Evaluation of a bull rotating system using natural mating: effect on the reproductive performance of zebu cows

摘要

In order to determine the effect of a rotational sire system on the reproductive performance in zebu cows, six Brahman bulls with sexual experience were used. These animals were evaluated previously for breeding soundness. A six weeks breeding period was subdivided in two non-consecutive three week period for rotation of bulls in a fixed mating system (EF; group A weeks 1, 2, and 3; and B weeks 5, 6, and 7) and a rotational system (ER; group A weeks 5, 6, and 7; and B weeks 1, 2, and 3). A total of88 mulliparous zebu cows with calf at foot and 61+-36 days postpartum, on average, were used. Blood samples to assess progesterone and ultrasonographic examination of the ovaries twice weekly, to evaluate ovarian function, and measurement of body condition, were taken. Response variables were the relation among cows that may become pregnant with the ones in anestrus, transition to cyclicity and cyclicity; besides, a comparison between cows cycling and pregnant was evaluated. During weeks 1-3 in group A(EF) more cows were in anestrus (group p=0.03 and week p=0.001); and in B (ER) more cows were in transition (group=0.003). During weeks 5-7, in group B (EF) cows in transition were reduced (week p=0.03) and 83 percent of the cows were pregnant. In groupA (EF) there were more cows pregnant (54 percent) in the first three weeks as compared to 46 percent in group A (ER) in weeks 5-7. It is possible that results were influenced by cows body condition. It is concluded that overall fertility of the herd (35percent) was related to amount of cows in anestrus (28 percent). This relationship was not affected by the type of mating program used.