Problems of Feed Evaluation Related to Feeding of Dairy Cows

Summary To ration concentrates effectively to the individual cow, the dairyman needs to know (a) how much TDN the cow needs and how much can be fed profitably, (b) the TDN value of the forage to be fed, and (c) how much of the particular forage will be ingested. Thus, effective rationing requires a satisfactory feeding standard and information on the over-all nutritive value of the particular forage (s) to be fed. A limitation in either the feeding guide employed or the appraisal of the nutritive value of the forage naturally is reflected accordingly in the amount of concentrates fed. Recent attempts have been made to develop rapid and inexpensive, but indirect, methods for the assessment of the nutritive value of forage in programs which have become known as forage testing. The ultimate aim in the use of a forage-testing program is that of determining the kind and amount of concentrates that should be included in the ration of the individual cow as dictated by the feeding standard. Although forage-testing schemes in their present form and manner of application provide an estimate of the TDN value per unit weight of forage, they do not provide an estimate of the more influential determinant of the total energy intake, the expected forage intake. As a consequence of this limitation, and others which have been detailed in the text, it is concluded that forage-testing schemes contribute very little information of genuine value to the daily rationing and the improvement in milk yield of the individual cow. This is particularly true when the shortcomings of forage testing are considered in relation to the limitations of existing feeding standards and certain commonly encountered defects in practical feeding. Existing energy-feeding standards are both inadequate and ineffectively used in dairy farming practice. Some of the apparent shortcomings of present-day energy standards are indicated by the following conditions: (a) The data on which the standards are based were obtained with low-producing cows, (b) though the degree of effect varies from, ration to ration, increasing inputs of feed result in an ever-decreasing nutritive value (e.g., TDN) per unit of feed ingested and an increasing rate of body-tissue gain, (c) as a consequence, increasing inputs of energy above the existing feeding-standard allowances result in increasing outputs of milk, though at an ever-decreasing rate, (d) the milk-yielding potential of the dairy cow is increasing gradually and many more very high producers exist now than ever before; thus, existing energy standards are much too low for many cows now and are becoming progressively less adequate with passing time, even for the national average herd, (e) current feeding standards take very little, or no, account of the effects on production of dry-period feeding and the consequent storage, and subsequent utilization, of body tissue as a source of milk energy, (f) the TDN values recorded in tables of feed values and used in conjunction with feeding standards for the purpose of rationing have been determined usually at about the maintenance level of intake, and (g) in view of this [(f) above], and the depressing effect of increasing planes of nutrition on the milk-producing values of the ration [(b) above], it is obvious that the dietary energy requirement per unit of milk produced increases with increasing level of feed intake or, conversely, with increasing output of milk, per unit of time. In view of the limitations of existing feeding standards, a tentative energy standard is presented here in which the TDN allowances are graduated in terms of milk output per day. This attempt to develop a more versatile feeding guide, which accounts for the level-of-in-take effect, is based in part upon theoretical considerations and in part on directly determined requirements. In this standard the following amounts (lb.) of TDN above the maintenance allowance are recommended for the production of 1lb. of 4% FCM, when the ranges in daily milk yield (lb.) are as follows: 0 to 10, 0.30; 11 to 20, 0.31; 21 to 30, 0.32; 31 to 40, 0.33; 41 to 50, 0.35; 51 to 60, 0.37; 61 to 70, 0.40; 71 to 80, 0.43; 81 to 90, 0.47; and 91 to 100, 0.53. Body tissue gain or utilization modifies the dietary requirement for energy. For example, the utilization of 100lb. of body tissue could provide sufficient energy to support the production of approximately 400lb. of 4% FCM. As a consequence, the utilization of body tissue, which (when it occurs) usually occurs during the first 75 days of lactation, would reduce the dietary requirement correspondingly during this period of time. The lack of, or ineffective, use of existing feeding standards contributes to other defects in feeding practice. Some cows receive insufficient amounts of energy at all times. Other cows receive a sufficient total amount of feed per year, but it is distributed ineffectively. A common expression of this defect is that of providing too little feed early in lactation and too much feed late in the lactation period. Associated with this is the failure to make effective use of the tissue gained during the dry period. Feeding plans followed in practice during early lactation demand that too large a proportion of the energy needed for milk production be provided by the catabolism of body tissue. Some degree of tissue utilization is inevitable for those cows whose milk-producing potential exceeds the limits of their appetite or stomach capacity. Also, this process is a necessity if the high-producing cow is to realize her maximum yield. Nevertheless, the alternate gaining of body tissue and its subsequent use to support lactation is inefficient energetically and should be restricted to a minimum. The finding by dairy-cattle geneticists that short-period lactation records reflect the total lactation-period yield suggests that feed inputs during the dry period and early lactation have a cumulative effect on the yield of milk throughout the lactation period. As a consequence, it is essential that the input of energy be so distributed that the output of milk reach the maximum level as soon as possible after calving, in order to attain the maximum yield for the total lactation period. A related time-distribution of input defect inherent in the application of all feeding standards needs to be remedied. This one is concerned with the fact that milk output dictates what the feed input should be, with a considerable time lag. In view of the shortcomings of forage-testing schemes and existing feeding standards, and the common defects in practical feeding, a simple feeding plan is proposed as a remedy. The main features of this plan are (a) the ad libitum feeding of high-quality forage, (b) accustoming the cow to a large intake of concentrates gradually, beginning a few weeks before the end of gestation, (c) after calving, allowing the cow to set her own pace on her intake of concentrates under the careful scrutiny of the dairyman and until she attains her maximum appetite or milk yield, (d) after this stage, determining by astute experimentation the lowest level of concentrates which is without effect upon the milk yield. This plan obviates the need for energy-feeding standards and tables of feed value and provides for the effective distribution of feed during the lactation cycle. However, it requires the measurement of the milk output and close attention to the individual cow.