The effects of inbreeding on productive and adaptive traits and temperament of tropical beef cattle

Data from up to nine calf crops of zebu-derived cattle reared in a dry, tropical environment were examined to determine the effects of inbreeding of the animal and of its dam on a range of productive traits (growth, fertility, feed conversion efficiency, carcass and meat quality attributes), adaptive traits (resistance to cattle ticks, gastrointestinal helminths, buffalo flies and heat stress) and temperament (flight speed). In general, inbreeding had adverse effects on all performance traits examined. However the effects over the 0-20% range of inbreeding that existed in this study were generally minor, and except for some growth and fertility traits, were not of statistical, economic or biological significance. For a 1% increase in inbreeding of the animal (F-A), there was a corresponding decrease of 0.04, 0.72, 1.07, 1.49, 2.07 and 1.52 kg in live weight at birth, 6 months, 12 months, 18 months, 30 months and 54 months, respectively. There was no significant effect of F-A on any measure of fertility of heifers joined for the first time at about 27 months of age, or for cows at their third and subsequent joinings. However, F-A reduced pregnancy rate, increased days to calving and unfavourably affected calving outcome (P < 0.05) when heifers were joined with their first calf at foot. These effects were independent of the effects of inbreeding on live weight. F-A had consistent negative effects on scrotal circumference at weaning, yearling and 18 months of age, but these effects were mainly through the effect of inbreeding on live weights. F-A increased meat toughness but had no significant effect on other meat quality or carcass attributes, feed intake, feed conversion efficiency, resistance to parasites and heat stress or on temperament. Inbreeding of the dam had no economic or biological effect on any of the traits examined. Selection for high growth rate to 600 days readily overcame any deleterious effects of inbreeding on live weights. For herds where initial inbreeding is low and active inbreeding is avoided, the economic effects of inbreeding are likely to be small. (C) 1998 Elsevier Science B.V.