A STUDY OF FACTORS AFFECTING EFFICIENCY OF FEED CONVERSION IN RED DANISH HEIFERS

Data from 692 daughters of 38 Red Danish bulls, tested as heifers in the Danish cattle progeny testing stations 1963–64, were analysed to provide information on the efficiency of feed utilization by dairy cows. The results showed that because of, the feeding system adopted, efficiency measured as FCM per food unit was automatically closely related to FCM yield. Analysis based on pooled, within-bull, values showed that (a) both efficiency and FCM were negatively associated with body-weight gain during lactation, suggesting that feed allowances per unit FCM were low in relation to those for maintenance, (b) weight measured after calving was positively associated with efficiency and FCM yield whereas the association of these latter variables with weight at the end of the winter period was negative, and (c) the gain in weight during lactation was much lower in cows heavy at calving and higher in those heavy at the end of the winter. The between-bull correlations, although less reliable than the within-bull values, clearly indicated that the selection for FCM yield would result in increased cow weight. It is suggested that the selection of dairy cattle should not be based solely on milk yield but that suitable adjustments should be made so that selection for efficiency is safeguarded. Quantitative assessment of such adjustments would necessitate changing feeding procedures at central testing stations. © 1968, Cambridge University Press. All rights reserved.