck. The mouth is slightly open and hatching - less preferred grooming sites the upper incisors scratch the other`s skin. stippled - the non-preferred grooming area used in the experiments.

The researchers were interested in seeing if horses groomed one another in preferred areas and if experimental grooming influenced the heart rate in the recipient horse.

In the first part of the study the scientists observed grooming in a herd of wild horses (Equus caballus) in the Camargue. They recorded behaviour seen in 38 grooming sequences by filming the horses, keeping the camera at right angles to the horse being groomed. Each time a horse put its teeth onto the skin of the other it was recorded as a `dental impact`.

In the second part of the study the researchers imitated grooming by scratching the skin of 16 hand-tame horses at the same rate as wild horses groom (twice per second). They scratched at a preferred site for 3 minutes and then at a non-preferred site for 3 minutes (see the stippled area of Figure 2 at the top of the leg). They recorded the heart rate of the horse being scratched before and then during the scratching at both the preferred and the non-preferred site.

* Feh, C. & De Mazieres, J. 1993. Grooming at a preferred site reduces heart rate in horses. Animal Behaviour, 46, 1191 - 1194.

1. What type of study was used to obtain the data for the wild Camargue horses? Underline which type of study you think it was.

   i) laboratory experiment ii) observation iii) survey iv) case study v) correlational study

   ( 1 )
2. Outline one advantage for researchers of filming the behaviour of animals or humans. ( 1 )
3. Why do you think the researchers kept the camera "at right angles" to the horses? ( 1 )
4. The scientists filmed 38 grooming sequences in 18 animals. They also recorded each time a horse made a dental impact on another horse when grooming it. There were 728 dental impacts in all. What would be the mean number of dental impacts per grooming sequence? ( 1 )
5. When is a mean value used in preference to a median value as a measure of central tendency in a set of data? ( 1 )
6. In the second study, one of the researchers scratched each of the 16 horses. What would be the advantage of the scientists scratching the horses? ( 1 )
7. The researchers counted the number of grooming episodes between male-female pairs and female-female pairs of horses. They used the Chi-squared test to determine if there was a significant difference in the frequency of grooming between the two groups: X_ = 5.57, df = 1, P < 0.05.
   1. Why was the Chi-squared test an appropriate test to use? ( 1 )
   2. What do the letters df stand for and what does this mean? ( 2 )
   3. Is the Chi-squared test a parametric or a non-parametric test? ( 1 )
   4. The researchers measured the heart rate (beats per minute) of the horses before and whilst grooming them. They examined the heart rates to see if there was a difference between the heart rates using a related t test.
      1. Why was a t test an appropriate test to use? ( 1 )
      2. Why was the related t test, rather than the unrelated t test, appropriate? ( 1 )

   [We are grateful to Elsevier Science for permission to copy Fig. 1 page 1192 and Fig. 2 page 1193, from Feh, C. & De Mezieres, J. 1993. Grooming at a preferred site reduces heart rate in horses. Animal Behaviour, 46, 1191 -1194, and to copy Fig. 1a page 116, from Sharpe, L. L. et al. 2002. Experimental provisioning increases play in free-ranging meerkats. Animal Behaviour, 64, 113 - 121.]