Performance efficiency of pasture-raised primiparous beef cows of three different biotypes and two milk production levels

ABSTRACT

Background: Productivity and efficiency of beef production systems should be estimated based on cow size, calf growthrate and cow reproduction rate, which are critical factors for the evaluation of production characteristics of beef cattle ofdifferent biological types. One of the ways to measure beef cow productivity is based on the ratio of calf weaning weightto cow weight. The purpose of this study was to evaluate the performance and reproductive efficiency of primiparous beefcows of three different biotypes and two milk production levels, from calving to weaning, in pasture-raised beef systems.Materials, Methods & Results: Forty-two primiparous Angus cows were classified according to body weight at calving,as follows Heavy (431 kg); Medium (388 kg); and Light (348 kg). Cow efficiency as a function of biotype was evaluatedat two different moments calving and weaning, based on the ratio of calf weight to cow weight*100 (in kilograms). Calfproduction efficiency was determined based on the ratio of calf weaning weight (CWW) to cow pregnancy rate (PR),resulting in the calf production index = kg of weaning calves per cow (CWW*PR/100). The experimental design was acompletely randomized factorial 3 x 2 x 2 design (three biotypes x two calf sexes x two milk production levels). The resultswere subjected to ANOVA and F-test. The Light and Medium cow groups produced more (P < 0.05) kilograms of calf perkilogram of cow (16.0 and 15.1 kg, respectively) than the Heavy group (14.0 kg). Light cows showed lower (P < 0.05) milkproduction and, as a result, lighter (P < 0.05) calves at weaning (151.9 ± 4.3 kg) than Medium and Heavy groups, 166.0± 3.7; 166.5 ± 4.0 kg, respectively. At beginning of the breeding season, cows of the Lower milk production group wereon average 27.49 kg heavier than cows in the Higher milk production group. There was an interaction (P < 0.05) betweentotal milk [...]