Comparison of gut fill in sheep (Ovis aries) measured by intake, digestibility, and digesta retention compared with measurements at harvest

Gut capacity is an important factor in digestive physiology and is often measured as dry matter fill (DMF) following dissection, which prevents repeated measures in the same animal. It was proposed to calculate DMF from food intake, digestibility, and gut mean retention time (MRT), but empirical tests of this are few. We calculated DMF from intake, digestibility, and the MRT of small-particle (1 mm) and large-particle (20 mm) markers in 20 sheep (Ovis aries L., 1758) fed at different intake levels and compared results with DMF at dissection at the end of the feeding trial. MRT for smaller particles was significantly shorter than for larger particles (34.4 ± 6.1 vs. 42.5 ± 7.6 h, respectively). Correspondingly, DMF calculated from smaller particles (0.98 ± 0.27 kg) was significantly lower than DMF calculated from larger particles (1.20 ± 0.30 kg). The latter was not significantly different from DMF measured at dissection (1.18 ± 0.34 kg). These results suggest that DMF can be estimated from measures of digestive physiology. The choice of particle marker to determine MRT is crucial for the accuracy of the proxy. In ruminants, where small particles are consistently eliminated faster than larger particles, considerations of marker particle size are particularly important.

Use of rumen–reticulum fill to examine nutrient transfer and factors influencing food intake in white-tailed deer (Odocoileusvirginianus)

Estimating relationships of gut fill in mammalian herbivores is useful to understanding digestive functions. Large animals might have more fluid in the gut to facilitate nutrient transfer between the gut lumen and the gut wall. Furthermore, relationships between concentrations of dietary refractory and indigestible fiber (CRIF) and gut fill might indicate whether chemostatic factors or physical distension of the gut affects food intake. We collected white-tailed deer (Odocoileus virginianus (Zimmermann, 1780); 122 males, 152 females) from three sites in central and south Texas that varied in diet quality as indexed by rumen–reticulum crude protein concentrations. Large animals did not have more fluid in their rumina–reticula than small animals because the scalar between body mass and wet mass of rumen–reticulum contents was not greater than the scalar estimated for dry mass of rumen–reticulum contents. We expected a positive or an inverse relationship when rates of forage comminution, digestion, and particle passage were high or low, respectively. At the site where deer had access to a high-quality pelleted diet, we detected a positive relationship between CRIF and dry mass. At sites with free-ranging deer and lower quality diets, relationships between CRIF and dry fill were inversely related. Food intake of deer was probably influenced by chemostatic factors at the site with a high-quality pelleted diet and by physical distension of the gut at the other two sites.

The catastrophe of meal eating

Optimisation of feed intake is a major aim of pasture and range management for ruminants and understanding what influences feeding behaviour may play an important role in satisfying this aim. An obstacle to such understanding is the fact that feeding is a two-state variable (eating or not eating, albeit with changes in rate of eating during meals), whereas the likely influencing factors are mostly continuous variables. These include gut-fill, concentrations and rates of utilisation of nutrients and metabolites, and changes in nutrient demand due to growth, reproduction and environment, both climatic and social. Catastrophe theory deals mathematically with situations in which an outcome is discontinuous (e.g. eating or not eating) and influencing variables (‘control’ variables in terms of catastrophe theory) are continuously variable (e.g. physiological and environmental factors affecting feeding). We discuss models of feeding and develop an approach in which the Type 2 catastrophe, illustrated by the bifurcation or cusp diagram, is adapted to use negative feedbacks and capacity to handle food and nutrients as the two controlling factors. Ease of prehension, as expressed by rate of eating, is modelled, as are pauses within, as well as between, meals. Quantification has not yet been attempted and the approach is presented to stimulate new thinking about the modelling and prediction of feeding behaviour and meal dynamics.

Effect of different levels of dietary energy on growth and carcass traits of Black Bengal goat

The present study was aimed to know the effect of dietary energy levels on growth and carcass characteristics in Black Bengal goats. Nine female Black Bengal goats were divided into three groups having three goats in each group. Three iso-nitrogenous diets containing three levels of metabolizable energy (9.17, 10.40 and 11.63 MJ/kg DM) were randomly assigned to three groups. Goats were stall fed and slaughtered after 150 days of trial. Results showed that live weight gain was higher (28.3 ± 1.7 g/day) in high energy fed goats than others. There were no significant differences on total and daily average dry matter intake in different groups of goats. Body length was significantly higher in high energy fed group than others. Carcass weight and dressing percentage were also higher (p<0.05) in high energy fed goats. Caul fat and gut fill weight differed significantly (p<0.05) among the treatment groups, and higher caul fat and lower gut fill were obtained in high energy fed goats than others. In conclusion, high energy diet enhanced the growth, dressing percentage and carcass gain of female goats.DOI: http://dx.doi.org/10.3329/bjas.v43i2.20719 Bang. J. Anim. Sci. 2014. 43 (2): 159-165

Repeatability and frequency of in-paddock sheep walk-over weights: implications for individual animal management

Sheep liveweight is an indicator of nutritional status, and its measure may be used as an aid to nutritional management. When walk-over weighing (WOW), a remote weighing concept for grazing sheep, is combined with radio frequency identification (RFID), resulting ‘RFID-linked WOW’ data may enable the liveweight of individual sheep to be tracked over time. We investigated whether RFID-linked WOW data is sufficiently repeatable and frequent to generate individual liveweight estimates with 95% confidence intervals (95% CI) of <2 kg (a sufficient level of error to account for fluctuating gut fill) for a flock within timeframes suitable for management (1-day and 5-day timeframes). Four flocks of sheep were used to generate RFID-linked WOW datasets. RFID-linked WOW data were organised into three groups: raw (unfiltered), coarse filtered (remove all sheep-weights outside the flock’s liveweight range), and fine filtered (remove all sheep-weights outside a 25% range of a recent flock average reference liveweight). The repeatability of raw (unfiltered) RFID-linked WOW data was low (0.20), while a coarse (0.46) and fine (0.76) data filter improved repeatability. The 95% CI of raw RFID-linked WOW data was 27 kg, and was decreased by a coarse (11 kg) and fine (6 kg) data filter. Increasing the number of raw, coarse and fine-filtered data points to 190, 30 and 12 sheep-weights, respectively, decreased the 95% CI to <2 kg. The mean cumulative percentage of sheep achieving >11 fine-filtered RFID-linked WOW sheep-weights within a 1-day and 5-day timeframe was 0 and 10%, respectively. The null hypothesis was accepted: RFID-linked WOW data had low repeatability and was unable to generate liveweight estimates with a 95% CI of less than 2 kg within a suitable timeframe. Therefore, at this stage, RFID-linked WOW is not recommended for on-farm decision making of individual sheep.

Adjustment of Animal Growth Rate Responses in Repeat Measurement Grazing Trials

In animal-response grazing trials there are sources of uncertainty in one-period one-off measurements, which as partial factorisation over time, become traceable and quantifiable sources of variation in repeat measurement trials. This is illustrated for a trial comparing sheep and goat live-weight gains under two stocking rates on mixed species pastures established by three contrasting sowing methods. It used variable plot size to give uniform animal numbers and tracked changes in individual animal performance and pasture growth in different periods. It was repeated on the same plots and animals over 17 grazing cycles. The variation explainable was greater with growth rates expressed as percent live-weight increase per day, than as weight or metabolic weight increase per day. The base data sets were adjusted for specific weighing-day effects of estimated gut-fill using moving averages, and for calibration for individual animal effects by genotype/environment analysis. Collectively these significantly increased the proportion explainable by 3.1-3.8% in variance analyses using qualitative treatment variables, and 2.7-3.7% in response function analyses relative to measured climate, pasture, plot and collective animal covariates. Simulation studies, to allow for variability in the independent variables as well as the dependent variables, indicated that the proportion explainable could increase by a further 0-1.2% and 1.1-1.9% respectively for the variance or response function approaches.