Effect of Environment on Nutrient Requirements of Domestic Animals (1981) / Chapter Skim
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SWINE
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Pages 96-108
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From page 96... ...
Cold stress and heat stress will be considered separately. LOWER CRITICAL TEMPERATURE In thermoneutral conditions, heat-production rate depends mostly on feed intake and metabolic body size.
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From page 97... ...
than that of those held singly. If specific alterations in animal activity or productivity raise or lower metabolizable energy intake at maintenance, the lower critical temperature will TABLE 28 Lower Critical Temperatures (LCT)
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From page 98... ...
Lower critical temperature (Table 28) can be assumed to be the lowest effective ambient temperature for optimal management of pigs at the feed intake rate specified.
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From page 99... ...
, is given. It may be assumed that the lower critical temperature of ad libitum-fed pigs on a partly wet, slotted floor will be about 18 to 19°C during the growing phase and 14 to 15°C for finishing hogs.
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From page 100... ...
calculated the extra feed needed to compensate for the increased rate of heat loss. They made separate calculations based on measurements near the lower critical temperature, as well as at 10°C of coldness.
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From page 101... ...
Extra feed intake is required during cold to compensate for reduced gain in restricted-fed pigs. For example, if rHE intake remains the same, body energy gain is reduced at environmental temperatures below the lower critical temperature due to extra heat to keep the body warm.
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From page 102... ...
For ad libitum-fed pigs, additional feed must be consumed during cold to maintain daily gain. There is, however, less information on voluntary feedintake rate in pigs under standardized environmental conditions than on heatproduction rate.
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From page 103... ...
15.~5.0 2~110 8.1 19.1 Verstegen et al., 1978 15.5-4.5 32-64 12 53 Heitman and Hughes, 1949 15.5~.5 75-95 54 41 Heitman and Hughes, 1949 mine that during cold pigs are able to increase feed intake so that body weight gain remains the same as at thermoneutrality. Another factor that affects estimates of extra feed required by cold exposure is a small, but consistent, reduction of dietary-energy digestibility in cold-stressed animals.
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From page 104... ...
From all this evidence, it seems justifiable to estimate arbitrarily that the extra feed requirement for pigs under cold stress in practical conditions averages in the range of 30 to 40 g/°C of coldness per day for the growing-finishing period when body weight ranges from 20 to 100 kg. In 1968, NRC estimated that ad libitum-fed pigs weighing from 20 to 100 kg have an average daily gain of 800 g and a gain/feed ratio of 0.29, provided they have a daily feed intake of 2.8 kg under optimal conditions.
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From page 105... ...
described upper critical temperature as that point at which a pig with dry skin can maintain maximal rate of heat loss. One may also use the point at which there is a rise in core temperature or frequency of respiration, as suggested by Heitman and Hughes (19491.
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From page 106... ...
Previous Iowa studies had also shown that pigs weighing less than 20 kg had much less decrease in feed intake than older pigs (Hazen and Mangold, 1960~. They reported figures from which a reduction of 30 and 7 g/°C of heat load in intake and gain, respectively, in the body weight range of 20 to 100 kg were calculated when 32 and 18°C were compared.
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From page 107... ...
To get some idea of the normal magnitude of environmental heat stress during hot weather, one must know both the optimum temperature range and the average EAT. Most investigators have found the range, 18 to 21°C, optimal for growing-finishing pigs.
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From page 108... ...
Increased heat loss during cold stress reduces rate of performance unless compensation is made by increasing rate of feed intake. During heat stress, rate of intake is depressed, resulting in lowered performance.
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