Diet Selection Of Sheep Research Articles

Diet selection of sheep shifted from quality to quantity characteristics of forages as sward availability decreased

Understanding the dynamic inter-relationship between grazing animals and the pasture sward is critical for sustainable grazing management. A field study was conducted to investigate the relationships between the quantity and quality characteristics of forages and diet selection of 30-kg Mongolian ewes in different seasons in Bromus inermis improved meadow steppe. Using a residual herbage mass method (1 000 kg/ha in spring, 800 kg/ha in summer and 600 kg/ha in autumn) to adjust stocking rate, three seasonal rest grazing strategies (spring rest, summer rest and autumn rest) combined with continuous grazing were studied. In each season, diet selection of sheep, quantified by diet composition and selectivity index, was estimated using a plant wax marker technique. Quantity (dry weight proportion, coverage, frequency, density and height) and quality (CP, NDF, ADF and DM digestibility) characteristics of forages consumed by sheep were determined simultaneously. Our results showed that in spring with the highest sward availability (herbage mass), diet selection of sheep could be predicted by the positive linear relationship between quality characteristics of forages and their selectivity index. In summer, the diet selection could be predicted by both positive linear relationship between quality characteristics and selectivity index, and the relationship between quantity characteristics and diet composition. While in autumn with the lowest sward availability, it could be predicted by the positive linear relationship between quantity characteristics and diet composition. During the whole grazing season, the diet composition of B. inermis (40.4%) and Leymus chinensis (35.1%) were larger than that of Potentilla bifurca (9.5%) and Carex (15.1%) and the selectivity index of P. bifurca was the highest (0.62), followed by Carex (0.17) and B. inermis (0.05), and L. chinensis (−0.29) was the lowest. The two parameters of diet selection above were positively related to their quantity and quality characteristics, respectively. These results suggested that the influence of quality characteristics on diet selection of sheep decreased gradually as a result of the decline in sward availability, while the influence of quantity characteristics increased. This study provides a comprehensive understanding of diet selection of sheep examining the trade-offs between quantity and quality characteristics of forages. The knowledge of diet selection of sheep and the corresponding prediction regressions acquired in this study could give the basis for designing appropriate grazing management strategies.

Phosphorus limitation relates to diet selection of sheep and goats on dry calcareous grassland

AbstractAimsWe aimed to (1) identify the nutritive value of late season herbage of principal species on dry calcareous grassland, (2) study the forage supply for sheep and goats and the degree of its exploitation by these animals, (3) identify the animals’ preference for particular plant species and types (grass, forb, shrub), and (4) identify the indicators of diet selection at the scale of the functional traits and nutritional value of selected plant species.LocationPálava Protected Landscape Area, Czech Republic (48°50′ N, 16°38′ E).MethodsThe investigation was based on the rotational grazing of sheep and goats for conservation purposes from Aug to Sept 2008. In all paddocks, the plant species composition and cover were identified. Animals were observed for 14 h a day to record their diet. Diet selectivity regarding 17 plant species and type was calculated. For ten plant species, the functional traits, i.e. canopy height, specific leaf area (SLA), leaf dry matter content (LDMC) and nutritive value, were measured. Differences in diet selection by sheep and goats and the drivers of diet selection were assessed.ResultsOf a total of 138 plant species recorded in all paddocks, sheep and goats grazed on 136 and 126, respectively. Sheep grazed more selectively on forbs than on grasses and shrubs, whereas goats grazed on forbs preferentially, on shrubs in conformity with supply in the vegetation cover, and avoided grasses. The diet selectivity of both sheep and goats was similar and was positively correlated with a high concentration of N, P, K, Ca and Mg, which were particularly high in the leaves of Prunus spinosa and lowest in Bromus erectus, and negatively correlated with the LDMC and fibre content in grasses.ConclusionsDry nutrient‐poor calcareous grassland in the late season did not offer animals more macronutrients than required for their maintenance. The animals adapted their foraging strategy to select preferentially forbs or woody species particularly rich in P and with a relatively low fibre content, the real indicators of diet selection. Late grazing could therefore contribute to the control of woody plant species, but cannot suppress expansive grasses.

Effects of the vertical and horizontal availability of food resources: the diet selection of sheep grazing on natural grassland

SUMMARYThe relationship between sheep diet selection and the vertical/horizontal availability of plant species on complex natural Leymus chinensis grassland was investigated. Two plots (low and high stocking rate plots) with different vegetation availabilities, created by adjusting sheep numbers, were studied for 3 months (June, July and August). In each month, the sheep's diet composition was estimated using n-alkanes in combination with long-chain alcohols and/or fatty acid markers. Vertical (sward surface height) and horizontal food availability (proportion cover of individual plant species) were determined simultaneously. The results revealed that sheep diet composition varied greatly according to seasonal variations in vegetation availability, and that sheep diet selection was related to the vertical and horizontal availability of plant species on both plots. Horizontal availability, which turned out to be the main influencing factor, was strongly and positively correlated with sheep diet composition in each month on both plots. On the low stocking rate plot, vertical availability affected sheep consumption in June, July and August. In contrast, a significant correlation between diet composition and vertical availability was only observed in July on the high stocking rate plot. These results suggest that the relative importance of vertical and horizontal availability differed between plots depending on vegetation availability. Horizontal availability played a more important role than vertical availability when sheep grazed freely on natural L. chinensis grassland. Finally, the changing selectivity index for each plant species in each grazing period on both plots indicated different grazing impacts on vegetation communities when vegetation availability differed.

Plant Trait Assembly Affects Superiority of Grazer's Foraging Strategies in Species-Rich Grasslands

BackgroundCurrent plant – herbivore interaction models and experiments with mammalian herbivores grazing plant monocultures show the superiority of a maximizing forage quality strategy (MFQ) over a maximizing intake strategy (MI). However, there is a lack of evidence whether grazers comply with the model predictions under field conditions.Methodology/FindingsWe assessed diet selection of sheep (Ovis aries) using plant functional traits in productive mesic vs. low-productivity dry species-rich grasslands dominated by resource-exploitative vs. resource-conservative species respectively. Each grassland type was studied in two replicates for two years. We investigated the first grazing cycle in a set of 288 plots with a diameter of 30 cm, i.e. the size of sheep feeding station. In mesic grasslands, high plot defoliation was associated with community weighted means of leaf traits referring to high forage quality, i.e. low leaf dry matter content (LDMC) and high specific leaf area (SLA), with a high proportion of legumes and the most with high community weighted mean of forage indicator value. In contrast in dry grasslands, high community weighted mean of canopy height, an estimate of forage quantity, was the best predictor of plot defoliation. Similar differences in selection on forage quality vs. quantity were detected within plots. Sheep selected plants with higher forage indicator values than the plot specific community weighted mean of forage indicator value in mesic grasslands whereas taller plants were selected in dry grasslands. However, at this scale sheep avoided legumes and plants with higher SLA, preferred plants with higher LDMC while grazing plants with higher forage indicator values in mesic grasslands.ConclusionsOur findings indicate that MFQ appears superior over MI only in habitats with a predominance of resource-exploitative species. Furthermore, plant functional traits (LDMC, SLA, nitrogen fixer) seem to be helpful correlates of forage quality only at the community level.

Evaluation of very long-chain fatty acids and n-alkane epicuticular compounds as markers for estimating diet composition of sheep fed heathland vegetation species

Application of very long-chain fatty acids (VLCFA) as an alternative or a complement to the alkane markers to estimate diet composition of sheep offered six different diets was evaluated. Twenty-four adult crossbred sheep were housed in metabolic crates and fed with diets composed of different proportions of herbaceous ( Lolium perenne and Trifolium repens) and woody species ( Erica spp., Calluna vulgaris and Ulex gallii). Diet composition was estimated from VLCFA (i.e., C 22–C 34) and alkane (i.e., C 25–C 33) concentrations in diet and faeces, by least-squares procedures, considering the plant species effectively offered to the animals (C1) or these plant species plus feeds that were not part of the diets but were available in the field at each experimental period (C2). Prior to this, faecal VLCFA and alkane concentrations were uncorrected for incomplete faecal recovery (FC0), corrected using recovery data for each individual ewe (FC1), corrected using mean recovery rate of the dietary treatment that the animal belonged to (FC2), or corrected using mean recovery rate across all experimental diets (FC3). For all diet components, total VLCFA concentrations were higher ( P<0.01) than those observed for alkanes, with a predomination of even-chain ( P<0.001) over odd-chain. Faecal recovery was incomplete and tended to increase with carbon-chain length in a curvilinear ( P<0.001) fashion for the even-chain VLCFA, and a linear ( P<0.001) one for odd-chain VLCFA and alkanes. Diet composition had an effect ( P<0.001) on faecal recovery of both markers. Estimates of diet composition obtained using alkanes alone were more accurate ( P<0.05) than those obtained with VLCFA alone while their combination resulted in an improvement ( P<0.05) of the accuracy. Estimates obtained when considering plant species offered effectively to the animals were more accurate ( P<0.001) than those obtained when considering more plant species as possible diet components. In general, use of faecal marker concentrations corrected with FC2 and FC3 provided equally accurate estimates of diet composition, indicating that an overall recovery data can be applied to these markers in grazing studies without losing accuracy in the estimation. Although the use of alkanes resulted in more accurate estimates of diet composition, results obtained in this study showed that VLCFA can be useful markers for studying diet selection of sheep grazing on shrubland vegetation communities. However, a suitable adjustment of their faecal concentrations prior to their application is recommended. It is also concluded that use of VLCFA in combination with alkanes could result in more accurate estimates of diet composition.

The use of the alkane technique to estimate diet selection of sheep grazing grass–clover/heather–gorse vegetation communities

AbstractThe n‐alkane technique was evaluated for estimating the diet composition of sheep grazing in heathlands. Six dietary treatments, composed by different proportions of herbaceous (Lolium perenne and Trifolium repens) and woody species (Erica umbellata, Erica cinerea, Calluna vulgaris and Ulex gallii) were offered to 24 sheep housed in metabolism crates. Diet composition was estimated from alkane concentrations in diet and faeces, by least‐squares procedures, using all available alkanes (C1) from C25 to C33, or only those with higher concentration (C2): C27, C29, C30, C31 and C33. Additionally, the effect of applying mean treatment faecal recoveries (R1), mean faecal recoveries of all experimental diets (R2) or no faecal recovery correction (R3) was studied in both selections of alkanes (C1 and C2). No significant differences were observed between the use of all alkane information (C1) or limited number of alkanes (C2) in the diet composition calculations. There were no significant differences between measured proportions of dietary components and those estimated with procedures R1 and R2. In contrast, the proportions calculated with R3 procedure differed significantly (P &lt; 0.05) from the measured proportions, overestimating feeds with higher content of long chain n‐alkanes. The results indicate that correction of faecal alkane concentrations to allow for incomplete faecal recovery is necessary in order to obtain accurate estimates of diet composition, using mean treatment faecal recoveries (R1) or mean faecal recoveries of all experimental diets (R2). Copyright © 2006 Society of Chemical Industry

Foraging in patchy grasslands: diet selection by sheep and cattle is affected by the abundance and spatial distribution of preferred species

Understanding the distribution of grazing activity and its management is valuable to en- sure the sustainability and productivity of heterogeneous grasslands. Controlled behavioural studies can provide insight into the cognitive abilities of herbivores and suggest new approaches to improve their grazing distribution. We compared the behaviour and diet selection of sheep and cattle in 1-ha fescue (Festuca arundinacea S.) plots, in which the number and size of preferred ryegrass (Lolium perenne L.) patches were varied. Five different patterns were used to investigate the effects of ryegrass abundance and spatial distribution on the searching success of the herbivores. Both heifers and ewes grazed ryegrass more when its abundance increased from 1.5 to 6% , and also when ryegrass was aggregated into a few 8 × 9-m patches, rather than being dispersed into a larger number of 3 × 3-m ones. Neither the interaction between ryegrass abundance and patch size, nor that between herbivore species and patch size was significant. At 6% abundance, aggregating ryegrass into a single 24 × 24-m patch tended to further increase its use by heifers, but not by ewes. Fescue less than 1 meter from the nearest ryegrass patch was usually selected more than the fescue located further away. Fescue be- tween 1 and 5 m from the nearest patch was never selected more than the fescue located further away. Our results, together with those for the diet selected by sheep, cattle and deer, when offered patches of a preferred food in aggregated or dispersed patterns, indicate that over a wide range of abundance, it is advantageous for herbivores to forage on patchy resources when the preferred vegetation is aggre- gated. This corroborates the prediction that foraging costs associated with patch distribution are in- volved in determining diet selection in patchy grasslands, but our results suggest that it is also influenced by some social characteristics of the animals, such as their social attraction and social tol- erance.

The effect of consumption of foods that differ in energy density and/or sodium bicarbonate supplementation on subsequent diet selection in sheep

The short-term consumption of foods that differed in energy density (ED) and/or NaHCO3 supplementation, on subsequent food intake and diet selection in sheep were measured. Thirty sheep weighing 35·9 (SD 2·89) KG WERE USED. TWO FOODS WERE FORMULATED: H HAD 11 AND L HAD 8 MJ METABOLIZABLE ENERGY/KG FRESH MATTER. FOUR FURTHER FOODS WERE FORMULATED BY ADDING EITHER 40 G NAHCO3/KG OR 16·5 G NACL/KG TO FOODS H AND L. NACL WAS ADDED TO GIVE THE SAME NA CONCENTRATION AS WITH 40 G NAHCO3/KG TO CONTROL FOR ANY EFFECTS OF NA PER SE. IN A PRELIMINARY TEST, IT WAS FOUND THAT A 2 H CONSUMPTION OF FOOD H SUPPLEMENTED WITH NAHCO3 COULD BUFFER POTENTIAL IMPACT ON THE RUMEN ENVIRONMENT OF SUBSEQUENT CONSUMPTION OF FOOD H ALONE (AS JUDGED BY RUMEN PH AND ACID-BUFFERING CAPACITY); HOWEVER, IT WAS NOT AS EFFECTIVE AS THE CONSUMPTION OF FOOD L ALONE IN DOING SO. EACH FOOD TREATMENT WAS OFFERED TO ONE OF SIX GROUPS (N 5) FOR 2 H FOLLOWING 16 H OF FOOD DEPRIVATION. SHEEP WERE THEN OFFERED A CHOICE BETWEEN H AND L FOR A FURTHER 6 H. SUPPLEMENTING H OR L WITH EITHER NAHCO3 OR NACL HAD NO SIGNIFICANT EFFECT ON EITHER INTAKE OR DIET SELECTION. ED SIGNIFICANTLY (P&lt;0·01) AFFECTED INTAKE DURING THE 2 H SINGLE FEEDING PERIOD, WITH SHEEP OFFERED H OR L CONSUMING 540 AND 663 (sed 37) g respectively, but had no effect on subsequent intake during the choice period. During the choice period all sheep showed a preference for food H, but sheep previously offered L selected significantly more H (0·873 g/g) than sheep previously offered H (0·544 (sed 0·028) g/g; P&lt;0·001). It is concluded that short-term consumption of foods that differ in ED, and hence in their potential impact on the rumen environment, significantly affects subsequent diet selection. This is in agreement with the hypothesis that ruminant animals select a diet to help maintain the rumen environment within a certain physiological range. Food H with 40 g NaHCO3 added/kg may not have been sufficient to affect subsequent diet selection. It is suggested that larger, rather than smaller, changes in the rumen environment achieved through previous feeding should be expected to alter subsequent diet selection.

The effect of consumption of foods that differ in energy density and/or sodium bicarbonate supplementation on subsequent diet selection in sheep.

The short-term consumption of foods that differed in energy density (ED) and/or NaHCO3 supplementation, on subsequent food intake and diet selection in sheep were measured. Thirty sheep weighing 35.9 (sd 2.89) kg were used. Two foods were formulated: H had 11 and L had 8 MJ metabolizable energy/kg fresh matter. Four further foods were formulated by adding either 40 g NaHCO3/kg or 16.5 g NaCl/kg to foods H and L. NaCl was added to give the same Na concentration as with 40 g NaHCO3/kg to control for any effects of Na per se. In a preliminary test, it was found that a 2 h consumption of food H supplemented with NaHCO3 could buffer potential impact on the rumen environment of subsequent consumption of food H alone (as judged by rumen pH and acid-buffering capacity); however, it was not as effective as the consumption of food L alone in doing so. Each food treatment was offered to one of six groups (n 5) for 2 h following 16 h of food deprivation. Sheep were then offered a choice between H and L for a further 6 h. Supplementing H or L with either NaHCO3 or NaCl had no significant effect on either intake or diet selection. ED significantly (P<0.01) affected intake during the 2 h single feeding period, with sheep offered H or L consuming 540 and 663 (sed 37) g respectively, but had no effect on subsequent intake during the choice period. During the choice period all sheep showed a preference for food H, but sheep previously offered L selected significantly more H (0.873 g/g) than sheep previously offered H (0.544 (sed 0.028) g/g; P<0.001). It is concluded that short-term consumption of foods that differ in ED, and hence in their potential impact on the rumen environment, significantly affects subsequent diet selection. This is in agreement with the hypothesis that ruminant animals select a diet to help maintain the rumen environment within a certain physiological range. Food H with 40 g NaHCO3 added/kg may not have been sufficient to affect subsequent diet selection. It is suggested that larger, rather than smaller, changes in the rumen environment achieved through previous feeding should be expected to alter subsequent diet selection.

Diet selection of sheep: sodium bicarbonate, but not the offering of hay, modifies the effect of urea on diet selection

AbstractThe hypotheses tested were that the expected preference of sheep for a food with adequate rumen degradable protein (RDP) supplemented with urea would be reduced both by the addition of a buffer (sodium bicarbonate (SB)) and by offering ad libitum access to hay. A control food (C), calculated to be adequate in its ratio of effective RDP to fermentable metabolizable energy (fME), was formulated. Other foods were made by adding 12·5 (U1) or 25 (U2) g urea per kg fresh matter (FM) to C and 20 g SB per kg FM to C, U1and U2. The acid buffering capacity (ABC) of each food was measured in vitro. The experiment consisted of two successive periods, each of 4 weeks. Ninety-eight female, Texel ✕ Greyface sheep were randomly allocated to 14 groups each with seven animals. Groups 1 to 6 were offered one of: C, U2, C + SB, U2+ SB, C with hay or U2with hay throughout the experiment. Groups 7 to 10 were offered the choices of C v. U1or C v. U2, either with or without hay in a change-over design; animals that received hay during period 1 (groups 8 and 10) did not do so during period 2 and vice versa (groups 7 and 9). Groups 11 to 14 (no. = 7) were offered the choices of C v. U1or C v. U2, either with or without SB supplemented to both foods, in a change-over design. Adding either urea, or SB, or both to C had no effects on intake or live-weight gain when offered alone. Both supplements significantly (P 0·001) increased the ABC of food C. Throughout the experiment hay consumption was very low (overall mean: 23 (s.e. 2·5) g hay per sheep day). Offering hay caused no change in the preference for the urea-supplemented foods. Sheep offered the choices C v. U1or C v. U2, with neither hay nor SB, selected 0.466 (s.e. 0·036) and 0.588 (s.e. 0·025) kg/kg total food intake (TFI) of U1and U2respectively. The proportions of the urea-supplemented foods were significantly reduced (P 0.01) by SB supplementation: to 0.348 (s.e.0·045) and 0·406 (s.e.0·059) kg/kg TFI of U1and U2respectively. The effect of SB addition on the diet selection of sheep could be due to its buffering properties. When SB is added to both foods the need for urea to be used as a buffer is reduced with a consequent decrease in the proportion selected as the urea-supplemented food. Effects of diet on buffering may override other diet selection objectives, such as the avoidance of an excess intake of RDP.

Diet selection of sheep: effects of adding urea to foods with different protein contents

AbstractTwo experiments were conducted in which growing sheep were given choices between foods differing in their contents of urea. The crude protein (CP) contents of both of the foods of the pair were also varied. The hypothesis tested was that the diets selected would be those that met the effective rumen degradable protein (eRDP) requirements of the animals and would avoid excess consumption of eRDP. Three basal foods, differing in CP were formulated. D was designed to be deficient in CP with 80 g CP and 58 g eRDP per kg DM; H was calculated to be adequate with 159 g CP and 114 g eRDP per kg DM; P had excess with 210 g CP and 148 g eRDP per kg DM. Other foods were made by adding 12·5 or 25 g urea per kg fresh matter to each of the three basal foods to make a further six foods. In both experiments Texel✕Greyface female sheep were used. In experiment 1, 34 sheep weighing 37·2 (s.d. 1·85) kg were randomly allocated to one of six groups and each group was offered a choice between a pair of foods. Groups 1 to 3 were offered pairs in the D series (Dv. D + 12·5 g urea per kg (no. = 6), Dv. D + 25 g urea per kg (no. = 6) and D + 12·5 g urea per kg v. D + 25 g urea per kg (no. = 5)). Groups 4 to 6 were offered the same pairs of foods but with H instead of D. In experiment 2, 96 sheep weighing 29·8 (s.d. 3·37) kg were randomly allocated to one of 12 groups. Groups 1 to 6 (no. = 6) were allocated a single food (D, D + 25 g, H, H + 25 g, P or P + 25 g urea per kg) throughout the experiment. Groups 7 to 12 were given a choice (no. = 10) between two foods. One food of the pair was the basal D, H or P. The other food was the same basal food supplemented with either 12·5 or 25 g urea per kg. On the single foods adding urea to D resulted in an increase in food intake and live-weight gain suggesting that D was deficient in eRDP. Adding urea to either H or P had no beneficial effects on intake or live-weight gain. This suggests that both contained sufficient eRDP in relation to energy. Across all choice treatments in both experiments there was a highly significant preference (P&lt; 0·01) for the food with the higher urea content. In experiment 1 0·62 (s.e. 0·04) of the diet selected was the food with the higher urea content. In experiment 2 the figure was 0·64 (s.e.0·03). The general preference for the food with the higher urea content was unaffected by the CP contents of the foods used. The results do not support the hypothesis that sheep will avoid excess eRDP when given a choice and suggest that eRDP may not be a relevant dimension in diet selection in the conditions of these experiments.

The interactive effects of novel food flavours and food composition on the diet selection of sheep

Animals have predispositions towards the organoleptic properties, such as flavours, of the foods available to them. These predispositions can influence the feeding behaviour and diet selection of animals and prevent from, or enable them to select a diet that meets their nutrient requirements, in both short - and longer - run (Forbes and Kyriazakis, 1995). In this experiment, we investigated whether predispositions of sheep for novel food flavours could affect their diet selection when offered a choice between two foods with different nutrient content. The specific hypotheses tested were that such predispositions are: (i ) influenced by the nutritional quality of the food that are associated with, and (ii) affected by the current nutritional state of the animal.

On the diet selection of sheep: effects of adding urea to foods with different protein contents

The basis of diet selection for protein in ruminants remains unclear. Tolkamp et al., (1998) proposed a hypothesis to account for the conflicting findings. They proposed that ruminants select their diet on the basis of effective rumen degradable protein (eRDP) rather than for MP yield. As the protein supply of ruminants comes largely from microbial protein, the idea that ruminants select a diet that meets the requirement for eRDP, which is captured and utilised by the microbes to produce microbial protein, is not an unreasonable one. The objective of this experiment was to test the hypothesis that both inadequate and abundant eRDP levels would be avoided by growing sheep when given choices of foods.

On the diet selection of sheep: sodium bicarbonate modifies the effect of urea on diet selection

It was hypothesised that both inadequate and abundant levels of effective rumen degradable protein (eRDP) would be avoided by ruminants given a choice of foods (Tolkamp et al, 1998). However, we have found that sheep do not appear to avoid the excess consumption of eRDP expected when they were offered a choice of foods that differed in eRDP content through the addition of urea to one of the foods (James et al., 2001). A possible reason could be due to the fact that the foods offered had low fibre contents. The sheep may have selected for the urea supplemented food in an attempt to buffer the rumen. The buffering ability of the urea could help to minimise the disruption of the rumen such as a fall in pH caused by the low fibre foods. The objective of this experiment was to test the hypothesis that the preference for the urea supplemented food would be reduced by the addition of sodium bicarbonate (buffer).

Effects of parasitic status and level of feeding motivation on the diet selected by sheep grazing grass/clover swards

An experiment was carried out to determine the effects of parasitic status and level of feeding motivation on the diet selected by sheep grazing perennial ryegrass/white clover swards. Twenty-four female Scottish Blackface weaned lambs were divided into four treatment groups each of six animals. Pre-grazing treatments were imposed to create two levels of feeding motivation, low (fed ad libitum) and high (0·60 of ad libitum diet) and two parasitic states, parasitized (daily dose of 2500 L3Ostertagia circumcincta) and non-parasitized. Each treatment group was placed in one of four 0·35 ha field plots and allowed to graze a mixed grass/clover sward. Mean clover height was manipulated pre-grazing by cutting so that it was less than the mean grass height. This maximized the probability that clover in the diet of sheep was due to selection. No fertilizer was added to the sward in order to ensure that the nitrogen content of the clover was higher than that of the grass. Each treatment group was rotated around the four plots on a daily basis for 2 weeks. Sheep with a high feeding motivation strongly and significantly selected clover and had a higher proportion of clover in their diet compared with sheep with low feeding motivation. Parasitic status had no significant effect on the diet selection of sheep; but the level of parasitic burden within parasitized sheep was positively correlated with the proportion of clover in the diet. Parasitized sheep spent less time grazing each day and had lower daily herbage intakes compared with non-parasitized sheep. This was a result of a reduction in the duration of feeding bouts and not a reduced number of bouts per day. Sheep with the higher feeding motivation had a greater number of feeding bouts per day and this resulted in those animals having a greater daily herbage intake. Level of feeding motivation had greater effects on the diet selection of sheep than parasitic status. Sheep with a high feeding motivation are able to select strongly for clover in their diet when there is low overall clover availability and are capable of dramatically affecting the species composition of a sward. This has implications to the maintenance of a desired grass/clover ratio in grazed swards.

The effect of consumption of foods that differ in energy density and/or sodium bicarbonate supplementation on subsequent diet selection in sheep

Consumption of a highly fermentable, high energy density (ED) food by ruminants results in changes within the rumen environment including a fall in pH. It has been shown that such changes can influence subsequent intake and diet selection in sheep as they attempt to correct these changes through their feeding behaviour (Cooper et al, 1995). The addition of a buffer eg NaHCO3 to a previously consumed high ED food or offering the sheep a low ED food would assist in preventing changes in the rumen environment hence the ruminant would not need to modify it’s diet selection in an attempt to correct these changes. The objectives were to determine (i) whether or not sheep would make a continuous non random selection between 2 foods of different ED (Test 1), (ii) to determine what concentration of NaHCO3 should be added to a food to obtain the most beneficial effects on rumen pH combined with intake (Test 2), and finally (iii) the main objective was to determine what consequences the ED of a food and the supplementation of NaHCO3 to a food offered for a short period of time had on subsequent diet selection made by sheep (Test 3).

Food intake and diet selection in sheep: the effect of manipulating the rates of digestion of carbohydrates and protein of the foods offered as a choice.

An experiment was designed to investigate whether the degree of synchrony between the rates of digestion of carbohydrates and N of foods offered as a choice would have an effect, through their consequences, on the short- and long-term diet selection of sheep. Four foods (RL, RH, SL and SH) with the same high metabolizable energy, and similar high metabolizable protein contents were made into pellets. Foods RL and RH were based on a rapidly fermentable carbohydrate source and foods SL and SH on a slowly fermentable carbohydrate source; within each source one food (RL or SL) had a low, and the other (RH or SH) a high, rumen-degradable protein (RDP) content. The foods within a carbohydrate source were offered either singly or as a choice (RL/RH or SL/SH) to eleven rumen-fistulated mature sheep. The design was two 3 x 3 Latin squares (replicated once) with 5-week periods; squares consisted of two single foods and their respective choice. Weeks 1, 3 and 5 were considered to be controls, and weeks 2 and 4 used for rumen infusions of either urea or fructose infused over 4 h (10.00-14.00 hours). Food intake (FI) and diet selections (DS) were recorded daily and every 2 h (08.00-16.00 hours) on days 2-5 of each week; rumen pH and NH3 concentrations were also measured during these time intervals of day 5. As expected, feeding treatment affected significantly the rumen measurements: rumen NH3 concentrations were higher on foods RH and SH, and rumen pH lowest on RL. Daily FI was lowest on treatments SL, and choice SL/SH. The mean daily proportion of the low-RDP food in the selected diet was lower when the carbohydrate source was rapidly (choice RL/RH) rather than slowly fermentable (choice SL/SH); this was consistent with the experimental hypothesis. Short-term infusions affected further rumen variables (in the expected directions), irrespective of feeding treatment. However, DS over the 4h infusion period were unaffected; these short-term DS were consistent with the ones selected over the longer term (daily). The results suggest that the long-term (daily) diet selection of sheep may be affected by the degree of synchrony of energy and protein to the rumen. The fact that diet selections were not altered further by short-term manipulations of these supplies might reflect inadequacies of the methodology (infusions) adopted here.

The effect of synchronising the supply of energy and protein to the rumen on the short and long-term diet selection of sheep

An experiment was carried out to investigate the hypothesis that the diet selection of ruminant animals from two foods of different rapidly rumen degradable protein contents could be affected by the differences in the rate of synchrony between carbohydrate fermentation and degradation of protein in the rumen. The diet selection of the animals was measured both in the 'long-term' (daily) and 'short-term' (2h intervals within the day).Twelve rumen fistulated mature female sheep (liveweight 59.1 kg) were used. Four foods (A,B,C and D) with the same ME (9.6 MJ/kg fresh food) and similar, high metab/sable protein contents were made into pellets. Two of the foods were based on a rapidly fermentable carbohydrate source (barley, A and B foods) and the other two on a slowly fermentable carbohydrate source (plain sugar beet pulp, C and D foods). Within each source one food (A or C) had a low (70) and the other a high (140 g/kg) concentration of effective rumen degradable content (RDP).

The effect of synchronising the supply of energy and protein to the rumen on the short and long-term diet selection of sheep

An experiment was carried out to investigate the hypothesis that the diet selection of ruminant animals from two foods of different rapidly rumen degradable protein contents could be affected by the differences in the rate of synchrony between carbohydrate fermentation and degradation of protein in the rumen. The diet selection of the animals was measured both in the 'long-term' (daily) and 'short-term' (2h intervals within the day).Twelve rumen fistulated mature female sheep (liveweight 59.1 kg) were used. Four foods (A,B,C and D) with the same ME (9.6 MJ/kg fresh food) and similar, high metab/sable protein contents were made into pellets. Two of the foods were based on a rapidly fermentable carbohydrate source (barley, A and B foods) and the other two on a slowly fermentable carbohydrate source (plain sugar beet pulp, C and D foods). Within each source one food (A or C) had a low (70) and the other a high (140 g/kg) concentration of effective rumen degradable content (RDP).

Long-term subclinical infection with Trichostrongylus colubriformis: effects on food intake, diet selection and performance of growing lambs

Growing lambs (mean liveweight 22.4 kg) were used to test for the effects of long-term subclinical infection with Trichostrongylus colubriformis (2500 larvae per day) on the voluntary food intake (VFI), diet selection and performance of sheep given a choice between two foods of different protein content (low versus high). Sheep were either uninfected controls or parasitised for 27 weeks (Group 27P). Additional sheep were infected for either 9 or 18 weeks (before and after the development of complete resistance to parasites, as assessed by faecal egg counts) and then treated with anthelmintic to remove the parasites (Groups 9P and 18P). Group 18P remained uninfected after anthelmintic treatment whereas Group 9P was infected again for the last 9 weeks after a 9 week worm-free period. The VFI declined or remained static from Week 5 up to Week 11/12 of continuous infection, for the 27P and 18P groups. For 9P sheep, VFI recovered within a few days after the anthelmintic administration and was unaffected during re-infection over the last 9 weeks of the experiment. Diet selection changed in such a pattern that the proportion of the high protein food (prop H) in the selected diet started to increase from Week 6 of the infection. The prop H selected remained higher over the interval 10–18 weeks of the continuous infection for 27P and 18P groups than the uninfected controls. There were no significant differences in diet selection among any of the groups beyond Week 18 of the experiment. The infection caused a growth check from Week 7 to approximately Week 12/14 of dosing; there was no evidence of compensatory growth following the development of resistance or recovery. The results are consistent with the view that sheep given a choice between two appropriate foods will modify their diet selection in order to moderate the adverse effects of subclinical nematode infection. The performance and diet selection of all sheep beyond Week 18 of infection suggest that no obvious nutritional penalties are incurred with the continuation of the infection once the animals have become resistant to parasites.