Nutritional Management of Dairy Cows During the Transition Period
Dry period and transition nutritional strategies may be evaluated based on their influence on critical factors of 1) dry matter intake (DMI) around and after parturition, 2) subsequent milk production and composition, 3) degree of postpartal negative energy balance and body fat mobilization, 4) concentrations of energy-yielding compounds (triglycerides and glycogen) in liver, 5) calcium homeostasis, and 6) metabolic and ruminal adaptations to lactation. Obesity at calving is a well-known risk factor for health problems and suboptimal productive performance. Likewise, extreme under-nutrition may adversely affect postpartum outcomes. Based on the body of research conducted, feeding to approximately meet the requirements of cows for energy and protein (and of course other nutrients such as minerals and vitamins), without greatly exceeding energy requirements, is the approach most likely to achieve consistent success. This concept may be applied by several approaches and with varying dietary formulation, ranging from limit-feeding of moderate-energy diets to ad libitum feeding of high-roughage low-energy diets. Requirements for metabolizable energy for dry cows and first-gestation heifers are quite modest (ca. 100 MJ) and can be met with relatively low-energy diets. Conversely, diets high in maize silage or whole-crop cereals and supplemented with additional concentrates will result in an excess of energy intake relative to requirements, as cows do not regulate intake to meet energy needs over the short-term. Energy over-consumption leads to marked decreases in DMI leading up to calving. The accumulated evidence is that these higher energy diets fed during the dry period do not increase subsequent milk production or energy balance. Our laboratory has obtained data from several lines of evidence to indicate that overfeeding results in changes analogous to obesity, with poor DMI, substantial body fat mobilization, increased fat deposition in the liver, and, if severe, impairment of liver function. Providing a consistent balanced diet of high bulk that will limit total energy intake with ad libitum DMI minimizes the drop in DMI before calving. Data available to date indicate that these high-bulk diets, if formulated and fed to meet nutrient requirements of the cows, decrease body fat mobilization, blood ketones, and liver fat accumulation postpartum. Bulky feeds such as straw must be processed so that cows do not sort the total mixed ration (TMR). The conclusions here are in agreement with the biologically sensible concept of priming the system for subsequent metabolic adaptations and production, rather than attempting to suppress these adaptations by high energy feeding during the dry period. Controlling energy intake to near the cows requirements also is consistent with observations in other animals and humans. These concepts must continue to be evaluated under both research and field settings, particularly with regard to reproduction and longevity. On the basis of available scientific data as a whole, however, we conclude that requirements for energy (and other nutrients) should be met but not greatly exceeded during the dry period. Careful feeding management is critical to ensure that formulated nutrient intakes are actually achieved in practice. How do we feed cows during the dry period and transition period to prevent health problems and promote high productivity? Although researched for several decades, the topic remains controversial yet timely for several reasons. Continued increases in milk production per cow, and perhaps more importantly milk energy per cow, demand optimized nutrition to maintain this productivity while keeping cows healthy. As a result of continued selection for high productivity and high peak milk during early lactation, fertility of dairy cows continues to worsen (Garnsworthy and Webb, 1999; Mee, 2004; Pryce et al., 2004). Most of the health problems encountered by dairy cows during lactation occur at or shortly after calving. The incidence of these health problems may be impacted by prepartum nutrition. The feed industry has developed and marketed a large number of additives, products, and programs for dry cows. Many of these products have merit in certain circumstances, but many also are expensive products that carry the potential for overuse when not indicated (Overton and Waldron, 2004). Overall, then, the dry period and transition play a critical role in profitability of dairy farming.
James K.Drackley
Department of Animal Sciences, University of Illinois, IL, USA
国际会议
奶牛营养与牛奶质量国际研讨会(ist International Symposium on Dairy Cow Nutrition and Milk Quality)
北京
英文
90-101
2009-05-04（万方平台首次上网日期，不代表论文的发表时间）