A Study of the Short-Term Use of Iodinated Casein for Milk Production

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Abstract
Three experiments at dif-ferent locations were performed in which a total of 55 cows, divided into 5 groups, were fed thyroprotein while 17 cows served as controls. Data on milk production, fat test, body weight, efficiency of production, and monetary returns were obtained. During the first 60 days of thyroprotein feeding there was a comparative increase of 6.0 lb. fat-cor-rected-milk (FCM), or an increase of 15% in FCM production, but no change in fat test. By combining all treatment and control groups the increase was significant (P< 0.01). At the end of the 60-day period thyroprotein was gradually withdrawn over the next 0, 10, 20, or 30 days. The different methods of thyroprotein removal in this experiment caused no significant difference in total milk produced after the withdrawal, variations between observed and expected yield during this time, and regression coefficient for production or body weight during the time of withdrawal. The feed efficiency for milk production and its change as lactation progressed was similar in control and thyroprotein-fed groups when the period during and after thyroprotein feeding was considered as a unit in 2 of the 3 experiments. Monetary returns above feed costs were dependent on the response of the cows. It increased with groups that gave the larger responses, but monetary returns decreased with groups that gave average or below average responses.