Effects of RFI classification and strategic supplementation of low quality diets to optimize beef cow performance

肉牛通常只在一年中的有限时间内满足营养需求。在一年中的其余时间，奶牛可能会被喂食缺乏或限制一种或多种营养的日粮。安大略省拥有生产营养丰富的牧草的能力，如果全年随意饲喂，这些牧草可能被浪费在肉牛身上。牛犊生产者可以通过将这些优质牧草喂给断奶的牛犊和种植牛来赚取更多的钱。需要制定营养战略，在有营养战略性补充的地方使用质量较低的牧草，以确保怀孕奶牛的健康和繁殖成功。这种方法为降低生产成本和增加牛犊生产者的回报提供了最可行的解决方案。这项研究将评估以下营养管理计划：1)随意饲喂优质饲料，以确保所有必需营养素的摄取，但代价是浪费营养物质，并在奶牛身上沉积多余的状况；2)饲喂大量作物残渣，这可能会在不补充的情况下损害奶牛的营养需求；以及3)战略性补充低质量日粮，仅在特定的时间间隔(每周、每周两次或每周3次)提供补充营养素。还需要研究来检查肉牛饲料效率或剩余饲料摄入量(RFI)的遗传学，并在不同的营养计划中评估这些遗传学。被归类为低RFI的奶牛在转换饲料用于维护和生产目的方面更有效率。如果奶牛群主要由低RFI奶牛组成，生产成本应该会降低。该项目的实验设计将测试特定营养管理计划的成功，以及特定遗传学在营养受限时的表现。这将包括评估生长性能、身体状况、繁殖性能和产犊性能。这个项目将展示特定的基因如何在不同的营养方案中发挥作用，以及如何使用低质量饲料的战略性补充来降低安大略省奶牛-牛犊生产者的生产成本。

The beef cow is often managed to meet nutrient requirements for only a limited time of the year. During the rest of the year, the cow may be fed diets, deficient or limiting in one or more nutrients. Ontario is blessed with the ability to produce nutrient dense forages which can be are wasted on beef cows if fed ad libitum throughout the year. Cow-calf producers can make more money on these high quality forages by feeding them to weaned calves and growing cattle. Nutritional strategies need to be developed to use lower quality forages where there is strategic supplementation of nutrients to ensure the health and reproductive success of the gestating cow. This approach offers the most viable solution to lower cost of production and increase returns to cow-calf producers. The study will evaluate the following nutritional management programs: 1) feeding high quality forages ad lib to ensure intake of all essential nutrients but at a cost of wasting nutrients and depositing excess condition on cows, 2) feeding high amounts of crop residues which may compromise the nutritional needs of the cow without supplementation, & 3) strategic supplementation of low quality diets such that supplementary nutrients are only provided at specific time intervals (weekly, twice per week, or 3 times per week). Research is also needed to examine genetics of feed efficiency or residual feed intake (RFI) in beef cows and evaluate these genetics across diverse nutritional programs. Cows classified as low RFI are more efficient at converting feed for maintenance and production purposes. Costs of production should decrease if the cow herd is made up predominantly of low RFI cows. The experimental design of the project will test the success of specific nutritional management programs and how specific genetics perform when nutrients are limiting. This will include assessing growth performance, body condition, reproductive performance, and calf production. This project will demonstrate how specific genetics perform across diverse nutritional regimens, and how strategic supplementation of low quality diets can be used to lower costs of production for Ontario cow-calf producers.