A meta-analysis of effects of feeding seaweed on beef and dairy cattle performance and methane yield

There has been considerable interest in the use of red seaweed, and in particular Asparagopsis taxiformis, to increase production of cattle and to reduce greenhouse gas emissions. We hypothesized that feeding seaweed or seaweed derived products would increase beef or dairy cattle performance as indicated by average daily gain (ADG), feed efficiency measures, milk production, and milk constituents, and reduce methane emissions. We used meta-analytical methods to evaluate these hypotheses. A comprehensive search of Google Scholar, Pubmed and ISI Web of Science produced 14 experiments from which 23 comparisons of treatment effects could be evaluated. Red seaweed (A. taxiformis) and brown seaweed (Ascophyllum nodosum) were the dominant seaweeds used. There were no effects of treatment on ADG or dry matter intake (DMI). There was an increase in efficiency for feed to gain by 0.41 ± 0.22 kg per kg [standardized mean difference (SMD) = 0.70 ± 0.35; P = 0.001], but not for gain to feed (P = 0.215), although the direction of the change was for improved efficiency. The type of seaweed used was not a significant covariable for ADG and DMI. Milk production was increased with treatment on weighted mean difference (WMD; 1.35 ± 0.44 kg/d; P <0.001); however, the SMD of 0.45 was not significant (P = 0.111). Extremely limited data suggest the possibility of increased percentages of milk fat (P = 0.040) and milk protein (P = 0.001) on DerSimonian and Laird (D&L) WMD evaluation. The limited data available indicate dietary supplementation with seaweed produced a significant and substantial reduction in methane yield by 5.28 ± 3.5 g/kg DMI (P = 0.003) on D&L WMD evaluation and a D&L SMD of −1.70 (P = 0.001); however, there was marked heterogeneity in the results (I2 > 80%). In one comparison, methane yield was reduced by 97%. We conclude that while there was evidence of potential for benefit from seaweed use to improve production and reduce methane yield more in vivo experiments are required to strengthen the evidence of effect and identify sources of heterogeneity in methane response, while practical applications and potential risks are evaluated for seaweed use.

are evaluated for seaweed use. Introduction 5 70 seaweed and cattle. We searched the reference lists of papers obtained to identify other studies. 71 One additional paper was identified from a personal communication. 72 For Google Scholar, 28,400 citation results occurred, and the screening of papers 73 stopped when 50 sequential citations were not relevant. Whereas only 58 and 55 results 74 occurred from Pubmed and ISI Web of Science, respectively. In one case, the authors of an 75 article were contacted to clarify results and to provide additional information. supplementation of cattle; they were randomized; they had a description of the randomization 83 processes employed; they had appropriate analysis of data; they contained sufficient data to 84 determine the effect size for production outcomes (e.g., the number of cattle or pens in each 85 treatment and control group); they had a measure of effect so that the data were amenable to 86 effect size (ES) analysis for continuous data (e.g., standardized mean difference, SMD); and 87 they had a measure of variance (SE or SD) for each effect estimate or treatment and control 88 comparisons. Studies that could not be adequately interpreted, used purposive and non-89 representative sampling methods or where authors did not respond to clarify their approach, 90 were excluded. Note, one article was included from the pre-print server for Biology, bioRxiv 91 (https://www.biorxiv.org/). analysis. The PRISMA checklist is provided in S1 File. After the initial search and screening 6 94 61 different articles (experiments) were identified and papers without a full text (5) were 95 excluded providing 56 papers that were assessed for eligibility. A total of 42 were excluded for 96 the following reasons: the abstract was in English but the full article was in another language 97 (3 experiments), the experiment was in vitro (8 experiments), the article was a review or book 98 chapter (7 articles), the experiment had group feeding resulting in pseudo-replication (2 99 experiments), the experiment was off topic or had irrelevant outcomes (20 experiments), or the 100 experiment lacked measures of variance (2 experiments). A list of articles excluded with the 101 reason is provided in S1 Table. A total of 14 experiments with 23 treatment comparisons were 102 included in the meta-analysis. A list of the experiments and comparisons included in the meta-103 analysis is provided in Table 1. Output variables extracted for meta-analysis included: final body weight (FBW, kg), 118 ADG (kg/head/d), dry matter intake (DMI; kg/head/d), gross feed efficiency [ratio of gain to 119 feed (G:F) and ratio of feed to gain (F:G)], milk yield (kg/d), milk fat percentage, milk protein 120 percentage, and methane yield (g/kg DMI) (Tables 2 and 3).
where m is the total number of experiments, k the total number of comparisons in the extracted are given identical weights, the robust variance estimate (v R ) reduces to: where Ť j is the unweighted mean of the estimates in the j th cluster, b1 is the estimate of the 156 weighted mean, and w j is the total weight given to estimates in the j th cluster. This is a kind of

184
The I 2 provides an estimate of the proportion of the true variance of effects of the treatment, 185 that is the true variance, tau 2 (τ 2 ) divided by the total variance observed in the comparison [ are provided to allow readers the opportunity to evaluate both metrics.

191
A key focus of meta-analysis is to identify and understand the sources of heterogeneity

204
The literature that was amenable to quantitative review on seaweed use in cattle was 205 reasonably limited with only 14 full texts suitable (Fig 1; Table 1). The experiments used were 206 all published after the year 2000, indicating that they are relatively current. Although these 207 were current some production data indicated only modest production performance (Tables 2   208   and 3). Funnel plots produced indicated that publication bias was not likely (data not shown).

209
The limited number of comparisons and even fewer experiments limited the type of meta-210 regressions that could be performed and the use of RR. Only 2 experiments, one on a dairy and 211 one on a beef production system, used Latin Square designs and this precluded evaluation of 212 the effect of study design. As the SD of these were similar to the randomized controlled designs 213 adjustments to the error terms for these were not made.

214
Differences in FBW were significant for treatment for both RR SMD and RR WMD 215 suggesting that the FBW was lower for treated cattle (    There was no effect of treatment on DMI (Table 4; Fig 3) and neither the effects of 247 dairy or beef production system nor type of seaweed significantly influenced results (Table 4).

248
Interestingly, these results were heterogenous among comparisons indicting substantial 249 variations in experimental measurement (I 2 > 60%; Table 4). The F:G was evaluated in 7-and  (Table 4). was not significant and was heterogenous (I 2 = 65.1%; Table 4). There were no significant 276 effects on percentages of milk fat or milk protein on SMD, which were both heterogenous (I 2

277
= 66.2% and 73.8%, respectively). However, the WMD for both milk fat and protein 278 percentages were significantly increased by 0.06% (Table 4). The milk production results

279
contrast with the lack of effect on ADG of treatment, but may be consistent with the efficiency 280 improvement in F:G. The differences in SMD and WMD results reflect sparse data and 281 differences in the weighting between these measures.

282
There is considerable interest in the potential for Asparagopsis to reduce methane  in milk could be substantially greater than those reported by [14].

304
Although the present analysis indicates that the supplementary feeding of A. taxiformis 305 to beef and dairy cattle has some positive effects on animal production and desirable inhibitory 306 effects on methane yields, questions are raised, albeit in a single study, that relate to iodine 307 concentration in A. taxiformis and the potential challenges this may bring regarding resultant 308 iodine concentration in milk when feeding A. taxiformis to lactating dairy cows.