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Efficiency and performance of primiparous Angus cows raised in a range system
The aim of this study was to evaluate the efficiency and performance from calving to weaning of primiparous beef cows in three different biotypes in a range system. Forty-two primiparous Angus cows (three years of age) in body condition score (BCS) 3 (on a 1 to 5 scale) were classified into three groups according to body weight at calving: Heavy (431 kg on average, ranging from 405 to 485 kg); Medium (388 kg on average, ranging from 373 to 403 kg); and Light (348 kg on average, ranging from 293 to 369 kg). Milk production was estimated by weight-suckle-weight method. Calf production efficiency was determined by the adjustment of calf weaning weight (CWW) and pregnancy rate (PR) of cows, resulting in calf production index (CPI) = kg of weaning calves per cow (CWW*PR/100). Data were analyzed using GLM procedures in SAS software. Total weight gaing from calving to weaning was affected (P < .0.05) by biotype, once light and medium cows had 51 and 25 kg gain, respectively, while the heavy group had a 3 kg loss during the same period. Calves from heavy and medium groups were heavier (P < 0.05) at weaning as compared to light cow calves, being 166.5 ± 4.0; 166.0 ± 3.7 and 151.9 ± 4.3 kg, respectively. The CPI evaluation demonstrated that light and medium cow groups were able to produce more (P < 0.05) kilograms of calves (16.0 ± 0.4; 15.1 ± 0.4 kg, respectively) than the heavy group (14.0 ± 0.4 kg). There was no difference (P > 0.05) in calf production efficiency among groups, being 63.4 ± 1.6; 62.2 ± 1.4; and 59.6% ± 1.5, respectively for light, medium and heavy cows. However, light cows had lower (P <0.05) milk production and, as a result, lighter (P < 0.05) calves at weaning (151.9 ± 4.3kg) than medium and heavy groups, 166.0 ± 3.7; 166.5 ± 4.0 kg, respectively. In conclusion, cows in small and moderate biotypes and are more efficient as compared to larger frames in graze production systems.
Keywords: milk production, weight weaning, reproduction