Effects of winter and summer energy levels on heifer growth and reproductive performance.
Three heifer development trials were conducted with 337 crossbred heifers (125, 105 and 107 heifers in trials 1, 2 and 3, respectively) over a 3-year period. Heifers were fed low quality fescue hay ad libitum plus 0, 1.22 or 2.45 kg of ground ear corn (GEC) daily during the winter feeding phase of all three trials. Winter gains and final winter and summer condition scores increased (P less than .05) in each trial as winter level of GEC increased. In each trial, summer gains followed the reverse order of winter gains (P less than .05). Conception rate, mean number of days pregnant (as determined by rectal palpation) and adjusted weaning weight of progeny increased linearly with winter level of GEC when pooled over trials. Differences between animals fed 0 and 2.45 kg of GEC were significant. Conception rate and adjusted weaning weight of progeny of the heifers retained in the breeding herd increased (P less than .05) as level of GEC increased when data were pooled over trials. Calving date and percentage live progeny were not significantly affected by winter treatment. Summer daily gains and condition scores were increased by additional summer energy (2.45 kg GEC/day) in trial 3. Conception rate and mean number of days pregnant (conception date) favored heifers given the summer supplementary feeding (2.45 kg GEC) treatment. Among heifers retained in the breeding herd, there were no significant differences between the 0- and 2.45-kg GEC summer treatment groups in conception rate, calving date, percentage live progeny or adjusted weaning weight of progeny.
D000818:Animals; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D004734:Energy Metabolism; D005260:Female; D005298:Fertility; D012621:Seasons