The impact of gastrointestinal parasites on weight gain, activity patterns and behaviours in cattle on pasture

Sammanfattning: Infections caused by gastrointestinal parasites are one of the most problematic health concerns for cattle all around the world. These parasites may cause a wide range of health problems ranging from subclinical disease to actual death. Animals infected with parasites usually respond to sickness with predictable pattern of behavioural changes. The aim with this master thesis was therefore to evaluate whether there were any differences in behaviour, activity patterns and weight gain between animals given a dose of parasites and animals treated with anthelmintics. The study was performed at Götala Beef and Lamb Research Centre outside Skara, between 18 May and 15 September in 2016. The research animals consisted of 63 steers, where 31 of them were of dairy breed (Swedish Holstein, SLB, or Swedish Red, SRB) and the other 32 steers were crossbred animals (SLB/Charolais and SRB/Charolais). Two pastures were used consisting of permanent semi-natural pastures. The animals were divided into two separate groups with 31 and 32 animals in each group, where each group consisted of half purebred and half crossbred steers. One group of steers were given an oral dose of the parasites Ostertagia ostertagi and Cooperia oncophora while the other group was treated with anthelmintics. The body weight recordings were performed bi-weekly on Tuesdays and consisted of 10 weighing periods during the summer. In order to measure the activity patterns IceTags were placed on 20 animals, 10 in each group. The behaviours of each group of steers were recorded using direct observations that were performed during selected weeks with start in May. Mean number ± SE was calculated in percentages for each category of behaviour. The current study revealed that parasitized steers had a lower weight gain throughout the pasture period than steers treated with anthelmintics (P<0.005). The average daily weight gain during different periods throughout the pasture period was significantly affected by treatment (P<0.0001) and period (P<0.0001). Anthelmintic treated steers had a higher mean daily weight gain during 31 May-14 Jun (P<0.0001), 29 Jun-12 Jul (P<0.0001) and 6-20 Sep (P<0.05) than infected steers. Significant interactions between period and treatment were also found on motion index and the number of steps taken, where the motion index (P= 0.0005) and the number of steps taken (P<0.05) was significantly higher in steers treated with anthelmintics. Significant interactions between period and treatment were also found on the number of lying bouts as well as the duration of lying and standing. The number of lying bouts was higher in steers infected with parasites (P<0.05) during 12-26 July. The duration of standing were higher in parasitized steers (P<0.05), while the duration of lying were higher in the anthelmintic treated steers (P<0.05) during 9-23 August. The results from the behavioural observation showed a different result where the infected steers appeared to walk more and lie less, which contradicts with the results from the IceTags. Moreover, social behaviours such as sniffing and licking others appeared to occur more frequently in steers with high parasite load than in steers with low parasite load. This study demonstrated that gastrointestinal parasites in steers at pasture cause a reduced daily weight gain and a decreased general activity level per 24 h, but an increased general activity level during day time.