Energy expenditure by dry and lactating Alpine does estimated by entry rate of carbon dioxide
Herselman, M. J., T. Sahlu, S. P. Hart, and A. L. GoetschJournal of Dairy Science 81:2469-2474. 1998
Energy requirements of animals are affected by production state, such as lactating versus dry. Effects of lactation on energy requirements of goats as suggested by the National Research Council (i.e., NRC) are currently based on only four publications between 1938 and 1979. Energy requirements are studied by measuring feed intake and total heat production, which is the sum of energy used to maintain the animal and that produced in metabolism for growth, milk production, or greater than normal activity. Total heat production can be quantified by a number of approaches, although most have limited application in practical production settings, particularly grazing. The carbon dioxide (CO2) entry rate technique has been developed, especially for grazing settings, as an indirect measure or index of CO2 production in the body, which can be used to estimate heat production. However, very little information exists regarding the advantages and disadvantages of different body fluids that may be sampled in this method. Likewise, several equations have been published over the years to predict heat production from the CO2 entry rate in small ruminants. In this experiment, the entry rate of CO2 derived from use of continuous collection of saliva was less variable than that determined from urine, serum, or breath samples, indicating that saliva was most suitable. The entry rate of CO2 was 34% greater for lactating does than for dry does, reflecting greater feed intake and milk production by lactating does. Energy requirements derived from the different equations tested yielded differed considerably, suggesting that the choice of equation warrants careful consideration and that further research is necessary to identify most appropriate equations for particular experimental or production conditions.
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