Voluntary intake and digestibility of reed canarygrass and timothy hay fed to horses1

What the hay: predicting equine voluntary forage intake using a meta-analysis approach

To properly formulate diets, the ability to accurately estimate feed intake is critical as the amount of feed consumed will influence the amount of nutrients delivered to the animal. Inaccurate intake estimates may lead to under- or over-feeding of nutrients to the animal. Individual differences in equine forage intake are well-known, but predictive equations based on animal and nutritional factors are not comprehensive. The objective of the present study was to consolidate the current body of knowledge in the published literature on voluntary forage DM intake (VFDMI) in equines and conduct a meta-analysis to identify driving factors, sources of heterogeneity, and develop predictive equations. Therefore, a systematic literature search was applied and identified 61 publications which met the inclusion criteria. From each study, the outcomes of interest (e.g., forage intake), diet composition (e.g., forage information, nutrient composition), and animal factors (e.g., sex, age, breed, BW, exercise level) were extracted. Forage intake was analyzed as two different outcome variables: (1) VFDMI in kg/d and (2) VFDMI in g/kg BW. Linear mixed model analysis treating study as a random effect was applied, using a backward-stepping approach to identifying potential driving variables for VFDMI (both units) where all terms have P < 0.1. The best fitting models for VFDMI included similar factors (also across kg/d and g/kg BW) such as forage quality (i.e., neutral detergent fiber or CP content), forage type (i.e., grass, legume, or mixed), the animals' size category (i.e., horses vs ponies), and some management factors (i.e., pasture access). As anticipated, forage intake increased when higher quality forages were fed (i.e., lower neutral detergent fiber or higher CP), potentially due to improved digestibility. Additionally, VFDMI increased as BW increased but ponies increased their VFDMI more per every kg increase in BW compared to horses. Lastly, pasture access (i.e., grazing) may influence VFDMI such that pastured animals consume less than stalled animals, possibly due to the time it takes to graze forage. In conclusion, equations to predict equine VFDMI with high accuracy and precision (concordance correlation coefficient  = 0.82 - 0.95; root mean squared error RMSE = 0.82-5.49) were developed which could be applied in practice by equine nutritionists or owners and managers. The results of this meta-analysis confirm that animal traits and forage quality have a significant impact on the VFDMI of equines and should be accounted for when formulating diets to ensure nutritional requirements are met.

Thirty-Two Weeks of Oral Supplementation with LinPro® Increases Hoof Growth in Healthy Mares

LinPro® is a commercial dietary supplement marketed to increase hoof growth and quality. Ten mature (5-15 years) non-pregnant Quarter Horse mares without existing hoof quality issues were used to test the hypothesis that 32 weeks of daily supplementation with 113 g of LinPro® would increase hoof growth rates as compared to non-supplemented controls. Hooves were trimmed at the start of the study and every 8 weeks thereafter. A mark was applied on the hoof wall surface at 2.5 cm below the junction of the hoof wall and coronary band. At each trimming, the distance between the mark and coronary band was measured and a new mark placed. For front hooves, horses assigned to LP had greater total hoof growth over 32 weeks (2.65 ± 0.15 vs. 2.18 ± 0.12 cm; P = 0.048; Figure 2) and tended to have greater hoof growth per 8 week trimming cycle (0.64 ± 0.03 vs. 0.55 ± 0.03 cm; P = 0.085) than horses assigned to CON. Horses assigned to LP had greater plasma biotin concentrations (2158 ± 69 vs. 636 ± 62 ng/L; P < 0.001) and proportions of erucic acid in hoof tissue (1.03 ± 0.08 vs. 0.76 ± 0.07 %; P = 0.049) as compared to CON. Further, the most abundant fatty acids in hoof tissue were stearic, palmitic, oleic, and linoleic acids. LinPro® may provide an effective treatment to improve hoof growth rates in horses with otherwise healthy hooves.

Population Dynamics of Eriophyid Mites and Evaluation of Different Management Practices on Timothy Grass

Several species of eriophyid mites are important economic pests of timothy grass in the Mid-Atlantic United States. Feeding causes stunting, curling, and brown discoloration of leaves, and yield losses ranging up to 50%. Carbaryl is the only approved chemical control for these mites. We investigated the population dynamics of field infestations, host plant resistance, and several cultural control measures to develop a more sustainable management strategy. Seasonal phenology and overall abundance differed among timothy fields and between years, with mean peak densities ranging up to 731 eggs and 1,163 mites per 2.5 cm of leaf blade. Population differences were related to the age of the field, the prevailing temperatures, and snow cover during the fall and winter months. All varieties of timothy tested were susceptible, whereas several other forage grasses were significantly resistant to eriophyid mites as possible alternatives for replacing timothy. Fall harvesting reduced the buildup of mites during the winter but populations eventually rebounded and still reached economic densities by April. Burn-down herbicide, prescribed burning, and urea-based fertilizer treatments prior to green-up in the early spring had variable effects and may help to prevent economic losses; however, several concerns about the benefit/costs and practicality of these practices are discussed.

Effect of Dietary Forage/Concentrate Ratio on Nutrient Digestion and Energy and Protein Metabolism in Adult Donkeys

Simple Summary

In recent decades, the donkey husbandry industry has developed rapidly, catering for their use in pharmaceutical, meat and milk production. However, compared with horses and other livestock, animal feeding studies have not been addressed to understand how nutrient digestion and metabolism are limited in donkeys. In this paper, the effect of the forage/concentrate ratio (F/C) in three experimental diets (low-fiber ration, medium-fiber ration and high-fiber ration) was investigated on N and energy balance using the total feces and urine collected method in a 3 × 3 Latin square experimental design. Decreasing the F/C significantly promoted protein digestibility and decreased fiber digestibility; increasing the F/C remarkably decreased N retention through the greater increase in N excretion in urine; decreasing the F/C linearly increased the conversion efficiency of digestible energy to metabolizable energy.

Abstract

The domestic donkey is a unique equid species with specific nutritional requirements; however, limited feeding studies have been addressed so far to understand nutrient digestion and metabolism in donkeys. In the present study, six adult female Xinjiang donkeys (180 ± 10 kg live weight) were applied in a 3 × 3 Latin square design to investigate the effect of the forage/concentrate ratio (F/C) in three experimental diets on N and energy balance within 12 weeks. Rice straw and alfalfa hay were chosen as forage ingredients, and the diets included the following: (1) a high-fiber (HF) ration (F/C = 80:20), (2) a medium-fiber (MF) ration (F/C = 55:45), and (3) a low-fiber (LF) ration (35:45). After the fixed amount of diets were daily allowed to the animals, total feces and urine were collected to determine total tract digestibility, N and energy balance. As a result, dry matter intake did not differ among the three diet groups. Decreasing the dietary F/C significantly promoted protein digestibility and decreased fiber digestibility. The N and energy balance analysis showed that increasing the F/C remarkably (p < 0.01) decreased N retention through the increase in N excretion in urine, and the highest N loss relative to N intake was observed in MF. Meanwhile, decreasing the F/C linearly increased the conversion efficiency of digestible energy to metabolizable energy. Taken together, the results obtained in the present study implicated that the dietary forage level should not be less than 55% to maintain greater N and energy utilization in feeding practice, otherwise, a donkey’s N utilization might be highly discounted.

Equine pre-caecal and total tract digestibility of individual carbohydrate fractions and their effect on caecal pH response

The working hypothesis was that a minor postprandial caecal pH decline would affect apparent total tract digestibility (ATTD) of the fibre fraction in horses and, hence, that soluble fibre would amplify fermentation and consequently increase ATTD of fibre. This study was a 4 × 4 Latin Square design with a sequence of 17 days adaptation to the ration followed by 8 sampling days. The feed rations consisted of only timothy hay (Group H), hay plus molassed sugar beet pulp combined with either whole oats (Group OB) or barley (Group BB) and hay plus loose chaff based concentrate (Group M). Four horses fitted with permanent caecal cannulas and collection harnesses were used. A pH electrode with logger was inserted through the cannula and caecal pH was recorded at 1 min intervals for 8 h. The mobile nylon bag technique was used to quantify pre-caecal loss (PCL) of individual feedstuffs. Fibre was analysed as dietary fibre (DF), non-starch polysaccharides, soluble non-cellulosic polysaccharides (S-NCP), insoluble non-cellulosic polysaccharide (I-NCP) and neutral detergent fibre. The ATTD of the S-NCP fraction was above 0.8, which was 60% higher than for the I-NCP fraction. The PCL of starch were 0.98 (oats) and 0.75 (barley). The BB diet lowered (p < 0.001) postprandial caecal pH more than the other diets and a significant correlation was found between the lowest pH and ATTD of I-NCP (r = -0.66; p = 0.005). In conclusion, this study successfully measured the in vivo digestibility of individual fibre fractions and found that S-NCP was more digestible than the I-NCP, and that a single meal of unprocessed barley was sufficient to decrease caecal pH to such an extent that the fibre digestibility of the whole diet was negatively affected.

Protein quality and utilization of timothy, oat-supplemented timothy, and alfalfa at differing harvest maturities in exercised Arabian horses

To evaluate the protein quality and postgut N utilization of full-bloom timothy hay, oat-supplemented timothy-hay diets, and alfalfa hay harvested at different maturities, apparent whole tract N digestibility, urinary N excretion, and serum AA profiles were determined in light to moderately exercised Arabian horses. Six Arabian geldings (16.0 ± 0.3 yr; 467 ± 11 kg of BW) were randomly allocated to a 6 × 6 Latin square design. Diets included full-bloom timothy grass hay (G), G + 0.2% BW oat (G1), G + 0.4% BW oat (G2), mid-bloom alfalfa (A1), early-bloom alfalfa (A2), and early-bud alfalfa hay (A3). Forages were fed at 1.6% of the BW of the horse (as-fed). Each period consisted of an 11-d adaptation period followed by total collection of feces and urine for 3 d. Blood samples were taken on d 11 for analysis of serum AA concentrations. During the 3-d collection period, urine and feces were collected every 8 h and measured and weighed, respectively. Approximately 10% of the total urine volume and fecal weight per period was retained for N analyses. Fecal DM output was less (P < 0.05) in A1, A2, or A3 compared with G, G1, or G2. Apparent whole tract N digestibility was greater (P < 0.01) in A1, A2, and A3 compared with G, G1, or G2, and was greater (P < 0.05) in G1 and G2 compared with G. Nitrogen retention was not different from zero, and there were no differences (P > 0.05) in N retention among diets. Urinary N excretion and total N excretion were greater (P < 0.05) in A1, A2, and A3 compared with G, G1, or G2. Plasma concentrations for the majority of AA increased curvilinearly in response to feeding G, A1, A2, and A3 (quadratic, P < 0.05), with values appearing to maximize 2-h postfeeding. Although alfalfa N digestibility increased with decreasing harvest maturity, N retention did not differ and urinary volume and N excretion increased, indicating that postabsorptive N utilization decreased. In contrast, inclusion of oats at either 0.2 or 0.4% of the BW of the horse to timothy hay markedly enhanced N digestibility without increasing N excretion, indicating improvement in postgut N utilization. These findings indicate that feeding oat-supplemented timothy hay is more environmentally sustainable than feeding alfalfa to the horse at maintenance or under light to moderate exercise.

Voluntary intake and digestibility of teff hay fed to horses

The objective of this study was to evaluate nutrient composition, voluntary DMI, and apparent DM digestibility of teff hay cut at 3 different stages of maturity to evaluate its potential as a preserved forage for horses. Six mature Quarter Horse mares (12 +/- 3 yr; 553 +/- 39 kg of BW) were used in a replicated balanced Latin square design with 3 periods and 3 maturities of teff hay. Eragrostis tef ('Tiffany' teff) was planted in May and harvested at the boot, early-heading, or late-heading stage of maturity through the summer. Horses were acclimated to a mixture of maturities of teff hay for 8 d before the beginning of the study. After this acclimation period, each period consisted of a 9-d voluntary DMI phase, followed by a 3-d DM digestibility phase. The percentages of nonstructural carbohydrates (NSC) increased from 5.4% in the boot stage to 8.4% in the late-heading stage, whereas concentrations of CP, K, Fe, and Mn decreased. The Ca:P ratio was 2.0 ± 0.3 for all maturities. Horses had less DMI of late-heading teff hay (1.5% BW) than teff hay of other maturities (1.8% BW; P < 0.05), indicating a preference for the earlier maturities. The intake and nutrient composition of the boot and early-heading maturities was sufficient to meet 90 to 97% of the average DE of the horses and most other nutrient requirements. Digestibility decreased from boot to late-heading teff hay for DM, CP, ADF, and NDF (P < 0.05). Digestibility increased from boot to early-heading to late-heading hay for nonfiber carbohydrates and water-soluble carbohydrates (P < 0.05). For all maturities of teff hay, the NSC intake was below 10% of the total intake. In conclusion, the low NSC and DE of teff hay grown in central Pennsylvania under the conditions in this study make it an appropriate forage source for obese horses and those at risk for laminitis or other metabolic disorders.