ENVIRONMENTAL-EFFECTS ON THERMOREGULATION AND BREATHING PATTERNS DURING EARLY POSTNATAL-DEVELOPMENT IN HAND-REARED LAMBS

This study examines the effect of hand-rearing developing lambs in a w arm (WR; 25 degrees C) or cool (CR; 10-15 degrees C) ambient temperatu re on the control of thermoregulation and breathing patterns, when mai ntained at a fixed level of nutrition over the first month of postnata l life. Measurements were made during non-rapid eye movement sleep whi lst lambs were maintained for at least 1 h at warm (28-19 degrees C) a nd cold (14-5 degrees C) ambient temperatures at 1, 7, 14 and 30 days of age. All lambs were able to maintain normal body temperature, but o xygen consumption was higher in CR lambs at 14 and 30 days of age. At 1 day of age shivering was rarely observed in any lambs, but at 7 and 14 days of age more WR than CR lambs responded to cold exposure via sh ivering. Plasma concentrations of triiodothyronine were higher at 7 an d 14 days of age in CR lambs. Breathing frequencies were similar in WR and CR lambs, and from 7 days of age the incidence of expiratory lary ngeal braking was higher in warm compared with cold study temperatures . By 30 days of age the recruitment of this mechanism was greater in C R lambs. Mean growth rate was slower over the first week of postnatal life in CR compared with WR lambs. This difference decreased over the first month of life, as growth rate increased from 83 to 130 g day(-1) in the CR group but remained constant at approximately 150 g day(-1) in the WR lambs. Total weight of the lungs and heart, but not the live r, were lower at 1 month but not at 1 week of postnatal life in CR lam bs. It is concluded that a modest decrease in the ambient temperature in which postnatal lambs are reared, when on a fixed feed intake, alte rs lung size, the recruitment of laryngeal braking and the control of body temperature.