Changes in the short‐term intake rate of herbage by heifers grazing annual grasses throughout the growing season

Abstract

Annual temperate grasses go through abrupt changes in morphological composition during the growing season, which can affect ingestive behavior of grazing cattle. However, few studies have examined the effects of gradual structural changes in annual temperate pastures on the herbage intake rate during the growing season. We hypothesized that lenient grazing (removal of 40% of the initial pre‐grazing height) maintains short‐term intake rate (STIR) of grazing cattle over the entire growing season, even with decreased leaf/stem ratios. The studied pastures contained Avena strigosa, Lolium multiflorum and a mixture of the two species. Short‐term intake rate was measured using the double weighing technique, evaluating both bite rate and bite mass. The percentage of stem + pseudostem and leaf lamina lengths in the herbage mass were measured. Relationships between sward structure and animal ingestive behavior were also examined. As the pasture growing season progressed, the STIR of heifers grazing annual temperate grass swards was affected more by the time required to take a bite than by bite mass. Moreover, the sward structure also changed after each grazing cycle, reducing the pre‐grazing leaf/stem ratio. However, reductions in the pre‐grazing leaf lamina mass (up to 37% of the sward herbage mass) and/or in the leaf lamina length (up to 52% of the extended tiller height) did not affect the STIR of grazing heifers, since the animals maintained their bite mass and time per bite. In summary, with a grazing down target of 40% of the pre‐grazing height, reductions in STIR of heifers grazing annual temperate grasses occurred when the pre‐grazing leaf lamina percentage was <37% of the sward herbage mass and/or <52% of the extended tiller height. These results suggested that to avoid STIR reductions during the last grazing cycles, managements to stimulate tillering and delay stem + pseudostem elongation are necessary and should be investigated.

Tall fescue sward structure affects the grazing process of sheep

“…Structural characteristics of the forage sward can stimulate, inhibit or limit the ingestive behaviour of animals 15 – 17 . These structural variables include leaf length and shape, cuticle thickness, stem physical properties, tiller density, proportion of senescent material, proportion and quantity of leaf blades, all of which are dependent on the species, growth habit, height, morphogenic characteristics, life cycle and longevity of the forage plant 17 – 24 . Thus, in the context of competition strategy at the plant–animal interface, the animals adapt to changes found in the pasture at the time of grazing, which promote behavioural changes, such as altering the pattern of displacement, food selection, the ratio of mass acquired and rate of harvest by animals, and mandibular and non-mandibular movements 25 – 28 .…”

Twenty-five-centimeter pre-grazing canopy height in palisade grass and forage peanut

“…Canopy structure modifies livestock short-term ingestion capacity (Carvalho et al, 2015;Guzatti et al, 2017). The highest instantaneous intake rate in CH25/ DS0 was due to the increased bite mass associated with a faster bite rate, which can be explained by the ease of selection, apprehension, and forage intake since the upper canopy stratum was characterized by a predominance of leaves.…”

What, how, and how much do herbivores eat? The Continuous Bite Monitoring method for assessing forage intake of grazing animals

“…Differences in estimation of intake between the two techniques may be associated with inherent error of both methodologies. Many studies in the literature reported high interindividual variability when using the DW method (Fonseca et al., 2012; Guzatti et al, 2017; Mezzalira et al., 2017). Other sources of variation, such as differences between paddocks and shifts (a.m. vs. p.m.) also add to the compound variation for many of the methodologies used for estimating intake (Bailey et al., 1996; Fraser, 2009; Gregorini, 2012).…”