Intake rate during meals and meal duration for sheep in different hunger states, grazing grass or white clover swards

Characterization of grazing behaviour microstructure using point-of-view cameras

Grazing patterns, intake structure, and diet selection are dynamic responses to animals' feeding environment. This study uses video sequences from animal-borne cameras to capture time- and scale-dependent grazing behaviour variables related to sward explanatory conditions. We observed grazing 'through' the sheep's eyes using point-of-view (POV) cameras coupled with event logging software. Time-specific sward features were measured by sampling 'really' grazed patches identified by applying a global navigation satellite system (GNSS) precision-grazing approach. Sward variables on a Mediterranean native sward were measured for two years during the active spring plant-growth cycle. Overall, the results demonstrate that POV cameras were able to capture grazing behaviour fine-tuning to changes in sward characteristics. Sheep compensate for the decrease in sward quantity and nutritive value by increasing the size and duration at each behavioural scale (i.e., meal, bout, and station) while increasing the bout rate and decreasing the station rate. Diet composition also changed as sward matured. The proportion of forbs in the diet remained high in early and late spring, and forbs and legumes were preferred to grasses in early spring. Grazing selectivity was more pronounced in late spring, with sheep favouring the middle stratum of the sward's vertical structure, preferring green vegetative material, while enlarging the feeding niches' span and spending more time at each niche, consequently reducing the station rate. Although data collected by individual animal-borne POV cameras were representative of the flock behaviour, they may underestimate the total grazing time outside major meals. The results indicate that the use of animal-borne video cameras is suitable for assessing variations in sheep grazing behaviour patterns in complex swards.

The effect of strain of Holstein-Friesian and feeding system on grazing behaviour, herbage intake and productivity in the first lactation

A comparative study of grazing behaviour, herbage intake and milk production was conducted using three strains of Holstein-Friesian (HF) heifer : 33 high production North American (HP), 33 high durability North American (HD) and 33 New Zealand (NZ) animals. Heifers were assigned, within strain, to one of three grass-based feeding systems : (1) the Moorepark (control) system (MP), (2) a high concentrate system (HC), (3) a high stocking rate system (HS). Strain of HF had no significant effect on grazing time or number of grazing bouts. The NZ strain had longer grazing bouts (P< 0.01) and spent a lower proportion of time ruminating (P< 0.05) than both the HP and HD strains. There was a significant strain ✕ feeding system interaction for biting rate. The biting rate of the NZ strain was reduced in the HC system. Biting rates in the HS feeding system were significantly higher (P< 0.001) than in the MP system. Heifers on HC had shorter grazing time (P< 0.01) with grazing bouts of shorter duration (P< 0.01). Increasing stocking rate (HS) decreased the proportion of time ruminating (P< 0.001) and tended to shorten grazing bouts (P = 0.06). The HP strain had higher (P< 0.05) herbage and total dry matter (DM) intakes than the NZ strain, while the HD strain was intermediate. Concentrate supplementation reduced (P< 0.001) herbage DM intake but increased (P< 0.001) total DM intake. The reduction of herbage DM intake per kg of concentrate DM intake (substitution rate) was greater for the NZ than the HP strain. The HP produced significantly higher milk, fat, protein and lactose yields than the NZ, while the HD strain was intermediate. The milk fat content of the NZ was higher than both the HP and HD strains, while the protein content was higher than the HP strain. Concentrate supplementation (HC v . MP) significantly increased yields of milk and milk components. Milk production responses to the HC system were much greater with the HP than the NZ strain. Increasing stocking rate (MP v . HS) significantly decreased milk protein yield. The results indicate that the choice of strain of HF may depend on the feeding system.

Effects of ewes grazing sulla or ryegrass pasture for different daily durations on forage intake, milk production and fatty acid composition of cheese

Sulla (Sulla coronarium L.) forage is valued for its positive impact on ruminant production, in part due to its moderate content of condensed tannin (CT). The duration of daily grazing is a factor affecting the feed intake and milk production of ewes. In this study, the effects of grazing sulla pasture compared with annual ryegrass, and the extension of grazing from 8 to 22 h/day, were evaluated with regard to ewe forage intake and milk production, as well as the physicochemical properties and fatty acid (FA) composition of cheese. During 42 days in the spring, 28 ewes of the Comisana breed were divided into four groups (S8, S22, R8 and R22) that grazed sulla (S) or ryegrass (R) for 8 (0800 to 1600 h) or 22 h/day, and received no feeding supplement. In six cheese-making sessions, cheeses were manufactured from the 48 h bulk milk of each group. Compared with ewes grazing ryegrass, those grazing sulla had higher dry matter (DM) intake, intake rate and milk yield, and produced milk that was lower in fat and higher in casein. Ewes grazing for 22 h spent more time eating, which reduced the intake rate, increased DM and nutrient intake and milk yield, and reduced milk fat. Due to the ability of CT to inhibit the complete ruminal biohydrogenation of polyunsaturated fatty acids (PUFA), the FA composition of sulla cheese was more beneficial for consumer health compared with ryegrass cheese, having lower levels of saturated fatty acids and higher levels of PUFA and n-3 FA. The FA profile of S8 cheese was better than that of S22 cheese, as it was higher in branched-chain FA, monounsaturated FA, PUFA, rumenic acid (c9,t11-C18:2), and had a greater health-promoting index. The effect of short grazing time on sulla was attributed to major inhibition of PUFA biohydrogenating ruminal bacteria, presumably stimulated by the higher accumulation of sulla CT in the rumen, which is related to a higher intake rate over a shorter eating time. Thus, grazing sulla improved the performance of ewes, thereby increasing, especially with short grazing time, the nutritional properties of cheese fat.

A tannin-blocking agent does not modify the preference of sheep towards tannin-containing plants

Sheep have been suggested to use their senses to perceive plant properties and associate their intake with consequences after ingestion. However, sheep with browsing experience do not seem to select against tannin-rich browsing materials in cafeteria trials. Thus, the objective of the present study was to evaluate the relationship between the chemical composition, selectivity index (SI), preference and intake rate (IR) of tannin-containing forage trees offered to sheep in cafeteria experiments. Four trees were selected for their condensed tannin content and their varying biological activities. Havardia albicans (high biological activity), Leucaena leucocephala (medium biological activity), Acacia gaumeri (low biological activity) and Brosimum alicastrum (very low biological activity) were used in this study. Ten hair sheep (23.7kg±1.43LW) with eight months of browsing experience in native vegetation were used in this study. Polyethylene glycol (PEG 3600MW) was administered to five sheep during all experiments. In experiment 1, fresh foliage from all trees was offered ad libitum for 4h. In experiment 2, B. alicastrum was withdrawn and the preference was determined again. The forage preference in experiment 1 was A. gaumeri (14.77gDM/kgLW)>B. alicastrum (11.77gDM/kgLW)>H. albicans (3.71gDM/kgLW)=L. leucocephala (1.87gDM/kgLW) (P<0.05). The preference in experiment 2 was A. gaumeri>H. albicans=L. leucocephala. PEG administration had no effect on the preference or IR. The intake rate seemed to have been affected by the plant density. Moreover, fiber compounds were found to be better predictors of DM intake than polyphenolic compounds at levels typically found in the evaluated forages. It was concluded that tannins and PEG did not modify the preferences of sheep in cafeteria trials. Thus, tannins are not involved in the preference regulation of animals with browsing experience.

Continuous bite monitoring: a method to assess the foraging dynamics of herbivores in natural grazing conditions

Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivores has been historically considered as a fundamental methodological difficulty, a difficulty that increases with the complexity of the feeding environment. Improving these methodologies will help understand foraging behaviours in natural grazing conditions, where habitat structure and interactions among different forages influence feeding decisions and patterns. During the past 30 years, we have been developing the ‘continuous bite-monitoring’ method, an observational method that allows continuous assessment of foraging behaviours, including bite mass, instantaneous intake rate and food selection, in simple to complex feeding environments. The centrepiece of the method is a ‘bite-coding grid’ where bites are categorised by structural attributes of the forage to reflect differences in bite masses. Over the years, we have been using this method with goats, sheep, llamas and cattle across a range of different habitats. After reviewing the development of the method, we detail its planning and execution in the field. We illustrate the method with a study from southern Brazilian native Pampa grassland, showing how changes in the forages consumed by heifers strongly affect short-term intake rate during meals. Finally, we emphasise the importance of studying animals grazing in their natural environments to first identify the relevant processes that can later be tested in controlled experiments.