HEAL ▶▶▶TH
Responses to cold stress T
BY DR SALAH H. ESMAIL, PH.D.
he following is a review of the limited work conduct- ed in this area, with particular reference to the diges- tive physiology and metabolism of cold-stressed cat- tle and their production response to such adverse
conditions. Management and feeding strategies to be adopted for alleviating cold stress effects are also looked at.
Feed intake and chewing behaviour Cold stress usually stimulates appetite and the increase has been assumed to reflect the increase in the metabolic de- mands of the animal. Modification of chewing behaviour also occurs with cold exposure. Rate of eating increased by 22- 31% for chopped hay and up to 10% for pellets at fixed in- takes, thereby reducing the duration of eating. Rumination time in cattle also increases in the cold, perhaps to compen- sate for decreased eating time. Chews per cycle of rumination also increased by about 10% due to cold exposure and by about 20% due to lactation. Thus it appeared that increased feed intake of these cold, lactating animals was accommodat- ed by proportional increases in the chewing effort, rather than by increases in efficiency of chewing.
Digestibility Table 1 shows dry matter (DM) and nitrogen (N) digestibility values in heifers and cows exposed to a low outdoor temper- ature compared to the animals kept indoors. The effect of cold exposure was more obvious for the calves compared to the matured cows, suggesting that the effects of temperature on digestion may be following the general principle that ani- mals of larger body size are less likely to be affected by envi- ronmental temperature changes than small animals. Despite the reduced digestibility, there is an associated in- creased appetite, as indicated above. In situations of abundant
Although much work has been done to examine the effects of heat stress and other environmental factors on animal physiology and production, the effects of cold stress have not been widely researched. Here we look at some of the findings on the digestive, metabolic and production responses to cold stress.
food supply, an animal may benefit more from the increase in appetite than the loss from the reduced ability to digest feed.
Metabolic responses to cold stress Blood flow and endocrine changes Exposure to cold decreases the portion of cardiac output flow- ing to the gastrointestinal tract, lower limb hoof bone, and di- aphragm, the latter being consistent with a reduced respira- tion rate. Cold stress also increases secretion of the catabolic hormones cortisol and catecholamine and the more modest changes in secretion of the anabolic hormone insulin which results in a net catabolic response. The combined effect of these endocrine changes is to increase the mobilisation of energy sources for use by the shivering muscles.
Pregnancy ketosis Cold weather is known to increase the susceptibility to preg- nancy ketosis. This may be a nonspecific response to stress or starvation. Additionally, some of the metabolic adaptations to cold exposure may increase susceptibility to ketosis when food supplies are limited.
Hypomagnesemia Cold exposure increases the incidence of hypomagnesemia in ruminants due to the reduced plasma magnesium levels. Ex- posure to a moderately cold environment failed to depress
Table 1 – Effects of air temperature on dry matter and nitrogen digestibility in heifers and cows.
Indoor Temperature (19 C)
Heifers
DM digestibility (%) N digestibility (%)
Cows (480 and 520 kg) DM digestibility (%) N digestibility (%)
Cold stress causes a reduction in milk secretion in lactating cows.
Source: R. J. Christopherson (1978) ▶ ALL ABOUT FEED | Volume 27, No. 9, 2019 15
65.65 64.95
61.8 73.0
59.40 59.90
60.8 71.3
Outdoor Temperature (12 C)
PHOTO: HENK RISWICK
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