The physical environment (temperature, humidity, and air quality) in the nursery can directly influence the pig's performance. Unless the pig is placed in comfortable, draft-free conditions, the incidences of diseases and/or diarrhea may increase. As a result of poor environmental conditions, the effectiveness of a good diet in achieving good performance responses will be lost.
Evidence of good physical environmental nursery conditions can be best evaluated by observing pig behavior. Piling of pigs in their nursery pens reflects poor environmental conditions because the pigs are attempting to conserve body heat, whereas when pigs have distributed themselves over the entire floor, nursery conditions are either comfortable or perhaps too hot. The latter condition can be recognized by high respiration rates, and steps should be taken to relieve this situation.
Because of the poor feed intake and loss of body fat during the initial days postweaning, nursery room temperatures should be raised slightly from the temperature in the farrowing house. The nursery temperature can be subsequently lowered as pigs become older, heavier, and accumulate more body fat. The type of flooring, bedding, heat pads, hovers, and pen height from the floor will influence the "comfort zone" of the pig and therefore help to determine the desired nursery temperature. An understanding of pig behavior helps determine the best nursery-room temperature and other environmental conditions.
The recommended room temperatures of the nursery depend largely on the weight of the pig and the amount of body fat that has accumulated during the nursing period. The outer fat layer (backfat or subcutaneous fat) rapidly accumulates while the pig is nursing, but a substantial amount of this fat can be lost during the first week upon weaning. The subcutaneous fat layer of younger and/or lighter-weight pigs at weaning is also lower at weaning than that of heavier-weight pigs. This outer layer of body fat provides insulation from low temperatures. To be within their "comfort zone," lightweight pigs need a warmer nursery-room temperature than heavier-weight pigs (Figure 3). As pigs become heavier, they regain their subcutaneous fat and the need for the "hot nursery" condition becomes less.
Most pigs, but particularly those of a light weight, have a poor appetite upon weaning, resulting in body fat being lost upon weaning. This makes them prone to being the victims of poor performance or becoming "poor doers." This effect is frequently demonstrated by their "rough" look during the initial weeks postweaning. The inclusion of plasma protein and lactose in the diet has resulted in an increased feed intake during this early postweaning period. Pigs of a heavier weaning weight grow faster, not only while in the nursery but also to market weight, than pigs of a lighter weaning weight.