Large Bite Size Research Articles

The ‘Carrot Test’: An approach to characterize individual differences in oral processing behaviour and eating rate

BackgroundEating rate is a modifiable risk factor for obesity and efficient methods to objectively characterise an individual’s oral processing behaviours could help better identify people at risk of increased energy consumption. Many previous approaches to characterise oral processing and eating rate have relied on specialised equipment or wearable devices that are time consuming, expensive or require expertise to administer. The current trial used video-coding of the consumption of a standardised test food (the ‘carrot test’) to measure oral processing. ObjectiveWe sought (i) to test whether self-reported eating rate (SRER) is predictive of food oral processing derived from coded eating behaviours captured in the laboratory with a standardised test food, and (ii) to test whether differences in SRER are predictive of oral processing behaviours, eating rate and intake of a test meal. MethodsTwo hundred and fifty-three volunteers (86 male and 167 female, mean age 39.5 ± 13.6 years, mean BMI 22.2 ± 3.4 kg/m2) provided their SRER and anthropometric measurements of height, weight and dual-energy X-ray absorptiometry (DEXA) percentage fat mass. Participants were also video recorded eating a fixed 50 g portion of carrot and an ad libitum lunch meal of fried rice. Average eating rate (g/min), bite size (g) and number of chews per bite for the carrot and lunch were derived through behavioural coding of the videos. Energy intake (kcal) was recorded at lunch and a later afternoon snack. ResultsFaster SRER significantly predicted faster eating rate, larger bite size and more chews per bite observed during intake of the carrot (ß = −0.26–0.21, p ≤ 0.001) and the lunch (ß = −0.26–0.35, p ≤ 0.014). SRER did not significantly predict intake at lunch or during the afternoon snack (ß = 0.05–0.07, p ≥ 0.265). Participants’ oral processing of the carrot significantly predicted oral processing of the lunch (ß = −0.25–0.40, p ≤ 0.047) and faster eating rate of the carrot significantly predicted increased lunch intake (ß = 0.119, p = 0.045). None of the oral processing behaviours predicted afternoon snack intake (ß = −0.01–0.05, p ≥ 0.496). None of these associations were moderated by BMI or body composition. ConclusionWe confirm that SRER is a valid measure of group level differences in individual oral processing behaviours, but did not predict an individual’s energy intake at a lunch-time meal. With this approach, it is possible to characterise differences in eating rate by coding eating behaviours for a standardized test food (in this case, a fixed portion of raw carrot). This approach could be used to provide an objective measure of a person’s habitual oral processing behaviour, and was shown to be a significant predictor of eating rate and energy intake for a later test meal.

Spread it on thick? Relative effects of condiment addition and slice thickness on eating rate of bread.

Manipulating eating rate (ER) by food properties may enhance or reduce food intake. Within composite foods, such as bread with condiments, the shape of carrier food and the use of condiments are known to influence ER. However, not much is known about their quantitative impacts and interactions. This study investigates the effect of bread slice thickness and addition of condiment on oral processing (ER, chews per g, bite size). In a full factorial design, 30 participants (BMI 21.6 ± 2.0 kg m-2, 23.3 ± 2.1 year) consumed two types of bread (wholewheat (WB); and sourdough (SB)), in three different slice thicknesses (1, 2, 4 cm), with three conditions of margarine addition (0, 2, 4 g per slice of 28 cm2). The results showed that addition of margarine in both breads led to ∼50% higher ER in a non-linear fashion mainly via less chews per g (all P < 0.001). Increasing bread slice thickness in both breads, resulted in ∼15% higher ER, mainly via larger bite sizes (all P < 0.001). The addition of margarine reduced or overruled the effect of slice thickness on all oral processing characteristics (interaction margarine × slice thickness, all P < 0.01). Perceived sensory dryness showed a strong negative correlation with ER. In conclusion, this study highlighted the importance of bread slice thickness, amount of a condiment, and their interactions in controlling ER. Lubrication of the dry crumbs was a main mechanism in controlling ER in this study. These insights can help the design of products with lower ER.

Eating rate and bite size were related to food intake across meals varying in portion size: A randomized crossover trial in adults

Serving larger portions leads to increased food intake, but behavioral factors that influence the magnitude of this portion size effect have not been well characterized. We investigated whether measures of eating microstructure such as eating rate and bite size moderated the portion size effect. We also explored how sensory-specific satiety (SSS; the relative hedonic decline of a food as it is eaten) was affected by eating microstructure and larger portions. In a randomized crossover design, 44 adults aged 18–68 y (66% women; 46% with overweight and obesity) ate lunch in the laboratory once a week for 4 weeks. The meal consisted of pasta that was varied in portion size (400, 500, 600, or 700 g) and 700 g of water. Meals were video-recorded to assess bite count and meal duration, which were used to calculate mean eating rate (g/min) and mean bite size (g/bite). At each meal participants also completed an assessment of SSS. The results showed that as larger portions were served, meal intake increased in a curvilinear manner (p < 0.0001). Measures of eating microstructure did not moderate the portion size effect but were related to intake across all portions; faster eating rate, larger bite size, higher bite count, and longer meal duration were associated with greater consumption at all meals (all p < 0.0001). SSS was not influenced by any measure of eating microstructure or by portion size (all p > 0.10). In summary, the portion size effect was not moderated by eating microstructure, but relatively faster eating rates and larger bite sizes at meals, along with large portions, combined to increase food intake.

Mastication in overweight and obese children: A comparative cross-sectional study

ObjectiveThe objective of this study was to analyze masticatory characteristics in children from 7 to 10 years, and to compare these characteristics among normal weight, overweight and obese children. MethodsThis is a cross-sectional study, conducted in northeast Brazil, with a sample of 160 children, aged 7 to 10 years. The authors evaluated: nutritional and dental status; food intake; masticatory parameters and orofacial myofunctional characteristics. The children were divided according to nutritional status into normal weight (n = 101), overweight (n = 33) and obesity (n = 26) groups. ResultsThe results showed that Obese children had a larger bite size (g) (median = 6.0, Q1-Q3 = 4.0-9.0, p = 0.049) and performed fewer masticatory sequences (median = 3.0, Q1-Q3 = 2.0-3.2, p = 0.024) than children with normal weight (median = 5.0, Q1-Q3 = 4.0-7.0; median = 4.0, Q1-Q3 = 3.0-5.0). Furthermore, obese children finished feeding in a shorter time (s) (median = 62.5, Q1-Q3 = 50.5-70.0, p = 0.039) than normal weight children (median = 66.0, Q1-Q3 = 56.5-78.0) and overweight children (median = 66.0, Q1-Q3 = 58.0-81.5). ConclusionsThe present results suggest that obese children present changes in mastication, evidenced by larger bite-size, performing fewer masticatory sequences and rapid mastication, which may contribute to increased food consumption and the development of excess weight.

Relationship between bite size per mouthful and dental arch size in healthy subjects.

Although multiple factors influence food bite size, the relationship between food bite size per mouthful and mandible or tongue size remains poorly understood. Here, we examined the correlations between food bite size and the lower dental arch size (an indicator of tongue size) in human subjects with good oral and general health, using fish sausage and bread as test foods. Notably, bite size of both foods was significantly positively correlated with the lower dental arch size, whereas masticatory performance (measured in terms of glucose extraction from a gummy jelly) showed no dependence on bite size. Further, bite size was significantly positively correlated with the body mass index. Our findings suggest that larger bite size is associated with larger tongue size, which might be a contributory factor to obesity.

Prospective associations between parental feeding practices and children's oral processing behaviours.

Previous research demonstrated that faster eating rates are linked with increased intake of energy during a meal. Here, we examined whether within-meal parental feeding practices show cross-sectional and prospective associations with children's oral processing behaviours and whether the previously demonstrated association between faster eating rates and higher energy intakes varies by parental feeding practices. A subset (n=155) of children and their mothers from the Growing Up in Singapore Towards healthy Outcomes cohort participated in an ad libitum meal at age 4.5years. Children's oral processing behaviours (eating rate, bite size, chews per gram, oral exposure time, and meal duration) and parental feeding practices (autonomy-supporting and coercive prompts, restrictions, hurrying, and slowing) were recorded during the meal. Subsequently, 94 of the children participated in a follow-up meal without their mothers at age 6years. Parental feeding practices were not consistently associated with child oral processing behaviours overall. However, exploratory post hoc analyses revealed some sex differences. The mothers of girls with faster eating rates, larger bite sizes, and fewer chews were more likely to use hurrying, slowing, and restrictions, but similar associations were not observed among boys. Children who had the most problematic eating style and were eating fast and for long experienced more restrictions, instructions to slow down, and prompts. Faster eating rates were linked with the highest energy intakes if children were additionally prompted to eat. Prospective analyses showed that children who were more often prompted using coercive techniques and less frequently hurried at age 4.5years had faster eating rates at 6years and a larger increase in eating rates between ages 4.5 and 6years but did not consume more energy. Although the direction of these associations cannot be assumed, these exploratory analyses suggest sex differences in the associations between feeding practices and oral processing behaviours and highlight the potential role of parents in the development of children's oral processing behaviours.

A description of an ‘obesogenic’ eating style that promotes higher energy intake and is associated with greater adiposity in 4.5 year-old children: Results from the GUSTO cohort

Recent findings confirm that faster eating rates support higher energy intakes within a meal and are associated with increased body weight and adiposity in children. The current study sought to identify the eating behaviours that underpin faster eating rates and energy intake in children, and to investigate their variations by weight status and other individual differences. Children (N=386) from the Growing Up in Singapore towards Healthy Outcomes (GUSTO) cohort took part in a video-recorded ad libitum lunch at 4.5years of age to measure acute energy intake. Videos were coded for three eating behaviours (bites, chews and swallows) to derive a measure of eating rate (g/min) and measures of eating microstructure: eating rate (g/min), total oral exposure (min), average bite size (g/bite), chews per gram, oral exposure per bite (s), total bites and proportion of active to total mealtime. Children's BMIs were calculated and a subset of children underwent MRI scanning to establish abdominal adiposity. Children were grouped into faster and slower eaters, and into healthy and overweight groups to compare their eating behaviours. Results demonstrate that faster eating rates were correlated with larger average bite size (r=0.55, p<0.001), fewer chews per gram (r=−0.71, p<0.001) and shorter oral exposure time per bite (r=−0.25, p<0.001), and with higher energy intakes (r=0.61, p<0.001). Children with overweight and higher adiposity had faster eating rates (p<0.01) and higher energy intakes (p<0.01), driven by larger bite sizes (p<0.05). Eating behaviours varied by sex, ethnicity and early feeding regimes, partially attributable to BMI. We propose that these behaviours describe an ‘obesogenic eating style’ that is characterised by faster eating rates, achieved through larger bites, reduced chewing and shorter oral exposure time. This obesogenic eating style supports acute energy intake within a meal and is more prevalent among, though not exclusive to, children with overweight.Clinical Trial Registry Number: NCT01174875; https://clinicaltrials.gov/.

Effects of food diameter on bite size per mouthful and chewing behavior

Obesity is well known to be associated with a wide variety of illnesses, and is an increasing problem not only in developed countries but also in developing countries. It is well known that large bite size contributes to excess energy intake and obesity, whereas an increased number of chews before swallowing the food bolus is associated with suppression of obesity. However, the effect of food diameter on bite size per mouthful and on chewing behavior remains poorly understood. Here, we examined the effects of food diameter on bite size and chewing behavior using a masticatory counter during the mastication of stick-type biscuits having the same length (10 cm) and ingredients, but with four different diameters (3.0, 3.5, 4.0, and 8.0 mm). Bite length and bite weight per mouthful were similar among the 3.0, 3.5, and 4.0 mm groups. However, bite length in the 8.0 mm group was significantly smaller, whereas bite weight was significantly greater than in the 3.0/3.5 mm groups. Further, the number of chews gradually increased, whereas the number of chews per bite weight gradually decreased, with an increase of biscuit diameter. These results indicate that a smaller biscuit diameter is associated with a smaller bite weight per mouthful and a greater number of chews per bite weight. This is the first report to quantity the effect of food diameter on bite weight per mouthful and on chewing behavior; these results should be helpful in the design of effective, safe, and low-cost behavioral modification therapy to combat obesity.

Oral processing characteristics of solid savoury meal components, and relationship with food composition, sensory attributes and expected satiation

Background: The modern food supply is often dominated by a large variety of energy dense, softly textured foods that can be eaten quickly. Previous studies suggest that particular oral processing characteristics such as large bite size and lack of chewing activity contribute to the low satiating efficiency of these foods. To better design meals that promote greater feelings of satiation, we need an accurate picture of the oral processing characteristics of a range of solid food items that could be used to replace softer textures during a normal hot meal. Aim: The primary aim of this study was to establish an accurate picture of the oral processing characteristics of a set of solid savoury meal components. The secondary aim was to determine the associations between oral processing characteristics, food composition, sensory properties, and expected satiation. Methods: In a within subjects design, 15 subjects consumed 50g of 35 different savoury food items over 5 sessions. The 35 foods represented various staples, vegetables and protein rich foods such a meat and fish. Subjects were video-recorded during consumption and measures included observed number of bites, number of chews, number of swallows and derived measures such as chewing rate, eating rate, bite size, and oral exposure time. Subjects rated expected satiation for a standard 200g portion of each food using a 100mm and the sensory differences between foods were quantified using descriptive analysis with a trained sensory panel. Statistical analysis focussed on the oral processing characteristics and associations between nutritional, sensory and expected satiation parameters of each food. Results: Average number of chews for 50g of food varied from 27 for mashed potatoes to 488 for tortilla chips. Oral exposure time was highly correlated with the total number of chews, and varied from 27s for canned tomatoes to 350s for tortilla chips. Chewing rate was relatively constant with an overall average chewing rate of approximately 1chew/s. Differences in oral processing were not correlated with any macronutrients specifically. Expected satiation was positively related to protein and the sensory attributes chewiness and saltiness. Foods that consumed in smaller bites, were chewed more and for longer and expected to impart a higher satiation. Discussion: This study shows a large and reliable variation in oral exposure time, number of required chews before swallowing and expected satiation across a wide variety of foods. We conclude that bite size and oral-sensory exposure time could contribute to higher satiation within a meal for equal calories.

Oral processing characteristics of solid meal components, and relations with food composition, sensory attributes & expected-satiation

The current obesogenic food environment is characterized by energy dense, softly textured foods that can be eaten quickly. Previous studies suggest that oral processing characteristics such as large bite size, low number of chews and low orosensory exposure contribute to the low satiating efficiency of these foods. The current study investigated the oral processing characteristics of 35-solid meal components and examined associations between oral processing characteristics, food composition, sensory properties and expected satiation. A panel of 15 subjects consumed 50 g of 35-foods representing various staples (potatoes, rice, pasta), vegetables (broccoli, carrot), and protein rich foods such as meat and fish. Subjects were video-recorded during consumption of each food and their eating behaviours were coded for the number of bites, chews and swallows and derived measures such as chewing-rate, eating-rate, bite-size, and orosensory residence time. Subjects rated expected fullness for the 35-foods and the sensory differences were quantified using a separate trained sensory panel. Oro-sensory residence time was highly correlated with the number of chews (R2 = 0.98) and chew-rate was relatively constant at approximately 1 chew/s. Expected fullness was positively correlated with energy density (R2 = 0.40), protein (R2 = 0.33) and the sensory attributes chewiness (R2 = 0.15) and saltiness (R2 = 0.12). Foods that were consumed in smaller bites, were chewed for longer and were expected to impart a higher satiation. This information may be used to design foods/meals lower in energy and higher in satiating efficiency per kcal consumed.

Effect of bite size and oral processing time of a semisolid food on satiation

Background:Food texture plays an important role in food intake regulation. In previous studies we showed a clear effect of viscosity on ad libitum food intake and found indications that eating rate, bite size, and oral processing time (OPT) could play a role. Objective:The objective was to determine the effect of bite size and OPT of a food on satiation, defined as ad libitum food intake. Design:Twenty-two healthy subjects participated in all 7 test conditions. Bite sizes were free or fixed to small bite sizes (≈5 g) or large bite sizes (≈15 g). OPT was free (only in combination with free bite size) or fixed to 3 or 9 s. Subjects consumed chocolate custard through a tube, which was connected to a peristaltic pump. Sound signals indicated OPT duration. Results:Subjects consumed significantly more when bite sizes were large than when they were small (bite size effect:P < 0.0001) and when OPT was 3 s rather than 9 s (OPT effect:P = 0.008). Under small bite size conditions, mean (±SD) ad libitum intakes were 382 ± 197 g (3-s OPT) and 313 ± 170 g (9-s OPT). Under large bite size conditions, ad libitum intakes were much higher: 476 ± 176 g (3-s OPT) and 432 ± 163 g (9-s OPT). Intakes during the free bite size conditions were 462 ± 211 g (free OPT), 455 ± 197 g (3-s OPT), and 443 ± 202 g (9-s OPT). Conclusion:This study shows that greater oral sensory exposure to a product, by eating with small bite sizes rather than with large bite sizes and increasing OPT, significantly decreases food intake.

Constraints on herbivory by grizzly bears

Although well known as carnivores and not capable of digesting plant fiber, grizzly bears (Ursus arctos horribilis) consume over 200 species of plants and are entirely vegetarian in some ecosystems. Even in ecosystems with abundant meat resources, green vegetation can be an important seasonal food resource. Therefore, we examined the morphological, physiological, and environmental constraints that determine the nutritional value of herbaceous vegetation to grizzly bears. Short-term, board foraging trials were used with captive grizzly bears to determine constraints on intake rate including bite size, bite rate, bear size, plant species, plant height, and plant distribution. Feeding trials were conducted to determine the effect of protein level (12-35%) and digestible dry matter intake on weight gain. Finally, maximum daily intake, daily foraging time, and weight change were measured for captive bears foraging on highly abundant and nutritious forbs and grasses during 12-day trials. Intake during short-term board trials overestimated the intake of freely foraging bears from two- to seven-fold depending on bear size. Because of their relatively larger bite sizes, smaller absolute energy requirements, and relatively larger intake capacity, smaller bears (<120kg) made greater weight gains than very large bears on herbaceous vegetation. Smaller bears with ad libitum access to palatable, nutritious forbs gained weight at rates equal to wild bears. However, depending upon plant characteristics, bite sizes and available daily foraging time increasingly prevented large bears (>120kg) from gaining weight on herbaceous vegetation. Both captive and wild bears select forbs over grasses at similar growth stages because forbs are generally higher in protein and more digestible than grasses. Therefore, the nutritional well-being of wild grizzly bears could be improved in areas where bears are largely herbivorous and, thus, relatively small by purposefully managing for nutritious forbs.

Autumn Foraging Dynamics of Woodland Caribou in Experimentally Manipulated Habitats, Northeastern Washington, USA

Foraging options of woodland caribou (Rangifer tarandus caribou) in the high snowpack ecosystems of western North America become narrowed after freezing temperatures in antumn precipitate leaf-drop in deciduous shrubs. The objectives of this research were to determine the influence of (1) removing arborca lichen (Ascompecytes) on windthrown trees and myrtle boxwood (Pachistime myrsinites) and (2) stand type (oldgrowth versus clearcnt) on woodland caribou foraging dynamics during autum. Foraging trials were conducted with 3 tame woodland caribou in 6 0.5-ha pens. In 3 treatment pens all windthrown arboreal lichen-bearing trees were removed from the old-growth portion of the pen and extant invrtle hoxwood plants were removed from the entire pen. In the 3 control pens all extant windthrown trees and invrtle boxwood plants were retained In addition, pens were constructed such that half of each pen was in an old-growth stand of western red-cedar (Thuja plicata)-western hemlock (Tsuga heterophylla) and half was in an adjacent clearent. Arboreal hcher had the greatest influence on dry-matter intake rate (DMIR) because of the large bite size provided by this forage. In control pens, caribou had higher DMIR (P = 0.006) and crude protein intake rate (CPIR) (P = 0.007) than in treatment pens where lichen-bearing windthrown trees had been removed. Arboreal lichen from windthrown trees was 52% (range 43-61) of the total DMI in the old-growth portious of control pens Arboreal lichen from windthrown trees comprised 81% (range = 75-92) of the arboreal lichen bites (i.e., 19% of arboreal lichen bites were from litterfall and standing trees), and 28% range = 16-48) of total bites in the timbered portion of control peus. The DMIR (P = 0.004) and CPIR (P = 0.004) of caribou was also greater in old-growth than in clearcat portions of pens. Search time was greater (P = 0.008) in clearent portions or pens than in old-growth portions. Myrtle boxwood comprised <0.4% of caribou diets. These data suggest that arboreal lichen is an important dietary component earlier in antamn than previously reported.

Co-ordination and catalytic chemistry of 1,1′-bis(diphenylphosphino)ruthenocene (dppr). Synthesis of [MCl2(dppr)] (M = Ni, Pd or Pt) and molecular structures of dppr and [PtCl2(dppr)]·0.5CH2 Cl2

Three complexes of 1,1′-bis(diphenylphosphino)ruthenocene (dppr) viz. [MCl 2 (dppr)] (M = Ni, Pd or Pt) were synthesized and characterized. An improved synthesis of dppr was elaborated. The crystal structures of dppr and [PtCl 2 (dppr)]·0.5CH 2 Cl 2 were determined by X-ray crystallography. That of dppr shows a ruthenocene derivatized by a PPh 2 group on each C 5 ring. It is centrosymmetric with two PPh 2 groups trans disposed and the C 5 rings staggered and anti. The C 5 (centroid) · · · C 5 (centroid) separation is 3.606 A. In [PtCl 2 (dppr)] the planar platinum(II) centre is angularly distorted by the large bite size of dppr to give a large bite angle (P–Pt–P) of 101.0(1)° with a compressed Cl–Pt–Cl angle of 85.6(1)° and other C 5 ring deformations. The C 5 rings in dppr are parallel (θ = 0°) but subtended at 8.8° in the platinum(II) complex. The catalytic efficiency of [PdCl 2 (dppr)] in the Grignard coupling of MgPhBr with 1,2-dibromobenzene, which results in 93% conversion of the latter and gives 2-bromobiphenyl (79%) and o-terphenyl (15%) under reflux conditions, is superior to that shown by [PdCl 2 (dppf)] and [Pd(dppf) 2 ] [dppf = 1,1′-bis(diphenylphosphino)ferrocene]. This catalytic enhancement by dppr is consistent with a greater C 5 ring separation and larger bite angle subtended by dppr compared to that of dppf.

Predation risk and habitat selection in the persistence of a remnant caribou population.

A small caribou herd of 24-77 animals resided on Pic Island (1138 ha) in Lake Superior from 1976 to 1984. Most of the caribou populations on the adjacent mainland had gone extinct earlier in this century. We tested three hypotheses for the persistence of this remanant population: (1) there was more forage available on the island than the mainland, (2) the animals on the island were isolated from white-tailed deer and did not develop the meningeal worm infection, and (3) there was less predation by wolves on the island. Forage was more abundant on the mainland than on Pic Island. The eggs of meningeal worms were not found in the feces of deer on the mainland or Pic island. Wolves seldom visited the island and when they did there was escape habitat available for the caribou. We concluded that the herd persisted because of this reduced predation risk and that the animals were prepared to select a reduced variety and phytomass of forage to remain for long periods in the relatively safe island habitat. When the animals did visit the mainland to feed they sclected forbs that provided a large bite size. On the island food supplies were too meager to select plants that gave a large bite size and the caribou spent long intervals feeding. Caribou by using habitats with a large phytomass and selecting for large bite size should minimize their time feeding which would allow them more time to watch for predators.

Influence of sward characteristics on grazing behaviour and growth of Hereford steers grazing tropical grass pastures

Relationships between sward characteristics, grazing behaviour and growth of Hereford steers were studied on nitrogen-fertilized (378 kg ha-1 yr-1) Setaria anceps cv. Nandi and Digitaria decumbens swards continuously stocked at 4.3, 6.2 and 8.0 beasts ha-1 during five periods over 2 years. Availability of herbage, as measured by bite size, and nitrogen content and in vitro digestibility of herbage in the top of the swards were the two most important factors influencing the performance of steers. The relative importance of these factors varied between seasons, between stocking rate treatments and to a lesser extent between pasture species. The highest growth rates were measured on the leniently stocked pastures because steers were able to harvest feed easily (a large bite size) and could more readily select the more nutritious plant parts from the top of the sward. The swards were highly heterogeneous, and numerical analysis of data showed that at the same herbage yield, spatial distribution of herbage (leaf bulk density and leaf to stem ratio) and the nutritive value (in vitro digestibility and nitrogen content) of herbage greatly influenced the growth of steers. Cattle were unable to satisfy their feed requirements on some high quality but low-yielding swards, despite increasing grazing time to compensate for the small bites prehended (up to 707 min in 24 hr in spring). Consequently nitrogen and digestibility contents of extrusa samples were at times poor indicators of performance.

The effect of plant structure on the intake of tropical pastures. II.* Differences in sward structure, nutritive value, and bite size of animals grazing Setaria anceps and Chloris gayana at various stages of growth

Bite size (organic matter content per bite) of cows grazing swards of Chloris gayana (rhodes) and Setaria anceps (setaria) regrown for 2, 4, 6, and 8 weeks was measured using oesophageal fistulated animals. Sward canopy structure was measured by stratification into five vertical layers, each 15 cm high; for each layer weights of leaf and stem components were estimated. Chemical composition and in vitro digestibility of plant fractions and oesophageal fistulae samples were determined. Cows grazing the 4 week regrowths of rhodes grass had a larger bite size (0.32 g OM/bite) than when grazing 2 week regrowths (0.27 g OM/bite) when the availability of herbage and leaf material was lowest. Despite a marked increase in herbage yield as the pastures matured (up to 8427 kg/ha) the mean bite size decreased to a mean of 0.15 g OM/bite at 6 and 8 weeks. The bite size of cows grazing setaria pastures was lower than on the rhodes grass pastures but followed a similar pattern. A high density of leaf within the sward (sward leaf density) as well as a low stem content were considered to be the main factors affecting bite size. Setaria and rhodes grass pastures had both low sward bulk densities (a range of 14–96 kg/ha cm) and low sward leaf bulk densities (a range of 12–43 kg/ha cm) compared with temperate pastures. Basal layers of the sward contained more dense herbage (up to 148 kg/ha cm), but sward leaf density was usually less than 80 kg/ha cm and apparently inaccessible. ___________________ *Part I, Aust. J. Agric. Res., 24: 809 (1973).