Growth, Reproductive Performance and Feed Utilization of F1 Crossbred Beef Heifers Calving as 2-Year-Olds1

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Abstract
Four types of F1 heifers of different potential mature size were individually fed from 8 weeks after weaning until first calving. Information was collected on body growth, reproductive performance, and feed utilization. Sim-mental × Angus (SA), Charolais × Angus (CA), Hereford × Angus (HA), and Jersey × Angus (JA) heifers born in 3 different years were used. Heifers were bred as yearlings to the same Red Poll bull. Heifers were randomly allotted to two levels of feeding about 16 weeks after first breeding. One level was sufficient to give "normal" growth and the other 10% higher feed intake. Heifers receiving the highest level of digestible energy (DE) in the last half of pregnancy were heavier (P<.05) at first calving. This increase in weight apparently resulted from greater soft tissue growth rather than skeletal growth. The percentage of heifers pregnant to first service was similar for the four breed types. The gestation period averaged 282 days and did not differ significantly between type of heifer; however, it did differ (P<.05) between years of birth. On the average, calves born to JA heifers were lighter (P<.05) than calves from the other three types of heifers although birth weights varied between years within breed types of heifers. JA and CA heifers had a higher percentage of unassisted births than HA or SA heifers. Total intakes of dry matter, digestible protein, and digestible energy were greater (P<.05) for SA and CA heifers than for HA and JA heifers in a 129 day pregestation period and during gestation. DE intake per unit of metabolic weight was less (P<.05) for HA heifers than for the other three types during the pregestation period but did not differ among the four breed types of heifers during the gestation period. Heifers on the higher level of DE intake during gestation consumed more DE per unit of metabolic weight and gained more than those on the lower level of intake. DE intakes in this study were lower than amounts recommended by N.R.C. (1976) or A.R.C. (1965) for heifers of corresponding body size and weights gains. Estimates of DE required, calculated by use of an equation developed in California with individually penned heifers, were closer to the actual DE intakes than estimates using N.R.C. (1976) or A.R.C. (1965) tables. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.