Forage production of some grass species in the false Thornveld of the Eastern Cape

Abstract

The most commonly occurring grass species in the False Thornveld (Acocks, 1953; veld type no. 21) were clipped before and after grazing on veld in good and poor condition at different times of the year. Herbage yield per species was expressed per unit basal tuft area, and the difference in yield before and after grazing was considered to reflect the production of available forage. Themeda triandra produced more forage than any other species at all times of the year. Sporobolus fimbriatus generally produced the second highest amount of available forage. Cymbopogon plurinodis, despite having the second highest herbage yield before grazing, was not grazed to a significant extent. On the basis of the results, Themeda triandra and Sporobolus fimbriatus were identified as key grass species in the False Thornveld of the Eastern Cape.     

Influence of soil pH and fertilization on the dry matter production,chemical composition and digestibility of perennial grasses: I. Anthephora pubescens nees 1

Abstract

The influence of soil pH and fertilization (N, P and Zn) on the dry matter (DM) production, chemical composition (crude protein, P, K, Ca, Mg and Zn content) and organic matter (OM) digestibility of Anthephora pubescens Nees was evaluated in pots. The highest Dm production was obtained in the neutral soil medium (pH 6,5 in H₂O). Both the acid (pH 4,5 in H₂O) and alkaline (pH 7,5 in H₂O) soil mediums adversely affected DM yield, crude protein (CP), Zn content and OM digestibility of A. pubescens. Fertilization invariably increased DM production.     

Apparent metabolisable energy and amino acid digestibility of microalgae Spirulina platensis as an ingredient in broiler chicken diets

ABSTRACT

1. This work investigates the apparent metabolisable energy (AME), its nitrogen-corrected form (AMEn) and amino acid (AA) digestibility coefficients of the microalgae Spirulina platensis as an ingredient in broiler chicken diets.

2. One group of birds was fed with a basal control diet (BD), and another was fed with a test diet composed of the BD with the addition of the microalgae at a proportion of 200 g/kg. AME and AMEn were assessed by total excreta collection and indigestibility analysis using acid-insoluble ash (AIA) as a marker.

3. The microalgae comprised 888.0 g/kg dry matter (DM), 18.42 MJ/kg gross energy, 514.7 g/kg crude protein, 9.9 g/kg ether extract, 10.6 g/kg crude fibre, 94.4 g/kg ash, 3.1 g/kg Ca and 11.0 g/kg P.

4. The values obtained for AME (13.48 MJ/kg DM) and AMEn (11.72 MJ/kg DM) were higher (p < 0.01) than those obtained using the AIA method (9.39–8.29 MJ/kg DM). The microalgae ileal digestibility coefficients were 0.80 ± 0.04 and 0.78 ± 0.04 for essential and non-essential AA, respectively.

5. Overall, the metabolisable energy content and digestibility of AA for S. platensis indicated that the microalgae are potentially an alternative nutrient source for broilers. The AIA method underestimated AME and AMEn in comparison to the total excreta collection method.     

Nutritive value of some tropical grasses used by traditional small farms in the highlands of Burundi

The objective was to estimate—according to the French feeding system—the nutritive value of three tropical grasses (Eragrostis olivacea, Setaria sphacelata and Tripsacum laxum) used in traditional small farms of Burundi. Dry matter (DM) yield was monitored on anti-erosive hedges or on small fields in 60 small farms for eight consecutive years. DM intake and digestibility values were measured on seven steers or seven male sheep. Degradability values were determined on three sheep. S. sphacelata exhibited higher DM yield (t ha⁻¹), energy (UF, kg⁻¹ DM) and protein (PDI, g kg⁻¹ DM) values (17.3, 0.73 and 68, respectively) than T. laxum (9.11, 0.64 and 47) and E. olivacea (not determined, 0.46 and 42). The UF and PDI intakes of these grass species were able to meet only 51% to 92% of the energy and 59% to 133% of the protein requirements for maintenance of the experimental animals.     

Dry Matter and Crude Protein Degradability of Four Parasitic Plants (Mistletoes) Associated with Browse Trees in Botswana

Four parasitic plants (Tapinanthus lugardii, Erianthenum ngamicum, Viscum rotundifolium and Viscum verrucosum) associated with browse trees in Botswana were evaluated for the degradability of their dry matter (DM) and crude protein (CP). All these plants have high levels of crude protein, ranging from 144.5 to 163.4 g/kg DM, with a significant (p<0.001) difference in crude protein content between the plants. The rate of degradation of DM was highest for V. rotundifolium (0.197 h⁻¹) and lowest for E. ngamicum (0.031 h⁻¹). The two Viscum species had the highest effective DM degradability at an outflow rate of 0.05%. The rate of degradation of crude protein was highest for V. rotundifolium (0.144 h⁻¹) and lowest for T. lugardii (0.0346 h⁻¹). The effective degradability (ED) of crude protein was highest for V. rotundifolium at 0.03 and 0.05 h⁻¹ outflow rates. T. lugardii and E. ngamicum had an apparently low effective degradability, but this may result from an association of their protein with tannins, which would be able to supply amino acids in the small intestine after dissociation due to the abomasal pH. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of tiller age and time of year on the growth of Themeda tri andra and Sporobolus fimbriatus in semi‐arid grassveld

Abstract

Sequential growth measurements were made on successive populations of Themeda triandra and Sporobolus fimbriatus tillers initiated at different times of the year. The independent influences of tiller age and time of year on tiller growth were isolated by deriving growth indices for tillers of the same age at different times of the year and for tillers of all ages at each time of the year respectively.

Isolating the effect of plant age on growth showed that T. triandra is most productive under a regime of long periods of undisturbed growth, while S. fimbriatus is better suited to frequent interruptions in growth. Isolating the effect of time of year shows that both species are particularly sensitive to perturbations in spring. However, the photosynthetic efficiency of T. triandra is strongly influenced by time of year while S. fimbriatus seems to be a more opportunistic assimilator of sunlight.     

Performance and dietary preferences of white‐tailed deer grazing chicory,birdsfoot trefoil or alfalfa in north central Alberta

Little information exists on the performance of deer on alternative forage species in northern temperate environments during summer and fall, the period of inherent maximum growth in deer. In performance and choice experiments, we compared live weight gain (g/kg^0.75/day), absolute [kg/ha dry matter (DM)] and relative (% DM) herbage utilization, relative preference index (RPI) as well as plant community visitation of white‐tailed deer grazing alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus) or chicory (Cichorium intybus) in north central Alberta, Canada. Herbage phytomass and quality was also measured on the grazed pastures. Alfalfa had higher dry matter yields and crude protein concentrations than chicory and trefoil. Chicory had lower neutral detergent fiber concentrations than the other forages. Tannin concentrations were greatest in birds foot trefoil (nearly 55 g/kg DM), well above those in the other forages (<5 g/kg DM). Live weight gain was similar among deer feeding within the paddocks seeded to birds foot trefoil and chicory, and more than two times higher (p < 0.05) than deer feeding in paddocks seeded to alfalfa. Deer spent more grazing time (about 40%) on chicory pastures than on alfalfa and birds foot trefoil pastures. RPI values were greatest for birds foot trefoil at 2.11, intermediate for chicory at 1.40, and lowest for alfalfa at <0.60. Absolute herbage utilization remained similar (p > 0.05) among the three forage species. In contrast, relative herbage utilization was greater from birds foot trefoil (52% DM) than chicory (40% DM) or alfalfa (25% DM). These results suggest that the use of alfalfa with other alternative forages may prove beneficial to deer production, rather than using alfalfa pasture alone.     

A comparative study of three veld types of the Northern Cape: Species evaluation and yield 1

A comparative study was undertaken of the grass component of the three main veld types of the Vryburg district; namely Sand veld, Dolomite veld and Lime veld. Results indicate that different species within the same veld type and the same species in different veld types differ in their dry matter production, digestibility and digestible organic matter production. Botanical composition and basal cover also varied between veld types. Veld types also differ in DM yields, digestibility and DOM yield.

The average digestibility of all species at three growth stages (leafy, flowering and mature) was 48,7% in sand veld, 54,8% in dolomite veld and 54,7% in lime veld. The average dry matter production and digestible organic matter production per m² at three growth stages were 2 083,9 g and 844,5 g in Sand veld, 2 108,6 g and 952,5 g Dolomite veld, and 1 776,0 g and 808,8 g in Lime veld, respectively. The possibility of deficiencies of Zn, Cu and P is indicated in all three veld types.

The percentage basal covers of sand veld, Dolomite veld and Lime veld were 4,3%, 2,1% and 5,0% respectively. The average DM yield and DOM yield of the veld types were 786,4 and 301,1 kg/ha in Sand veld, 403,9 and 189,2 kg/ha in Dolomite veld, and and 365,7 kg/ha in Lime veld respectively. The average digestibility of the veld types were 44,0%in Sand veld, 56,3% in Dolomite veld and 52,3% in Lime veld.     

The influence of stocking rate and grazing system on the crude protein content and digestibility of Tarchonanthus veld in the northern cape 1

Abstract

Four stocking rates (10, 7, 6 and 4 ha/large stock unit), in both rotational and continuous grazing, have been applied with cattle on Tarchonanthus veld. The crude protein content and digestibility of organic matter of handcut samples and herbage samples collected by means of oesophageal fistulated steers in the different treatments, were determined.

The results indicated that the crude protein content (3,9 to 6,7%) and digestibility (48,7 to 59,4%) of handcut samples was not representative of the diet of grazing cattle. The crude protein content of the samples collected by means of oesophageal fistulated steers varied from an average of 13,6%. (October to December) to an average of 5,3% (July and August). On average, the digestibility of the fistula collected samples varied between 60,4% (February to April) and 50,2% (July to October). The crude protein content of the fistula collected samples tended to increase with increasing stocking rate while digestibility declined. Both crude protein content and digestibility of the fistula collected samples did not differ significantly between rotational and continuous grazing.     

Adaptation of a decreaser and an increaser grass species to defoliation in semi‐arid grassveld

Abstract

Grasses have developed through natural selection to deter, escape and tolerate herbivory, and to escape and tolerate fire. In the semi‐arid grassveld of the Eastern Cape, the species Themeda triandra and Sporobolus fimbriatus have been classified as Decreaser and Increaser II plants respectively. Both species have well‐developed escape and tolerance mechanisms, although T. triandra readily tolerates defoliation only during the dormant season, while S. fimbriatus is adapted to tolerating defoliation throughout the year. Furthermore, T. triandra has only moderately developed deterrents to herbivory, in contrast to S. fimbriatus, where deterrents are well developed. It follows that the Decreaser species T. triandra is adapted to relatively frequent fire and no more than modest herbivory, while the Increaser II species, S. fimbriatus, is adapted to heavy herbivore usage, but infrequent fire.     

Assessment of in vitro digestibility and fermentation parameters of alfalfa hay‐based diet following direct incorporation of fenugreek seed (Trigonella foenum) and asparagus root (Asparagus officinalis)

This study was completed to evaluate the effect of fenugreek seed (Trigonella foenum; FS) and asparagus root (Asparagus officinalis; AR) on in vitro nutrient digestibility and fermentation patterns. Different levels [0%, 5%, 10%, 15% and 20% of dry matter (DM)] of the medicinal plants were included using alfalfa hay (AH) as a basal substrate at different incubation times (12, 18, 24 and 48 h). Total phenolic components of AH, FS and AR were 5.9, 10 and 8.3 g/kg DM, whereas total tannins were 0.4, 3.8 and 1.5 g/kg DM, respectively. Corresponding values for saponins were 10.4, 27.3 and 40.3 g/kg DM. Fenugreek seed increased (p < 0.05) in vitro organic matter (OM) digestibility at different incubation times and decreased (p < 0.05) crude protein (CP) digestibility at 18 and 24 h of incubation. Asparagus root also increased (p < 0.05) in vitro OM digestibility and decreased (p < 0.05) CP digestibility at different incubation times. Neutral detergent fibre digestibility was increased (p < 0.05) by the addition of AR or FS at low levels, but decreased (p < 0.05) noticeably by increasing level of two plants in the basal substrate. Ammonia‐N concentration was markedly reduced (p < 0.05) by the addition of AR at different incubation times, and this reduction was accompanied by the decrease in CP digestibility. True DM degradability and partitioning factor (ratio of substrate DM truly degraded to gas volume produced at different times of incubation) were increased, and total volatile fatty acid concentration and total gas production were decreased (p < 0.05) with the addition of FS (at 10% and 15% DM levels) or AR (at 5%, 10% and 15% DM levels) at different incubation times. Results suggest that FS and AR may have potential as feed additives to increase the efficiency of nutrients’ utilization, particularly of nitrogen in ruminant diets.     

Seasonal influence on diet selection of sheep grazing a weedy dryland lucerne pasture

The experiment was conducted to determine the seasonal effects on the availability, chemical composition and digestibility of a grazing dry-land lucerne pasture, as measured on samples either collected by hand or with oesophageally fistulated (OF) sheep. The pasture was monitored monthly for a period of thirteen months. An overall mean amount of 647 kg DM ha^?1 of material was monitored during the experimental period. Lucerne, as a percentage of the total DM availability was relatively low (approximately 19%), probably due to the preference of sheep to select lucerne in spite of the other available material. Both the crude protein (CP) content and the organic matter (OM) digestibility of the samples showed a seasonal tendency with higher values during the winter and lower values during the summer. Mean OM, CP, organic matter digestibility (OMD), acid detergentfibre (ADF) and neutral detergent fibre (NDF) contents of 91.7%, 10.7%, 57.5%, 47.1% and 74.0%, respectively, were obtained with hand-clipped samples, while the corresponding composition of samples collected by OF sheep was 83.1%, 21.0%, 64.7%, 38.2% and 58.4%, respectively. The sheep were able to select forage samples with a higher CP content than those collected by hand throughout the year. This was, however, not the case with the organic matter digestibility of the samples during the growing season July to October. The CP content of fistula extrusion samples (f) could be predicted from hand-clipped samples (h) from the linear relationship, CP_f = 10.51 + 0.97CP_h (r = 0.59). The study provided figures on the chemical composition and digestibility of dryland lucerne pasture at grazing in a Mediterranean environment.     

Determination of in vitro digestibility of forage species used in ruminant feeding

Within the evaluation of the quality of forage resources, the main parameter that defines it is the digestibility of dry matter, which together with the amount of neutral and acidic detergent fibers and crude protein constitutes the basic information to assess forages which are supplied in the diet of the cattle. This research was carried out at the University of Los Llanos (Villavicencio, Colombia), and its objective was to determine the digestibility of three forages in cattle through three different in vitro techniques: inoculation with ruminal fluid and with feces and enzymatic digestibility technique, making the comparison with the in situ technique in order to validate the techniques and equipment that are being used for these procedures. The following species were evaluated: Pennisetum purpureum (PP), Tithonia diversifolia (TD), and Bauhinia variegata (BV), assessing the curve and rate of degradation of dry matter (DM), neutral detergent fiber (NDF), and total protein (TP) (0 to 72 h). A design of repeated measures was used, under which the analysis of variance was carried out to determine the ranges of deviation between the techniques and thus establish the trend of the data; the variables evaluated were the DM, NDF, and TP digestibilities of the three forages using the four techniques (three in vitro and one in situ). After verifying the differences between the variances of the digestibilities and checking the sphericity assumption with the Mauchly test, multiple comparisons were made with the Bonferroni test with a significance of 5%. The digestibility of DM, NDF, and TP varied between 38.62 and 44.22, 54.18 and 66.97, and 47.54 and 57.05%; 49.07 and 70.70, 72.52 and 75.44, and 62.61 and 74.02%; 29.93 and 34.84, 26.21 and 70.88, and 25.67 and 50.60% respectively in forages PP, TD, and BV, depending on the technique used for their estimation. Despite finding statistically significant differences between several of the comparisons made in the digestibility techniques, a high coefficient of determination and a high correlation between the in vitro estimations with respect to the in situ estimation were found; therefore, it is possible to use these techniques routinely thus avoiding the need to have cattle with fistulae to perform digestibility tests, with enzymatic digestibility technique being the most practical one.

     

Influence of condensed tannin on intake, digestibility, and efficiency of protein utilization in beef steers fed high concentrate diet

This trial was conducted to evaluate if the effect of condensed tannin (CT) is associated with a true protein source on intake, ruminal and total digestibility, ruminal digestion rate, protein efficiency, and microbial efficiency in beef steers fed high concentrate diet (87% of DM). Four Bos indicus steers (407 ± 12 kg of BW) fitted with rumen cannula were assigned to a 4 × 4 Latin square design, arranged in a 2 × 2 factorial arrangement. Treatments consisted of either inclusion (0.4% of DM) or exclusion of condensed tannin (CT) from quebracho extract (76% of CT) with or without the use of soybean meal (SBM) as source of true protein. The level of inclusion was calculated to provide a daily intake of 1 g/10 kg of BW of CT. Intake of DM and nutrients was not affected (P > 0.10) by CT inclusion. However, there was an effect (P < 0.10) of CT inclusion on ether extract digestibility. An interaction (P < 0.10) was observed between CT and SBM on ruminal digestibility and digestion rate of crude protein (CP): when mixed with soybean meal, CT decreased the ruminal digestibility and, consequently, reduced the digestion rate of CP. Intake of CP increased (P < 0.10) with the inclusion of SBM. No differences in DM passage rate were observed (P > 0.10) among treatments. Effects of the interaction (P < 0.10) between CT and SBM were observed on flux of rumen undegradable protein (RUP), metabolizable protein (MP), and on the ratio MP:CP. In the presence of soybean meal, the addition of CT increased (P < 0.10) the flux of RUP and MP, and improved the ratio MP:CP. The yield of microbial protein on the abomasum and the microbial efficiency did not differ among treatments (P > 0.10). There was no difference (P > 0.10) on the pH, VFA, and ruminal ammonia (N-NH₃) with the addition of condensed tannin. The N-NH₃ increased and the ruminal pH decreased with the inclusion of soybean meal (P < 0.10). The utilization of condensed tannin as an additive in beef cattle diets with high level of concentrate and soybean meal as a source of true protein implies positive effects on crude protein utilization, decreasing digestion rate and ruminal digestibility of crude protein and consequently increasing the levels of metabolizable protein, with no changes in the ruminal fermentation parameters.     

Intake,digestibility, ingestive behavior,and nitrogen balance of goats fed with diets containing residue from tamarind fruit

This study is aimed at determining the maximum inclusion level of tamarind (Tamarindus indica) residues in the diet of goats on intake, digestibility, ingestive behavior, and nitrogen (N) balance. Twenty-four crossbred (Boer × undefined breed) castrated goat kids (5 months old and with an initial weight of 23.9?±?0.3 kg) were assigned in a completely randomized design (4 treatments and 6 replicates). Diets consisted of Tifton 85 (Cynodon sp.) hay as the roughage (400 g/kg) source and concentrate (600 g/kg); the levels of tamarind residue inclusion were 0.0, 7.0, 14.0, and 21.0% on a dry matter (DM) basis. The experimental period lasted 23 days (15 of adaptation and 8 of sampling). Inclusion of tamarind residue in the goat kid diets did not affect (P?>?0.05) the intake and digestibility of DM, crude protein, neutral detergent fiber (NDF), and total digestible nutrient; intake of N, urinary N, and retained N (g/day); time spent ruminating; numbers of times/day feeding, ruminating, or idling; eating efficiency of DM and NDF; number of boluses/day; and amount (g) of DM/bolus. However, there were a linear reduction in ether extract digestibility (P?=?0.011) and a linear decreasing trend in non-fibrous carbohydrate digestibility (P?=?0.083). The addition of tamarind residue had a positive linear effect (P?=?0.041) on the time spent feeding and promoted a decreasing linear trend for the time spent idling (P?=?0.063). It is recommended to include the residue from tamarind fruit at a level of 21% in diets for goat kids, as it does not affect nutrient intake and digestibility and the N balance.

     

Degradation characteristics and tannin bioassay of some browse forage from Kenya harvested during the dry season

The potential nutritional value of six species of browse forage from Kenya harvested during the dry season were evaluated by chemical composition, in sacco dry matter (DM) degradation and in vitro gas production technique. The effect of tannins on the rumen fermentation of the forage was evaluated using polyethylene glycol (PEG) in an in vitro study. The chemical composition of the species of browse forage differed significantly (P < 0.05). The content of organic matter ranged from 846.7 to 946.5 g/kg DM. The forage had a high crude protein content (155.5–280.9 g/kg DM) and variable content of neutral detergent fiber (NDF, 236.2–682.8 g/kg DM). The content of total extractable tannins was generally low (0.6–38.5 g/kg DM). At 24 h of incubation, the in sacco DM disappearance ranged from 31.2% to 84.2%. The effective DM degradability also ranged from 29.7 to 73.5%. The gas production after 96 h incubation ranged from 17.5 to 44.2 mL/200 mg DM. Use of PEG indicated that tannins had an inhibitory effect on rumen microbial fermentation and this is dependant upon the amount and activity of the tannins present. The estimated in vitro organic matter digestibility and metabolizable energy also increased numerically with the PEG addition. The result of this study indicates that such species of browse forage have the potential to be used as feed supplements for ruminants, especially during the dry season.     

Effect of field pea (Pisum sativum L.) level on intake,digestion, ruminal fermentation and in vitro gas production in sheep fed maintenance diets

The objective of this study was the characterization of the nutritive value, ruminal fermentation and nutrient digestibility of field pea (Pisum sativum L.) hay (FPH) by‐product through in situ, in vitro and in vivo tests. A FPH diet was administered ad libitum to four sheep (live weight (LW) 38.0 ± 2.0 kg) at four inclusion levels (0, 25, 50 and 75%) over a conventional sorghum grain/oat straw ration in a 4 × 4 Latin square design. The in situ degradability of FPH was 67% dry matter (DM), 71% crude protein and 66% neutral detergent fiber (NDF). The inclusion of FPH did not affect (P ≥ 0.05) the DM (61 ± 0.4 g/LW^0.75/day) and organic matter (OM) intake (56 ± 0.7 g/LW^0.75/day). Total DM digestibility (68 ± 2.5%), OM (70 ± 3%), and NDF (60 ± 3%), were not different (P ≥ 0.05) between control and FPH inclusion diets. The diet had no effect on ruminal pH, ruminal ammonia concentration, total and individual volatile fatty acids. The chemical composition and sheep intake behavior indicate that FPH by‐product is medium quality forage when incorporated in maintenance rations.     

Digestibility and nitrogen utilization in sheep fed enset (Ensete ventricosum) pseudostem or corm and graded levels of Desmodium intortum hay to wheat straw‐based diets

The aim of this study was to investigate the effects of different levels of Desmodium intortum (Desmodium) hay supplementation in sheep fed fixed amounts of enset pseudostem or corm and a basal diet of wheat straw on intake, digestibility and nitrogen utilization. Eighteen male sheep with a mean (± SD) live weight of 20.5 ± 1.45 kg were assigned to six treatments in a completely randomized design and fed either 108 g dry matter (DM) enset pseudostem or 165 g DM enset corm each with three levels (100, 200 and 300 g) of hay supplementation. For the pseudostem diets, there was no significant difference in total DM intake. Total crude protein (CP) intake and N retention increased with increasing levels of hay in both pseudostem and corm diets. The apparent digestibility of DM, OM, CP, acid detergent fibre and neutral detergent fibre (NDF) and microbial nitrogen supply (MN) at 100 g was lower that other levels of supplementation. For the corm diets, total DM and OM intake and MN supply increased with increasing levels of hay. The digestibility decreased (p < 0.001) with increasing levels of supplementation. The results suggest that at least 300 g (395 g/kg dietary DM) of Desmodium hay is required in pseudostem diets, whereas 200 g (337 g/kg dietary DM) may be sufficient in corm diets for efficient nutrient utilization.     

Effects of corn particle size on nutrient utilization in pigs evaluated under optimal and heat stress conditions

The effects of corn particle size on nutrient digestibility and energy utilization in pigs were determined under optimal (experiment 1, 25?±?1 °C) or heat stress (experiment 2, 37?±?1 °C) conditions. In Exp. 1 and 2, five experimental diets were tested using a 5?×?5 Latin square design involving five barrows (Landrace × Yorkshire × Duroc, average initial body weight of 30?±?1 kg and 45.0?±?1.8 kg, respectively, in individual metabolic cages). Dietary treatments were as follows: 200-, 300-, 400-, 600-, 800-μm corn particle sizes obtained by mesh screens. Under optimal thermal conditions, digestibility of dry matter (DM) and crude fiber (CF) from 200-μm diet was higher (P?<?0.05) compared to that from the 300-μm and 400-μm diets. The digestibility of crude protein (CP) and ether extract (EE) was the highest (P?<?0.05) at the 200-μm particle size. The apparent total tract digestibility of energy was significantly higher (P?<?0.05) on the 200-μm diet. Under heat stress, digestibility of CF when corn was ground to 600 μm was higher (P?<?0.05) compared to 300 and 400 μm. Digestibility of NDF and ADF was the highest (P?<?0.05) at 600-μm corn particle size. In conclusion, grinding corn to 200-μm corn particles had a positive effect on DM, CP, EE, and CF under optimal thermal condition, while the 600-μm corn particle size had positive effects on digestibility of CF, NDF, and ADF than 200-μm corn particle size under heat stress.

     

Fatty Acid Metabolism in the Digestive Tract of Lactating Cows Fed Tallow in Increasing Amounts at Two Feed Levels

Abstract

Long-chain fatty acid metabolism in the digestive tract was studied in lactating cows fed at two levels of dry matter intake (L, 8.6 kg DM and H, 12.6 kg DM), with 0, 4 and 6% added tallow at low feed level (L0, L4 and L6), and 0, 2, 4 and 6% fat at high feed level (H0, H2, H4 and H6). Mean fatty acid balance from mouth to duodenum was about zero when corrected for endogenous fatty acids from bile. However, regression analysis showed a microbial synthesis of 68 g at zero fatty acid intake, and a trend which indicated declining de novo synthesis of fatty acids with increasing fat level in the diet. As a mean 68% of the unsaturated C18 fatty acids were hydrogenated in the rumen.

Fatty acid and crude fat true digestibilities decreased with increasing fat intakes owing to a decrease in stearic acid (C18:0) digestibility.