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

肉牛通常只能在一年中有限的时间内满足营养需求。在一年的其余时间里，奶牛可能会被喂食缺乏或限制一种或多种营养物质的饲料。安大略省有能力生产营养丰富的饲料，如果全年随意喂养，这些饲料可以浪费在肉牛身上。通过将这些高质量的饲料喂给断奶的小牛和正在生长的牛，小牛生产者可以从这些饲料中赚取更多的钱。需要制定营养策略，在有营养补充的情况下使用低质量的饲料，以确保妊娠奶牛的健康和繁殖成功。这种方法为降低生产成本和增加小牛生产者的回报提供了最可行的解决方案。该研究将评估以下营养管理方案：1)饲喂高质量的饲料，以确保所有必需营养素的摄入，但代价是浪费营养，并将多余的条件沉积在奶牛身上；2)饲喂大量的作物秸秆，这可能会损害奶牛的营养需求，而不进行补充；3)策略性地补充低质量的日粮，以便只在特定的时间间隔（每周、每周两次或每周3次）提供补充营养素。还需要研究肉牛饲料效率或剩余采食量（RFI）的遗传学，并在不同的营养方案中评估这些遗传学。被分类为低RFI的奶牛更有效地将饲料转化为维持和生产目的。如果奶牛群主要由低RFI奶牛组成，则生产成本应降低。该项目的实验设计将测试特定营养管理计划的成功，以及当营养有限时特定基因的表现。这将包括评估生长性能、身体状况、繁殖性能和犊牛产量。该项目将展示特定基因如何在不同营养方案中发挥作用，以及如何利用低质量日粮的战略性补充来降低安大略省小牛生产者的生产成本。

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.