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Fasting Energy Metabolism during Lactation^*

Department of Dairy Husbandry, University of Missouri, Columbia

ABSTRACT

Preliminary data obtained by an open-circuit-mask respiration method indicate that the total heat production of a lactating cow during fasting is about 10 per cent higher than that of a dry cow. Up to 60 hours of fast the heat production curves of both animals are essentially parallel, reaching a level at about 36 to 48 hours after feed. After 60 hours the heat production of the lactating animal further declined about 20 per cent. Certain data indicate that the higher level of total energy metabolism in the lactating cow is in a large measure due to heat increment of nutriment.

During 72 hours of fast, the lactating cow continued to produce a relatively constant amount of milk fat, although her milk yield declined about 50 per cent. It is believed, therefore, that within the limits of these experiments, lactation as a mechanism was unchanged by fasting.

Further investigation of digestion, absorption, and incident heat increment of nutriment appears to be necessary in order to evaluate true physiologic maintenance in the fasting ruminant. The probability of considerable absorption occurring 72 hours after food, suggests that the fasting level of total heat production is not an accurate measure of physiologic maintenance in the ruminant. Furthermore, differences in the speed of movement of alimentary residue during fasting, indicate that the fasting levels of total heat production in the lactating and dry cow are not comparable without further correction.

^* Paper No. 171 in the Herman Frasch Foundation Series. Contribution from the Department of Dairy Husbandry, Missouri Agricultural Experiment Station Journal Series No. 565.