A Bayesian meta-analysis of the effects of administering an intra-vaginal (CIDR) device in combination with other hormones on the reproductive performance of cycling, anoestrous and inseminated cows

205

173

The objectives of this paper are to provide an introduction to meta-analysis and systematic review and to discuss the rationale for this type of research and other general considerations. We highlight methods used to produce a rigorous meta-analysis and discuss some aspects of interpretation of meta-analysis drawing on examples from the animal and veterinary science literature. Meta-analysis is a rapidly expanding area of research that has been relatively underutilized in animal and veterinary science. It is a quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis. The examination of variability or heterogeneity in study results is also a critical outcome. The benefits of meta-analysis include a consolidated and quantitative review of a large, and often complex, sometimes apparently conflicting, body of literature. Meta-analytic methods place less emphasis on dichotomous outcomes from null hypothesis significance testing and greater emphasis on determining the magnitude and the precision of an effect of interest. A substantial benefit of meta-analysis is the potential to investigate new hypotheses using existing data, both through the development of a priori hypotheses and by examination of the heterogeneity in study responses. The specification of the outcome and hypotheses that are tested is critical to the conduct of meta-analyses, as is a sensitive literature search. A failure to identify the majority of existing studies can lead to erroneous conclusions; however, there are methods of examining data to identify the potential for studies to be missing; for example, by the use of funnel plots. Many of the statistical methods to conduct meta-analysis are widely used. Bayesian methods are well suited to meta-analysis. The post-hoc methods used to evaluate heterogeneity and publication bias, which include the I 2 statistic, L'Abbé plots, Galbraith plots, Rosenthal's N, and influential study analysis are exclusively used in meta-analysis. Examples where meta-analyses have been repeated in animal science or veterinary medicine show good consistency in estimates of effect. Findings of studies to date have provided new understandings of rumen modifiers, milk fever, parasite control, mastitis, somatotropin, and reproductive manipulations. Rigorously conducted meta-analyses are useful tools to improve animal well-being and productivity. The need to integrate findings from many studies ensures that meta-analytic research is desirable and the large body of research now generated makes the conduct of this research feasible.

Section: Discussionmentioning

confidence: 99%

“…Rabiee et al (2004Rabiee et al ( , 2005 used this method in exploring sources of heterogeneity in the controlled internal drug-releasing insert (CIDR) and Ovsynch data. Baker and Jackson (2008) have proposed a method that reduces the weight of studies that are outliers in meta-analyses.…”

Section: Approaches To Heterogeneitymentioning

confidence: 99%

Invited review: Use of meta-analysis in animal health and reproduction: Methods and applications

Lean¹,

Rabiee

Duffield

et al. 2009

205

173

“…Although in many of the aforementioned studies the experimental designs did not allow for the establishment of causality, these results point out that high concentration of progesterone during follicle development is important for fertility in dairy cows. However, supplementing progesterone using a single intravaginal insert has not enhanced fertility in a consistent manner (Rabiee et al, 2004). Improved P/AI has been reported in some (Stevenson et al, 2006;Bisinotto et al, 2010b;Colazo et al, 2013), but not all studies (Galvão et al, 2004;Lima et al, 2009;Bilby et al, 2013;.…”

Section: Introductionmentioning

confidence: 99%

Meta-analysis of progesterone supplementation during timed artificial insemination programs in dairy cows

Bisinotto

Lean²,

Thatcher

et al. 2015

A systematic review of the literature was performed with the objective to evaluate the effects of progesterone supplementation using a single intravaginal insert during timed artificial insemination (AI) programs on fertility in lactating dairy cows. A total of 25 randomized controlled studies including 8,285 supplemented cows and 8,398 untreated controls were included in the meta-analysis. Information regarding the presence of corpus luteum (CL) at the initiation of the synchronization protocol was available for 6,883 supplemented cows and 6,879 untreated controls in 21 experiments. Studies were classified based on service number (first AI vs. resynchronized AI), use of presynchronization (yes vs. no), and insemination of cows in estrus during the synchronization protocol (inseminated in estrus and timed AI vs. timed AI only). Reproductive outcomes of interest were pregnancy per AI (P/AI) measured on d 32 (27 to 42) and 60 (41 to 71) after AI, and pregnancy loss between d 32 and 60 of gestation. Random effects meta-analyses were conducted and treatment effect was summarized into a pooled risk ratio with the Knapp-Hartung modification (RRK+H). The effect of moderator variables was assessed using meta-regression analyses. Progesterone supplementation increased the risk of pregnancy on d 32 [RRK+H = 1.08; 95% confidence interval (CI) = 1.02-1.14] and 60 after AI (RRK+H = 1.10; 95% CI = 1.03-1.17). The benefit of progesterone supplementation was observed mainly in cows lacking a CL at the initiation of the timed AI program (d 60: RRK+H = 1.18; 95% CI = 1.07-1.30) rather than those with CL (d 60: RRK+H = 1.06; 95% CI = 0.99-1.12). Progesterone supplementation benefited P/AI in studies in which all cows were inseminated at timed AI (d 60: RRK+H = 1.20; 95% CI = 1.10-1.29), but not in studies in which cows could be inseminated in estrus during the timed AI program (d 60: RRK+H = 1.04; 95% CI = 0.92-1.16). Progesterone supplementation tended to reduce the risk of pregnancy loss (RRK+H = 0.84; 95% CI = 0.67-1.00). Service number and presynchronization did not influence the effect of progesterone supplementation on fertility. In summary, progesterone supplementation using a single intravaginal insert during the timed AI program increased P/AI mostly in cows without CL and reduced the risk of pregnancy loss in lactating dairy cows. Insemination of cows in estrus during the synchronization protocol eliminated the benefit of supplemental progesterone on P/AI.

“…Some strategies to increase submission rates may reduce conception rates. For example, treatment of anestrous cows with intravaginal devices increases submission rates but decreases conception rates (Rabiee et al, 2004), and false positive insemination frequency can increase when herd managers and staff attempt to increase estrus detection sensitivity (Fetrow, 1993) and inseminate cows showing signs less predictive of estrus. However, herd managers inseminate a high proportion of cows not seen standing to be mounted but showing other signs, and achieve moderate conception rates in these cows (Badinga et al, 1985).…”

Section: Correlations Between Submission and Conception Ratesmentioning

confidence: 99%

Interrelationships between herd-level reproductive performance measures based on intervals from initiation of the breeding program in year-round and seasonal calving dairy herds

Morton¹

2010

In year-round calving herds, reproductive performance has traditionally been described in relation to each cow's calving date. This research described reproductive performance in year-round and seasonal calving dairy herds using herd-level measures based on interval from each cow's initiation of breeding program date, and assessed interrelationships between such measures. A large, prospective, single cohort study, implemented in 1997 and 1998, included 29,327 cows from 167 Australian dairy herds. Herd reproductive performance was described using 2 measures of primary importance to herd managers: the proportion of cows that became pregnant by 6wk after their initiation of breeding program date (6-wk pregnancy rate) and the proportion of cows that were nonpregnant 21wk after their initiation of breeding program date (21-wk nonpregnancy rate). Measures that contribute to these primary measures (secondary measures) were calculated for each herd for both the first and second 3-wk periods of each cow's breeding program; submission rates were calculated as proportions of cows that were inseminated at least once in the 3-wk period, and conception rates were calculated as the proportions of inseminations in the 3-wk period that resulted in pregnancy. The individual herd was the unit of analysis. The study results indicate that high submission rates are essential if herd reproductive performance is to be achieved. Six-week pregnancy rate was predicted to increase by 6 to 8 percentage points following a 10-percentage-point increase in submission rates in both 3-wk periods, and by 6 to 10 percentage points following a 10-percentage-point increase in conception rates. Submission rates were more variable than conception rates, indicating that managers may be able to achieve large increases in submission rates more easily than substantial increases in conception rates. However, the predicted benefits of increasing submission rates were greatest when conception rates were high and vice versa, highlighting the need to improve both submission and conception rates when both are low. The study results indicate that some herd managers can concurrently achieve high submission and conception rates.