A scientific approach to feeding dry cows
Our thanks to the author and Conference Organisers, a Committee consisting of both University and Industry colleagues.
The full paper will appear in the Conference Proceedings ('Recent Advances in Animal Nutrition - 2007', edited by Phil Garnsworthy and Julian Wiseman) published by Nottingham University Press in the autumn of 2007 www.nup.com
Courtesy of the 41st Annual University of Nottingham Feed Conference www.nottingham.ac.uk/biosciences/ah/research/conferences.php
Feeding dairy cows during the dry period has long been controversial. Opinions, often not substantiated by scientific data but perhaps based on personal experience, have variously favoured ‘steaming up’, limit-feeding, maximizing dry matter intake (DMI), feeding additional concentrates, feeding supplemental fats and oils, or feeding high-roughage lowenergy diets. Although considerable research has been conducted, no clear scientific consensus has emerged.
Application of total mixed rations (TMR) to dry cows allows delivery of consistent nutrient profiles to cows. Many studies published before the mid 1980s relied on forages and concentrates fed separately and often had questionable determinations of total feed intake.
A common flaw with the vast majority of research studies is their limited cow numbers, which makes reliability and repeatability of results problematic. Cow numbers are chosen to provide adequate replication for metabolic indicators (e.g., NEFA in blood, lipid in liver) or perhaps subsequent milk production data, but lack statistical power to truly detect meaningful differences in milk yield.
Moreover, studies cannot be conducted in university or research institute settings that include sufficient numbers of cows to determine influences of dry period nutrition on periparturient health disorders. Thus, inferences are made from selected metabolic variables (or metabolic profiles) consistent with diseased cows, whch will be highly correlated with actual disease incidence on a population basis; the validity of this assumption has rarely been questioned.
What then should be the scientific basis for determining optimal dry period nutrition? The desired outcomes must first be defined. Most would agree that minimizing periparturient health problems, maximizing subsequent productivity and achieving satisfactory fertility are desirable goals. Unfortunately, most producers, and many nutritionists and researchers, tend to look at these factors in isolation.
What is desperately needed is a more holistic or ‘systems’ approach that seeks to integrate effects of dry period nutrition on dairy profitability, which of course is a function of health and well-being, milk production and quality, feed conversion efficiency, reproductive success, and longevity. In this context, a program optimized for only one parameter, such as high peak milk, may not be the most profitable approach for dairy farms.
If research resources were not limited (of course highly unlikely to ever come to pass!), the scientific approach would be to conduct studies to titrate responses in these integrated outcome variables to different planes of nutrition, balances of nutrients, and diet composition. Studies would utilize adequate cows (hundreds per treatment) that would provide statistically reliable results for productivity, disease incidence, fertility, and longevity.
A further complication is that optimal nutrition may depend on or interact with dry period length, body condition, and age of the cows. Management factors such as overcrowding, poor comfort of stalls or cubicles, and frequent group changes likely will impact success on individual farms. Because a true factorial and systematic answer is highly unlikely to ever be delivered, field experiences with large numbers of farms and cows often may be more meaningful to practicing nutritionists than controlled research studies with questionable numbers of cows.
In the absence of being able to truly evaluate various dry period strategies under representative field conditions, extrapolations must be made from various metabolic and production responses in research studies. Dry period nutritional strategies may be evaluated based on their influence on critical factors of 1) 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, it appears that 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 surprisingly (perhaps) low-energy diets. Conversely, diets high in maize silage or whole-crop cereals and supplemented with additional concentrates will result in an excess energy intake relative to requirements, as cows do not regulate intake to meet energy needs over the shortterm. Energy over-consumption leads to marked decreases in DMI leading up to calving.
The accumulated evidence is that 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 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 TMR.
The conclusions here are in agreement with the concept of the ‘biological sense’ of ‘priming the system’ for subsequent metabolic adaptations and production as argued by Friggens and colleagues, 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. Pig producers consistently limit feed intake during gestation to avoid excessive loss of body condition after farrowing, with subsequent loss of fertility. Medical recommendations for human pregnancy generally advocate modest gain in excess of foetal and maternal reproductive tissues, to avoid complications with delivery, vitality of the newborn, and health of the mother.
There is continued need to evaluate these concepts 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 necessary, of course, to ensure that formulated nutrient intakes are actually achieved in practice.
Author: James K. Drackley, Ph.D
Department of Animal Sciences, University of Illinois at Urbana-Champaign, USA
