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Take Home Messages
Introduction
Just 10 years ago, 10,000 kg herd averages were achieved only by the best managed herds; today 13,500 kg and more are becoming widespread. New individual milk production records seem to be set nearly every year. Just recently, a new world milk record was set in Wisconsin with 28,804 kg of milk produced in 365 days by a cow milked twice daily. In 1983, Walton (30) predicted that by the year 2000, top individual milk production records would approach 32,000 kg per cow per year, and the best herd averages would approach 16,000 kg per cow per year. Although in 1983, this prediction seemed unduly optimistic to me, it now seems like a near certainty. Although the Holstein breed dominates the dairy cow population in the U.S. (94% of the cows), the Jersey breed is making strong progress. Recently it was noted by Halladay (14) that one Jersey herd with the fifth highest production in the U.S. averaged 8,550 kg milk, 420 kg fat, and 325 kg of protein per year, considerably higher than the U.S. average for Holsteins (7,530 kg).
For at least a decade, the genetic progress in Holsteins for milk has been about 118 kg per year or 1180 kg for the 10 yr interval. In Jerseys, the genetic change for milk was estimated by Nizamani and Berger (23) to be 76 kg annually from 1960 to 1987, but 137 kg from 1983 to 1987. An important advantage of the pervasive genetic merit for high milk yields is that dairy cows are highly responsive to good environment in the broad sense of that word. In more markets, price incentives for low somatic cells encourage better control of udder infections; more precise engineering of milking systems and environmental management systems have reduced these constraints. Development of repartitioning agents especially bovine somatotropin (BST) now focus attention on the constraints associated with nutrition and feeding management which often now limit higher, but economic yields of milk. My objectives for this paper are to describe several key features of nutrition and management in high-yielding U.S. dairy herds and suggest several areas for improved efficiency.
Dairy Management Practices
We are fortunate to now have a National Animal Health Monitoring System which includes a major emphasis on dairy. In May, 1996 Part I: Reference of 1996 Dairy Management Practices, was published (2) and this document contains a large array of data concerning the management and conditions of U.S. dairying. Twenty states participated representing 83.1% of the U.S. milk cows. The data were obtained from 2,542 dairy producers who were surveyed with an on-farm questionnaire to provide a representative sample. A few of the results are presented in Table 1 and others will be referred to in subsequent sections.
Feed Sources
Although corn, sorghum, barley, and oats continue to be dominant feed grains for cattle and soybean meal and cottonseed meal are important plant protein supplements, many alternative feeds, sometimes called byproducts and more recently and correctly called co-products are used in cattle feeds in the U.S. A regional bulletin by Bath et al. (4) listed 357 tabular entries with 49 feedstuffs discussed individually. Many are well known, including molasses, brewers' grains, hominy feed, wheat bran, and corn distillers' grains. Others are less well known including almond hulls, apple pomace, buckwheat middlings, caproco, peanut skins, cow peas, vetch seeds, and many more. Most are available only in specific regions, for example, in California, and some only during certain seasons. Probably no more than 10 to 15 are consistently available in most of the U.S. Two national alternative feeds symposia have been held (1991 and 1995) to address the issues of these feedstuffs in the rations of dairy and beef cattle.
Table 1. Examples of U.S. dairy information and management practicesa
| Record-Keeping System | % Operations | % Dairy Cows |
| Hand written (as ledger) | 80.7 | 73.3 |
| Dairy Herd Improve. (DHIA) | 43.4 | 54.6 |
| Computer at the location | 15.1 | 36.9 |
| Computer -off location | 9.9 | 13.2 |
| Other system | 6.0 | 5.1 |
| Any system | 100.0 | 100.0 |
| Identification Type | % Operations | % Dairy Cows |
| Ear Tags (all types) | 81.2 | 87.3 |
| Collars | 22.3 | 16.3 |
| Photograph or sketch | 17.4 | 10.3 |
| Branding (all methods) | 4.9 | 12.3 |
| Implanted electronic ID | 0.3 | 0.2 |
| Tattoo (other than brucellosis) | 6.5 | 7.8 |
| Other | 10.1 | 6.4 |
| None | 8.8 | 2.5 |
aPart I: Reference of 1996 Dairy Management Practices (NAHMS)(2)
Grasser et al. (11) surveyed an array of industry representatives to evaluate the importance of 9 major by-products used in livestock feeding in California in 1992. These are listed in Table 2 with their individual tonnage and market value at that time. California is now the No. 1 milk producing state in the U.S. and these 9 by-products accounted for more than 2.5 million tons and about 27% of all concentrates used in California that year. Whole cottonseed was the most important by-product studied and it accounted for 31% of the total tonnage and it provided about 66% of the total crude protein (CP) and 53% of the total net energy for lactation (NEl) of the 9 by-products. Moreover, cottonseed constitutes about 62% of the total cotton crop yield (lint plus seed). It has become such a respected and sought after feed that now nearly 78% of the California cottonseed crop is fed to cattle, with 20% crushed for oil and the remainder is used for planting seed. Although it is grown across the southern U.S., it is valued so highly that it is shipped into all of the major dairy states on the northern tier. Brewers grains are used exclusively (100%) for cattle feed. It was determined that these 9 by-products could have provided the CP or NEl for more than 31% of the milk produced in California during 1992.
A nationwide survey of feedstuffs fed to lactating dairy cattle was recently completed by Mowrey and Spain (19). Dairy nutritionists from 28 states responded and the results were grouped into 5 regions, midwest (MW), northeast (NE), northwest (NW), southeast (SE), and southwest (SW). The predominant concentrate energy feed was corn followed by barley, sorghum, oats, and wheat. The primary protein supplements were soybean meal, cottonseed meal, soybean seed, and canola meal. The predominant by-products were whole cottonseed, soybean hulls, wheat milling by-products, and field corn milling by-products. Alfalfa (hay plus silage) was the principal forage fed, followed by corn forage (silage) and grass forage (hay plus silage) and 15 other forages. Probably the majority of U.S. dairy producers believes that to achieve top production, some alfalfa hay or silage must be part of the forage program. However, a recent article by Merrill (18) described a forage program without either alfalfa or corn silage in which production averaged 10,900 kg per year. A combination of grasses (primarily stored) provided the forage for this herd.
Table 2. Nine important by-products used in California in 1992a.
| By-product | Total as fed | Percentage of total Concentrate | Market Price | Total Value |
| tons (1000) | (%) | ($/ton) | $ (1000) | |
| Almond hulls | 498 | 5.19 | 66 | 32,881 |
| Beet pulp | 267 | 2.78 | 132 | 35,191 |
| Brewers grains (wet) | 409 | 4.26 | 35 | 14,318 |
| Citrus pulp, (17% DM) | 336 | 3.50 | 13 | 4,372 |
| Citrus pulp, (30% DM) | 91 | .95 | 35 | 3,182 |
| Corn gluten feed, (wet) | 15 | .15 | 57 | 829 |
| Corn gluten meal, (dry) | 16 | .17 | 358 | 5,853 |
| Whole cottonseed | 814 | 8.48 | 154 | 125,356 |
| Rice bran | 127 | 1.33 | 77 | 9,802 |
| Total | 2,573 | 26.81 | 231,786 |
aGrasser et al. (11)
As part of a symposium which addressed management for herds to produce 13,620 kg of milk per cow per year, Jordan and Fourdraine (17) sent survey forms to 128 producers who had been identified as high milk producing herds, and from 61 surveys returned, found that corn silage was the dominant forage fed followed by legume hay, legume silage, and grass hay. These producers on the average fed 6.7 feed additives and 3.5 alternative feeds. As part of the same symposium, Chase (7) reviewed some of the practices and applications of using the NRC [1989] recommendations for high-yielding cows. In general, the nutrient guidelines were in relatively close agreement with the rations fed in herds with high production. However, when the nutrient profiles of rations fed some high-yielding herds is compared to NRC [1989] requirements, there seems to be a rather large amount of oversupplementation. Justification for this extra fortification would probably be that requirements are based on average production by today's standards and today's cows are likely in negative energy balance longer and to a greater degree. But as Van Horn (28) has shown, excesses will be excreted and must be dealt with as manure and used by crops so that accumulations do not occur in soils or ground water. In the future we may be required to show nutrient balances to demonstrate that buildups are not occurring. Several examples of rations fed to high-producing herds in Wisconsin in 1992 are shown in Table 3 (13). A wide array of feedstuffs is apparent, in concert with the high dry matter intake (DMI) necessary to support such intense lactation.
Systems of Feed Management
Forty years ago pasture was a dominant forage for most dairy herds in the U.S., followed by hay and silage. Nearly all dairies fed concentrates in the barn at the time of milking so that eating occurred during milking (8). In the late 1950's and early 1960's it was discovered that many lactating dairy cows would respond to additional concentrates above the feeding standards used then. As herd sizes increased during the 1960's there was an increased emphasis on labor efficiency and a corresponding increase in the construction of milking parlors. As production increased there was also greater mechanization in the parlor which further reduced the time cows spent there to be milked. Even when additional time was provided and precision equipment was operated carefully, there was no way to ensure that the appetite of the cow would induce her to consume the required concentrate. Most parlor concentrate feeding then became free choice feeding for two 10-minute intervals per day. And the resulting "slug feeding" of highly soluble protein and carbohydrate must have been highly disruptive to a ruminal fermentation system which functions best as a steady-state system.
Table 3. Some rations of Wisconsin high yielding herds with production >11,350 kg/cow per yeara.
| Ingredient | Dairy | |||||
| A | B | C | D | E | F | |
| Hay | 3.6 | |||||
| Haylage | 21.7 | 21.9 | 18.8 | 24.8 | 12.1 | 17.4 |
| Corn silage | 4.2 | 7.6 | 12.0 | |||
| High-moisture S. corn | 14.3 | 15.8 | 13.3 | 20.6 | ||
| High-moisture E. C. | 16.5 | 15.4 | ||||
| High-moisture barley | 6.4 | |||||
| Distillers' grains | .8 | .3 | 1.1 | |||
| Wet brewers grains | 5.8 | |||||
| Corn gluten meal | 1.1 | .75 | .65 | .6 | .5 | |
| Liquid molasses | .26 | |||||
| Soybeans (roasted) | 7.6 | .75 | 4.75 | 1.9 | 5.2 | 1.1 |
| Soybeans (raw) | 2.8 | |||||
| Soybean meal | .9 | 2.75 | 2.2 | 2.2 | ||
| Soybean M (expeller) | 1.25 | 1.1 | ||||
| Fish meal | .8 | 1.2 | ||||
| Whole cottonseed | 4.7 | 4.7 | 7.4 | |||
| Meat & bone meal | 1.1 | 2.1 | .7 | |||
| Blood meal | .35 | .30 | .40 | .95 | ||
| Tallow | 1.0 | 1.0 | .7 | |||
| Urea (46%) | .20 | .13 | .35 | |||
| Sodium bicarbonate | .35 | .50 | ||||
| Dicalcium phosphate | .55 | .23 | .85 | .27 | .55 | .56 |
| Limestone | .24 | .20 | .06 | .35 | .38 | |
| White salt | .25 | .08 | .25 | .18 | .25 | .25 |
| Magnesium oxide | .10 | .06 | .08 | .09 | .10 | |
| Zinc methionine | .01 | .01 | .01 | |||
| Micromins/Vits | .09 | .05 | .08 | .05 | .09 | .13 |
| Yeast | .25 | .25 | ||||
aGunderson (13); High-group rations, % of dry matter.
The resolution of the parlor concentrate feeding dilemma has taken several forms (8): 1) feed some concentrate outside separate from or blended with forage; 2) use computer controlled concentrate feeders (CCCF); 3) feed all of the concentrate outside the parlor either through the computer feeders or blended with forage as a totally mixed ration (TMR). This system of feeding has been reviewed (8, 24). I define the TMR as a quantitative blend of all dietary ingredients, mixed thoroughly enough to prevent separation and sorting, formulated to specific nutrient concentrations, and offered ad libitum. The national survey (2) showed that among all operations only 35.6% fed a TMR, but among the operations with 200 or more cows, 83.5% fed a TMR. Muller (20) notes that both research and farmer experiences have shown that the milk production per year increased from 450 to 900 kg or more when herds were switched to a well formulated TMR.
The CCCF was developed to resolve the dilemma of parlor concentrate feeding and under some conditions it has been quite successful (8). Its greatest application is in smaller herds and where pasture is the dominant forage program. The feeders may restrict the cow's rate of eating and the proportion of the 24-hr allotment which a cow can receive at any one meal. Some allow 25% of the day's allowance to be eaten during each 6-hr quadrant of the day. But the CCCF deals only with the concentrate portion of the ration; forage(s) must be dealt with by another system. The problem of all concentrate fed separately from forage is that some cows seem to prefer concentrate to forage and other cows vice versa, and it is difficult to ensure that a cow will eat her needed forage if she is given a large allotment of concentrate which is increasingly necessary as higher production becomes the norm. Moreover, a few cows never learn to use the feeders and social dominance may cause disturbances around the feeders. The feeders are relatively expensive and require routine maintenance and frequent resetting as cows' requirements change. I feel that there are a least three cogent reasons for feeding different TMR rations within the milking herd: 1) The cows can be fed rations which are formulated so that their ad libitum consumption will result in more closely meeting the cows' nutrient requirements than some average formulation; 2) Feed costs can usually be reduced by feeding rations of lower nutrient density to the lower producing cows; 3) There will be less transfer of certain nutrients (e.g., nitrogen, phosphorus and sodium) to the manure by using formulations tailored to requirements, primarily milk production.
Ideally cows would calve in close calendar proximity so that they could remain in the same group for their entire lactation and the diet composition could be adjusted gradually as lactation advanced. This is most feasible for first lactation cows whose pregnancies were synchronized when they were heifers and who reside in large herds. Most cows will need to change groups as they advance in lactation in order to prevent overcondition and to reduce feed costs. Albright (1) recommends to "Move small groups of cows...Not only is there social pressure on the cow in her new group, but she may have different amounts of feed, a new milker, and a different milking time. Try to keep group size stable and no larger than 100 cows".
Milking Frequency
The Dairy Records Processing Laboratory in North Carolina in 1996 (5) reported that 757 herds out of a total of 11,557 herds (6.5%) milked their cows 3 times per day (3X). However, the 3X herds averaged 334 cows compared to an all herds average of 113 cows.
Therefore, 19.4% of the cows whose records are processed by that center are milked 3X. It is not known whether this number represents the U.S., but because many larger herds are in the southwest and west, it is probably a low estimate.
DePeters et al. (9) used 38 multiparous cows and 15 primiparous cows (Holsteins) in full lactation studies to compare the effects of twice daily milking (2X) with three times daily milking (3X) on production and reproductive performance. The older cows milked 3X produced 15% more milk during the complete lactation and the young cows produced 6% more milk during their first lactation. In both groups, neither dry matter nor energy intakes were affected by milking frequency, but neither group gained as much weight during the lactation as their herdmates milked 2X. Reproductive performance of the cows was not affected. These authors emphasized that herds milked 3X successfully will need careful nutrition and reproductive management.
From a study of 28 California herds (average size, 537), Gisi et al. (10) compared the response of these herds to 2X milking for 3 to 17 mo, and after a switch to 3X milking for 36 mo. In California during 1984, 11% of the herds and 15% of the cows were being milked 3X. In this study, milk production of all herds increased 12% above that when they were milked 2X. First lactation cows increased their production by 14%, but the range in response among herds was -2 to +32%. It was further noticed that most of the increased response occurred during the first 3 mo the herds were milked 3X. It was emphasized that if increased response to 3X milking is to be sustained for the long term, better nutrition, especially improved forage and perhaps increased feeding frequency may be essential. I do not know how soon after a 3X milking regimen begins, that an increase in appetite will occur. I have calculated the increase in feed energy which is necessary to support a 15% increase in milk production (Table 4), and for 27 kg of milk, about 10% more energy is required of the same ration. I know of no reason to assume an increased metabolic efficiency, so the increased milk production must be supported with greater dietary nutrient intake.
Table 4. Effect of a 15% increase in milk yield on feed required to maintain body energy status.
| Initial yield (a 15%
increase)
------------(kg/day)----------- | ||
| 30.0 | 34.5 | |
| Net energy required for:a | ------ NEl (MJ/day)-------- | |
| Maintenanceb | 40.58 | 40.58 |
| Growth (+10%) | 4.06 | 4.06 |
| Milk | 86.61 | 99.58 |
| Total NEl required | 131.25 | 144.22 |
| Difference | 12.97 | |
| (%) | ||
| Percentage increase in feed requiredc | 9.88 | |
a From NRC Dairy Cattle (1989).
b Calculated for 600 kg second lactation, nonpregnant cow, giving milk of 3.5% fat.
c Assumes no change in digestive or metabolic efficiency and a diet of uniform composition.
A study from Michigan by Speicher et al. (25) shows that the effects of BST and 3X milking are largely additive, although primiparous cows responded more to the combination of BST and 3X milking than did the multiparous cows. If both of these factors are imposed simultaneously, dairy producers should be prepared for the large increase in appetite which will eventually occur.
Bovine Somatotrophin (BST)
BST has been used commercially in the U.S. for more than three years. The national survey (2) showed that of all operations only 9.4% used BST, but in herds of 100-199 cows, 18.5% used this product, and in herds with >200 cows, 31.9% had used BST. So resistance to use was greatest in the small herds of <100 cows. The percentage of cows that are receiving BST is considerably larger than 10%. Use of BST causes an increase in milk yield within two to four days of its first use, although maximal response usually takes from four to six weeks of sustained use. One survey showed that dairymen were getting an average increase of 4.8 kg of milk per cow per day from BST use. At today's relatively high milk prices, this is about $1.68 of additional milk. With a product cost of about $.40 per cow per day, and an increased feed requirement of about 2 kg ($.35) and extra labor of $.10, the return is highly favorable. Studies with the respiration chambers at USDA-Beltsville, MD by Tyrrell et al. (26), showed that neither digestive nor metabolic efficiency was changed when BST was used. Therefore, the increased milk which occurs with BST use must be paid for with increased feed. Additional milk of 4.8 kg will require about 2 kg more of feed DM of a well balanced TMR. There is no free lunch with the use of this product. One feature of a cow's appetite, is that there is a lag of four to six weeks after the first BST injection, before the appetite increases for the additional feed. During this lag period, the nutrients to pay for the additional milk must come from body stores, feed, or a combination of the two. Feed nutrients must be available when the appetite increases so that cows have the chance to replenish nutrient reserves as lactation advances. As with 3X milking, some dairy producers have felt that the sharp response to the initial use of BST has not continued for long term, but it is likely in these cases, that the feed nutrients were not available to sustain the increased milk yields which occurred. So cows respond to BST in three ways; a) they produce more milk; b) after a lag period they eat more feed; and c) when they eat more feed, they produce more heat. Therefore, use of BST affects two primary management systems: a) nutritional management, and b) environmental management.
Galton's group at Cornell University (27) has suggested that because of the increased persistency of cows treated with BST, it may be economically desirable and feasible to deliberately extend the calving interval to as much as 18 months. These workers used nine herds to address this subject with some cows assigned to treatments which allowed extended calving intervals and some cows were never rebred, but all treatment cows received BST beginning at 63 days postpartum. In a preliminary report of this study, it was found that as lactation advanced, milk yield response to BST increased, so that an important difference in persistency occurred. Profitability was greater by nearly $.75/cow/day for cows that had an 18 month calving interval vs. those with a 13.2 month interval. This increase in profitability occurred because of greater persistency, fewer postpartum metabolic problems and less culling with fewer replacements required. If the results of this study are confirmed and if they receive wide acceptance, major changes in the management of dairy cows will occur.
Implications of Continued Emphasis on High Yield for
Cow Health, Reproduction, and Longevity
Grohn, Eicker and Hertl (12) examined the relationship between previous 305-day milk yield and disease in 8070 Holstein cows of second and later parity from within 25 herds in New York State. It was felt that because many disorders occur early in lactation, it was better to use the previous 305-day mature equivalent production. Cows that calved between June 1990 and November 1993 were used in this analysis. A separate statistical model was used to study the occurrence of each of seven disorders including: retained placenta, metritis, ovarian cysts, milk fever, ketosis, abomasal displacement, and mastitis. The incidence risk as a percentage and the median day of occurrence postpartum is shown in Table 5. Only mastitis showed an increased incidence with increasing milk yield. However, it was cautioned that this did not necessarily mean a cause and effect relationship. It was explained that often cows with mastitis and low production are culled, whereas higher producing cows with mastitis may be kept in the herd as treatment is applied. Therefore, the continued presence of higher yielding cows with mastitis in the herd may cause an apparent relationship even if none is present.
Table 5. Lactational incidence risks and the median days to the postpartum occurrence of disorders in Holstein cowsa.
| Disorder | Lactational
incidence risk
(%) |
Median postpartum day of occurrence (day) |
| Retained placenta | 7.4 | 1 |
| Metritis | 7.6 | 11 |
| Ovarian cyst | 9.1 | 97 |
| Milk fever | 1.6 | 1 |
| Ketosis | 4.6 | 8 |
| Displaced Abomasum | 6.3 | 11 |
| Mastitis | 9.7 | 59 |
aGrohn et al. (12); based on 8070 cows in New York State.
Although studies reported prior to 1975 showed little relationship of higher milk yields to reproductive performance, later work has accumulated a considerable volume of research to show that some antagonistic relationship exists between high milk production and reproduction as reviewed by Nebel and McGilliard (22). As these workers have noted, recent studies have described a detrimental effect of high yields particularly through a delay in ovarian activity and by a lower conception rate. But it was emphasized that managerial actions can have a major effect which greatly minimize the effect of the high milk production. In this context, adverse effects of an extended negative energy balance (NEB) can be minimized by formulation strategems such as use of supplemental fat to reduce the interval and degree of NEB. No doubt some of this antagonism is expressed as dairy producers try to achieve the dogma of an ideal calving interval (CI) of 12 to 13.5 months. As noted above, if through the use of BST and/or other management tools, persistency can be maintained at a higher level and a CI of 13 months is no longer sought, then this antagonism may diminish greatly or even disappear.
There is much interest and concern for the nutrition and management of the transition cow, defined as the peripartum period from about 21 days prepartum to 15 to 30 days postpartum. Some work suggests that using low potassium diets and/or adjusting the cation/anion relationship to near zero or slightly negative during the two to three week prepartum will result in less subclinical as well as clinical hypocalcemia and less depression in feed intake at parturition which will result in reducing the magnitude of NEB in the early postpartum. If this strategem is successful, it will likely diminish the degree of antagonism between high yields and reproductive performance.
Heat Stress and High Yields
For those of us who live in the sub-tropics or tropics, another dimension to higher milk yields is that the greater the feed intake, the greater the metabolic heat production. As Dennis Armstrong says, "a cow is a little furnace". And the greater the feed intake, the hotter the furnace. In summer the modern dairy cow does not belong in the sun, so shades, sprinklers, and fans are all important from the view of the alleviation of heat stress. But the primary reason for a decline in milk yield in hot weather is a voluntary reduction by the cow in feed intake. From a nutritional perspective, Chandler (6) states that some feed ingredients have a lower heat increment (the heat associated with the metabolism of nutrients) than others. These include the fats especially, and in general, the lower fiber ingredients. But apart from nutrition, it is clear that if dairy producers in the warmer regions of the world are to keep up with the pace of increasingly higher production, technologies which reduce heat stress will become increasingly mandatory.
Problems of Ration Formulation
The Cornell Net Carbohydrate Protein System (CNCPS) is our most advanced system of feed formulation, but it too is undergoing a nearly constant revision (3). It uses both carbohydrate and protein fractions that are partitioned based on their ease and speed of degradation in the rumen. But nearly all formulation programs require definitions of degradable intake protein (DIP) and undegradable intake protein (UIP). The National Research Council (NRC) for dairy cattle [1989] recommends 35% UIP and 60% DIP for a cow producing 40 kg of milk per day. Recently, Huber and Santos (16) summarized the responses of a number of research studies from the literature which compared diets in which soybean meal (SBM) protein was replaced with a less degradable protein such as blood meal, brewers grains, feather meal, fish meal, and blends of these. From 97 comparisons which involved lactation trials published from 1985 through 1994, it was found that milk yield increased in only 19% of the comparisons, there was no significant change in 73% and there was a significant decline in 9% of the trials (16). If better protein nutrition was the goal in these studies, it was not reflected in the milk protein percentage because there was no change or even decreases in most of the trials. This comparison shows that much more care and refinement is needed in the successful application of the UIP/DIP system. Because microbial protein produced in the rumen has the best amino acid profile for milk synthesis, much more effort should be directed to those conditions which maximize the growth of ruminal microbes. In addition, the UIP protein needs an amino acid profile which complements the ruminal microbes. In the above comparison, fish meal substituted for SBM resulted in greater milk yields in 46% of the trials. A major problem for feed formulators is that there is no well accepted method for the determination of DIP/UIP. Therefore, too often we are faced with using best estimates based on book values or from laboratory methods which are at best, compromises.
To provide optimal substrate for ruminal microbes in formulation, an expression for nonfiber carbohydrates is needed. Again, lack of rapid, inexpensive laboratory procedures presents a serious obstacle. As Hoover and Miller (15) note, the determination of nonfiber carbohydrate (NFC), also called nonstructural carbohydrate (NSC) by the difference method (easier method used frequently by feed testing laboratories) compared to the enzymatic method which is more tedious, shows large differences for some feedstuffs. The objective is to measure or designate the sugars and starches, the rapidly digestible carbohydrates, but until more data become available from the enzymatic method or another more rapid determination becomes available, progress is seriously hampered.
Another formulation quandary relates to the appropriate energy expression to use at the production intakes of lactating cows. The problem arises because there is a substantial disagreement between two authorities, the NRC [1989] for dairy cattle (21) and Van Soest, et al. (29), especially for certain co-products. The disagreement arises over the amount of the depression in digestibility which occurs as intakes go from maintenance to three or four times maintenance. This depression occurs as cows eat more feed which results in a faster rate of passage through the digestive tract and hence a lower digestibility for the feed. But how much less? The NRC assumes 8% less for all feeds at an intake of 3 times the intake equal to that required for maintenance. Van Soest et al. (29) say that each feed ingredient differs, based on its own special characteristics. In Table 6 a comparison of the two systems is shown for several co-products. Some large differences are obvious. So what is a dairy producer or a ration formulator to do in light of this controversy? For the time being I am staying with NRC (21). We need to be alert to the possibility that the energy values attached to some of the co-products are not truly reflective of their real energy values, especially under some conditions. When a substitution is made to include a certain commodity, do high producers at their peak maintain their production well or even increase, or do they decline? Although this is very subjective, this may be the best indication we have that an appropriate energy value has been used for that co-product.
Table 6. Comparison of net energy for lactation by Van Soest et al. (29) and NRC for Dairy Cattle-1989 (21).
| -------(Nel)----- | |||
| Feed | Discounta | 3Ma | NRCb |
| (%) | ------(MJ/kg DM)---- | ||
| Molasses-Cane | 0.0 | 6.19 | 6.86 |
| Bakery Waste | 2.0 | 9.00 | 8.62 |
| Alfalfa Hay | 3.2 | 6.57 | 6.30 |
| Whole Cottonseed | 4.0 | 9.20 | 9.33 |
| Soybean Meal (44%) | 5.1 | 7.45 | 8.17 |
| Rice Bran | 6.6 | 6.49 | 6.69 |
| Wheat middlings | 7.0 | 7.95 | 6.57 |
| Brewers Grains (wet) | 10.7 | 5.61 | 6.28 |
| Corn Distillers (wet) | 14.0 | 6.90 | 8.33 |
| Corn Hominy | 15.0 | 6.74 | 8.41 |
| Pineapple Bran | 18.0 | 4.35 | 6.49 |
| Soy Hulls | 18.0 | 5.40 | 7.41 |
a Van Soest et al. (29);
b NRC, Dairy Cattle, 1989, (21)
Summary and Conclusions
An old saying seems as true today as it was 50 years ago: "cows are better bred than fed". Geneticists have done an incredible job with their science; but this is good news to nutritionists and those in the feed business. Now when ration changes are made which are true improvements, cows usually respond with greater milk yields. The food industry generates a large array of byproducts which ruminants can use productively to produce milk and meat. This is not to suggest that there are a lot of free lunches out there, because in a free market, feed ingredients tend to be sold at a price which reflects their true nutritive value as buyers see them. Yet the availability of these products extends the feed supply and in some cases makes special contributions to the diet and to the environment.
About the time that dairy producers began to expand their herds, and mixer wagons with electronic load cells became available, the TMR system of feeding evolved and now is used widely. At first it was used before the merits of its inherent advantages were recognized, but today a large majority of enthusiastic users attest to its value. In larger herds, cows are housed in groups for managerial reasons, so that different formulations of TMR's can be used without special housing.
A number of dairymen have tried 3X milking, but have returned to 2X milking. The primary reason seems to be that the initial increase in milk seen did not seem to persist, or cows were required to stand on concrete for an extended period and feet and leg problems developed. But an increase in milk yield must be paid for at some point with additional feed nutrients, and the opportunity for cows to eat that extra feed may not have been there in some cases.
The approval of BST for commercial use in the U.S. was accompanied by some controversy, despite years of research done in quadruplicate. Most of the controversy has disappeared or at least it has quieted down. The consistency of response of cows to this product and its successful use by some of the best herds has not yet caused its widespread adoption, despite a clear economic payback. This will probably come with time.
Despite a rather general impression that high yields are accompanied by increased incidence of metabolic problems, except for mastitis, this does seem to occur. There is some antagonism between reproductive competence and high yields, but most dairy producers seem willing to accept this downside. If current research comparing 13.5 month calving intervals with 18 months in conjunction with BST use is supported by additional work, even the lower reproductive performance may diminish or disappear.
Hot weather is a major constraint during summer in many parts of the U.S. If herd owners in the more humid and hotter areas of the world are to keep pace with their colleagues in more temperate regions, major expenditures must be made on technologies for heat stress abatement.
Feed formulators could be much more precise in the construction of diets if more accurate values could be used for DIP/UIP, NSC, and net energy. Today, much uncertainty exists for some of the numbers which we use for these nutrient expressions. The bottom line is that excess supplementation results and considerable money is wasted and unfortunate transfer of nutrients to soils and ground water occurs. Despite these uncertainties, production continues upward with no limit in sight.
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