Three general types of nutritional management systems are typically used in dairy production: confinement systems with total mixed rations (TMR), confinement systems in which concentrates and forages are fed separately (component feeding), and pasture-based systems.
Total Mixed Rations for Feeding Dairy Cattle
A total mixed rations diet (TMR) is one in which all dietary components are included in a single uniform mixture that is fed one or more times per day. There is nutritional advantage of approximately 8%–12% in feeding a TMR over component feeding due to facilitating rumen nitrogen and carbohydrate resources to optimize microbial growth in providing fiber and nonfiber ration components in uniform proportions. This minimizes fluctuations in rumen pH and promotes healthy rumen conditions, even at relatively high rates of energy intake.
Advantages of TMR feeding are critically dependent on proper diet preparation. There are a range of mixer wagons for TMR preparations that vary in their capabilities to incorporate dry forage adequately. Mixer wagons should be properly sized and not overfilled. Mixing time should be monitored and ingredient filling order followed according to manufacturer recommendations. Accurate weighing of each mixture component is requisite to successful TMR preparation. Several types of suitable mixers with self-contained weighing devices are available commercially.
Maintaining particle size adequate to deliver sufficient effective fiber can be a challenge with TMR diets. Limiting the duration of the mixing process helps maintain sufficient effective fiber if silages have adequate particle length initially and the particles are not further reduced during the mixing process. Sieves to monitor particle size in TMR mixes are available commercially. See table Particle Size Recommendations for Total Mixed Rationsa for recommended particle size distribution in TMR mixes, based on a popular sieving system.
Particle Size Recommendations for Total Mixed Rationsa
Pore Sizeb (mm) | Particle Sizec (mm) | Percentage by Weight | |
|---|---|---|---|
Upper sieve | 19.1 | >19.1 | 2–8 |
Middle sieve | 7.9 | 7.9–19.1 | 30–50 |
Lower sieve | 4.0 | 4.0–7.9 | 10–20 |
Lower sieve | 1.8 | 1.8–7.9 | 30–50 |
Bottom pan | None | < 4.0 or < 0.18 | 30-40 or ≤20 |
aBased on the use of the Penn State Particle Separator. Data from J. Heinrichs and P. Kononoff, Pennsylvania State University. | |||
bPores are square, so the largest opening is the diagonal. | |||
cParticle size dependent upon lower sieve used; larger proportion weight is associated with 4-mm sieve | |||
Frequent monitoring of moist feed dry-matter content is particularly important in the management of TMR diets. Diets are formulated based on feed nutrient concentrations on a dry-matter basis; however, ingredients are mixed based on their wet weight. Therefore, accurate dry-matter concentrations are critical to ensure the mixed diet nutrient profile is as intended. Ensiled forages should have their dry-matter content monitored weekly or multiple times per week. Routine analysis of a representative TMR sample for major nutrient fractions is useful in assuring that the ingredient nutrient profiles and proportions are consistent with the intended diet formulation and are consistent over time.
Feed bunk management is another important aspect in the use of TMR mixes. Cattle should have continuous or nearly continuous access to feed. Adequate bunk space is important, with recommendations for optimal linear space usually 45–60 cm/animal. Bunks should be cleaned daily, and the orts (refused feed) weighed so that daily feed intake for the group may be calculated. To assure optimal feed availability, orts should be 2%–5% of the total amount fed. Orts particle size distribution should be evaluated to determine if feed sorting, which usually results in large particles (top sieve) being left behind, is not occurring.
All feeding groups, replacement heifers, nonlactating, and lactating cows can benefit from TMR systems. One challenge may be the difference in dry cow group size relative to mixer wagon capacity. Mixing for small groups may result in inadequate ingredient mixing efficiency. For economic use of TMR diets, cows should be separated into feeding groups (optimally, two or more lactating cow groups). Diets for lactating cow groups should be formulated with a lead factor, meaning the diet should be balanced for more milk production than the mean of the group. This is to ensure that the nutrient requirements of the higher-producing cows in the group are met. Optimal lead factors depend on the number of feeding groups and their stage of lactation. When two groups of lactating cows are used, feeding for >20% of the mean production is frequently recommended.
Unmixed or Component-fed Rations for Feeding Dairy Cattle
Traditional confinement barns, such as tie-stall, comfort stall, or stanchion barns, typically use feeding systems in which concentrates are fed separately from forages. There are smaller mixer wagons that can be used in these barns. Advantages of the component-fed system relative to a total mixed ration system include a defined individual feeding space, lack of need for specialized mixing and feed delivery equipment, and ability to adjust individual cow diets by modifying concentrate feeding amounts. Disadvantages include a labor-intensive feeding process and the potential for large fluctuations in rumen pH, which may impair fiber digestion and contribute to poor rumen health. Rumen health issues are related to starch and other nonfiber carbohydrates being provided in a small number of meals per day, typically at milking time. Feeding order recommendations to feed some forage before any concentrate as a first meal in the morning and possibly provide more concentrate meals per day can help to mitigate the rumen health issues.
In addition to the potential for fluctuations in rumen pH, another challenge of component feeding systems is the inability to monitor forage intake. Generally, there is no direct need to weigh the amount of forage offered if it is not being mixed with other diet components. Thus, there is no means to accurately adjust concentrate intake to match fluctuations in forage consumption. This becomes a problem in hot weather during which forage consumption may be reduced substantially while concentrate consumption is less affected. This leads to alterations in the intended proportions of fiber and nonfiber carbohydrates in the diets.
Pasture-based Feeding System for Dairy Cattle
Pasture-based feeding systems can range from pasture alone with only mineral supplements (typical of New Zealand dairy systems), supplementing grain in a milking parlor, or providing a partial mixed diet. Pasture management has evolved to optimize use of forage resources in pasture systems. Such systems require intensive management of pasture for optimal dry matter and nutrient yields and for optimal feeding and nutrition of high-producing modern dairy cows. To achieve these objectives, paddocks must be rotated frequently, so forages are consumed at an optimal stage of growth and overgrazing does not occur. Pastures are typically divided into paddocks via the use of easily moved electric fences. Cattle are rotated through paddocks as forages reach stages of growth optimal for both dry-matter yields and nutrient composition.
From a nutritional standpoint, the three major challenges of pasture-based dairy systems are maintaining favorable rumen fermentation conditions, maintaining adequate dry-matter intake, and meeting energy requirements. Milk production rates in nonsupplemented pasture feeding situations are seldom >25 kg/day. Consumption of lush pasture results in high water intake and faster rate of passage. This may facilitate rumen conditions as well as pass some of the readily degradable protein to the small intestine, thus providing a bypass protein source. A major challenge of a pasture system is the potential limitation on grazing period relative to forage growth and weather conditions. In nonsupplemented pasture systems, cow requirements must be timed with pasture forage growth and quality, leading to a seasonal dairy production system.
Managing rumen health and dietary fiber adequacy can be as challenging with pasture-based systems as with other dairy feeding systems. Lush, rapidly growing pasture grasses with high energy and protein density typically have low NDF concentrations. Thus, rumen fermentation conditions, particularly pH, may be a problem. Supplementing the pasture with dry forages to maintain adequate effective fiber concentrations may be necessary.
