The effect of social dominance on the productivity, activity and cortisol levels in a herd of Holstein-Friesian crossbreeds in an Automated Milking System in Scotland
03 Feb 2021
By Paul Smith
Take-home message: Medium ranked dairy cows, in terms of herd dominance, exhibited a higher degree of stress than lower ranking animals on a commercial farm fitted with an Automated Milking System.
The enhanced availability of modern management technology to the dairy industry has the potential to increase the supply of dairy products to the benefit of the rapidly growing global population. Automated milking systems (AMS) have elevated in popularity throughout Europe and the USA since their introduction in 1992. The initial appeal of the automated system was the reduced labour requirement on dairy farms although recent evidence suggests additional benefits to milk yield. However, the AMS may have potential negative implications to animal welfare as they are thought to increase the display of dominance behaviours within the herd. To assess any potential concerns to animal behaviour associated with the AMS, this study aimed to evaluate the impact of social dominance on milk yield, activity and cortisol levels.
This study evaluated the association of social ranking (dominance value; DV) with milk yield, activity and milk cortisol levels in a commercial Scottish cross-breed Holstein-Friesian dairy herd, fitted with the AMS. Over the course of several visits to the farm spanning a seven week period, DVs were determined for 35 focal animals with the use of continuous observational sampling. Animals were ranked as high (n=12), medium (n=12) or low (n=11) in terms of DV. In addition, comparisons amongst DV and phenotypes (milk yield, milk composition, body condition score and body weight), age and lactation were conducted. Milk cortisol levels were assessed for each cow while animal activity was recorded with the use of an accelerometer collar.
The social ranking of cows was not observed to be correlated with any parameters of milk production, interactions with the AMS or lactation number. However, a moderate positive association of body weight and DV (0.34) was observed. Milk yield was found to be positively associated with age, rumination behaviour and lactation number but had a negative relationship with body condition score and refusals from the AMS. DV was not correlated with animal activity however both lactation number and age exhibited moderate negative associations with animal activity. Visits to the AMS were positively associated with animal activity. Finally, cortisol levels, indicative of stress, were observed to be significantly higher in the milk of medium ranked animals when compared to their low counterparts.
Although of benefit to labour efficiency on farm, findings from this study highlight the need for further research to assess the potential impact the AMS has on dairy cow behaviour and subsequently animal welfare. In this study, some 38% of antagonistic interactions amongst dyads occurred as animals were queuing to visit the AMS. Therefore, an appreciation of the impact AMS layout has on the dynamics of the herd, may help to limit behavioural related stress to middle socially ranked dairy cows.
This study was conducted by Alex Frances Kerley (University of Aberdeen), as part of her BSc Hons degree in Zoology. Well done Alex on researching this interesting topic and the very best of luck for the future!
Teagasc PhD Walsh Scholar
Paul is a long standing member of the BSAS Early Careers Council and is in the final year of his PhD at Teagasc. His PhD aims to determine a link between the rumen microbiome, host genetics and methane output in beef cattle. Paul is registered at University College of Dublin.