Cow weights and reproduction on native rangeland and native rangeland-complementary forage systems.

Replicated cow herds of 15 Angus x Hereford (AH) and 15 Brahman x Hereford (BH) F1 cows each were placed on native rangeland (NR) or native rangeland-complementary forage (NRCF) systems. The NR was 8.1 ha of sagebrush-mixed prairie per cow-calf unit and the NRCF used the same mixed prairie complemented by .4 ha of double-cropped winter wheat and summer annual forage replacing about 30% of the mixed prairie for each cow unit. Calving seasons, spring for NR and fall for NRCF, were selected to complement the respective forage systems. Cow weights, reproductive performance, and population demographics were measured through seven calf crops to investigate their relationship to forage systems and cow breed types. Seasonal average cow weights increased from 484 +/- 7 (SE) kg during calf crop 1 to a peak weight of 568 +/- 8 kg at calf crop 5. Average weight of AH cows was 514 +/- 3 kg, compared with 539 +/- 3 kg for the BH cows (P < .01). Angus x Hereford and BH cows were 38 and 44 kg heavier, respectively, on the NRCF system than on the NR system. The average percentage of reproduction for AH cows was 90 +/- 2%, compared with 87 +/- 2% for the BH cows (P < .13). Both breeds had approximately 87 (AH) to 89% (BH) reproductive rate on the NR system. In contrast, AH cows had 94 +/- 2% reproduction on the NRCF system, compared with 84 +/- 2% for the BH cows.(ABSTRACT TRUNCATED AT 250 WORDS)