Nutritional aspects of developing replacement heifers 1
Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and heifer pregnancy rates. Thus, postweaning growth rate was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target BW can increased pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target BW and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target BW guidelines, subsequent research demonstrated that the growth pattern heifers experience before achieving a critical target BW could be varied. Altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs. Recent research has demonstrated that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to lighter target BW ranging from 50 to 57% of mature BW.
Feed efficiency - how should it be used for the cow herd?
Andrew J. Roberts USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT, andy.roberts@ars.usda.gov Rick Funston University of Nebraska West Central Research and Extension Center, North Platte, rfunston2@unl.edu Travis Mulliniks USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT, travis.mulliniks@unl.edu Mark Petersen USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT Mike MacNeil USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT
Application of attribute recognition method for evaluating on sustained developmental degree of water resource systems.
Taking Ping Ba area as an example, this paper explores the method of comprehensive evaluation on sustained developmental extent of water resources systems and sets up an evaluation model by applying the attribute recognition theoretical model The result shows that it is coherence to the result of the fuzzy comprehensive evaluation method, meanwhile, this method is easy and understood, and it suit for evaluating on system quality with standardsKey words: water resources systems; attribute recognition theoretical model; fuzzy comprehensive evaluation method