Use of inert markers to predict diet composition, forage intake, digestibility and passage rate in sheep.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.The mechanisms that regulate intake and composition of selected diets in ruminants are complex and vary among animals of the same species and cross species. These are governed by highly variable aspects, which range from animal factors to physio-chemical properties of feeds. Understanding how ruminants select their diets is imperative to improve their utilisation of feed resources regarding the diversity of plant species that can be used as their sources of feed. The objectives of the study were to: (1) determine the effect of group feeding and removal of dietary ingredient (Sorghum bicolor) on diet selection, nutrient and total dry matter intake, and digestibility in choice-fed sheep; (2) asses the effect of animal stocking rate on dry matter and nutrient intake, botanical composition, nutrients selected, total tract digestibility and passage rate of diet consumed by sheep; and (3) predict dry matter and nutrient intake, botanical composition, nutrients selected and total tract digestibility using inert markers. Twelve sheep (mean weight: 29.7 ± 4.63 kg) were assigned to three treatments. In treatment one, five feeds were fed to sheep fed as a group of 9 sheep (G). In the second treatment, five feeds were fed to sheep penned in isolation (I) and in the last treatment, four feeds with sorghum stover (SS) removed were fed to sheep penned in isolation (R). There were five experimental feeds: veld hay (VH), sorghum stover (SS) and maize stover (MS) fed ad-libitum, and Lucerne hay (LH) and bean straw (BS) fed at restriction levels of 0.15 and 0.35 kg/day per sheep, respectively, in a group or individually fed sheep. Diet compositions were similar (p >0.05) between sheep fed individually with or without SS. Similarity in proportion of these dietary ingredients consumed between R and I may be due to less selection of SS; therefore, its removal did not significantly influence consumption and selection of other dietary ingredients. Group feeding of sheep relative to individual feeding with similar dietary ingredients influenced selection of SS. Sheep fed individually had lower intake levels of SS. Establishment of a dominance hierarchy in group-fed sheep may have caused dominant animals to feed on poor quality stovers just to prevent sheep lower in the hierarchy from eating resulting in high consumption of stovers. Fifteen sheep (mean body weight 46.5 ±3.3 kg) were blocked by weight into four groups and each sheep was randomly allocated to four stocking rates (treatments) of 1, 2, 4 and 8 sheep per pen and fed: MS, SS, and VH. All feeds were fed on separate feeding troughs ad-libitum. To evaluate the effect of animal stocking rate (SR) on passage rate of digesta, one sheep each from stocking rates one (SR1) and two (SR2) animals per pen and two sheep each pair from stocking rates of four (SR4) and eight (SR8) animals per pen were randomly selected and dosed with Ytterbium (particulate) and cobalt-ethylenediamine tetraacetic acid (Co-EDTA; liquid) markers. An optimisation procedure was used to predict diet selection by minimising the sum of the squared discrepancies between the proportional concentration of markers (acid insoluble ash: AIA, modified acid detergent fibre: MADF, and acid detergent lignin: ADL) in faeces (A) and their proportional concentration in dietary components (E) (MS, SS and VH), corrected for faecal recoveries of markers. Fractional passage rate (liquid and particulate) from both the rumen and in the hind gut, mean retention time, and total mean retention times across treatments were similar (p >0.05). Similarly, intake of dietary ingredients, nutrients (crude protein: CP, neutral detergent fibre: NDF and acid detergent fibre: ADF), total dry matter intake and composition of diets selected were not different across treatments. Selectivity index factors of diets selected were all within the range of 1.56-3.80, which reflected that animals were able to retain the diets they selected long enough in the gastro intestinal tract (GIT) for efficient digestion. Total tract digestibility and mineral intake (Ash) differed (p <0.05) in relation to animal stocking rate. Sheep in SR2 had the highest digestibility and consequently increased dry matter intake. Predicted dry mater intake and total tract digestibility of a diet selected by sheep were less sensitive to correction of incomplete faecal recovery of the markers and they tended to be similar to observed dietary parameters. Therefore, inert markers can be used to predict several components of a diet selected by grazing sheep and other classes of ruminants

Stocking rate has no confounding effect on the use of internal and inert markers to predict botanical composition, diet quality, degradability and passage rate kinetics in sheep

This study investigated if there is any confounding effect of stocking rate on the use of internal markers to determine and predict the dietary ingredient composition, dry matter intake (DMI) and digestibility of diets consumed by sheep. Fifteen sheep were randomly allocated to stocking rate treatments of one (SR1), two (SR2), four (SR4) and eight (SR8) sheep per pen (space allowance: 31.04 m2 , 15.52 m2 , 7.76 m2 and 3.88 m2 per sheep, respectively) and fed ad libitum maize stover, sorghum stover and veld hay by supplying 110% of previous day’s intake. Sheep were rotated across the treatments in four periods of 10 days. The proportion of feeds selected and total DMI were similar across all stocking rate treatments. However, diets selected by sheep in SR2 had the highest digestibility compared to other treatments. The prediction of the effective degradability of dry matter using acid detergent fibre content achieved an accuracy of 84.6%. A combination of crude protein and neutral detergent fibre contents achieved 63% accuracy in the prediction of the rate of degradation of feeds. The use of acid insoluble ash (AIA) as an internal marker to predict nutrient intake, digestibility, DMI and dietary ingredient intake accounted for 84.3%, 81.2%, 53.0% and 64.1% of the variation, respectively. The predictions of dietary feed proportions and nutrient quality selected obtained with least squares procedure using a combination of modified acid detergent fibre (MADF), acid detergent lignin (ADL) and AIA accounted for 81.0% and 72.4% of the variation, respectively. In conclusion, regardless of the different stocking rate tested in this study, a combination of MADF, ADL and AIA as internal markers can be used to estimate diet and nutrient selection by sheep using the least squares procedure. Hence, these markers can be used to predict ingredient composition of diet, diet and nutrient selection, nutrient intake and digestibility in free ranging animals.The National Research Foundation of the Republic of South Africahttp://www.mdpi.com/journal/animalspm2021Animal and Wildlife Science

Techniques used to determine botanical composition, intake, and digestibility of forages by ruminants

The botanical and chemical composition of diets consumed by ruminants is different from the composition of plant species available in the rangeland or pastures on which they graze. Exploring alternative and improving existing methods of estimating botanical composition (diet selection) is imperative in advancing sustainable feeding practices in extensive production systems. The ability to predict the intake and digestibility of the diet consumed is important in designing grazing management for different feeding systems as well as supplementation strategies. This facilitates the efficient use of feed resources for optimal animal performance. This review assesses the merits, limitations, and potential advancements in techniques used to estimate botanical composition, forage intake, and digestibility in ruminants. Supplements containing sufficient quantity and identifiable n-alkanes can be used to determine the total forage intake in grazing ruminants without dosing the animals with synthetic even-numbered n-alkanes. When the botanical composition, intake, and digestibility of diet are estimated using internal markers, the results should be validated with those of faecal near-infrared reflectance spectroscopy (NIRS) or plant cuticular compounds to enhance the prediction accuracy. This should be done to determine the degree of error in the use of internal markers. Conclusively, the use of internal markers with automated solver routine software is a prudent approach to predicting botanical composition due to the analytical ease of the markers involved and the associated model assumptions.The National Research Foundation of the Republic of South Africa. Article processing charges was made available by F.A and A.H through the Future Africa Early Career Research Leader Fellowship Programme of the University of Pretoria.https://www.mdpi.com/journal/agronomyam2023Animal and Wildlife Science

Techniques Used to Determine Botanical Composition, Intake, and Digestibility of Forages by Ruminants

The botanical and chemical composition of diets consumed by ruminants is different from the composition of plant species available in the rangeland or pastures on which they graze. Exploring alternative and improving existing methods of estimating botanical composition (diet selection) is imperative in advancing sustainable feeding practices in extensive production systems. The ability to predict the intake and digestibility of the diet consumed is important in designing grazing management for different feeding systems as well as supplementation strategies. This facilitates the efficient use of feed resources for optimal animal performance. This review assesses the merits, limitations, and potential advancements in techniques used to estimate botanical composition, forage intake, and digestibility in ruminants. Supplements containing sufficient quantity and identifiable n-alkanes can be used to determine the total forage intake in grazing ruminants without dosing the animals with synthetic even-numbered n-alkanes. When the botanical composition, intake, and digestibility of diet are estimated using internal markers, the results should be validated with those of faecal near-infrared reflectance spectroscopy (NIRS) or plant cuticular compounds to enhance the prediction accuracy. This should be done to determine the degree of error in the use of internal markers. Conclusively, the use of internal markers with automated solver routine software is a prudent approach to predicting botanical composition due to the analytical ease of the markers involved and the associated model assumptions

Removal of sorghum stover from feed choices has no confounding effect on the quantity and quality of diets selected by group or individually fed sheep

ABSTRACTThe study determined the effect of reducing dietary ingredients and group feeding on diet selection, nutrient intake and digestibility in choice-fed sheep. Three feeds comprising of veld hay (VH), sorghum stover (SS) and maize stover (MS) were offered ad-libitum while lucerne hay (LH) and bean straw (BS) were offered at restriction. Twelve sheep were allocated into three groups (i) group-fed in 3 sheep per pen, (ii) individually fed and, (iii) individually fed with SS exclusion. Sheep were rotated across the groups in four periods of 10 days. Diet selected, intake, refusals, spillages and faeces were monitored for seven days. The proportion of BS and LH consumed did not differ between group-fed and individually fed sheep with or without SS inclusion. Intake of MS and SS was lower in individually fed sheep while intake of VH was higher (p  0.05). Diet selection was influenced by group feeding, but not the removal of SS. The scarcity of one dietary component may not result in the selection of undesired but available feeds if the quality is similar or poorer to the absent feed