Dr. Kirby Krogstad, Assistant Professor, Department of Animal Sciences, The Ohio State University
Introduction
This year, in each edition of the Buckeye Dairy News, we will explore critical fundamentals of effectively assembling rations for lactating dairy cows. The goal is that by the end of the year, we will have covered the major macronutrients, provided context on what nutritional models “know” and “don’t know,” and wrapped up with concrete examples of rations and how the cows performed compared to estimates.
The most important part of effectively feeding livestock is understanding and accurately estimating feed intake. Feed intake is controlled by multiple factors that integrate to lead to a ‘net effect’ that increases or decreases an animal’s intake at any given point during its life cycle. Dairy cows are especially challenging because we suspect that the primary controllers of feed intake change as a cow advances through her lactation. While one mechanism rarely controls intake alone, these factors shift in importance as metabolic status, physiology, and milk production change.
What Drives Feed Intake and How Does One Control It?
Physical Constraints
The rumen can hold a large amount and volume of feed – but it is not unlimited. Rumen evacuation experiments recently conducted at Ohio State University demonstrate that an early lactation Holstein cow’s rumen holds 125-250 lb of feed contents. At some point, the volume and weight in the rumen will begin to limit the amount a cow can eat within a day or a meal. This was neatly demonstrated by experiments that filled the rumen with air or water filled bladders; as volume of these bladders in the rumen increased, the cows’ intake decreased (Schettini et al., 1999). Thus, when feeding cattle, we need to be conscious of physical gut fill as too much fill will reduce feed intake and thus reduce the nutrients supplied to the cow for milk production.
What factors determine gut fill? The primary factors are feed degradation rate and feed passage rate. The more rapid a feed degrades, the less its impact on rumen fill. Think of feeding a readily digestible immature grass versus feeding an equivalent amount of an overly mature indigestible grass. The immature grass will probably result in far less rumen fill and have greater dry matter intake (DMI) potential because it is being degraded more quickly, which leaves more physical space to be filled in the rumen. Feed passage is generally dictated by feed type. Diets with greater forage concentration have slower passage rates than diets with less forage (Krogstad et al., 2021). Also, grasses tend to pass through the rumen more slowly than legumes like alfalfa (Kammes and Allen, 2012), which may lead to reduced feed intake when feeding grasses compared to feeding legumes (Johansen et al., 2018).
Forage particle size is another factor to consider as grinding and pelleting hay increases passage rate compared to feeding regular grass hay (Ramirez Ramirez et al., 2016). The increased passage rate from reducing particle size may increase feed intake. Reducing particle size of alfalfa from a theoretical chop length of 22.3 mm to 4.8 mm increased DMI (Kononoff and Heinrichs, 2003b); the same was also true for corn silage (Kononoff and Heinrichs, 2003a). Reducing forage particle size is not without risk though as reducing forage particle size may reduce milk fat composition and yield (Kononoff and Heinrichs, 2003a; Ramirez Ramirez et al., 2016).
At this point, the best way to assess particle size of the diet is to use the Penn State Particle Separator – the recommended particle size distributions from Grant and Cotanch (2023) are listed in Table 1.
Table 1. Recommendations for particle size of lactating cow TMR using the Penn State Particle Separator.1,2
|
Sieve |
Recommendations, % as fed |
|
19 mm |
2-5 |
|
8 mm |
>50 |
|
4 mm |
10-20 |
|
Pan |
25-30 |
1Listed in Grant and Cotanch, 2023.
2Based on high-corn silage diets in the Upper Midwest and Northeast US.
Metabolic Signals
The metabolic signals produced by digestion and metabolism also controls the animal’s urge to consume feed. The predominant framework used to explain intake regulation in dairy cattle is the ‘Hepatic Oxidation Theory’. Briefly, the theory stipulates that the liver serves as the metabolic hub that integrates a variety of signals to control an animal’s feed intake. Propionate receives the greatest attention within this framework and has been the most investigated for its influence on feed intake in ruminants. Propionate is produced from microbial fermentation of feed, with greater propionate arising from starch degradation than from NDF or sugar degradation. Propionate is critical because it is a precursor to glucose synthesis in the liver. Through various infusion experiments, we have learned that propionate can reduce feed intake (Oba and Allen, 2003a). Propionate reduces feed intake even when compared to infusions of acetate, another important volatile fatty acid (Oba and Allen, 2003b) or glucose (Gualdrón-Duarte and Allen, 2018).
Figure 1. Feeding high moisture corn (HMC) in place of dry ground corn (DGC) during the postpartum period reduces feed intake. Adapted from Albornoz and Allen (2018).
Based on these data, controlling propionate production in the rumen by reducing dietary starch concentration or feeding starch sources that are less rumen degradable may increase DMI during important lactation periods, like the early postpartum period. Albornoz and Allen (2018) observed that feeding high moisture corn during the postpartum period reduced intake when compared to feeding dry ground corn and the effect was greatest in diets with greater starch concentration (22% vs. 28%; Figure 1). The reduced feed intake then resulted in reductions of yields of milk, milk fat, and milk protein when feeding high moisture corn.
Some evidence is also compatible with the concept that increasing dietary starch in late lactation cows reduces feed intake (Krogstad and Bradford, 2023), suggesting that metabolic signals may increase their control over feed intake as milk yield declines and lactation progresses (NASEM, 2021).
Shift in controls
The difficult part, in practice, is understanding which factors are limiting intake at a given point for a group of cows. The current understanding is that physical constraints play a larger role in limiting feed intake during periods of high feed intake, like peak lactation milk production, than during the very early or late lactation periods.
The early lactation period is a very interesting example of signals controlling feed intake. The postpartum dairy cow’s intake is rarely limited by physical space in the rumen. Despite being in a nutrient deficit early after calving, she still does not eat to her gut fill at maximum. During this period, cows are awash in metabolic and inflammatory signals, which likely limit feed intake (Brown and Bradford, 2021).
Suggestions and Best Practices
According to an extensive review by Allen (2023), we should limit rapidly degradable starch sources like wheat, barley, or high moisture corn during the fresh period (0-14 days in milk) as these may reduce feed intake because of the increased propionate production. As lactation progresses, physical distention reduces feed intake and reducing forage NDF (fNDF), to a point, may increase DMI. NASEM (2021) suggests that fNDF should be between 17 and 27% of diet DM. Allen (2023) suggests targeting 20-23% fNDF for fresh cow rations while reducing fNDF for high producing and mid-lactation cows. During later lactation, the goal should be maintaining BCS – whichever fNDF maintains DMI and body condition should be used.
References and Suggested Reading
Albornoz, R. I. and M. S. Allen. 2018. Highly fermentable starch at different diet starch concentrations decreased feed intake and milk yield of cows in the early postpartum period. J. Dairy Sci. 101(10):8902-8915. https://doi.org/10.3168/jds.2018-14843
Allen, M. S. 2023. Symposium review: Integrating the control of energy intake and partitioning into ration formulation. J. Dairy Sci. 106(3):2181-2190. 10.3168/jds.2022-22473
Brown, W. E. and B. J. Bradford. 2021. Invited review: Mechanisms of hypophagia during disease. J. Dairy Sci. 104(9):9418-9436. 10.3168/jds.2021-20217
Grant, R. J. and K. W. Cotanch. 2023. Perspective and Commentary: Chewing behavior of dairy cows: Practical perspectives on forage fiber and the management environment. Applied Animal Science 39(3):146-155. https://doi.org/10.15232/aas.2022-02371
Gualdrón-Duarte, L. B. and M. S. Allen. 2018. Fuels derived from starch digestion have different effects on energy intake and metabolic responses of cows in the postpartum period. J. Dairy Sci. 101(6):5082-5091. https://doi.org/10.3168/jds.2017-13607
Johansen, M., P. Lund, and M. R. Weisbjerg. 2018. Feed intake and milk production in dairy cows fed different grass and legume species: A meta-analysis. Animal 12(1):66-75. 10.1017/S1751731117001215
Kammes, K. L. and M. S. Allen. 2012. Rates of particle size reduction and passage are faster for legume compared with cool-season grass, resulting in lower rumen fill and less effective fiber. J. Dairy Sci. 95(6):3288-3297. https://doi.org/10.3168/jds.2011-5022
Krogstad, K. C. and B. J. Bradford. 2023. The effects of feeding α-amylase-enhanced corn silage with different dietary starch concentrations to lactating dairy cows on milk production, nutrient digestibility, and blood metabolites. J. Dairy Sci. 106(7):4666-4681. 10.3168/jds.2022-23030
Kononoff, P. J. and A. J. Heinrichs. 2003a. The effect of corn silage particle size and cottonseed hulls on cows in early lactation. J. Dairy Sci. 86(7):2438-2451. 10.3168/jds.S0022-0302(03)73838-7
Kononoff, P. J. and A. J. Heinrichs. 2003b. The effect of reducing alfalfa haylage particle size on cows in early lactation. J. Dairy Sci. 86(4):1445-1457. https://doi.org/10.3168/jds.S0022-0302(03)73728-X
Krogstad, K. C., K. J. Herrick, D. L. Morris, K. J. Hanford, and P. J. Kononoff. 2021. The effects of pelleted dried distillers grains and solubles fed with different forage concentrations on rumen fermentation, feeding behavior, and milk production of lactating dairy cows. J. Dairy Sci. 104(6):6633-6645. 10.3168/jds.2020-19592
NASEM. 2021. Nutrient Requirements of Dairy Cattle. 8th rev. ed. The National Academies Press, Washington, DC.
Oba, M. and M. S. Allen. 2003a. Dose-response effects of intrauminal infusion of propionate on feeding behavior of lactating cows in early or midlactation. J. Dairy Sci. 86(9):2922-2931. 10.3168/jds.S0022-0302(03)73889-2
Oba, M. and M. S. Allen. 2003b. Intraruminal infusion of propionate alters feeding behavior and decreases energy intake of lactating dairy cows. J. Nutrition 133(4):1094-1099. https://doi.org/10.1093/jn/133.4.1094
Ramirez Ramirez, H. A., K. J. Harvatine, and P. J. Kononoff. 2016. Short communication: Forage particle size and fat intake affect rumen passage, the fatty acid profile of milk, and milk fat production in dairy cows consuming dried distillers grains with solubles. J. Dairy Sci. 99(1):392-398. 10.3168/jds.2015-10006
Schettini, M. A., E. C. Prigge, and E. L. Nestor. 1999. Influence of mass and volume of ruminal contents on voluntary intake and digesta passage of a forage diet in steers. J. Anim. Sci. 77(7):1896-1904. 10.2527/1999.7771896x