Kahn, H.E., Department of Forage Crops and Range Management, The Volcani Center, Bet Dagan, Israel
Lehrer, A.R., Department of Animal Reproduction, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

The TAMU model equations (Sanders & Cartwright, 1979) for the calculation of conception probability in beef cows were examined and modified in the light of data on individual cow reproductive performance and weight change. Additional factors, relating to the effects of suckling, sterility and age on the conception rate and its distribution, were identified and quantified on the basis of data obtained from a commercial herd in Israel. The modified and additional equations were incorporated in a simulation model and validated with data from another commercial herd, pertaining to two consecutive reproduction cycles. The results showed close correspondence between recorded and simulated conception distribution during the mating period and total conception rate, and sensitivity to the nutritional and other factors which affect reproductive performance. © 1984.