T h e first measurements of the basal metabolism of the young calf were reported by Brody (1930), who used the indirect calorimetric method of measuring oxygen consumption by means of a closed-circuit spirometer. Determinations were made on forty-three calves of less than 3 weeks of age but most of the values obtained were restricted to ages of 10-21 days. No definite trends during the first 3 weeks of life were observed and with two calves values obtained on consecutive days from birth showed a high variability. Brody concluded, from a consideration of mean heat production at monthly intervals, that resting metabolism/kg body-weight increased from birth to 2 months of age and decreased rapidly thereafter. When expressed on the basis of body-surface area, however, metabolism increased steadily to 6 months of age and then remained constant or tended to decline. Recently, Hawkins, Pope, Roy, Shillam, Ingram & Greatorex (1957) have shown a marked change in pulse and respiration rate during the first 3 weeks of life of calves given 400 ml. separated colostrum followed by whole milk at the rate of I lb./Io lb. live weight and growing normally under the conditions of low ' infection' reported by Roy, Palmer, Shillam, Ingram & Wood (1955). The mean pulse rate of forty-four calves, which was about 110 beatslmin on the 1st day of life, fell rapidly during the 1st week and then more slowly to the value of 75-80 by the end of the 3rd week. Respiration rates showed the same trend, falling from a value of 45 respirations/min on the 1st day of life to 22-25 by the end of the 3rd week. This pattern was similar to that found by Lewis & Ralston (1953) for the concentration of plasma-proteinbound iodine in the calf.As it is well known that the heat production of an animal is roughly proportional to its pulse rate, it seemed necessary to investigate whether this relationship was valid in the very young calf. If such a relationship did exist, it would indicate that the maintenance requirement of the calf during the first 2 weeks of life was considerably higher than during the 3rd week.

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