Case study models cost of drench resistance

// Worms

At a potential starting cost of $96,390 per annum, left unaddressed, drench resistance could ultimately threaten the future viability of one family’s hill country sheep and beef operation.

drenching ewes

This figure was calculated by BakerAg farm consultant Ed Harrison using a Wairarapa family’s 1890ha farming business as a case study. In what was a modelling exercise, the cost of drench resistance and the financial ramifications of any farm system changes the family could make to address it were assessed. 

From a baseline total gross margin (gross income minus variable costs) of $1,186,920, Ed calculated that drench resistance at the lower end (drench efficacy 70-90%) could cost the business $96,390 annually, reducing the business’s gross margin to $1090,530.

If drench efficacy were to fall below 70%, then production losses would increase further and financial losses increase exponentially.

The case study family is typical of many sheep and beef farmers throughout the country who are proactively working to prevent drench resistance becoming a production-limiting issue. 

They are part of the Wairarapa-based Beef +Lamb New Zealand Livestock Parasite Management Group, made up of 12 farming businesses, who are all looking at ways to protect their business from a potential drench resistance challenge. 

Formed by Beef + Lamb New Zealand, the Group is facilitated by local vet Sara Sutherland of The Vet Clinic Wairarapa.

Gathering together at one of their four yearly meetings, the Group listened as Ed ran through five system-change scenarios, all modelled using Farmax, which the case-study family could consider as they work to reduce their reliance on drench but maintain profitability. 

These scenarios were; reducing ewe numbers, running a store lamb policy, selling in-lamb ewes, increasing their cattle ratio and only using terminal sires (buying in two-tooth replacements). These scenarios could potentially be used in combination

Ed says it is important that any changes made to a farm system are able to be practically implemented, that they suit the farm team and don't have any unintended consequences e.g. increased GHG emissions.

Drench resistance can have a massive impact. Reduced lamb growth in the face of resistant worms means lambs stay on the farm longer, more drench is used and more feed is needed leading to higher costs, further escalation of the existing drench resistance problem and animal welfare issues.

Even in a low to moderate drench resistance scenario, Ed says average lamb growth rates drop from 110 to 60 grams/day and ewes lose condition as feed is partitioned into slow-growing lambs. As a result, scanning percentages fall away, lactation declines along with pre-weaning lamb growth rates and lambs are retained for longer to achieve saleable weights.

Resistance problems compound in a challenging year, says Ed, and costs increase because more stock is carried for longer.

Assess the cost of farm system changes

From a base Total Gross Margin of $1,186,920, Ed calculated the variances from this baseline of the five scenarios. Reducing ewe numbers by 1000 generated an additional $71,820, a store lamb policy would cost the business $39,690 while selling scanned in-lamb ewes would reduce the total gross margin by $15,120.

Increasing the cattle ratio by 6%, from 27–33%, would add $77,490 to the bottom line and a terminal sire policy would, in theory, add $66,150 to the Total Gross Margin.

Reducing ewe numbers

In the reducing ewe number scenario, fewer ewes would mean more available feed, ewes would therefore in better condition and more resilient to internal parasites. Ewes would be heavier at mating, increasing scanning percentages, and if that condition were to be maintained through winter on the extra feed available, they would produce more milk which would drive lamb survivability and pre-weaning growth rates. Heavier lambs at weaning would mean more lambs sold at the weaning draft. Cull ewe weights would also higher.

In this scenario, extra feed could be partitioned into ewe lambs, allowing hoggets to be mated.

Ed admits that it does require both a change of mindset and confidence to reduce ewe numbers. In this scenario, there is a reliance on achieving an increased percentage of lambs that are marketable at weaning. 

Increasing cattle numbers

To maintain pasture quality, increasing the cattle numbers would complement the reduced ewe number scenario. Cow numbers would increase from 400 to 500 (including heifers) with a significant (1050) drop in ewe numbers.   

This scenario would see ewe performance improve due to more feed available being available. This would result in increased weaning weights, higher scanning percentages and reduced wastage with more lambs sold at the weaning draft.

Terminal policy

Using terminal sires over the entire ewe flock would increase weaning weights by 2–3kgs, so more lambs would be sold at weaning.   This would reduce pasture contamination by parasites. Fewer lambs would also mean the ewes would be better fed over summer which would increase scanning percentages, lambing percentages and weaning weights.

The challenge with this scenario is sourcing the 2,700 two-tooths replacements required every year to maintain ewe numbers at 9700. It is therefore the least practical of the five options modelled. 

The critical factor in all these scenarios was weaning weights. Increasing weaning weights and the number of lambs sold at the weaning draft provides options.

“On a farm with drench resistance, however you get the best weaning weights is the way to go. This means less lamb days on farm therefore less contamination of pasture with resistant parasites,” says Ed.