The effect of insecticidal fly tags on cattle liveweight gain in the Douglas Daly region

T Schatz , A Feez^B, M Hearnden and C Heeb

Northern Territory Department of Primary Industry and Resources; ^BY-Tex Corporation.

Introduction

Buffalo flies can cause irritation to cattle resulting in reduced growth although the response to control measures in northern Australia has been variable (Bean et al. 1987). An experiment was conducted at Douglas Daly Research Farm, NT, to determine the effect of a new type of insecticidal fly tag (development tag number YT1625) on growth. The tags are a sustained-release, plastic ear tag containing a synergized formulation of Zetacypermethrin, an enriched S-isomer pyrethroid compound and Abamectin (made by Y-Tex), which have not previously been used in combination on cattle.

Materials and methods

On 14 November 2018, 118 one year-old Brahman and Brahman cross bulls (average weight = 153 kg) were weighed and randomly allocated (stratified for weight) to either a CONTROL (n=59) or TAGGED (n=59) treatment group. Weight was recorded again the following day after an overnight curfew with no feed or water and the TAGGED group were each fitted with two fly tags while the CONTROL group did not receive any treatment for fly control. Each treatment group rotationally grazed a block of eight x six ha uniform paddocks of Buffel pasture in such a way that they were never in adjacent paddocks. They were moved to a new paddock every three days and both treatments were always moved on the same day. Each time the treatments completed a rotation around the block of eight paddocks they swapped blocks of paddocks so that TAGGED grazed the paddocks that had previously been grazed by CONTROL and vice versa. Both treatments had ad libitum access to mineral lick blocks and were managed in the same way throughout the study except for the fly tag treatment.

The cattle were weighed after an overnight curfew on 8 March 2019 (after 16.1 weeks) and without a curfew on 9 May 2019 (after 25.1 weeks) although the tags only have an approved control period of 16 weeks. Liveweight gain (LWG) was calculated using curfewed weights for the 16.1 week period and un-curfewed weights for the 25.1 week period. The average (LWG) of the two treatments over these periods was compared using a linear model adjusted for the initial weight covariate.

Results and discussion

After 16.1 weeks the average LWG of the TAGGED group was 9.8 kg more than CONTROL (P<0.001) so the growth rate was 0.085 kg/day higher in TAGGED. LWG was 16.7 kg (0.095 kg/day) higher in TAGGED (P<0.001) over the extended 25.1 week period. This was similar to the increase in LWG as a result of repeated spraying with insecticide reported by Bean et al. (1987) where treated cattle gained 14.7 kg more over 24.1 weeks (ie. 0.087 kg/day), and less than the 33 kg increase in LWG over 19 weeks (0.247 kg/day) from using diazanon ear tags reported by Spradberry and Tozer (1996).

The increase in LWG of 16.7 kg found in this study was worth $48.43/head at the current cattle price of $2.90/kg. The cost of the fly tags was $7 per head so the return on investment from the TAGGED treatment was 692 per cent assuming that the difference in weight gain persists through to the time of sale.

References

Bean KG, Seifert GW, MacQueen A, Doube BM (1987) Aust. J. Exp. Ag. 27, 329–334.

Spradbery JP, Tozer RS (1996) Aust. Vet. J. 73 (1), 6-11.