Acclimatization of Scottish Blackface sheep to cold. 2. Skin temperature, heart rate, respiration rate, shivering intensity and skinfold thickness

Effects of Housing and Management Systems on the Growth, Immunity, Antioxidation, and Related Physiological and Biochemical Indicators of Donkeys in Cold Weather

The study was designed with a 2 × 2 factorial experiment to evaluate the effects of growth performance, immune function, antioxidant status, blood biochemical indexes, and hormone levels of donkeys in different housing and management systems in cold weather. Twenty-four male donkeys with similar body weight and age were randomly allocated into four treatment groups that were as follows: a cold-water-drinking group without a windproof facility, a lukewarm-water-drinking group without windproof facilities, a cold-water-drinking group with a windproof facility, and a lukewarm-water-drinking group with a windproof facility. The experiment lasted for 42 days. The results showed that windproof facilities increased average daily gain (ADG) and decreased average daily feed intake (ADFI) and feed-to-gain ratio (F:G) at all time periods (p < 0.01) of the experiment. Windproof facilities increased the digestibility of dry matter (DM), crude fat (CF), crude protein (CP), ash, calcium (Ca), and phosphate (P) on day 21 (p < 0.01), and increased the digestibility of DM, CF, ash, and P on day 42 (p < 0.01). The respiration rate and the skin temperature of the abdomen and legs increased (p < 0.05) and rectal temperature tended to increase (p = 0.083) by adopting windproof facilities at 07:00; the windproof facilities tended to increase the skin temperature of the ears and abdomen (p = 0.081, p = 0.091) at 14:00. For the blood parameters, with windproof facilities, the concentrations of total protein (TP), blood urea nitrogen (BUN), triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) increased (p < 0.05) and glucose (GLU) concentration decreased (p < 0.05) at 07:00 on day 21; the concentrations of TG and cholesterol (CHO) increased and the concentrations of TP, BUN, and GLU decreased at 07:00 on day 42 (p < 0.05). The concentrations of adrenocorticotropic hormone (ACTH), cortisol (COR), triiodothyronine (T3), and thyroxine (T4) decreased (p < 0.05) at 07:00 on day 21, and T4 concentration decreased (p < 0.05) at 07:00 on day 42. The concentrations of interleukin-4 (IL-4), immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM) increased (p < 0.01) and the concentrations of interleukin-1β (IL-1β) and tumor necrosis factor-alpha (TNF-α) decreased (p < 0.01) on days 21 and 42. The activities of total superoxide dismutase (T-SOD) and glutathione peroxidase (GPx) increased (p < 0.05), and malondialdehyde (MDA) concentration decreased (p < 0.01) on day 21; the activities of T-SOD and catalase (CAT) increased (p < 0.05), and MDA concentration decreased (p < 0.01) on day 42. However, under the conditions of this experiment, water temperature did not affect the above indexes on days 21 and 42. These results indicated that adopting windproof facilities in a cold climate can mitigate the effects of atrocious weather on the production performance of donkeys.

Resistance to body cooling in male and female sheep, and the effects of previous exposure to chronic cold, acute cold and repeated short cold shocks

Twenty-eight female and 26 uncastrated male Scottish Blackface sheep were shorn and subjected to two acute cold exposures one week apart. Between exposures and for one week before the first exposure the sheep were kept either at +30°C (thermoneutral), or at +8°C (subcriticai), or at + 30°C with daily short cold shocks. Food intakes were restricted.

Females showed significantly greater resistance to body cooling than males during both acute exposures.

Both males and females showed acclimatization (increased resistance to body cooling) as a result of the first acute exposure.

Exposure to +8°C for one week did not produce significant acclimatization. Exposure to +8°C for two weeks tended, in females only, to increase acclimatization above that resulting from the first acute exposure.

Daily short cold shocks reduced cold resistance and inhibited acclimatization in females, but had little effect in males.

The male sheep lost significantly more weight during treatment and became thinner than the females. It was suggested that this, and their low cold resistance, might be related to a lesser ability of males to store fat as a subsequent source of energy.

Cold Exposure of Southdown and Welsh Mountain Sheep. 2. Effects of breed, plane of nutrition and previous acclimatization to cold upon skin temperature, heart rate, shivering and respiration rate

Shorn Southdown and Welsh Mountain sheep on high or maintenance levels of nutrition were subjected to two acute (−20°C; 4 mph wind) cold exposures in climate chambers. Before and between exposures the sheep were kept in either a cold (+8°C) or a thermoneutral (+30°C) environment.

1. At +8°C, all the sheep shivered and showed sustained vasoconstriction and elevated heart rates.

2. At + 30°C, heart rates, skin temperatures on the extremities and muscular tone were all consistently higher in sheep which had previously been kept at +8°C.

3. During cooling, the onset of vasoconstriction and increase in heart rate were both delayed in sheep previously kept at + 8°C.

4. These effects (2, 3) were retained for at least 2 days but less than 12 days after the sheep returned to thermoneutrality. They decayed faster than the increased resistance to body cooling produced simultaneously in the same sheep (Sykes and Slee, 1969), since this was still detectable after 2 weeks.

5. Breed differences were mainly small.

6. It was concluded that acclimatization induced by chronic cold exposure was associated with a temporary increase in basal metabolic rate.

Body temperature and vasomotor responses in Scottish Blackface and Tasmanian Merino sheep subjected to slow cooling

1. Scottish Blackface and Tasmanian Merino one-year-old males were exposed to cold in climate chambers. The environmental temperature fell slowly from +10°C to −15°C in the first experiment when the sheep were in full fleece and from +30°C to −5°C in the second experiment when the same sheep were closely shorn. In the second experiment each sheep received two identical exposures separated by one day spent in a cool environment. Rectal temperatures and skin temperatures on the body and the extremities were recorded.

2. In experiment 1 skin temperatures on the feet and ears generally fell sharply due to vasoconstriction, especially in the Blackface sheep. The Blackface sheep showed earlier and more intense vasoconstriction than the Merinos.

3. In experiment 2 foot and ear skin temperatures fell smoothly with gradual vasoconstriction. In contrast to experiment 1, both breeds were similar in the time of onset of vasoconstriction. Foot temperatures, however, were significantly higher and vasoconstriction correspondingly later during the second exposure of experiment 2 than during the first exposure.

4. The skin temperature at which vasoconstriction occurred remained similar irrespective of breed, shearing or exposure occasion. But the ambient temperature at vasoconstriction was significantly influenced by all these variables.

5. Cold-induced vasodilatations were more frequent in experiment 1 than in experiment 2.

6. Retarded vasoconstriction among the Merinos in experiment 1 could, except for two sheep, be accounted for by their superior fleece cover. In experiment 2, the delayed foot vasoconstriction on second exposure was attributed to increased blood flow resulting from acclimatization.

Physiological adjustment to repeated wind exposure in sheep

An experiment was undertaken to examine the possibility that progressive adjustments in tissue insulation on the trunk might occur following repeated wind cooling. Two sheep were exposed at right angles to an air flow of 12 mph for 6 hr daily on each of 7 consecutive days.

When first exposed to the wind the heat loss from the fleece-covered surfaces increased due to a reduction in insulation and apparently increased vaso-dilatation. After the first day there was a progressive increase in surface vaso-constriction before exposure and a gradual decrease in the extent of the vaso-dilatation during exposure. The results indicate the possibility of centrally-induced peripheral adjustments in blood flow occurring on the trunk of the sheep in response to repeated wind cooling.

A comparison of inbred and outbred sheep on two planes of nutrition 2. Responses to acute cold and heat exposure

Four groups each of 14 sheep aged 11 to 13 months comprising outbred (O) and inbred (I, inbreeding coefficient 0·37 or 0·5) sheep reared on either a low plane (L, maintenance) or on a high plane (H, ad libitum) of nutrition from the age of 6 months were exposed first to acute cold and 1 week later to heat. Exposures in climate chambers ended for each sheep when rectal temperature decreased to 36°C (in the cold) or increased to 42·5°C (in the heat) subject to a limit of 8 h. Throughout the experiment, sheep were kept in matched quartets comprising one sheep of each type.

The average cold resistance times (min) were 161, 267, 348 and 381 for the LI, LO, HI and HO groups respectively, showing a significant effect of both inbreeding and plane of nutrition (P < 0·01). Five sheep in the HO group lasted the full 8 h in the cold chamber with little or no reduction in rectal temperature. Skin temperature at the mid side was significantly higher in L than in H sheep throughout cold exposure, but there was no effect of inbreeding.

Respiration rates were much higher before and during cold exposure in the H sheep, but there was no effect of inbreeding.

The residual correlation of cold resistance with live weight was 0·58, but differences in live weight do not explain all the differences in cold resistance and particularly do not explain the rapid decrease in rectal temperature of the LI sheep. It was concluded that under cold exposure a high level of nutrition was able to compensate partly for the disadvantages of inbreeding, and that outbreeding was able to compensate partly for the adverse effects of poor nutrition.

With heat exposure, there were no significant differences among the four groups in heat tolerance time, but within the 1st h, H sheep had slightly higher rectal temperatures and much higher respiration rates than L sheep. Inbreeding affected only the time taken to reach a respiration rate > 200 per min, which was longer in I (131 min) than in O sheep (113 min) and longer in L (149 min) than in H animals (96 min).

Cold exposure of Southdown and Welsh Mountain sheep. 4. Changes in concentrations of free fatty acids, glucose, acetone, protein-bound iodine, protein and antibody in the blood

Twenty-four Southdown and 24 Welsh Mountain year-old female sheep, half on high-plane and half on low-plane nutrition, were shorn and given two acute cold exposures in climate chambers. For 2 weeks before and 2 weeks between exposures the sheep were kept in a subcritical (+ 8°C) or a thermoneutral (+30°C) environment. Before the temperature treatment each sheep received an injection of Brucella abortus vaccine. Blood samples were taken during exposure to + 8°C and + 30°C and during the acute cold exposures for estimation of free fatty acid (FFA), protein-bound iodine (PBI), glucose, acetone, serum protein and antibody levels. FFA and glucose levels alone were measured in 32 similarly treated Scottish Blackface sheep.

1. Low plane sheep had higher PBI levels at all temperatures, and higher glucose levels during acute cold exposure than high plane sheep. Otherwise most major effects were attributable to ambient temperature.

2. At +8°C the PBI, FFA, glucose, serum protein and acetone levels were higher than at + 30°C.

3. Blackface sheep had lower FFA and glucose levels than Southdown and Welsh sheep at both temperatures.

4. During acute cold exposure, PBI, acetone and FFA levels increased further. PBI levels were highest in sheep previously at + 30°C, and acetone highest in sheep previously at + 8°C. Very high FFA levels were recorded, especially in sheep not previously cold-acclimatized.

5. Glucose levels increased initially, but fell towards the end of acute exposure, suggesting that relatively less carbohydrate and more fat was utilized for energy metabolism during this period.

6. Serum protein levels fell during acute exposure, possibly because protein catabolism increased. The proportions of albumin and γ-globulin increased and decreased respectively.

7. No effects of temperature on antibody levels were detected.

Food intake and grazing behaviour of sheep varying in body condition

Herbage intake and grazing times were measured in four experiments in which adult sheep grazed short and long pastures. The digestible organic matter (DOM) intake of adult wooled Merino and Corriedale wethers was higher, both absolutely and per kg live weight, when they were lower in live weight due to prior under-nutrition. The relative differences were similar on both abundant and scant pasture and were proportional to the relative differences in live weight. The higher intakes were achieved by differences in the time spent grazing and in the rate of intake per hour of grazing. DOM intake of shorn sheep was increased by up to 44% per kg live weight within 5 weeks of shearing in two experiments when the mean temperature was 8°C but no increase in DOM intake was observed in four other experiments when the mean temperature was 11°C. Shorn sheep achieved higher intakes on both abundant and scant pastures by increasing intake per hour of grazing.