Polyethylene glycol compared with ytterbium oxide as a total faecal output marker to predict organic matter intake of dairy ewes fed indoors or at pasture

Several external markers can be used for estimating total faecal output in view of assessing ruminant intake at pasture. Among them, ytterbium (Yb) has been used for many years in various conditions. Polyethylene glycol (PEG) is a promising external marker because it can be rapidly determined using near-infrared spectroscopy (NIRS). The study consisted of 24 adult lactating dairy ewes over three periods (P1, P2 and P3), fed with three different diets: P1, total mixed ration (TMR); P2, Italian ryegrass (IRG); and P3, pasture. After an adaptation period, the ewes were administered a daily dose of ytterbium oxide (0.35 g/day) and PEG (20 g/day) for 2 weeks. During the last week, the daily organic matter intake (OMI_OBS) was measured. Faecal samples were collected at milking time (0800 and 1600 h) to determine marker content, using only samples collected in the morning (PEG_m) or by averaging samples (Yb, PEG_ma). Faecal marker content made it possible to assess total faecal output, either using the two recovery rates for PEG (0.98 or 0.87) or not. The OMI_OBS was assessed on the basis of total faeces estimated with Yb (OMI_Yb) or PEG (OMI_PEG), and the digestibility was calculated on the basis of feed analysis. With total TMR (P1), the OMI_PEG, corrected with recovery rate (OMI_PEGm98) or not corrected (OMI_PEGm) was 2.40 kg/day and 2.50 kg/day, respectively, and was not different (P>0.05) from OMI_OBS (2.51 kg/day), whereas OMI_Yb was lower (2.14 kg/day) (P<0.001). With IRG (P2), OMI_PEGm98 (1.67 kg/day), OMI_PEGm87 (1.51 kg/day) and OMI_Yb (1.59 kg/day) were not different (P>0.05) from OMI_OBS (1.57 kg/day). With pasture (P3), the OMI_PEGm (1.54 kg/day) and OMI_PEGm98 (1.48 kg/day) were not different (P>0.05) from the OMI assessed from the biomass measurement (1.52 kg/day). The OMI_Yb (1.36 kg/day) was lower (P<0.05) but not different from OMI_PEGm98 and OMI_PEGm87. Spearman’s rank correlation between OMI_OBS and other OMIs (predicted with Yb or PEG P1 and P2) showed that it is possible to rank animals using PEG when there is a sufficiently wide range of OMI_OBS (1.65 to 2.8 kg/day in P1) but not within a narrower range (1.47 to 1.72 kg/day in P2). In conclusion, the present study confirms that PEG is a valuable external faecal marker, easy to prepare (solution), administer and determine (NIRS). It can be used to assess intake with numerous animals at pasture, but only for groups, and not to quantitatively estimate individual OMI.     

Organic matter digestibility of condensed tannin-containing Lotus corniculatus and its prediction in vitro using cellulase/hemicellulase enzymes

Three digestion experiments involving cryptorchid weaned lambs were conducted for 14-day periods in the spring, summer and autumn to determine the in vivo digestibility of dry matter (DMD), gross energy (GE), organic matter (OMD), digestible organic matter in the dry matter (DOMD) and estimated metabolisable energy (ME) concentration of Lotus corniculatus L. (birdsfoot trefoil; cv. Grasslands Goldie) at different stages of maturity. The experiments were carried out indoors at Massey University's Riverside farm, in the Wairarapa, North Island, New Zealand. In vivo digestibility samples were then used as standards to investigate if the enzymic in vitro system of [Roughan, P.G., Holland, R., 1977. Predicting in vitro digestiblities of herbages by exhaustive enzymic hydrolysis of cell walls. J. Sci. Food Agric. 28, 1057–1064] could predict OMD and DOMD of condensed tannin (CT)-containing L. corniculatus.Digestibility of L. corniculatus declined as it matured, but the rate of decline was much less than that which occurs for perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture. It was concluded that the in vitro enzymic system of [Roughan, P.G., Holland, R., 1977. Predicting in vitro digestiblities of herbages by exhaustive enzymic hydrolysis of cell walls. J. Sci. Food Agric. 28, 1057–1064] can be used to predict OMD and DOMD of L. corniculatus with a high degree of accuracy, provided a standard curve involving in vivo data generated with L. corniculatus is used. Using a standard curve with in vivo data from perennial ryegrass/white clover pasture led to bias which increased at lower OMD values. Reasons for the differences between L. corniculatus and pasture standard curves are discussed, including possible effects of bound CT.     

The influence of breed,season and photoperiod on semen characteristics,testicular size,libido and plasma hormone concentrations in rams

Twenty-seven adult rams (9 Suffolk, 9 Texel and 9 Dorset Horn) were raised under natural photoperiod and were trained to serve into an artificial vagina. On 1 April they were abruptly exposed to 3 different photoperiods as follows: (i) 8 hours light and 16 hours darkness (8L : 16D); (ii) 16 hours light and 8 hours darkness (16L : 8D); (iii) natural photoperiod. All rams were kept at pasture daily between 09.30 h and 16.00 h except when required indoors for experimental work. Rams on artificial photoperiod had appropriate supplemental lighting in an environmental chamber. Semen collection was attempted from each ram on alternate weeks during the experiment which lasted for 6 months. Semen was evaluated for volume, density, motility and abnormalities. Testicular length and circumference were recorded at 2-week intervals and libido was recorded at 4-week intervals. Three blood samples were collected from each ram at 30-min intervals on a weekly basis and the plasma was stored at ?20°C until assayed for testosterone and prolactin.Photoperiod had no significant effect on semen volume, motility and percentage dead or abnormal cells. Breed of ram had a significant effect on semen motility (P < 0.05) with Dorset Horn rams producing semen with the highest motility. Volume and motility scores both increased as the breeding season approached (P < 0.05), while the percentage of abnormal cells decreased (P < 0.01). Breed or photoperiod did not significantly affect scrotal measurements although animals exposed to 8L : 16D had the highest measurements. Month affected testicular measurements which generally increased from April to September. Suffolk rams had higher testosterone concentrations, and this breed also completed the highest number of mounts within an allocated test time (P < 0.05). Dorset Horn rams reached a peak in testosterone concentrations in June/ July whereas Suffolks and Texels reached a similar peak in August. Prolactin concentrations decreased from a maximum at the start and rams on natural photoperiod tended to have highest levels. These results show that month can have a bigger influence on semen characteristics than imposed artificial photoperiods in rams which have been exposed to increasing natural daylength for some months.     

Performance,profitability and greenhouse gas emissions of alternative finishing strategies for Holstein-Friesian bulls and steers

Modifying finishing strategies within established production systems has the potential to increase beef output and farm profit while reducing greenhouse gas (GHG) emissions. Thus, the objectives of this study were to investigate the effects of finishing duration on animal performance of Holstein-Friesian (HF) bulls and steers and evaluate the profitability and GHG emissions of these finishing strategies. A total of 90 HF calves were assigned to a complete randomised block design; three bull and three steer finishing strategies. Calves were rotationally grazed in a paddock system for the first season at pasture, housed and offered grass silage ad libitum plus 1.5 kg DM of concentrate per head daily for the first winter and returned to pasture for a second season. Bulls were slaughtered at 19 months of age and either finished indoors on concentrates ad libitum for 100 days (19AL), finished at pasture supplemented with 5 kg DM of concentrate per head daily for 100 (19SP) or 150 days (19LP). Steers were slaughtered at 21 months of age and finished at pasture, supplemented with 5 kg DM of concentrate per head daily for 60 (21SP) and 110 days (21LP) or slaughtered at 24 months of age and finished indoors over the second winter on grass silage ad libitum plus 5 kg DM of concentrate per head daily (24MO). The Grange Dairy Beef Systems Model and the Beef Systems Greenhouse Gas Emissions Model were used to evaluate profitability and GHG emissions, respectively. Average daily gain during the finishing period (P<0.001), live weight at slaughter (P<0.01), carcass weight (P<0.05) and fat score (P<0.001) were greater for 19AL than 19SP and 19LP, respectively. Similarly, concentrate dry matter intake was greater for 19AL than 19SP; 19LP was intermediate (P<0.001). Live weight at slaughter (P<0.001), carcass weight (P<0.001), conformation score (P<0.05) and fat score (P<0.001) were greater for 24MO than 21SP and 21LP, respectively. During the finishing period concentrate dry matter intake was greater for 21LP than 21SP with 24MO intermediate; 542, 283 and 436 kg DM, respectively. Although pasture-based finishing strategies had lower gross output values, concentrate feed costs were also reduced thus net margin was greater than indoor finishing strategies. Reducing concentrate input increased GHG emissions for bulls and steers slaughtered at the same age, respectively. Although prolonging the finishing duration reduced GHG emissions for bull and steer production systems, finishing bulls and steers over a longer period at pasture did not enhance animal performance and profit.     

Reproductive performance of South African indigenous goats inoculated with DHP-degrading rumen bacteria and maintained on Leucaena leucocephala/grass mixture and natural pasture

This study examined the reproductive performance of dihydroxy pyridone (DHP)-inoculated South African indigenous (SAIG) female goats maintained on two dietary treatments: (i) Leucaena leucocephala/grass mixture and (ii) natural pasture prior to conception, and during gestation. Leucaena leucocephala/grass mixture was nutritionally superior (crude protein and mineral elements) than the natural pasture. The average daily gain, products of pregnancy and foetal development in gravid goats raised on leucaena/grass mixture were significantly (P<0.03, P<0.009 and P<0.005, respectively) higher than those raised on natural pasture. Conception rate of goats fed natural pasture was higher than the band fed Leucaena leucocephala/grass mixture. Leucaena/grass mixture fed goats had kids that were heavier at birth than their counterparts on natural pasture. Pre-weaning kid mortality over the period of study was significantly (P<0.01) higher in the Leucaena leucocephala/grass mixture treatment. Colostrum from kidded goats fed leucaena was viscous and difficult to sample. The absence of mimosine toxicity symptoms suggests a possibility of safe use of leucaena as a feed resource to DHP-inoculated SAIG.     

The use of carbon isotope ratios to evaluate legume contribution to soil enhancement in tropical pastures

Soil carbon distribution with depth, stable carbon isotope ratios in soil organic matter and their changes as a consequence of the presence of legume were studied in three 12-year-old tropical pastures (grass alone —Brachiaria decumbens (C₄), legume alone —Pueraria phaseoloides (C₃) and grass + legume) on an Oxisol in Colombia. The objective of this study was to determine the changes that occurred in the¹³C isotope composition of soil from a grass + legume pasture that was established by cultivation of a native savanna dominated by C₄ vegetation. The¹³C natural abundance technique was used to estimate the amount of soil organic carbon originating from the legume. Up to 29% of the organic carbon in soil of the grass + legume pasture was estimated to be derived from legume residues in the top 0–2-cm soil depth, which decreased to 7% at 8–10 cm depth. Improvements in soil fertility resulting from the soil organic carbon originated from legume residues were measured as increased potential rates of nitrogen mineralization and increased yields of rice in a subsequent crop after the grass + legume pasture compared with the grass-only pasture. We conclude that the¹³C natural abundance technique may help to predict the improvements in soil quality in terms of fertility resulting from the presence of a forage legume (C₃) in a predominantly C₄ grass pasture.     

Prediction of the digestibility of primary growth and regrowth grass silages from chemical composition, pepsin-cellulase solubility and indigestible cell wall content

Prediction of organic matter (OM) digestibility (OMD) of primary growth and regrowth grass silages was studied based on their chemical composition, pepsin-cellulase solubility of OM (OMS) and indigestible neutral detergent fibre (INDF) content. Twenty-five primary and 28 regrowth silages were harvested from mixed timothy (Phleum pratense) meadow fescue (Festuca pratensis) or timothy cocksfoot (Dactylis glomerata) swards by varying the dates of the first and second harvest. In vivo OMD was measured with sheep and indigestible NDF was determined by 12 days ruminal incubation of forage samples in nylon bags using dairy cows fed a forage-based diet. Chemical composition of the silages was significantly correlated with digestibility, but single regression equations led to an unacceptable prediction accuracy of OMD (RMSE>40 g/kg DM). Pepsin-cellulase solubility reliably predicted OMD of primary growth silages (RMSE = 10.8 g/kg DM), but was less accurate for regrowth silages (RMSE = 25.9 g/kg). The prediction accuracy of OMD could be improved by using different equations for the two silage types. Indigestible NDF predicted OMD more accurately than OMS for all silages and especially for the regrowth silages. In contrast to OMS, the relationship between INDF and OMD was similar for both silage types.     

Metabolisable energy of grass and red clover silages fed to sheep at maintenance level

This study investigated the effect of forage type (grass or red clover) and harvesting time (primary growth or regrowth) of silage on energy and N utilisation by sheep fed at maintenance level. Specifically, the assumption of constant loss of energy of digestible organic matter from energy losses in urine and CH₄ applied in evaluation of silage metabolisable energy (ME) was investigated. Urinary excretion of high-energy phenolic compounds related to solubilisation of lignin was assumed to affect urinary energy (UE) losses from sheep fed highly digestible grass silage (GS). A total of 25 primary growth and regrowth silages of timothy (Phleum pratense) and meadow fescue (Festuca pratensis) grass mixtures and red clover (Trifolium pratense) samples collected in digestibility trials with sheep, including faecal and urine samples, were used for energy and N determinations. Urinary concentration of monophenolic compounds and CH₄ emissions in vitro were also analysed. Daily faecal N output, CH₄ yield (MJ/kg DM intake), proportion of CH₄ energy in digestible energy (DE) and proportion of UE in DE were greater (P ≤ 0.03) in sheep fed red clover silage (RCS) than GS. Furthermore, less (P = 0.01) energy was lost as UE of DE in sheep fed primary growth GS compared with the other treatments. The relationship between UE and silage N intake or urinary N output for both silage types (i.e. grass v. red clover) was strong, but the fit of the regressions was better for GS than RCS. The CH₄/DE ratio decreased (P < 0.05) and the UE/DE ratio increased (P < 0.05) with increasing organic matter digestibility in RCS. These relationships were not significant (P < 0.05) for the GS diets. The regression coefficient was higher (P < 0.05) for GS than RCS when regressing ME concentration on digestible organic matter. The results of this study imply that ME/DE ratio is not constant across first-cut GS of different maturities. The ME production response may be smaller from highly digestible first-cut GS but could not be clearly related to urinary excretion of monophenols derived from solubilisation of lignin. Furthermore, energy lost in urine was not clearly defined for RCS and was much more predictable for GS from silage N concentration.     

Comparison of organoleptic quality and composition of beef from suckler bulls from different production systems

Bull beef production is traditionally based on high concentrate rations fed indoors. Inclusion of grazed grass, which is generally a cheaper feed, would decrease the cost of bull beef production, but may affect beef quality. Accordingly, the organoleptic quality and composition of beef from continental-sired suckler bulls (n=126) assigned to either ad libitum concentrates to slaughter (C), grass silage (GS) ad libitum for 120 days followed by C (GSC) or GS followed by 100 days at pasture and then C (GSPC) and slaughtered at target carcass weights (CW) of 360, 410 or 460 kg was examined. Tenderness, flavour liking and overall liking were lower (P<0.05) for GSPC than for C and GSC. Intramuscular fat content and soluble collagen proportion were lower (P<0.05) for GSPC than GSC which was lower (P<0.05) than C. Soluble collagen proportion was lower (P<0.05) for 460 kg than 410 kg CW, which was lower (P<0.05) than 360 kg CW. Inclusion of a grazing period decreased the ratings of tenderness, flavour liking and overall liking, but age of the bulls at slaughter had no clear influence on sensory characteristics.     

The repeatability of feed intake and feed efficiency in beef cattle offered high-concentrate,grass silage and pasture-based diets

Breeding values for feed intake and feed efficiency in beef cattle are generally derived indoors on high-concentrate (HC) diets. Within temperate regions of north-western Europe, however, the majority of a growing beef animal’s lifetime dietary intake comes from grazed grass and grass silage. Using 97 growing beef cattle, the objective of the current study was to assess the repeatability of both feed intake and feed efficiency across 3 successive dietary test periods comprising grass silage plus concentrates (S+C), grazed grass (GRZ) and a HC diet. Individual DM intake (DMI), DMI/kg BW and feed efficiency-related parameters, residual feed intake (RFI) and gain to feed ratio (G : F) were assessed. There was a significant correlation for DMI between the S+C and GRZ periods (r = 0.32; P < 0.01) as well as between the S+C and HC periods (r = 0.41; P < 0.001), whereas there was no association for DMI between the GRZ and HC periods. There was a significant correlation for DMI/kg BW between the S+C and GRZ periods (r = 0.33; P < 0.01) and between the S+C and HC periods (r = 0.40; P < 0.001), but there was no association for the trait between the GRZ and HC periods. There was a significant correlation for RFI between the S+C and GRZ periods (r = 0.25; P < 0.05) as well as between S+C and HC periods (r = 0.25; P < 0.05), whereas there was no association for RFI between the GRZ and HC periods. Gain to feed ratio was not correlated between any of the test periods. A secondary aspect of the study demonstrated that traits recorded in the GRZ period relating to grazing bite rate, the number of daily grazing bouts and ruminating bouts were associated with DMI (r = 0.28 to 0.42; P < 0.05 - 0.001), DMI/kg BW (r = 0.36 to 0.45; P < 0.01 - 0.001) and RFI (r = 0.31 to 0.42; P < 0.05 - 0.001). Additionally, the number of ruminating boli produced per day and per ruminating bout were associated with G : F (r = 0.28 and 0.26, respectively; P < 0.05). Results from this study demonstrate that evaluating animals for both feed intake and feed efficiency indoors on HC diets may not reflect their phenotypic performance when consuming conserved forage-based diets indoors or when grazing pasture.     

Effects of zinc source and dietary concentration on serum zinc concentrations,growth performance,wool and reproductive characteristics in developing rams

Dietary Zn has significant impacts on the growth and development of breeding rams. The objectives of this study were to evaluate the effects of dietary Zn source and concentration on serum Zn concentration, growth performance, wool traits and reproductive performance in rams. Forty-four Targhee rams (14 months; 68 ± 18 kg BW) were used in an 84-day completely randomized design and were fed one of three pelleted dietary treatments: (1) a control without fortified Zn (CON; n = 15; ~1 × NRC); (2) a diet fortified with a Zn amino acid complex (ZnAA; n = 14; ~2 × NRC) and (3) a diet fortified with ZnSO₄ (ZnSO₄; n = 15; ~2 × NRC). Growth and wool characteristics measured throughout the course of the study were BW, average daily gain (ADG), dry matter intake (DMI), feed efficiency (G : F), longissimus dorsi muscle depth (LMD), back fat (BF), wool staple length (SL) and average fibre diameter (AFD). Blood was collected from each ram at four time periods to quantify serum Zn and testosterone concentrations. Semen was collected 1 to 2 days after the trial was completed. There were no differences in BW (P = 0.45), DMI (P = 0.18), LMD (P = 0.48), BF (P = 0.47) and AFD (P = 0.9) among treatment groups. ZnSO₄ had greater (P ≤ 0.03) serum Zn concentrations compared with ZnAA and CON treatments. Rams consuming ZnAA had greater (P ≤ 0.03) ADG than ZnSO₄ and CON. There tended to be differences among groups for G : F (P = 0.06), with ZnAA being numerically greater than ZnSO₄ and CON. Wool staple length regrowth was greater (P < 0.001) in ZnSO₄ and tended to be longer (P = 0.06) in ZnAA treatment group compared with CON. No differences were observed among treatments in scrotal circumference, testosterone, spermatozoa concentration within ram semen, % motility, % live sperm and % sperm abnormalities (P ≥ 0.23). Results indicated beneficial effects of feeding increased Zn concentrations to developing Targhee rams, although Zn source elicited differential responses in performance characteristics measured.     

Dry matter,protein, energy and fibre intake by dairy heifers grazing a Rhodes grass (Chloris gayana) pasture

Dry matter (DM), protein, energy and fibre (ADF) intakes of Friesian and Ayrshire dairy heifers grazing a Rhodes grass pasture in Central Kenya were studied by indicator techniques for ten 22-day periods, each comprising 10 preliminary days and 12 collection days.Digestibility coefficients of DM, CP, GE and fibre were higher (P < 0.05) in the wetter periods and generally declined during the drier periods, as pasture matured. Intakes of DM, DCP and DE decreased (P < 0.05) as herbage matured. Average daily intake per kgW^0.75 was 73.9-g DM, 4.1-g DCP, 31.8-g ADF and 167-kcal DE. Average daily gain (ADG) also varied (P < 0.05) with period and was positively related to intake of digestible dry matter, protein and energy. When conditions were wet, ADG was satisfactory at 480 g. In dry conditions, the heifers ingested 26.1-g DDM, 1.6-g DCP and 110-Kcal DE per kgW^0.75 daily and gained at 200 g/day, and supplementation was deemed necessary to sustain an optimum ADG of 550 g. The factors which may have limited pasture intake by the grazing heifers are discussed. In general, a Chloris gayana pasture, grazed at an appropriate stocking-rate, will meet the requirements of dairy heifers for maintenance and, to a variable degree, those for growth in areas of Kenya with an annual rainfall of 1400 mm and with a high potential for increased cattle production.     

The distribution of leaf photosynthetic activity in a mixed grass-legume pasture canopy

The distribution of net photosynthetic activity of leaves was measured in a mixed grass (Setaria sphacelata var. sericea)-legume (Desmodium intortum) pasture stand using a method based on concurrent measurement of the rate of CO₂ exchange, and ¹⁴CO₂ dosing followed by rapid harvesting according to height strata. Comparisons were also made between plots which differed in the period of regrowth following defoliation. The usual superiority of leaf net photosynthetic rates of a C₄ grass, compared with C₃ legume leaves, was found in the upper, well illuminated strata. These rates were, however, much lower than those usually described for horizontally exposed leaves, primarily because leaves in the pasture stand were inclined to the horizontal. At greater depth in the canopies, the superiority of rates in the grass was less evident, and consequently the relative contributions of grass and legume to canopy photosynthesis became more dependent on their leaf area indices. Attention is drawn to the relative simplicity of the method for examining the contribution of leaves, which may differ according to species or position in the canopy, to productivity of the whole stand.     

The distribution of leaf photosynthetic activity in a mixed grass-legume pasture canopy

The distribution of net photosynthetic activity of leaves was measured in a mixed grass (Setaria sphacelata var. sericea)-legume (Desmodium intortum) pasture stand using a method based on concurrent measurement of the rate of CO₂ exchange, and ¹⁴CO₂ dosing followed by rapid harvesting according to height strata. Comparisons were also made between plots which differed in the period of regrowth following defoliation. The usual superiority of leaf net photosynthetic rates of a C₄ grass, compared with C₃ legume leaves, was found in the upper, well illuminated strata. These rates were, however, much lower than those usually described for horizontally exposed leaves, primarily because leaves in the pasture stand were inclined to the horizontal. At greater depth in the canopies, the superiority of rates in the grass was less evident, and consequently the relative contributions of grass and legume to canopy photosynthesis became more dependent on their leaf area indices. Attention is drawn to the relative simplicity of the method for examining the contribution of leaves, which may differ according to species or position in the canopy, to productivity of the whole stand.     

The effects of graded levels of concentrate supplementation on colour and lipid stability of beef from pasture finished late-maturing bulls

Finishing late-maturing bulls on grass may alter the antioxidant/prooxidant balance leading to beef with higher susceptibility to lipid oxidation and a lower colour stability compared to bulls finished on cereal concentrates. In this context, lipid oxidation and colour stability of beef from late-maturing bulls finished on pasture, with or without concentrate supplements, or indoors on concentrate was assessed. Charolais or Limousin sired bulls (n = 48) were assigned to four production systems: (1) pasture only (P), (2) pasture plus 25% dietary DM intake as barley-based concentrate (PC25), (3) pasture plus 50% dietary DM intake as barley-based concentrate (PC50) or (4) a barley-based concentrate ration (C). Following slaughter and postmortem ageing, M. Longissimus thoracis et lumborum was subjected to simulated retail display (4°C, 1000 lux for 12 h out of 24 h) for 3, 7, 10 and 14 days in modified atmosphere packs (O₂ : CO₂; 80 : 20). Lipid oxidation was determined using the 2-thiobarbituric acid-reactive substances assay; α-tocopherol was determined by HPLC; fatty acid methyl esters were determined using Gas Chromatography. Using a randomised complete block design, treatment means were compared by either ANOVA or repeated measures ANOVA using the MIXED procedure of SAS. Total polyunsaturated fatty acid (PUFA) concentrations were not affected by treatment, n-3 PUFAs were higher (P < 0.001) and the ratio of n-6 to n-3 PUFAs was lower (P < 0.001) in muscle from P, PC25 and PC50 compared to C. α-Tocopherol concentration was higher in muscle from P compared to PC50 and C bulls (P = 0.001) and decreased (P < 0.001) in all samples by day 14. Lipid oxidation was higher in muscle from C compared to P bulls on day 10 and day 14 of storage (P < 0.01). Finishing on pasture without supplementation did not affect beef colour stability and led to lower lipid oxidation, possibly due to the higher α-tocopherol concentration compared to concentrate finished beef.     

Effect of pre-grazing herbage mass on dairy cow performance,grass dry matter production and output from perennial ryegrass (Lolium perenne L.) pastures

A grazing study was undertaken to examine the effect of maintaining three levels of pre-grazing herbage mass (HM) on dairy cow performance, grass dry matter (DM) production and output from perennial ryegrass (Lolium perenne L.) pastures. Cows were randomly assigned to one of three pre-grazing HM treatments: 1150 – Low HM (L), 1400 – Medium HM (M) or 2000 kg DM/ha – High HM (H). Herbage accumulation under grazing was lowest (P<0.01) on the L treatment and cows grazing the L pastures required more grass silage supplementation during the grazing season (+73 kg DM/cow) to overcome pasture deficits due to lower pasture growth rates (P<0.05). Treatment did not affect daily milk production or pasture intake, although cows grazing the L pastures had to graze a greater daily area (P<0.01) and increase grazing time (P<0.05) to compensate for a lower pre-grazing HM (P<0.01). The results indicate that, while pre-grazing HM did not influence daily milk yield per cow, adapting the practise of grazing low HM (1150 kg DM/ha) pasture reduces pasture DM production and at a system level may increase the requirement for imported feed.     

Sward characteristics and performance of dairy cows in organic grass–legume pastures shaded by tropical trees

The silvopastoral system (SPS) has been suggested to ensure sustainability in animal production systems in tropical ecosystems. The objective of this study was to evaluate pasture characteristics, herbage intake, grazing activity and milk yield of Holstein×Zebu cows managed in two grazing systems (treatments): SPS dominated by a graminaceous forage (Brachiaria decumbens) intercropped with different leguminous herbaceous forages (Stylosanthes spp., Pueraria phaseoloides and Calopogonium mucunoides) and legume trees (Acacia mangium, Gliricidia sepium and Leucaena leucocephala), and open pasture (OP) of B. decumbens intercropped only with Stylosanthes spp. Pastures were managed according to the rules for organic cattle production. The study was carried out by following a switch back format with 12 cows, 6 for each treatment, over 3 experimental years. Herbage mass was similar (P>0.05) for both treatments, supporting an average stocking rate of 1.23 AU/ha. Daily dry matter intake did not vary (P>0.05) between treatments (average of 11.3±1.02 kg/cow per day, corresponding to 2.23±0.2% BW). Milk yield was higher (P<0.05; 10.4±0.06 kg/cow per day) in the SPS than in the OP (9.5±0.06 kg/cow per day) during the 1^st year, but did not significantly differ (P>0.05) in subsequent years. The highest (P<0.05) values for herbage mass and milk yield were observed during the 3^rd year. In the SPS, with moderate shade (19% shade relative to a full-sun condition), the grass CP was higher (P<0.05) than in the OP, although the NDF content and digestibility coefficient were not modified. The animals spent more time (P<0.05) idling in the SPS than in OP. The higher legume proportion in the SPS was associated with the higher CP level in B. decumbens relative to the OP, which could explain the better (P<0.05) performance of the cows in silvopastoral areas during the 1^st year. However, during the 2^nd and 3^rd years, similarities in the legume percentages of both systems resulted in similar (P>0.05) milk yields. Low persistence of Stylosanthes guianensis was observed over the experimental period, indicating that the persistence of forage legumes under grazing could be improved using adapted cultivars that have higher annual seed production. The SPS and a diversified botanical composition of the pasture using legume species mixed with grasses are recommended for organic milk production.     

Effect of perennial ryegrass (Lolium perenne L.) cultivars on the milk yield of grazing dairy cows

The objective of this experiment was to investigate the effect of four perennial ryegrass cultivars: Bealey, Astonenergy, Spelga and AberMagic on the milk yield and milk composition of grazing dairy cows. Two 4 × 4 latin square experiments were completed, one during the reproductive and the other during the vegetative growth phase of the cultivars. Thirty-two Holstein–Friesian dairy cows were divided into four groups, with each group assigned 17 days on each cultivar during both experiments. Within each observation period, milk yield and milk composition, sward morphology and pasture chemical composition were measured. During the reproductive growth phase, organic matter digestibility (OMD) was greater for Bealey and Astonenergy (P < 0.001; +1.6%). AberMagic contained a higher stem proportion (P < 0.01; +0.06) and a longer sheath height (P < 0.001; +1.9 cm). Consequently, cows grazing AberMagic recorded a lower milk yield (P < 0.001; −1.5 kg/day) and a lower milk solids yield (P < 0.001; −0.13 kg/day). During the vegetative growth phase, OMD was greater (P < 0.001; +1.1%) for Bealey, whereas the differences between the cultivars in terms of sward structure were smaller and did not appear to influence animal performance. As a result, cows grazing Bealey recorded a higher milk yield (P < 0.001; +0.9 kg/day) and a higher milk solids yield (P < 0.01; +0.08 kg/day). It was concluded that grass cultivar did influence milk yield due to variations in sward structure and chemical composition.     

Effect of the replacement of a native savanna by an African Brachiaria decumbens pasture on the CO2 exchange in the Orinoco lowlands,Venezuela

In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C₄ grass, Brachiaria decumbens Stapf. We addressed following questions: (1) How does the replacement of the native vegetation affect CO₂ exchange on seasonal and annual scales? (2) How do biophysical constraints change when the landscape is transformed? To assess how these changes affect carbon exchange, we determined simultaneously the CO₂ fluxes by eddy covariance, and the soil CO₂ efflux by a chamber-based system in B. decumbens and herbaceous savanna stands. Measurements covered a one-year period from the beginning of the dry season (November 2008) to the end of the wet season (November 2009). During the wet season, the net ecosystem CO₂ exchange reached maximum values of 23 and 10 μmol(CO₂) m^?2 s^?1 in the B. decumbens field and in the herbaceous savanna stand, respectively. The soil CO₂ efflux for both stands followed a temperature variation during the dry and wet seasons, when the soil water content (SWC) increased above 0.087 m³ m^?3 in the latter case. Bursts of CO₂ emissions were evident when the dry soil experienced rehydration. The carbon source/sink dynamics over the two canopies differed markedly. Annual measurements of the net ecosystem production indicated that the B. decumbens field constituted a strong carbon sink of 216 g(C) m^?2 y^?1. By contrast, the herbaceous savanna stand was found to be only a weak sink [36 g(C) m^?2 y^?1]. About 53% of the gross primary production was lost as the ecosystem respiration. Carbon uptake was limited by SWC in the herbaceous savanna stand as evident from the pattern of water-use efficiency (WUE). At the B. decumbens stand, WUE was relatively insensitive to SWC. Although these results were specific to the studied site, the effect of land use changes and the physiological response of the studied stands might be applicable to other savannas.     

An automated method for the evaluation of ram libido in real mating conditions

We investigated if sexual behaviour of rams can be assessed with an electronic Alpha-Detector (AD) which automatically records mounts of mating rams. To evaluate the rams’ libido (i.e. all sexual activities), we used six intact and six vasectomised rams in pen tests in three different seasons (late spring, autumn and early spring). The pen tests consisted of 30-min visual observations of each ram placed in a group of six Merino ewes (three ewes in oestrus and three ewes not in oestrus). In the pen tests, sexual behaviour was recorded and divided into two categories: pre-copulatory and copulatory. For validation purposes, during the pen tests the 12 rams were equipped with the AD and the number of times the 18 oestrous ewes were mounted were counted over a period of 3 days. Of the 1191 mounts visually identified in the six 30-min sessions, 1026 were recorded automatically by the AD (i.e. 94%). The paddock test is an automated method consisting of the same rams wearing an AD and placed in a flock of ~250 Merino ewes on two occasions (late spring (spring 1) and early spring of the following year (spring 2)), their copulatory activities were automatically recorded over a 5-day period. The results of the pen tests in the three seasons revealed no difference between the two types of rams (breeding v. detecting rams). Based on live observations high correlations (r=+0.81, P<0.003 for breeding and r=+0.76, P<0.02 for detecting rams) were found between pre-copulatory and copulatory behaviours. The libido of the two types of rams measured in pen tests showed high repeatability across the three seasons (83 and 75%, P<0.05 for copulatory and pre-copulatory behaviours, respectively). When measured automatically in paddock tests over two consecutive springs, even higher repeatability was observed in both breeding (94%; P<0.01) and detecting rams (97%; P<0.004) in the number of mounts. In addition, high correlations (+0.89<r<+0.94) between copulatory behaviours, as measured by live observations, and those measured by the AD were obtained. The automatic measurement of ram libido in paddock tests appears to be more reliable than pen tests and far less time consuming. We therefore recommend this automated method to estimate the libido of rams. In addition, this method can be used at any season of the year provided that ewes in oestrus are present in the flock.