Cazzuli Fiorella, Sánchez Javier, Hirigoyen Andrés, Rovira Pablo, Beretta Virginia, Simeone Alvaro, Jaurena Martín, Durante Martín, Savian Jean Victor, Poppi Dennis, Montossi Fabio, Lagomarsino Ximena, Luzardo Santiago, Brito Gustavo, Velazco J Ignacio, Bremm Carolina, Lattanzi Fernando A
Instituto Nacional de Investigación Agropecuaria (INIA), Programa Pasturas y Forrajes, Estación Experimental INIA Tacuarembó, Tacuarembó, Uruguay.
Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PEI, Canada.
Transl Anim Sci. 2023 Mar 10;7(1):txad028. doi: 10.1093/tas/txad028. eCollection 2023 Jan.
Supplementing growing cattle grazing native subtropical grasslands during winter improves the low, even negative, average daily weight gain (ADG) typical of extensive animal production systems in Uruguay. Nonetheless, to render the practice profitable, it is crucial to control supplement feed efficiency (SFE), that is, the difference in ADG between supplemented and control animals (ADGchng) per unit of supplement dry matter (DM) intake. Little has been studied specifically on how SFE varies in these systems. The objective of this study was to quantify the magnitude and variation in SFE of growing beef cattle grazing stockpiled native grasslands during winter and assess putative associations with herbage, animals, supplements, and climatic variables. We compiled data from supplementation trials carried out in Uruguay between 1993 and 2018, each evaluating between one and six supplementation treatments. The average ADG of unsupplemented and supplemented animals were 0.13 ± 0.174 and 0.49 ± 0.220 kg/animal/day, respectively. In both cases, ADG decreased linearly as the proportion of green herbage in the grazed grassland was lower, but the ADG of unsupplemented animals was further reduced when winter frosts were numerous. Estimated SFE were moderately high, with an average of 0.21 ± 0.076 ADGchng/kg DM, resulting from average ADGchng of 0.38 ± 0.180 kg/animal/day in response to an average supplementation rate of 1.84 ± 0.68 kg supplement DM intake/animal/day (0.86% ± 0.27% body weight). No association was found between SFE and supplementation rate or type (protein vs. energy-based; > 0.05), but forage allowance negatively affected it, and herbage mass positively affected it, yet in a smaller magnitude, suggesting that a balance is needed between the two to maximize SFE. Weather conditions during trials affected SFE ( < 0.05), with greater SFE in winters with lower temperatures and more frosts. Daytime grazing time was consistently lower in supplemented animals compared to their unsupplemented counterparts, whereas ruminating time during the day was similar, increasing as the proportion of green herbage decreased. Herbage intake estimated from energy balance suggested the existence of some substitution effect. This agrees with the moderately high SFE and with the total digestible nutrients-to-protein ratio of these subtropical humid grasslands being higher than in semi-arid rangelands and dry-season tropical pastures but lower than in sown pastures.
在冬季为放牧于亚热带天然草原的生长育肥牛补充饲料，可改善乌拉圭粗放型畜牧生产系统中普遍存在的低水平甚至负增长的日均增重（ADG）情况。然而，要使这种做法有利可图，控制补充饲料效率（SFE）至关重要，即每单位补充干物质（DM）摄入量下，补充组与对照组动物的日均增重差异（ADGchng）。关于这些系统中SFE如何变化的专门研究较少。本研究的目的是量化冬季放牧于天然草原的生长肉牛的SFE大小及变化，并评估其与牧草、动物、补充饲料及气候变量之间的假定关联。我们收集了1993年至2018年在乌拉圭进行的补充试验数据，每个试验评估了1至6种补充处理。未补充和补充饲料的动物的平均日均增重分别为0.13±0.174和0.49±0.220千克/头/天。在这两种情况下，随着放牧草地中青草比例降低，日均增重呈线性下降，但当冬季霜冻较多时，未补充饲料动物的日均增重进一步降低。估计的SFE适中偏高，平均为0.21±0.076 ADGchng/千克DM，这是由于平均补充率为1.84±0.68千克补充DM摄入量/头/天（0.86%±0.27%体重）时，平均ADGchng为0.38±0.180千克/头/天。未发现SFE与补充率或类型（蛋白质型与能量型；>0.05）之间存在关联，但牧草供应量对其有负面影响，牧草质量对其有正面影响，但影响程度较小，这表明两者之间需要达到平衡以实现SFE最大化。试验期间的天气条件影响SFE（<0.05），在温度较低且霜冻较多的冬季，SFE更高。与未补充饲料的动物相比，补充饲料的动物白天放牧时间始终较短，而白天反刍时间相似，且随着青草比例降低而增加。根据能量平衡估算的牧草摄入量表明存在一定的替代效应。这与适中偏高 的SFE相符，也与这些亚热带湿润草原的总可消化养分与蛋白质比例高于半干旱牧场和旱季热带牧场，但低于人工草地的情况相符。
