The aim of this study was to evaluate the influence of two sub-periods of the calving season and two cow maturity stages on the efficiency of beef cows and their calves. A total of 159 cow-calf pairs were divided by calving time (early or late) within the calving season and maturity stage (young or adult). Calves were weaned at 42 or 63 days after birth and evaluated until 210 days of age. Cows and calves had their development examined based on their weight and body condition score at calving, at weaning, and at 210 days. Reproductive performance was evaluated on the basis of time to become pregnant again. Milk yield was assessed by the direct method on three occasions spaced 21 days apart. Adult cows were heavier than young cows, at calving (398.5 vs 327.5 kg, respectively), weaning (397.3 vs 324.1 kg, respectively) at the end breeding season (424.1 vs 342.1 kg, respectively). Reproductive performance was influenced by calving time. Adult cows had higher pregnancy rates (83.75 and 69.17%, for early and for late calving, respectively) than young cows (57.03 and 35.01% for early and for late-calving, respectively). Calves from early-calving young cows weighed 158.8 kg at 210 days of age vs. 123.7 kg for those born from late-calving adult cows. However, latecalving cows produced 10.7% more milk than those that calved early in the season (227.0 vs 205.0 liters, respectively). Early calving associated with non-requirement of growth determine higher productivity efficiency in beef cows.
This study aimed to evaluate the production, reproductive performance, and productive efficiency of predominantly Charolais cows and their calves (Straightbred, ¾ C, ¼ N) according to body size at calving. Sixty-three cow-calf pairs were used and classified into three weight groups: Light (331.3±5.8 kg), Moderate (385.9±5.3 kg), and Heavy (424.4±6.2 kg). The classes were formed using half standard deviations above or below the average weight of the cows at calving. For each pair, the body weight was evaluated at calving, at weaning (63 days), at the beginning and at end of the reproductive period, and at 9 months for the calves. Pregnancy rates were similar (P > 0.05) between weight groups. The calves did not differ (P > 0.05) in terms of body weight and weight gain from calving until pregnancy diagnosis (210 days). The heavy cows had greater weight variations from 210 days to 270 days than the light cows. The calf production rate (kg calf/cow kept in herds) did not differ between weight groups. However, in relation to the weight of the cows at 210 days, light cows were 11.28% and 13.02% more productive (P < 0.05), than moderate and heavy cows, respectively. Light cows were more efficient than the other classes of cows at calving and at 210 days old. Our simulations showed that there were more kilograms for sale in herds of light cows (53.085 kg) than moderate and heavy cows (52.310 and 52.870 kg, respectively), while maintaining the structures of the herd constant. The size of the Charolais cow did not influence the weight of calves from calving until 7 months of age or their reproductive performance provided they were weaned early. The need for space for the maintenance of the cow-calf pair increased as the weight of the cows increased. In herds with smaller cows, higher numbers and a higher production of weight for sale are observed than in herds with moderate and heavy cows. Light cows were the most efficient at calving and during pregnancy diagnosis at 210 days.
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