Sheahan A J, Kay J K, Roche J R
DairyNZ, Private Bag 3221, Hamilton, 3240, New Zealand.
J Dairy Sci. 2013;96(12):7818-29. doi: 10.3168/jds.2013-6981. Epub 2013 Oct 4.
Supplementary feeds are offered to grazing dairy cows to increase dry matter (DM) and metabolizable energy (ME) intakes; however, offering feed supplements reduces pasture DM intake, a phenomenon known as substitution. The objective of the study was to investigate changes in blood factors associated with intake regulation in monogastric species in pasture-fed dairy cows supplemented with either a starch- or nonforage fiber-based concentrate. Fifteen multiparous Friesian × Jersey cross cows were assigned to 1 of 3 treatments at calving. Measurements were undertaken in wk 8 of lactation. Treatments were pasture only, pasture plus a starch-based concentrate (3.5 kg of DM/cow per day; STA), and pasture plus a nonforage fiber-based concentrate (4.4 kg of DM/cow per day). Pelleted concentrates were fed at an isoenergetic rate in 2 equal portions at a.m. and p.m. milkings. Measurements were undertaken to investigate differences in pasture DM intake, feeding behavior, and profiles of blood factors for 4h after a.m. and p.m. milkings, the periods of intensive feeding in grazing cows. Supplementing cows with STA concentrate reduced pasture DM intake to a greater extent than the fiber concentrate, although time spent eating did not differ between treatments. The blood factor response to feeding differed between the a.m. and p.m. feeding events. Blood factors associated with a preprandial or fasted state were elevated prefeeding in the a.m. and declined following feeding, whereas satiety factors increased. In comparison, the blood factor response to feeding in the p.m. differed, with responses to feeding delayed for most factors. Plasma ghrelin concentration increased during the p.m. feeding event, despite the consumption of feed and the positive energy state remaining from the previous a.m. feeding, indicating that environmental factors (e.g., sunset) supersede physiological cues in regulating feeding behavior. The greater reduction in pasture DM intake for the STA treatment in the p.m. may be related to the level of hunger or satiety before the feeding event and not solely to the consumption of supplement. Data indicate that neuroendocrine factors are, at least in part, responsible for the substitution of pasture for supplementary feeds.
给放牧的奶牛提供补充饲料，以增加干物质（DM）摄入量和可代谢能量（ME）摄入量；然而，提供饲料补充剂会降低牧场干物质摄入量，这一现象被称为替代效应。本研究的目的是调查在以牧场为食的奶牛中，补充淀粉或非饲草纤维浓缩物后，与单胃动物摄入调节相关的血液因子变化。15头经产的弗里生×泽西杂交奶牛在产犊时被分配到3种处理中的1种。在泌乳第8周进行测量。处理方式分别为仅放牧、放牧加淀粉基浓缩物（3.5千克干物质/头·天；STA）和放牧加非饲草纤维基浓缩物（4.4千克干物质/头·天）。颗粒状浓缩物以等能量速率在上午和下午挤奶时分两次等量投喂。进行测量以研究上午和下午挤奶后4小时（放牧奶牛的集中采食期）牧场干物质摄入量、采食行为和血液因子谱的差异。用STA浓缩物补充奶牛时，牧场干物质摄入量的减少幅度比纤维浓缩物更大，尽管各处理间采食时间没有差异。上午和下午采食事件的血液因子反应不同。与餐前或禁食状态相关的血液因子在上午采食前升高，采食后下降，而饱腹感因子增加。相比之下，下午采食时的血液因子反应不同，大多数因子的采食反应延迟。尽管采食了饲料且前一天上午采食后仍处于正能量状态，但下午采食期间血浆胃饥饿素浓度仍升高，这表明环境因素（如日落）在调节采食行为方面取代了生理信号。下午STA处理的牧场干物质摄入量减少幅度更大，可能与采食事件前的饥饿或饱腹感水平有关，而不仅仅与补充剂的采食有关。数据表明，神经内分泌因子至少部分导致了牧场被补充饲料替代。
