Several studies on methane (CH4) emissions have focussed on selecting high and low CH4-emitting animals. One challenge faced by this work is the lack of consistency, or repeatability, in animal rankings over time. Repeatability for individual animals over time needs to be high to reliably detect high and low CH4-emitting animals. A possible explanation for the lack of repeatability is a relatively high within-animal variation in daily CH4 emissions, meaning that animals could then change their ranking when compared at different points in time. An experiment was undertaken with four non-lactating dairy cattle to assess the within- and between-animal variation in CH4 emissions over time when measured using the sulfur hexafluoride (SF6) tracer technique. Two contrasting diets were fed to the cattle at maintenance energy levels: lucerne silage (diet 1) and a cereal + lucerne + straw mixed ration diet (diet 2). Daily CH4 measurements were undertaken for 23 days on diet 1 and 30 days on diet 2. There was a significant (P < 0.001) difference between diet 1 and diet 2 in daily CH4 production, with mean (±s.e.) production of 124.3 (11.1) g CH4/day from diet 1 and 169.8 (±11.0) g CH4/day from diet 2. Lower CH4 yield (g CH4/kg dry matter intake) was recorded on diet 1 (22.8 ± 2.0) than diet 2 (32.0 ± 2.0). Cows differed significantly (P < 0.05) from one another in daily CH4 yield (diet 1: cow 1 = 19.4 ± 0.6, cow 2 = 22.2 ± 0.8, cow 3 = 23.2 ± 0.7, cow 4 = 25.4 ± 0.6; diet 2: cow 1 = 26.0 ± 0.7, cow 2 = 36.4 ± 0.7, cow 3 = 29.3 ± 0.7, cow 4 = 36.6 ± 0.7). Variances for daily CH4 yield were smaller for diet 1 (within animal = 6.91, between animals = 6.23) than for diet 2 (within animal = 10.09, between animals = 27.79). Estimates of repeatability (variation between animals/total variation) for daily CH4 yield were 47 and 73% in diet 1 and 2, respectively. Coefficients of variation in average daily CH4 emissions in this experiment ranged from 8 to 18% despite the fact that each animal received the same quantity and quality of feed each day. While further research is required, the high within-animal variability in CH4 emissions measured using the SF6 tracer technique may explain why there has been difficulty in obtaining consistent rankings in CH4 yields when animals are measured on multiple occasions. The results also suggest that the SF6 tracer technique may exaggerate apparent between animal differences in CH4 emissions.

Previous experiments have suggested that estimates of methane (CH 4 ) emissions from ruminant animals made using the sulphur hexafluoride (SF 6 ) tracer might be influenced by the permeation rate of SF 6 (PR). This study examined the latter issue with cattle. For this, analyses of data sets from two grazing trials involving large herds (exps. 1 and 2) and a specifically designed controlled trial (exp. 3) were conducted. Individual daily CH 4 emissions from 296 (exp. 1) and 388 (exp. 2) Friesian )Jersey cows in mid-lactation were measured with herds subdivided into four (exp. 1) or five (exp. 2) measurement groups and dry matter intake (DMI) estimated by energy metabolism algorithms. The ranges of tracer PR in exps. 1 and 2 were 2.624Á5.689 and 2.214Á3.594 mg d(1 , respectively. Experiment 3 was conducted using 12 rumenfistulated beef steers pen-fed on lucerne silage and design arranged as a 4)4 Latin square with three replications. Permeation tubes with four levels of nominal PR (three tubes each): low (L), medium (M), medium-high (MH) and high (H) were randomly assigned to four rumen deployment sequences (L-M-MH-H, H-MH-M-L, MH-L-H-M and M-H-L-MH).The grazing experiments revealed a positive effect of PR on the CH 4 emission estimates (1 mg SF 6 d(1 accounting for 0.6Á2.3 g kg (1 DMI), but this effect was significant (R 2 00.06Á0.23, PB0.05) only when there was a large range in PR (exp. 1), whereas with a narrower PR range (exp. 2) the effect was not significant (R 2 B0.04, P!0.05). Experiment 3 revealed that the influence of PR upon CH 4 emission estimates was linear. It is concluded that despite an influence of PR on CH 4 emission estimates, accuracy and precision of the tracer technique is warranted provided that PR are used in a narrow range and balanced between the experimental treatments.

Vlaming, J. B., Brookes, I. M., Hoskin, S. O., Pinares-Patiño, C. S. and Clark, H. 2007. The possible influence of intra-ruminal sulphur hexafluoride release rates on calculated methane emissions from cattle. Can. J. Anim. Sci. 87: 269-275. Estimates of methane (CH 4 ) production from grazing animals are routinely made using the sulphur hexafluoride (SF 6 ) tracer technique. While this technique is generally regarded as useful, some investigators report a higher variability in measurements when compared with calorimetry. The SF 6 technique is a marker dilution method in which a known release rate of SF 6 from an intra-ruminal permeation tube is used to calculate CH 4 emissions from the ratio of SF 6 :CH 4 in expired breath. The release rate of SF 6 is unique for each tube, and although calculated CH 4 emissions should be independent of SF 6 release rate, an analysis of research conducted in New Zealand has suggested a possible influence of SF 6 release rate upon calculated CH 4 emissions. A modified cross-over design, with two groups of six steers given either one (2.878 mg SF 6 d -1 ) or two (7.336 mg SF 6 d -1 ) permeation tubes and offered either energy maintenance (M) or 2 × M levels of feed intake was undertaken to determine the effect of SF 6 release rate and intake on calculated CH 4 emissions. A high SF 6 release rate elevated the calculated CH 4 emission per day (P < 0.001) and per kg dry matter intake (kg DMI) by 19% (P < 0.001) irrespective of the level of intake. Release rate of SF 6 can affect the calculated CH 4 emissions from animals when employing the SF 6 tracer technique. 269-275. On estime couramment la quantité de méthane (CH 4 ) libérée par les animaux en paissance en recourant à l'hexafluorure de soufre (SF 6 ) comme traceur. Malgré l'utilité généralement reconnue de cette technique, certains chercheurs signalent que les résultats obtenus varient plus que ceux venant de la calorimétrie. La technique du SF 6 consiste à diluer le marqueur puis à utiliser le taux de libération de SF 6 connu d'un tube de perméation intra-ruminal pour calculer les dégagements de CH 4 dans le volume d'air expiré au moyen du ratio SF 6 :CH 4 . Le taux de libération de SF 6 est unique à chaque tube et, si le calcul des émissions de CH 4 devrait en être indépendant, une analyse des travaux effectués en Nouvelle-Zélande laisse croire que le taux de libération de SF 6 pourrait en réalité influer sur le calcul des émissions de CH 4 . Les auteurs ont procédé à une expérience en chassé-croisé modifiée, attribuant à deux groupes de six bouvillons un (2,878 mg de SF 6 par jour) ou deux (7,336 mg de SF 6 par jour) tubes de perméation et une ration suffisante pour maintenir le bilan énergétique (M) ou le double de cette ration afin d'établir quel effet le taux de libération de SF 6 et le taux d'ingestion des aliments pouvait avoir sur le calcul des émissions de CH 4 . Un taux de libération élevé de SF 6 augmente les émissions de CH 4 par jour (P < 0,001) et par kg de matière sèche ingérée de 19 % (P < 0,001), peu importe le ...

The major limitation to perennial ryegrass-based systems is low soil moisture which reduces perennial ryegrass growth. irrigation can maintain adequate soil moisture levels for pasture growth, however, the associated cost requires high levels of forage water use efficiency.

There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated.