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Anim. Reprod.; 9(3): 370-387, 2012.

Artigo em Inglês | VETINDEX | ID: vti-8352

Resumo

Reproduction continues to be a critical component to maintain a dairy farm economically viable. For every farm and for every cow, there is an optimum time for pregnancy, which is mostly influenced by level of production, persistency of lactation, and parity. In general, as production decreases, lactation number increases, and persistency of lactation decreases, cows should be bred sooner postpartum and pregnancy obtained early in lactation. The voluntary waiting period is determined based on the desired interval postpartum to pregnancy and the pregnancy rate of the farm. As pregnancy rates increase, the voluntary waiting period can be delayed, particularly when milk production is high. Studies in the literature have compared several breeding strategies to obtain a pregnant cow. In general, pregnancies obtained by artificial insemination are cheaper than those originated by natural service. The major reason is that AI programs result in similar or better reproductive performance and are cheaper to implement than natural service programs because of the high costs of acquiring and feeding bulls. Within the AI program, those that incorporate timed AI for first insemination followed by detection of estrus result in lowest median days open and more profit per cow, and the benefits of improving reproduction are greater when milk prices ar e low. The use of embryo technologies as a breeding program for lactating dairy cows, with the aim to improve reproductive performance, is only attractive when the differential in fertility relative to AI is large. In most cases, AI programs have to result in very poor fertility (<15%) for the typical results from embryo transfer (40-45% pregnancy) to be economically attractive at current costs. For dairy heifers, there is littl e justification to incorporate timed AI programs when detection of estrus is excellent, above 70%; however, for farms with detection of estrus below 60%, either timed AI for first AI followed by detection of estrus or timed AI alone improve reproductive performance and reduce the cost per pregnancy.(AU)

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