During early lactation, both primiparous (PP) and multiparous (MP) cows are commonly fed diets rich in starch and low in forages to support their high energy requirements. Yet, the PP cows experience this dietary challenge for the first time, which might result in higher odds for them to develop rumen and systemic health disorders. The primary objective of this study was to evaluate the effect of decreasing the amount of forages in the diet on chewing and sorting behaviors and rumen and systemic health variables in PP and MP dairy cows. Twenty-four lactating Simmental cows [8 PP, average dry matter intake (DMI) of 19.1 ± 1.1 kg/d; 16 MP, average DMI of 22.5 ± 1.1 kg/d] with a body weight of 737 ± 90 kg and 50 ± 22 days in milk were used in this study. Cows were first fed a total mixed ration with 60% forage and 40% concentrate [on a dry matter (DM) basis] considered marginal in forages for 2 wk. Then, cows were switched to a diet low in forages with 40% forage and 60% concentrate (on a DM basis) for 4 wk. Reticular pH was measured continuously with wireless pH-sensors inserted into the reticulum to calculate the subacute ruminal acidosis (SARA) index. Chewing activity was measured with noseband-sensor halters, and feed sorting was measured weekly. Blood samples were collected weekly and analyzed for metabolic and inflammation markers. Switching PP and MP cows from a marginal to low-forage diet decreased the time spent eating and ruminating per kilogram of DM. Primiparous cows chewed longer per kilogram of DMI than MP cows. Also, the PP cows sorted more pronounced for longer particles and against fine particles than MP cows did. Despite higher rumination activity per kilogram of DMI and the adaptive sorting behavior, the PP cows spent on average 4.6 h/d longer below a pH of 5.8 and had a higher SARA index (i.e., area pH <5.8/DMI) than MP cows, especially during the first week of the low-forage diet (9.5 vs. 4.8). The concentration of liver enzymes increased with the low-forage diet, which was especially pronounced in the PP cows. In conclusion, this study demonstrated greater susceptibility of PP cows to SARA and liver damage than MP cows fed the same diets. Although PP cows demonstrated greater chewing and ruminating activity per kilogram of DMI, as well as adapted sorting behavior in favor of large particles during the low-forage high-starch feeding, they developed more severe signs of SARA. This suggests higher forage fiber requirements for PP cows and the need for improved feeding strategies to mitigate rumen fermentation disorders during early lactation in these cows.

在哺乳初期，初乳（PP）和多胎（MP）母牛通常都饲喂富含淀粉和低草料的饲料，以支持其高能量需求。然而，PP奶牛第一次遇到这种饮食挑战，这可能导致他们出现瘤胃和全身性健康疾病的几率更高。这项研究的主要目的是评估减少饲料中饲草量对PP和MP奶牛咀嚼和分选行为以及瘤胃和全身健康变量的影响。二十四头西门塔尔奶牛[8 PP，平均干物质摄入量（DMI）为19.1±1.1 kg / d；本研究使用16 MP，平均DMI为22.5±1.1 kg / d]，体重为737±90 kg，乳汁中为50±22天。首先给母牛饲喂总混合定量的饲料，其中混合饲料中含有60％的草料和40％的浓缩物（以干物质（DM）为基准），连续2周。然后，将母牛改饲低饲草，饲喂40％的草料和60％的精料（以DM为基础），持续4周。用无线pH传感器连续地测量网状pH，将其插入到网状结构中以计算亚急性瘤胃酸中毒（SARA）指数。用鼻带传感器吊带测量咀嚼活动，每周测量一次饲料分选。每周收集血样并分析其代谢和炎症指标。将PP和MP奶牛从少量饲喂改为低草饲喂，减少了每公斤DM的进食和反刍时间。初乳牛每公斤DMI的咀嚼时间比MP牛多。也，与MP奶牛相比，PP奶牛在较长颗粒和较细颗粒方面的分选更为明显。尽管每公斤DMI有更高的反刍活性和适应性的分选行为，但PP奶牛在pH值低于5.8时平均花费4.6 h / d，比MP奶牛具有更高的SARA指数（即，pH <5.8 / DMI）。尤其是在低饲草饮食的第一周（9.5比4.8）。低饲草饲料中肝脏酶的浓度增加，在PP奶牛中尤为明显。总之，这项研究表明，与饲喂相同日粮的MP奶牛相比，PP奶牛对SARA和肝脏损害的敏感性更高。尽管PP奶牛表现出更高的每千克DMI咀嚼和反刍活性，并且在低饲喂高淀粉喂养期间表现出对大颗粒有利的分选行为，他们出现了更严重的SARA体征。这表明PP奶牛的饲用纤维需求量更高，并且需要改进饲喂策略以减轻这些奶牛早期泌乳期间的瘤胃发酵障碍。