DAIRY NEWS NOVEMBER 10, 2015
28 // ANIMAL HEALTH
Turning down heat in the calf shed GEMMA CHUCK
AS SUMMER
approaches and much of Australia prepares for the long hot months ahead, it is time to reflect on the
Consider the impact of heat on calves this summer, says Australian vet Gemma Chuck.
effect of heat stress in our dairy calves. The effect of heat stress in the milking herd is well known and farmers are using shade and sprinkler systems to reduce the impact on
YOU DO HAVE A CHOICE
if you need to use a nil withholding time antibiotic on your herd! For treating footrot, metritis or bacterial respiratory disease. Ask your veterinarian if KELACEF is a more cost effective ceftiofur for use in your herd. • Nil milk withholding period • 2 day meat withholding period • Excellent suspension • Easy to syringe OTHER PRODUCTS FROM PHOENIX PHARM
TYLO 200
SOLUTION FOR INJECTION 100 ml and 250 ml plastic vials
INDICATIONS Lung infections, especially mycoplasmosis and other infections as pneumo-enteritis, metritus, mastitis, foot-rot, swine dysentry, arthritis, erysipelas, caused by sensitive organisms in cattle, pigs, sheep, and goats.
PHARMACILLIN 300
KELAPROFEN 10%
SUSPENSION FOR INJECTION
100 ml vial
100 ml and 250 ml plastic vials
INDICATIONS
INDICATIONS For treatment of infections caused by bacteria sensitive to penicillin in cattle, pigs, sheep, horses, cats and dogs.
WITHDRAWAL PERIOD
WITHDRAWAL PERIOD 21 days for meat, 3 days milk WHT.
7 days for meat, 3 days milk WHT.
SOLUTION FOR INJECTION
Cattle and Horses: Anti-inflammatory, analgesic and antipyretic treatment of respiratory disorders, acute mastitis, mammary oedema, colic, and musculoskeletal disorders.
WITHDRAWAL PERIOD 4 days for meat. Nil milk WHT.
Use antibiotics responsibly and as directed by your veterinarian Products registered pursuant to the ACVM Act 1997, No. A10848, A9851, A7798, A6340. See www.foodsafety.govt.nz for registration conditions.
Phoenix Pharm Distributors Ltd PO Box 31-363, Milford, Auckland, New Zealand Telephone: 0-9-476 7391 Email: phoenixvet@xtra.co.nz
milk production. However, the effect of high ambient temperatures on dairy calves is often not considered. The ‘normal’ core body temperature of a young calf is 38.6oC (range 38.5– 39.5oC). There is an ambient temperature range at which a calf is comfortable and needs no extra energy to warm or cool its body. This is the ‘thermoneutral’ zone -- for a new-born dairy calf 10-25oC. This zone changes as a calf grows due to the production of heat from fermentation in the rumen. For example, the thermoneutral zone for a one month old dairy calf is 0oC to 25oC. Calves tolerate higher ambient temperatures better than adult cows: their larger body surface to live-weight ratio allows better dissipation of heat. The exact ambient temperature at which calves start to show signs of heat stress is not clearly defined. However, clinical signs arise with higher ambient temperature (outside the thermoneutral zone) and relative humidity and with increased time of exposure. Ambient temperature greater than 25oC, with relative humidity of ~80%, pose an increased risk of heat stress to young calves. When high daytime temperatures are followed by cooler nights, calves (and cows) are able to dissipate accumulated body heat. Thus calves are at highest risk of heat stress when there are high ambient temperatures on consecutive days, with no drop in temperature overnight. Research in North America has shown that calves born in summer have lower daily weight gains than calves born at other times of the year. This is due to an increased energy demand to maintain body temperature and decreased grain intake during hot weather. In periods of cold stress, calves older than three weeks will often compensate for the increased energy demand to regulate body tempera-
ture by consuming more starter (grain). This is not the case for calves enduring heat stress, which will often consume less starter. Combined with the fact that more energy is directed towards maintaining body temperature through evaporative cooling (sweating and panting), the result is a reduction in average daily weight gain. Reduced starter intake can slow rumen development, increasing the risk of a slump in growth postweaning. Additionally, heat stress can also compromise immunity rendering heat-stressed calves more susceptible to disease. The severity of heat stress will vary depending on the duration, temperature and humidity, however the signs include: ■■ Reluctance to move ■■ Reluctance to lie down ■■ Reduced feed (milk and grain) intake ■■ Increased water consumption ■■ Seeking shade ■■ Standing/splashing water ■■ Increased respiratory rate ■■ Panting/open-mouth breathing There will also be an increase in rectal temperature and if this exceeds 41.5oC, then a calf is at a very high risk of death from heat stroke. In strategising to manage heat stress, aim to reduce the ambient temperature to within the thermoneutral zone so that calves are utilising less energy to regulate their body temperature. Shade is essential to help achieve this, along with assessing and modifying shed design to improve ventilation. Side-wall vents, openpitched roofs and whirlybirds can be utilised in passive ventilation systems. Fans and positive pressure ventilation tubes are not widely used in calf sheds in Australia but have been successful in North America in active ventilation systems. • Gemma Chuck is a vet with the Vet Group in Victoria, Australia.