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Scroll down for the English version Bill Weiss 奥特奇郭闪闪翻译 奶牛营养需要第八修订版，现在是NASEM，于2021年12月发布，取代了2001版。这本新书有一章专门介绍围产期奶牛营养。 跟其他阶段一样，围产期奶牛（妊娠最后几周和泌乳期前几周）需要营养物质来保证机体运转，如维持，产奶或初乳和妊娠。 围产期这段时间干物质采食量(DMI)和营养需要变化非常快，所以几乎不可能做出能满足围产奶牛营养需要的日粮。 在产犊前的最后几天，每天采食量减少的同时伴随着胎儿的快速生长，这需要额外的营养，此时初乳开始合成，这也需要非常多的能量，蛋白质，一些矿物质和维生素。 产犊后产奶量和采食量均会增加，但产奶所需营养物质的增加速度快于干物质采食量的增加。 鉴于这些挑战，除了围产奶牛的营养需要，新的NASEM也强调了一些可以减少分娩期间常出现的健康问题的营养措施。 与前一版相比，整个干奶期平均营养需要量变化不大；但是，干奶期的蛋白和能量需要更低，而围产期的蛋白和能量需要更高。用于计算这些需要量的新公式比以前的公式更准确，能更好地预测干奶牛和围产牛的营养需要量。 上一版NRC认为用淀粉代替一些纤维来增加围产期日粮的能量密度，可以减轻产前干物质采食量的正常下降。然而，基于过去15年的试验发现，增加围产期日粮的淀粉浓度没什么好处，而且可能会增加产后代谢紊乱。2021年的委员会不建议这种做法。 我们知道产犊前后氧化应激显著增加。氧化应激增加一点是正常的，也是正常分娩所需要的，但增加过度就会抑制免疫功能。 为了对抗过量的氧化应激，该委员会建议围产期奶牛每天摄入大约2000IU的维生素E，这是之前委员会推荐量的两倍。其他维生素和矿物质的需要量与上一版本相同。 新版讨论了围产期营养对产犊后产奶量的影响。委员会总体得出的结论是，饲喂比妊娠后期蛋白需要（大约12%的粗蛋白）更高的蛋白对产奶量没有影响。也就是说，给围产牛饲喂过量的蛋白收效甚微，还会增加饲料成本。 但对于后备牛却不是这样。给妊娠后期的青年牛饲喂超过维持和妊娠蛋白需要（日粮粗蛋白大约在15%）的蛋白通常会在产犊后产生更多的牛奶和乳蛋白。 然而，如果要使后备牛达到一个合理的生长目标（加上因胎儿生长导致的体重变化，每天约0.73kg），定制日粮的粗蛋白含量大约需在15%。 委员会认为，如果能满足产前的能量需求，饲喂更高能量密度的日粮对产奶量没有影响。初乳的产量和质量对犊牛的健康极其重要，但委员会发现，大多数围产牛的试验并没有包含初乳这个部分。因此，我们不知道当前的营养推荐量对初乳是否足够。 初乳营养物质浓度很高，代表了一个重要但是短期的营养需求。例如，首次挤出的20磅初乳所含的能量和维生素A大约相当于一头妊娠晚期的奶牛的一天所需。 围产期这一章包含了关于常见的健康问题以及减少这些问题的营养上的推荐量的深入讨论。 对于低血钙，推荐使用负的DCAD日粮或含有钙吸附剂的日粮。 此外，不给围产牛饲喂过量的磷和镁也很重要。临产前干物质采食量降低幅度能够最小化可以减少酮病。达到这个目的的方法就是在整个干奶期饲喂刚好能满足奶牛能量需要的高纤维日粮。 NASEM开发的用于预测干奶牛和围产牛DMI的新公式涉及日粮NDF含量，NDF较高的日粮预采食量下降幅度小于NDF较低的日粮。 在下个月的奥特奇中国反刍技术年会中，奥特奇也为客户与朋友邀请到了第8版《奶牛的营养需要》审稿委员会的James Drackley博士，为您带来关于微量元素与蛋白质的解读。请联系您当地奥特奇销售，获取更多会议咨询。 -【END】- What’s new with transition cow nutritional recommendations Bill Weiss The Eighth Revised Edition of the Dairy NRC (National Research Council), now called NASEM (National Academies of Science, Engineering and Medicine) was published in December 2021, replacing the previous version published in 2001. The new book has a chapter dedicated to transition cow nutrition. Just like other animals, transition cows (cows during the last few weeks of gestation and the first few weeks of lactation) require nutrients to perform functions such as maintaining themselves, producing milk or colostrum and maintaining pregnancy. However, formulating diets to meet the nutrient requirements of transition cows is almost impossible because both daily dry matter intake (DMI) and nutrient needs are changing very rapidly during this time. During the last several days prior to calving, daily intake decreases while at the same time, the fetus is growing rapidly, requiring extra nutrients, and colostrum is starting to be produced – which also requires very high amounts of energy, protein and some minerals and vitamins. After calving, both milk production and intake are increasing, but the nutrient demand to produce milk increases more rapidly than does DMI. Because of these challenges, in addition to describing nutrient requirements for transition cows, the new NASEM emphasizes nutritional practices which will reduce the prevalence of health disorders that commonly occur around parturition. Compared to the previous version, average nutrient requirements for dry cows did not change greatly; however, protein and energy requirements are lower for far-off dry cows and greater for pre-fresh cows. The new equations used to calculate those requirements are more accurate than the previous ones and should better estimate the nutrient needs of both far-off and pre-fresh cows. The previous NRC recommended increasing the energy density of pre-fresh diets by replacing some fiber with starch because it was thought it might mitigate the normal drop in intake that occurs prepartum. However, based on experiments conducted in the last 15 years, increasing the starch concentration of pre-fresh diets usually provides little benefit and may increase health disorders after calving. The 2021 committee did not recommend that practice. We know that oxidative stress increases markedly around calving. Some increase in oxidative stress is normal and is actually desirable for normal parturition – but when it becomes excessive, immune function can be inhibited. To combat excess oxidative stress, the committee recommended that pre-fresh cows be fed about 2,000 IU of vitamin E per day, which is twice what the previous committee recommended. Requirements for the other vitamins and minerals are about the same as given in the previous version. The new publication discusses the effect of prepartum nutrition on milk production after calving. In general, the committee concluded that feeding more protein than what a late-gestation cow requires (approximately 12% crude protein) did not affect milk yield. In other words, feeding excess protein to pre-fresh cows will provide little benefit but will increase feed costs. That was not true for springing heifers. Feeding protein in excess of that needed for maintenance and pregnancy (diets with approximately 15% crude protein) to late-gestation heifers often results in greater milk and milk protein production after calving. However, if a reasonable growth target (approximately 1.6 pounds per day in addition to the bodyweight change associated with fetal growth) is included when formulating diets for springing heifers, dietary requirements would calculate out to about 15% crude protein (CP). The committee concluded that feeding more energy-dense diets prepartum did not affect milk yield if prepartum energy requirements were met. Colostrum yield and quality is extremely important to the well-being of calves, but the committee noted that most experiments with pre-fresh cows did not include colostrum as a response measure. Therefore, we do not know whether current nutrient recommendations are adequate for colostrum. Colostrum is extremely nutrient-dense and represents a significant but short-term need for nutrients. For example, 20 pounds of first-milking colostrum has about as much energy and vitamin A as that needed to maintain a late-gestation cow for one day. The transition cow chapter contains an in-depth discussion of common health disorders and nutritional recommendations to reduce the prevalence of those problems. For hypocalcemia, a negative DCAD diet or a diet containing calcium binders are recommended. In addition, it is important that pre-fresh cows not be fed excess phosphorus and be fed excess magnesium. Ketosis is reduced if the drop in DMI that usually occurs shortly before calving is minimized. One way to do this is to feed high-fiber diets that just meet the energy requirements of cows during the entire dry period. The new equations developed by NASEM to estimate DMI of dry and pre-fresh cows include dietary NDF concentration, and diets with higher NDF have a lesser estimated decrease in intake prepartum than diets with lower NDF. |
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