Prediction of heterosis from DNA fingerprints in chickens.

To assess the value of DNA fingerprints for the prediction of heterosis in chickens, retrospective analyses of data from three crossbreeding experiments and DNA fingerprints (DEP) of parental strains were conducted using two minisatellite and one middle-repetitive DNA probes. DEP bands were assessed on pooled DNA samples of 10-15 individuals per parental genetic group. The number of DEP bands evaluated in the experiments ranged from 81 to 139. The probes varied in their predictive value, but predictability of heterosis generally increased with multiple probes. Highly significant correlations (0.68-0.87) between band sharing ratios (SH) and heterosis were found in 25 crosses of White Leghorns in the first egg production cycle for age at sexual maturity, egg production, and mature body weight: traits with heterosis of 10% or more of the means. Regressions on SH explained 78.4% of the variation in heterosis in age at sexual maturity, 60.2% in egg production and 46.4% in mature body weight. For "broiler" traits with heterosis of < 1%, none of the correlations, based on 13 crosses, were significant. It was concluded that multilocus probe DFP of pooled DNA samples show promise as predictors of heterosis.

Antiketogenic effects of monensin in early lactation.

Holstein cows, second lactation or later, were gradually introduced to monensin-containing concentrate 1 wk prepartum and fed complete diets containing 15 and 30 g monensin/ton of DM for 3 wk postpartum. The addition of 30 g monensin/ton of feed decreased the incidence of subclinical ketosis from 6 out of 12 to 1 out of 12. The concentration of beta-hydroxybutyrate in blood from cows in the high monensin group was decreased during the 3-wk postpartum experimental period. Acetate: propionate ratios decreased from 2.32 in the control group to 1.44 in the high monensin group. Feed intake in the low monensin group was less than in the control group, but there were no significant differences in body weight changes or milk production. Monensin, when added to the diet, lowered milk fat in one of the monensin fed groups (low) but not in the other. Milk protein and lactose concentrations were not changed by the addition of monensin to the diet. No other adverse treatment effects were observed. Two cows from each group were culled for causes unrelated to treatment; the remainder completed the normal 305-d lactation and were rebred without problems.