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

Effect of winter environment on growth of young beef cattle 1. Effects of exposure during winter to rain or wind and rain combined on performance of 9-month-old Friesian steers fed on two planes of nutrition

Three experiments were conducted to compare the performance of 9-month-old Friesian steers wintered in three environments, (a) conventional cattle houses, (b) wind-sheltered roofless sawdust pads and (c) unsheltered roofless sawdust pads. Within each environment animals were fed on two planes of nutrition.

In each experiment, winter live-weight gains of animals accommodated on the three winter environments were similar as were weight changes during the subsequent four weeks at grass in Experiments 2 and 3.

No interaction on live-weight gain was found between plane of nutrition and winter environment. Health of outwintered animals was good throughout. The response to feeding barley with hay in these experiments (obtained by comparing low-plane with high-plane treatment groups) showed that on average 5·5 kg of barley dry matter were required to produce 1 kg of additional live-weight gain above that obtained from hay fed alone.

Cold Exposure of Southdown and Welsh Mountain Sheep. 3. Changes in plasma calcium, phosphorus, magnesium, sodium and potassium levels

Southdown and Welsh Mountain female sheep, equal numbers on high and low plane nutrition, were shorn and subjected to two acute cold exposures (−20°C, 4 mph wind) in climate chambers. Before the first exposure the sheep were kept in either a cool (+8°C) or a thermoneutral (+30°C) environment for two weeks. Between exposures these environmental temperatures were reversed within groups. Blood samples were withdrawn at the beginning and end of the two week exposures and on three occasions during acute cold exposure. Plasma analyses of Ca, P, Mg, Na and K were carried out. Exposure to +8°C caused a 12% reduction in plasma Mg levels of all sheep, but had no effect on Ca, Na or K levels. There were breed × temperature interactions with respect to plasma P levels. Acute cold exposure caused reductions in plasma Mg and Ca levels and an increase in plasma P levels of all groups of sheep. Changes in plasma Na and K levels could have been caused by plasma concentration.

Electrolyte levels initially displaced by exposure to +8°C showed no evidence of a return to normality two weeks later. Only for Ca was there evidence that prior exposure to +8°C modified the response to acute cold exposure.

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.

Effect of shearing and level of concentrate feeding on the performance of finishing lambs

The response of finishing Blackface lambs (mean initial live weight 29·6 kg) to shearing and level of concentrate supplementation on a silage-based diet was examined in two experiments. Silage intake decreased as concentrate level increased at mean rate of 0·13 and 0·26 g silage dry matter (DM) per g concentrate DM, in experiments 1 and 2 respectively, with no significant differences between unshorn and shorn lambs. Lambs gained 36, 97, 135, 193 and 224 g/day (s.e. 9·1; P < 0·001) in experiment 1 and 97,133,170,185 and 222 g/day (s.e. 9·9; P < 0·001) in experiment 2 when 0, 200, 400, 600 g/day and concentrate ad libitum were offered respectively. Shearing increased silage DM intake from a mean of 0·50 to 0·56 kg/day (s.e. 0·016; P < 0·05) in experiment 1, and from 0·80 to 0·90 kg/day (s.e. 0·013; P < 0·001) in experiment 2. There was no interaction between shearing and the level of concentrate offered. Despite higher DM intakes by shorn lambs, their live-weight gains were lower than those of unshorn lambs. Gains of unshorn and shorn lambs averaged 153 and 120 g/day (s.e. 5·8; P < 0·001) in experiment 1 and 162 and 161 g/day (s.e. 5·7; P > 0·05) in experiment 2 respectively. This appears to have resulted because shorn lambs could not fully compensate for their increased energy requirements after shearing, by increasing their DM intake. Shearing did not significantly influence carcass characteristics.

It was calculated that with lambs gaining 150 g/day, concentrate requirement was increased from 286 to 335 g/day and total DM intake from 965 to 1107 g/day as a result of shearing.