Álvaro García
Straw, once considered a mere filler in dairy rations, has gained recognition as a strategic ingredient in managing the energy and metabolic balance of transition dairy cows. This review synthesizes current evidence on the nutritional characteristics of straw and its physiological role in dry-cow feeding programs. Emphasis is placed on its influence on intake regulation, rumen function, and metabolic adaptation during the transition period. Findings from recent research show that properly processed straw, when included at moderate levels, helps maintain rumen health, promotes stable dry-matter intake, and reduces post-partum metabolic disorders. The paper also discusses how particle size, ration moisture, and mixing uniformity affect feeding behaviour and performance. These principles have relevance for dairy systems in warm or resource-limited regions, where the use of cereal crop residues remains a practical approach to energy control and rumen health.
Introduction
The transition period, spanning three weeks before and after calving, is the most metabolically demanding phase of a dairy cow’s cycle. Nutrition during this stage aims not at maximizing production but at preparing the animal’s metabolism and rumen for the high nutrient flow of early lactation. Excess energy intake during the dry period leads to over-conditioning, fatty-liver infiltration, and an elevated risk of ketosis and displaced abomasum after calving (Overton & McArt 2015). Consequently, formulating rations that supply adequate nutrients without promoting excessive body-fat deposition has become a central focus of modern dairy management.
Straw is uniquely suited to this objective. Although low in protein and energy, it provides bulk and effective fiber that stimulates rumination and saliva secretion, maintaining rumen buffering capacity. This simple by-product of cereal production, once viewed as nutritionally poor, is now appreciated as an economical and physiologically valuable component of controlled-energy diets. In regions where high-quality forages are often scarce and expensive, properly processed straw can be an effective means of managing nutrient density while supporting gut health.
Nutritional role of straw in dry-Cow diets
Straw’s nutritional composition contrasts sharply with that of common forages. Wheat or barley straw typically contains only 3–5 % crude protein and less than 1.0 Mcal NEL kg⁻¹ dry matter, compared with over 1.4 Mcal kg⁻¹ in high-quality haylage. Its neutral detergent fiber content commonly exceeds 70 %, providing structure but limited digestible energy. This composition allows straw to dilute energy-dense diets without restricting dry-matter intake.
When incorporated at levels of 15–30 % of ration dry matter, straw supports a dietary energy concentration near 1.3 Mcal kg⁻¹ DM, an optimal range for non-lactating Holstein cows of moderate body condition. Such diets allow cows to consume sufficient feed volume to maintain rumen fill and microbial activity while preventing excess energy intake (Havekes et al. 2020a). Cows fed controlled-energy, straw-based diets before calving exhibit improved metabolic indicators, lower concentrations of β-hydroxybutyrate and non-esterified fatty acids after calving, compared with cows receiving unrestricted energy diets (Janovick et al. 2011).
Beyond energy dilution, straw’s fibrous texture encourages chewing and saliva production, which in turn buffer rumen pH and promotes a stable microbial environment. These effects support a smoother transition to post-calving rations rich in fermentable carbohydrates. In contrast, feeding exclusively high-digestibility forages before calving can suppress rumination and predispose cows to acidosis once lactation diets are introduced.
Particle size, mixing uniformity, and feeding behaviour
While nutrient composition defines straw’s potential, its physical characteristics determine its practical success in the ration. Particle size governs how cows interact with feed at the bunk. Long particles exceeding about 8 cm often lead to selective feeding: cows push aside fibrous material in favor of more palatable silage or concentrate, resulting in unequal nutrient intake and rumen pH fluctuations. Conversely, particles shorter than 2 cm reduce the “scratch factor” necessary for stimulating rumination and may produce dusty, unpalatable feed.
Research has demonstrated that chopping straw to an intermediate length of 2–3 cm achieves the best compromise between uniform mixing and effective fiber stimulation (Havekes et al. 2020a). At this length, cows are unable to sort appreciably, ensuring that the ration consumed closely matches that formulated. Maintaining this uniformity is essential, as inconsistencies in physical structure can cause variation in dry-matter intake, erratic rumen fermentation, and metabolic disorders such as subclinical ketosis.
Mixing sequence and moisture also influence the success of straw inclusion. Because straw is light and elastic, it mixes poorly if added early to the mixer. Many practitioners achieve greater consistency by loading silages first, followed by concentrates and minerals, and straw last. The ration should be mixed long enough to disperse fiber evenly but not so long that particle size is destroyed. Excessively dry rations accentuate sorting, while adding modest water or incorporating wetter silage helps bind fine particles to the fiber fraction, producing a cohesive texture.
Monitoring cow behaviour provides early feedback on ration effectiveness. Large refusals containing long fibers suggest sorting, whereas reduced appetite or visible dust indicates over-processing. Consistent feed availability, frequent push-ups, and minimal time gaps between feedings maintain stable intakes during the critical days preceding calving.
Physiological and management implications
Effectively managed straw inclusion influences not only feed intake but also rumen structure and liver metabolism. Controlled-energy diets that incorporate straw maintain hepatic insulin sensitivity and reduce excessive mobilization of body fat, thereby lessening the incidence of fatty liver and associated disorders (Janovick et al. 2011). Rumen papillae remain active, pH remains above 6.0, and cows transition to lactation diets with fewer off-feed events.
Quantitative research underscores these benefits. Havekes et al. (2020a) reported that cows offered straw chopped to 2–3 cm consumed approximately 1.5 kg DM d⁻¹ more during the pre-partum period and had 30 % lower post-partum ketone concentrations than cows offered 10 cm straw. In a companion study, moisture adjustment of high-straw diets improved intake uniformity and reduced metabolic disturbances (Havekes et al. 2020b). Collectively, such findings show that physical processing and feeding management often determine the success of straw utilization more than its inherent nutrient content.
These insights hold value for dairy operations where forage quality fluctuates markedly across seasons and cereal residues are widely available. Incorporating chopped straw into controlled-energy rations allows producers to stabilize transition performance without heavy reliance on expensive concentrates. With proper balancing for protein, minerals, and, where required, anionic salts, straw-based diets can equal the health outcomes achieved in temperate-region systems using higher-quality forages.
Conclusions
Straw, when processed and managed correctly, is far more than a low-quality by-product. Its strategic inclusion in dry-cow rations moderates energy intake, sustains rumen health, and reduces metabolic disorders in early lactation. Success depends on consistent particle size, adequate mixing, and attention to ration moisture and bunk management. In resource-limited or warm-climate dairy systems, straw represents an accessible tool to achieve nutritional precision and improve transition success. Embracing its proper use reflects a broader shift in dairy nutrition: from viewing straw as filler to recognising it as the core of controlled-energy feeding.
The full list of references used in this article is available upon request.
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