A Simple Vegetation Criterion (NDF Content) May Account for Diet Choices of Cattle Between Forages Varying in Maturity Stage and Physical Accessibility

The management of extensively grazed pastures requires an understanding and prediction of the diet choices of herbivores grazing on vegetation that is qualitatively (maturity stage) and quantitatively (biomass, sward height) heterogeneous. The Optimal Foraging Theory (OFT, Stephens & Krebs, 1986), bases its predictions on the relative energy intake rate (EIR) of forages. However, as EIRs are difficult to assess at pasture and are subject to wide intra- and inter-individual variations, another vegetation criterion was sought (accessibility, quality), by-passing the animal\u27s influence, to predict cattle diet choices quantitatively

A Simple Vegetation Criterion (NDF Content) May Account for Diet Choices of Cattle Between Forages Varying in Maturity Stage and Physical Accessibility

The management of extensively grazed pastures requires an understanding and prediction of the diet choices of herbivores grazing on vegetation that is qualitatively (maturity stage) and quantitatively (biomass, sward height) heterogeneous. The Optimal Foraging Theory (OFT, Stephens & Krebs, 1986), bases its predictions on the relative energy intake rate (EIR) of forages. However, as EIRs are difficult to assess at pasture and are subject to wide intra- and inter-individual variations, another vegetation criterion was sought (accessibility, quality), by-passing the animal\u27s influence, to predict cattle diet choices quantitatively

How Herbivores Optimise Diet Quality and Intake in Heterogeneous Pastures, and the Consequences for Vegetation Dynamics

Understanding the interplay between foraging behaviour and vegetation dynamics in heterogeneous pasture is an essential requirement for evaluating the value of the resource for large herbivores and for managing that resource. The orientation of selective grazing behaviour between intake and diet quality depends on the spatial and temporal scales considered. In the short-term scale of a grazing sequence, there is evidence that large herbivores tend to optimise the intake rate of digestible materials by adaptation of their biting behaviour and by patch choice. On a day-to-day scale, there is evidence that large herbivores tend to prioritise the quality of the diet to minimise digestive constraints within the time that they can spend grazing. On a pasture scale, the search for areas giving the best trade-off between quantity and quality of intake leads to the optimisation of their foraging paths, in particular by modulating their sinuosity in response to heterogeneity. Repeated grazing of preferred patches creates a positive feedback on forage quality and enhances heterogeneity. Long-term consequences on vegetation dynamics, botanic composition and grassland quality are less understood

Choix alimentaire de jeunes bovins au sein d'un couvert herbacé hétérogène (comment gèrent-ils le compromis quantité ingérée-qualité du régime sous différentes contraintes d'accessibilité ?)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Feeding behaviour and diet choices of cattle with physical and temporal constraints on forage accessibility : An indoor experiment

An indoor choice experiment was conducted to assess the extent to which heifers offered two forages of different quality will attempt to consume the better quality forage when the weight/number of constraints applied on its harvesting increase. The experiment involved six Salers heifers, a leafy ( L) and a coarse (C) hay, and two combined or single accessibility constraints. A physical constraint consisted of reducing the prehensibility of L by covering the trough with a steel grid of either 4 cm or 6 cm mesh size ( L4 or L6 v. L∞ for no grid). A temporal constraint limited the daily access time to both hays to 4 v. 24 h. The hays were either offered alone or together over 2-week periods. Dry-matter intake and feeding time were recorded daily. As expected, the physical constraint (only L4 was efficient) made the heifers decrease their choice (proportion of feeding time or intake) for L regardless of access time, whereas the temporal constraint had no significant effect on choice. The heifers greatly modulated their intake rate of L even under strong physical constraint ( L4), and then unexpectedly managed to ingest L faster than C. This emphasizes their motivation to keep ingesting the better quality forage, and underlines the difficulties in comparing diet choices with the optimal foraging theory predictions based on the relative values of a behavioural component subject to large variation, i.e. intake rate. In a very constraining situation ( L4 and 4-h access), heifers made a choice that allowed them to increase their total daily digestible organic matter (DOM) intake compared with L4 or C offered alone because of an inverse relationship between feeding time and intake rate on L4. They did not however maximize their total daily DOM intake in a less constraining situation ( L∞ or L6 and C, with 4-h access), since they did not consume L exclusively and showed a marked preference for a mixed diet

Constraining the time available to graze reinforces heifers' preference for sward of high quality despite low availability

International audienc

Food sensory characteristics: their unconsidered roles in the feeding behaviour of domestic ruminants

When domestic ruminants are faced with food diversity, they can use pre-ingestive information (i.e. food sensory characteristics perceived by the animal before swallowing the food) and post-ingestive information (i.e. digestive and metabolic consequences, experienced by the animal after swallowing the food) to evaluate the food and make decisions to select a suitable diet. The concept of palatability is essential to understand how pre- and post-ingestive information are interrelated. It refers to the hedonic value of the food without any immediate effect of post-ingestive consequences and environmental factors, but with the influence of individual characteristics, such as animal’s genetic background, internal state and previous experiences. In the literature, the post-ingestive consequences are commonly considered as the main force that influences feeding behaviour whereas food sensory characteristics are only used as discriminatory agents. This discriminatory role is indeed important for animals to be aware of their feeding environment, and ruminants are able to use their different senses either singly or in combination to discriminate between different foods. However, numerous studies on ruminants’ feeding behaviour demonstrate that the role of food sensory characteristics has been underestimated or simplified; they could play at least two other roles. First, some sensory characteristics also possess a hedonic value which influences ruminants’ intake, preferences and food learning independently of any immediate post-ingestive consequences. Further, diversity of food sensory characteristics has a hedonic value, as animals prefer an absence of monotony in food sensory characteristics at similar post-ingestive consequences. Second, some of these food sensory characteristics become an indicator of post-ingestive consequences after their initial hedonic value has acquired a positive or a negative value via previous individual food learning or evolutionary processes. These food sensory characteristics thus represent cues that could help ruminants to anticipate the post-ingestive consequences of a food and to improve their learning efficiency, especially in complex environments. This review then suggests that food sensory characteristics could be of importance to provide pleasure to animals, to increase palatability of a food and to help them learn in complex feeding situations which could improve animal welfare and productivity

How do grazing heifers choose between maturing reproductive and tall or short vegetative swards ?

International audienceWe offered heifers the choice between a tall abundant reproductive sward (RS), evolving from ear emergence to full flowering in the course of the experiment, and a short (8-cm high, treatment S) or tall (14-cm high, treatment T) vegetative sward (VS). This aimed to create a trade-off between intake (maximal on RS) and diet quality (maximal on VS) to test heifers motivation to keep grazing the better quality forage (VS) as its accessibility and the quality of the alternative decreased. Six heifers were allocated per treatment and placed in experimental choice conditions for three successive 10-day periods. Feeding choices were recorded for 2 days per period from dawn to dusk. Total intake and diet quality were estimated from nitrogen and chromic oxide contents in faeces sampled during the last 5 days of the periods. Additional short-term intake rates were measured on all swards once per period. As expected, preference for VS increased as RS matured in both treatments (S or T). The behavioural response of the heifers to the decrease in VS height depended on RS maturity: the heifers increased their preference for RS in the first period and did not modify their choice in the second period. In the last period, not only they did not increase their grazing time on RS, but increased that on VS, even though potential DM and DOM intake rates remained higher on RS. They thus clearly expressed a strong preference for the vegetative sward. Increases in grazing time and biting rate enabled them to maintain both total intake and diet digestibility at the day scale. This emphasises the importance of the time scale used when observing diet choices of ruminants, particularly when these are offered a choice between foods of different digestibility and fill effect in the rumen. The results also suggest that if cattle are required to consume tall ageing RS swards in extensive grazing systems, then any VS patches should be very short or the animals should have high nutritional requirements and/or be given shorter daily grazing times