Heat Stress is when the heat load in cows is greater than their ability to lose heat. Cows are more sensitive to heat stress than humans, due to their rumen’s activity by-product being heat.

In New Zealand, a cow will be in heat stress at a temperature of 21ºc and 70% humidity. Although cows may not show behavioural signs of being in heat stress, they are more susceptible to health issues such as increased somatic cell (SCC) and increased lameness due to supressed immunity.

Under heat stress, not only is immunity supressed but DMI and rumination is decreased leading to decreases in milk production and changes in milk composition.

Remember when cows are on the yard, their overall body temperature and impact of heat stress increases, due to being in close proximity to other heat stressed stock, lack of air flow and being yarded on warm surfaces such as concrete.

How to combat heat stress and maintain productivity in the herd? 

A simple, cost effective method to reduce the effects of heat stress is to add Kemtrace Organic Liquid Chromium to the diet. Organic Chromium aids with homeostatic thermoregulation. Giving the animal the ability to cope with warmer environments while still being productive. Herds supplemented with Kemtrace Organic Liquid Chromium are able to maintain productivity through thermoregulation, increased appetite, leading to increase DMI and energy.

DBC Client farming 50km Inland in the heart of Marlborough, where grapes enjoy intense heat, dairy cows do not. This is their experience using Kemtrace Organic Liquid Chromium:

“Last season we added Kemtrace Chromium to the dosatron. It reduced the symptoms of heat stress, this was especially evident during afternoon milking. In the pass despite presenting good number of cows for A.I, we have wondered if heat stress was causing cows to abort early into pregnancy. Last season we had a much improved in calf rate. While we cannot soley prove this was entirely due to the Chromium, we will continue to use Kemtrace Chromium as we think improved in calf rates were due to cow facing less stress from heat despite being a hot summer. ” 

We are beginning to see the effects of pasture production from mowing pasture earlier in the season. With farms that have mowed post grazing being able to maintain quality for longer when compared to pastures mowed before the herd. If mowing isn’t an option on farm, evaluate your pasture quality and determine if round length is something that needs to be changed.Differences between Pre and Post Grazing Mowing

Mowing in front of the herd can allow cows to consume more but only if the standing pasture is low in DM. Physically cows will consume the grass faster but that does not necessarily mean there is an increase in total grass consumed. Mowing before grazing blends the higher quality, more palatable feed with the poorer quality, less palatable feed limiting the sorting ability of the cow. This can often reduce the average ME in the diet.

Pre-mowed pasture is wilted, becoming drier. If the grass was at only 12%DM that means the cow has to consume 9kg wet grass to equal 1kgDM. This can send messages to the rumen weight receptors that the animal is feeling full, therefore stops grazing due to extra water content in the rumen. Just because the animal has stopped grazing, does not always indicate that she is fully fed.

It is recommended to mow before the herd if DM is below 15%.

Many young stock who are grazed off farm in drier areas are often fed on pastures such as Fescues. Fescues are a pasture species used as an alternative to rye grass in summer dry areas due to their extensive rooting systems tolerating both drought and periodical waterlogging.Fescue foot is when stock become lame, predominately in their back feet. It is derived from Fescue endophytes producing Ergovaline alkaloids. Although Ergovaline can provide control from insects such as Black Beetle, these alkaloids restrict blood circulation around the animals body, impacting the “tips” of the animal.

First signs is often lameness, if toxicity continues then stock will develop scald like symptoms on their ears, nose and tail. In extremely severe cases, the animals hooves, tail and ears can fall off. Ergovaline alkaloids can also cause heat stress and significant reductions in animal performance which can be difficult to regain.

How Prevent and Treat Fescue Foot

Fescue Foot is easily treated with a white penicillin, however, to avoid antibiotic usage we can manage this through strategic grazing.

The endophyte lives in the crown of the plant and in the seed head. Graze only when the pasture is in a leafy green stage. Avoid stock grazing the seed head and grazing residuals below 1500KgDM. When toxicity is apparent, limit the animals access to Fescue pastures, add silage or straw to the diet to slow down the endophytes metabolism in the rumen.

Management such as topping seed heads will aid in preventing endophyte toxicity in cattle.

If toxicity persists under appropriate pasture management then it is advisable to contact your local vet.

Across the country we are seeing periods of continued dry for regions such as Canterbury, with lack of pasture growth and feed shortages beginning to have an impact. Here at DBC we encourage you to re-evaluate your feed budgets to ensure you have enough to fully feed your herd for the latter half of the season.It is important to maintain adequate feed inputs and also appropriate mineral supplementation to maintain BCS, production and strong cycling cows who hold in calf.

The DBC reps are busy helping farmers overcome these challenging times providing feed options such as heifer summer feed blends to Canterbury farmers to combat the dry.

Things to check: