Relentlessly hot summers appear to be on the rise, and this has one Dubbo sheep producer worried.
Roseville Park Merinos principal, Matthew Coddington, has seen extreme summer temperatures negatively effect one of his key profit drivers, fertility.
"Dubbo in January averaged 40.5 degrees for a maximum, and for February exactly the same - it was just unrelenting," he said.
"Until then a heat wave might last a week... and be gone. We were up to 47 degrees out here, and for a month to average 40.5 and then the next month to follow on was just extreme."
But this trend of increased average temperatures has continued since 1998, said Mr Coddington.
During research conducted across multiple years by Greg Sawyer as part of his masters studies he found ewe body temperature was having an affect on embryo viability.
Mr Sawyer, formally with Australian Wool Network and now with Elders, conducted the study across a number of properties, and across several embryo transfer (ET) programs.
"(At Roseville Park) Greg took body temperatures of 16 sheep (donors in the ET program), taking temperatures at pre-AI (artificial insemination), post-AI, and morning and afternoon," said Mr Coddington (also on our cover).
"We do our ET programs in December and again six weeks later in early February with the same sheep. This particular program was done in summer, and I think some of the days were 41 to 42 degrees."
Mr Coddington said they found ewes with a body temperature under 39.5 degrees had an 89 per cent embryo viability, meaning those embryos were able to be transferred into surrogate ewes, while the remaining 11pc were either degenerative or unfertilised.
"Once the ewe body temperature was over 39.6 (degrees) we had the total opposite," he said. "We had 17pc of the embryos viable, and 83pc of them chucked down the sink."
With an Australian average of seven transferable embryos per sheep and five live lambs on the ground, this superovulation of ewes allows producers to get a lifetime of reproduction in one ET program, but if the amount of viable embryos is low, farmers start to ask "why?".
Each ewe costs $1000 to flush, according to Mr Coddington, so each lamb is worth $200 before it is born and to throw those embryos down the drain has a massive impact on businesses.
"We have been doing ET since 1989 ... our ET donors have been ET bred, all our top sires have been ET bred and those rams at our on-property sale averaged $3322 last year and sell up to $25,000 each. They all come from flushing," he said.
The study also found those ewes that flushed well and had a low body temperatures didn't necessarily pass on those traits Mr Coddington said, indicating low heritability.
"What we found, when you do natural joining and artificial insemination joinings, condition score is king," he said.
"Condition score on any farm throughout the year should be three or better, but what we found in the donor ewes is if we locked them up and stripped the body fat right out of them back to a 2.5 body condition score (BCS), they handled the heat a lot better.
"We also found the ability to take drugs into the system with less fat meant they superovulated better. And we also always do a pre-shear to get them to thermoregulate a bit better.
"Since dropping them to 2.5 BCS and doing a pre-shear we have been able to average around 10 transferable embryos per ewe over the last four programs."
Heat stress in sheep is influenced by temperature combined with humidity, air flow and hot surfaces.
He said this past summer, 40.5 degree averages in January and then 80 millimetres of rain and no wind, created conditions rife for pneumonia in young sheep.
"The vets couldn't believe it," he said.
"Little, short heat waves are fine, it will heat up and cool down. But when we have these relentless days where the ewes cannot thermoregulate and get their body core temperatures down of a night, it puts continuous stress on sheep.
"This heat stress increases body temperature, respiration and heart rates, water intake, and it can lead to embryo mortality in ewes, or effects sperm concentration and viability in rams."
The Temperature Humidity Index (THI) accounts for the combined effects of environmental temperature, humidity and wind and is used to identify and assess the risks of heat stress on livestock.
"Where the humidity increases and the day time temperature increases... the ability of the ewe to thermoregulate is decreased which has an effect on embryo mortality," he said.
"For example on a 33 to 35 degree day at 100 per cent humidity, the effect it has on the stress of the animal and embryo mortality in sheep is increased."
He said even from 28.6 to 32.3 degrees is a danger area, especially with sustained heat - this year totalling as long as nine weeks.
He said night time temperatures needed to drop below 25 degrees for sheep to thermoregulate properly, to get that core temperature down for the next day.
But what is striking is that the THI had increased by 250pc since 1998.
"Back in December we had an ET and AI conference in Sydney with Australian Wool Innovation and we bought together all the artificial breeding vets, animal health reps and research specialists in reproduction from across Australia," he said.
"All of them said they have seen reduced AI conception rates, funnily enough since 1998."
To help overcome the heat stress in stock when joining in December and through to January, Mr Coddington said he ensures he puts teasers out with the ewes.
"There are a couple of mobs we didn't put teasers out with and they didn't start lambing till two weeks after they should which means the rams were running around serving ewes in 40 degree heat, and actually making themselves infertile quicker," he said
"If ewes are ready and running hot the day the ram goes in and he is ready to work, it will not only tighten your joining up but you will get more lambs just from that because the rams sperm motility is going to be a lot better."
Mr Coddington said the only problem with trying to manage heat stress is that the more heat stress resistant producers make their sheep, the less cold tolerant they are.
"We are creating a sheep, (for example) that in Orange most your lambs might die," he said. "You need to be careful of all this so we are even measuring that. And that is where the genetic fat and muscle comes into play.
