From a young age, dairy cows react differently from each other to stimuli from their surroundings. An animal's temperament determines how it reacts in stressful situations, but may also influence its general health. In the future, temperament could be bred as a selective trait to improve the robustness and wellbeing of dairy cows.
This is the conclusion reached by zootechnician Kees van Reenen, who will receive a PhD from the University of Groningen on 30 March 2012.
Van Reenen studied black-and-white Holstein-Friesian cows as they developed from calf to cow. He carried out behavioural tests and physiological examinations in order to determine how the animals react to external stimuli. He focused on the following, among others: fear responses, lowing (vocalization), stamping, pulse and the release of cortisol as the external characteristics of underlying traits -- including timidity, the need for social contact and movement -- that, taken together, determine the temperament.
In order to study the differences in the reactions, Van Reenen subjected the animals to potentially stressful situations, namely securing them with a halter for a short period, separating them from the rest of the herd, and confronting them with a person or unfamiliar object. The unfamiliar object he used was a jerry can. 'In this test, the calf or cow enters an empty room in which, after a few minutes, a coloured jerry can appears using a pulley', Van Reenen explains. The differences between the animals' responses were very clear: some of them made contact with the jerry can after just a few seconds, while others didn't dare to approach it at all during the ten-minute test.'
Van Reenen was also able to measure the fear response physiologically: the animals that investigated the jerry can thoroughly and for the longest time had lower levels of the stress hormone cortisol in their blood than the animals that were more cautious. In order to prove that the caution was indeed a fear response, Van Reenen administered an anxiolytic drug (Brotizolam) to the animals. Van Reenen: 'The length of contact with the jerry can increased considerably in the animals that had been given an anti-anxiety drug, and the cortisol levels fell more quickly after the test.
Although lowing could be easily interpreted as a fear response in the first instance, this was not the case. Van Reenen: 'The frequency of the lowing did not change when the Brotizolam was administered. Apart from that, calves that lowed a great deal when separated from others in the herd had a higher milk yield when they were milked for the first time later, as heifers, than the animals that were less vocal. Therefore, lowing is not a fear response, but probably a form of social behaviour: a sign that they like to be near other cows. Animals that exhibit this behaviour could benefit from social contact with other animals in stressful situations -- when they are being milked, for example.
Notably, the differences in temperament in individual animals proved consistent throughout the research period. Van Reenen: 'This shows that temperament is a stable underlying trait in the animal. We know from research into other species, such as coal tits and rats, that temperament can influence an animal's health and wellbeing. If that also applies to dairy cows, temperament could be bred as a selective trait to produce robust animals, in the same way as traits such as good bone structure, fertility and low susceptibility to mastitis.'
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