Can animal performance be predicted from short-term grazing processes?

Abstract

Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and fundamental process, which is bite gathering. We hypothesised that because the mechanics of bite formation dominate the foraging process, changes in short-term bite mass are reflected in longer-term animal performance across a wide range of sward conditions. We focus at the meal level of foraging, using experiments in which the effect of abiotic factors and digestive constrains are minimised, making intake rate the main currency. We estimated bite mass across a wide range of structural challenges to large-herbivore foraging in a long-term experiment with heterogeneous native grasslands. A conceptual model was developed for average daily gain, where energy gain and energy costs were proximate causal variables. Energy gain was a function of diet quality and components of daily intake rate, where bite mass was the main component estimated. In turn, components of intake rate were determined by sward structure and bodyweight. Energy costs were a function of bodyweight and abiotic conditions. Finally, sward structure, bodyweight and abiotic conditions were determined by experimental treatments, seasons and years. Then, the conceptual model was translated into statistical models that included variables measured or estimated, and coefficients representing all links in the conceptual model. Weight gain was a function of bite mass, forage characteristics, and animal and abiotic conditions. Models were set up to test whether forage and stocking conditions affected monthly gain beyond the effects through bite mass, after correcting for abiotic factors. Forage mass, height and disappearance did help predict monthly gain after bite mass was included in the model, which supported our hypothesis. However, stocking treatments and season had significant effects not incorporated in bite mass. Although the model explained 77.9% of liveweight gain variation, only 35.2% was due to fixed effects, with 10.8% accounted by bite mass and its interactions. Concomitant experiments showed that sward structure (first with sward height and the second with tussock cover) does determine bite mass and short-term intake rate in the complex native grasslands we studied. Yet, other temporal varying components of monthly gain not correlated with bite mass, temperature or wind, added most of the observed variation in monthly animal performance. Part of the model failure to account for variation in performance may be related to a significant and temporally variable grazing of tussocks. We used a bite mass model that assumed no tussock grazing. In light of these results and a parallel experiment, we conclude that tussock grazing must be incorporated in future versions of the model.

Fire‐induced negative nutritional outcomes for cattle when sharing habitat with native ungulates in an African savanna

“…Within each herbivory treatment, column means with different superscripts in parentheses differ significantly between fire treatments, while those with different subscripts without parentheses differ significantly between sampling periods. herbage quantity have been reported elsewhere (Hirata, Kunieda & Tobisa 2010;Heuermann et al 2011;Carvalho et al 2015;Raynor, Joern & Briggs 2015) and are generally associated with reduced bite depth or bulk density. However, we are the first to show that shared foraging with wild herbivores in burned areas can reduce herbage quantity, thereby reducing forage and nutrient intake by cattle.…”

“…; Carvalho et al . ; Raynor, Joern & Briggs ) and are generally associated with reduced bite depth or bulk density. However, we are the first to show that shared foraging with wild herbivores in burned areas can reduce herbage quantity, thereby reducing forage and nutrient intake by cattle.…”

El auto-suministro mejoró el desempeño de terneros pastoreando campo natural diferido en invierno en sistemas ganaderos extensivos

“…Grassland plant communities are inherently heterogeneous because of plant species diversity (Toombs et al, 2010), giving animals the chance to exercise selectivity. Diet quality is determinant of energy intake (Carvalho et al, 2015), therefore selecting the highest quality diet is of utmost importance to increase ADG (Boval et al, 2015). In both experiments, dead forage content was not affected by treatments (Table 1), so it can be assumed that all animals had the same opportunity to select green forage (leaves in particular) within each experiment.…”

“…In order to compensate for the reduced intake rates caused by constraints of canopy structure, grazing time allocation may increase as a compensatory behaviour mechanism (Glienke et al, 2016). Besides, according to Carvalho et al (2015), when diet quality is low, and animals have little opportunity to change it through selectivity, grazing time should be the main variable explaining variation in ADG. In both experiments, grazing activities were highly correlated with non-supplemented animals (Figure 1), even though this increased grazing time allocation was not enough to compensate for the lack of nutrients that would have allowed them to register similar ADG as the supplemented treatments.…”

Vegetation composition and forage mass in grassland with a double structure under two winter grazing regimes

“…In natural, sharp, double-structured pastures, estimation of forage mass is complex and sometimes inaccurate. The under-or over-estimation of forage mass stems from unequal distribution of the strata, which makes it difficult to predict exactly what will be consumed by animals, resulting in a low correlation between forage mass allowance and weight gain of live animals (CARVALHO et al, 2015;SOARES et al, 2015). Therefore, to achieve guaranteed animal performance, some farmers have used "forage accumulation" instead of "forage allowance" (TRINDADE et al, 2016).…”