Nitrogen Retention and Nutrient Digestibility in Geldings Fed Grass Hay, Alfalfa Hay, or Alfalfa Cubes

Changes in eating time, chewing activity and dust concentration in horses fed either alfalfa cubes or long-stem hay

BACKGROUND

Chewing is an essential physiological process in horses; yet, the physical form of feeds may affect their chewing and feeding behaviour with consequences for equine digestion and health.

OBJECTIVES AND METHODS

The present study evaluated the potential of a commercial forage cubes made from alfalfa and mixed meadow grasses to maintain chewing activity when compared with a traditional long and fibre-rich hay. An additional aim was to measure the dust formation during feeding. The experiment was a crossover design with six horses (11 ± 4 years old, mean ± SD), fed with 5 kg (as-fed basis) of their feed (long hay or alfalfa cubes) overnight. Eating and chewing activity was measured using the EquiWatch system with a sensor-based halter.

RESULTS

Data showed that by feeding the same amount of feed overnight, cube feeding led to 24% shorter eating time (on average 67 min less) and 26% fewer total chews compared to the long hay. On an hourly basis, horses also spent more time eating and chewing the long hay compared to the cubes. The cube feeding led to a higher dust concentration of the inhalable fraction (<100 μm), but not of the thoracic (<10 μm) fraction. Nevertheless, average dust concentrations were generally low for both cubes and hay, whereby both were of sound hygienic status.

CONCLUSION AND RECOMMENDATION

Our data suggest that feeding alfalfa-based cubes overnight generated shorter eating time and less chews than the long hay without major differences in the thoracic dust. Therefore, because of the decreased eating time and chews, alfalfa-based cubes should not be fed a sole forage source, especially when it is to be fed without restriction.

Effects of Mowing Times on Nutrient Composition and In Vitro Digestibility of Forage in Three Sown Pastures of China Loess Plateau

Mowing, Mowing, which affects the nutritional levels of grasslands, is the main utilization of sown pasture. We sowed alfalfa monoculture grassland, tall fescue monoculture grassland and tall fescue + alfalfa mixed grassland in typical steppe of the Loess Plateau to investigate the nutrient compositions and in vitro degradability of those three grasslands under different mowing stubble times and to provide reference for nutrient management of sown pastures. The results showed that the stubble time significantly affected (p < 0.05) the nutrient compositions and mineral elements of forages in alfalfa monoculture grassland, whereas had no effects on the nutrient compositions and dry matter digestibility of forages in tall fescue monoculture grassland and alfalfa + tall fescue mixed grassland. The relative feeding value of mixed grassland of alfalfa and tall fescue was increased by 2.6−22.4% as compared to monoculture grasslands. The model constructed based on forage nutrient content could accurately predict the forage dry matter degradability of alfalfa monoculture, tall fescue monoculture and mixed alfalfa and tall fescue, respectively.

Evaluation of Two Equations for Prediction of Digestible Energy in Mixed Feeds and Diets for Horses

Several authors have developed equations for estimating digestible energy in horse feeds as an alternative to the inconveniences of in vivo digestibility assays. We aimed to evaluate two of such equations. A dataset was constructed from the literature with 32 mixed feeds and diets of known proximate composition, whose digestibility was measured in in vivo assays. Then, the digestible energy of the mixed feeds and diets was predicted with both equations from their proximate components. Precision, accuracy, reproducibility, bias, and decomposition of total error of predictions were determined. Both equations performed almost equally well (R2 = 0.89 vs. 0.87, root mean square error of prediction = 183 vs. 217 kcal/kg dry matter, concordance correlation coefficient = 0.91 vs. 0.86, and linear error = 24.6 vs. 33.6% of total error). Linear bias (p < 0.01 in both equations) resulted in overvaluation of low digestible energy feeds and, to a lesser extent, undervaluation of high digestible energy feeds and was significantly (p < 0.05) related to crude fiber. The obtained results indicate that the accuracy of both equations could be improved by reassessing the effects of crude fiber on the digestibility of the other proximate components.

Protein Source and Intake Effects on Diet Digestibility and N Excretion in Horses-A Risk of Environmental N Load of Horses

Simple Summary

The aim of this experiment was to study how protein source and intake effect diet digestibility and N excretion in adult horses. The results showed that protein feeds improved diet DM, OM and CP digestibilities compared to forage diets. Urine excretion was greater for forage-only diets compared with diets including protein supplements. Horses excreted more nitrogen in their urine (85–139 g/d) than in dung (42–52 g/d), and N excretion differed between the diets. Horses on a haylage-only diet excreted 51.6 g N in faeces/day and on hay-only diet 51.4 g N/day. On the other hand, when protein content in forages increased, N excretion via urine increased. Horses excreted less N in urine with hay-only diet (64 g/d) than with haylage-only (104 g/d) or protein-supplemented diets (105–111 g/d). The results indicated that feed choices affected the amount of nitrogen excreted. Feeding recommendations should consider not only the horse category and work level, but also the protein source. When good quality protein is fed, smaller N intakes can be applied to reduce the N excretion via urine and dung. At the farm level, improved understanding of feed quality, as well as feeding planning and practices, is a way to decrease the risk of N leaching and evaporation.

Abstract

Six Finnhorse mares were used in a digestibility trial, in which six typical horse diets were compared. The diets were: (A) haylage 100%; (B) hay 100%; (C) hay 70% and oats 30%; (D) hay 70% and soybean meal + oats 30%; (E) hay 70%, rapeseed meal + oats 30% and (F) hay 70 %, linseed meal + oats 30%. The trial was conducted according to an unbalanced 6 × 4 Latin square design with four 3-week experimental periods. The experimental period consisted of 17-day preliminary feeding which was followed by a 4-day total faecal and urine collection periods to evaluate N excretion. The digestibilities of DM (p < 0.001) and OM (p < 0.001) in the haylage-only diet were lower compared to the other diets. The supplemental protein feeds improved the diet digestibility of CP (p = 0.002) compared to a hay + oats diet. Furthermore, the DM (p = 0.019), OM (p = 0.006), and CP (p = 0.016) digestibilities of the soya-supplemented diet were better than those of the rapeseed- and linseed-supplemented diets. Faecal excretion was greater for haylage (19.3 kg fresh faeces and 3.6 kg DM/day) and hay (18.7 kg fresh faeces and 3.6 kg DM/day) diets (p < 0.001) compared with the other diets. Urine excretion was also greater for forage-only diets compared with diets including protein supplements. Horses excreted 14.0 L urine/day on haylage-only diet (p = 0.026) and 14.3 L/day on a hay-only diet (p = 0.003). Horses excreted more nitrogen in their urine than in dung. N excretion differed between the diets. Horses on a haylage-only diet excreted 51.6 g N in faeces/day and on hay-only diet 51.4 g N/day. On the other hand, when protein content in forages increased, N excretion via urine increased (haylage vs. dried hay). Horses excreted less N in urine with hay-only diet than with haylage-only or protein-supplemented diets (p < 0.001). When N excreted in faeces and urine was counted together, horses excreted less N with a hay-only diet (p < 0.001) than with a supplemented one (oats and/or protein feeds). The results showed that feed choices affected the amount of nitrogen excreted. Feeding recommendations should consider not only the horse category and work level, but also the protein source. When good quality protein is fed, smaller N intakes can be applied to reduce the N excretion via urine and dung. At the farm level, improved understanding of feed quality, as well as feeding planning and practices, is a way to decrease the risk of N leaching and evaporation.

Apparent digestibility, fecal particle size, and mean retention time of reduced lignin alfalfa hay fed to horses

Reduced lignin alfalfa (Medicago sativa L.) has the potential to provide a higher-quality forage source for livestock by improving forage digestibility. This study was conducted to evaluate apparent digestibility when feeding reduced lignin and nonreduced lignin alfalfa hay to adult horses, and to examine mean fecal particle size (MFPS) and mean retention time (MRT) between alfalfa forage types. In 2017, reduced lignin ("54HVX41") and nonreduced lignin ("WL355.RR") alfalfa hay was harvested in Minnesota at the late-bud stage. Alfalfa hays were similar in crude protein (CP; 199 g/kg), neutral detergent fiber (NDF; 433 g/kg), and digestible energy (2.4 Mcal/kg). Acid detergent lignin concentrations were lower for reduced lignin alfalfa hay (74 g/kg) compared to nonreduced lignin alfalfa hay (81 g/kg). Dietary treatments were fed to six adult, stock-type horses in a crossover study. Experimental periods consisted of a 9-d dietary adaptation phase followed by a 5-d total fecal collection phase, during which horses were housed in individual boxstalls and manure was removed on a continuous 24-h basis. At 12-h intervals, feces were thoroughly mixed, subsampled in duplicate, and used for apparent digestibility and MFPS analysis. On day 2 of the fecal collection phase, horses were fed two indigestible markers, cobalt (Co) and ytterbium (Yb), which were fed as Co-ethylenediaminetetraacetic acid and Yb-labeled NDF residue, respectively. Additional fecal samples were taken at 2-h intervals following marker dosing until 96-h post-dosing to evaluate digesta MRT. Data were analyzed using the MIXED procedure of SAS, with statistical significance set at P ≤0.05. Dietary treatment (i.e., alfalfa hay type) was included as a fixed effect, while experimental period and horse were considered random effects. Dietary treatments were similar in dry matter intake (1.6% bodyweight) and time to consumption (7.6 h). Apparent dry matter digestibility (DMD) was greater for reduced lignin alfalfa (64.4%) compared to nonreduced lignin alfalfa (61.7%). Apparent CP and NDF digestibility did not differ between dietary treatments, averaging 78% and 45%, respectively. Dietary treatments were similar in MFPS (0.89 mm) and MRT for both liquid (23.7 h) and solid (27.4 h) phase material. These results indicate an improvement in DMD for reduced lignin alfalfa hay when fed to adult horses, with no change in forage consumption, fecal particle size, or digesta retention time.

The Horse Gut Microbiome Responds in a Highly Individualized Manner to Forage Lignification

Although contributions of the equine gut microbiome to forage utilization are well recognized, the impact of alfalfa (Medicago sativa L.) lignification on the equine gut microbiome remains unknown; thus, we characterized microbial communities in the equine gut when feeding reduced lignin (RL) and conventional (CON) alfalfa hays to adult stock-type horses. Dietary treatments were fed to six horses in a crossover study. Experimental periods consisted of a 9-day dietary adaptation phase followed by a 5-day total fecal collection phase, during which horses were housed in individual box stalls and manure was removed on a continuous 24-hour basis. At 12-hour intervals, manure was mixed, frozen, and processed for V4, 16S rRNA amplicon MiSeq sequencing. Reduced lignin alfalfa did not shift microbiome composition equally across all horses; however, each subject's microbiome responded to hay lignin content in an individualized manner, mostly, in terms of beta diversity. Amplicon sequence variants affiliated to Akkermansia, Fibrobacter succinogenes, Treponema, and Paludibacter fluctuated significantly when RL alfalfa was fed, with abundance patterns unique to each horse. Horse-specific associations between individual gut microbiome traits and characteristics of the digested CON or RL alfalfa were also observed, mainly in regards to dry matter digestibility and mean fecal particle size. These results indicate that the horse gut microbiome responds in an individualized manner to changes in the amount of acid detergent lignin in alfalfa hay, potentially impacting several feed digestibility characteristics. The implications of these horse-specific responses to hay lignification, for metabolic health and performance, remain to be elucidated.

Digestibility and Retention Time of Coastal Bermudagrass (Cynodon dactylon) Hay by Horses

Simple Summary

Longer retention of forages with increased fiber concentrations may be a compensatory digestive strategy in horses. We investigated the digestive characteristics of bermudagrass hay, a prominent warm-season grass in the southeast United States that has greater fiber concentrations than other common forages fed to horses. The morphological structure and photosynthetic pathway of warm-season grasses differ from cool-season grasses and legumes which may have important impacts on equine digestion and digesta transit through the gastrointestinal tract. The retention time of Coastal bermudagrass was longer than alfalfa or orchardgrass hay. The digestibility of Coastal bermudagrass decreased with increasing maturity, but the fiber digestibility of alfalfa and orchardgrass was similar to the earliest maturity of Coastal bermudagrass hay. The chemical composition of the plant cell wall influences diet digestibility and is a major difference between warm-season and cool-season forages. The increased retention time of Coastal bermudagrass allows for microbial fermentation to occur longer, adapting to more difficult-to-digest plant cell walls in warm-season forages. The decrease in diet digestibility when horses consume warm-season forages can be reduced by feeding early maturity forage, by harvesting hay at an earlier stage of growth or managing pastures in a vegetative state.

Abstract

Bermudagrass (Cynodon dactylon) and other warm-season grasses are known for their increased fiber concentrations and reduced digestibility relative to cool-season grasses and legumes. This study investigated the digestive characteristics and passage kinetics of three maturities of Coastal bermudagrass hay. A 5 × 5 Latin square design experiment was used to compare the digestion of five hays: alfalfa (Medicago sativa, ALF), orchardgrass (Dactylis glomerata, ORCH), and Coastal bermudagrass harvested at 4 (CB 4), 6 (CB 6), and 8 weeks of regrowth (CB 8). Horses were fed cobalt-ethylenediaminetetraacetic acid (Co-EDTA) and ytterbium (Yb) labeled neutral detergent fiber (NDF) before an 84-h total fecal collection to determine digesta retention time. Dry matter digestibility was greatest for ALF (62.1%) and least for CB 6 (36.0%) and CB 8 diets (36.8%, SEM = 2.1; p < 0.05). Mean retention time was longer (p < 0.05) for Coastal bermudagrass (particulate 31.3 h, liquid 25.3 h) compared with ORCH and ALF (28.0 h, SEM = 0.88 h; 20.7 h, SEM = 0.70 h). Further evaluation of digesta passage kinetics through mathematical modeling indicated ALF had distinct parameters compared to the other diets. Differences in digestive variables between forage types are likely a consequence of fiber physiochemical properties, warranting further investigation on forage fiber and digestive health.