Review: Use and misuse of meta-analysis in Animal Science.

In animal sciences, the number of published meta-analyses is increasing at a rate of 15% per year. This current review focuses on the good practices and the potential pitfalls in the conduct of meta-analyses in animal sciences, nutrition in particular. Once the study objectives have been defined, several key phases must be considered when doing a meta-analysis. First, as a principle of traceability, criteria used to select or discard publications should be clearly stated in a way that one could reproduce the final selection of data. Then, the coding phase, aiming to isolate specific experimental factors for an accurate graphical and statistical interpretation of the database, is discussed. Following this step, the study of the levels of independence of factors and of the degree of data balance of the meta-design represents an essential phase to ensure the validity of statistical processing. The consideration of the study effect as fixed or random must next be considered. It appears based on several examples that this choice does not generally have any influence on the conclusions of a meta-analysis when the number of experiments is sufficient.

A meta-analysis of nutrient intake, feed efficiency and performance in cattle grazing on tropical grasslands.

It is essential to quantify the potential of tropical grasslands to allow significant feed efficiency for grazing livestock in controlled conditions such as at pasture. We conducted a quantitative analysis of published studies reporting the experimental results of average daily gains (ADG) and diet characteristics obtained specifically under grazing conditions (17 publications and 41 experiments), which have been less studied compared with controlled conditions in stalls. The database was analyzed to determine the average and range of values obtained for ADG (g/kg BW), dry matter digestibility, intake (DMI) and digestible DMI (DDMI, g/kg BW) and feed conversion efficiencies (FCE), as well as to predict the response of these parameters to the main strategies investigated in the literature - that is, mainly the stocking rate (SR) and the concentrate intake (CI). The ADG reached 1.2 kg BW per day and was directly linked to DDMI (ADG=-1.63+0.42 DDMI -0.0084 DDMI2, n=90, r.m.s.e=0.584, R 2=0.93). The DDMI, which was representative of the nutrient input, was driven mainly by DMI rather than dry matter digestibility, whereas these two parameters did not correlate (r=0.068, P=0.56). The average global FCE (0.11 g ADG/g DDMI) showed a greater association with the metabolic FCE (0.17 g ADG/g DMI) than the digestive FCE (0.62). The CI (g DM/kg BW) increased ADG (ADG=2376+CI 56.1, n=16, r.m.s.e.=441, R 2=0.95). The SR expressed as kg BW/ha decreased the individual ADG by 1.19 g/kg BW per additional ton of BW/ha, whereas the global ADG calculated per ha increased by 0.57 per additional ton BW/ha. When the SR was expressed as kg BW/ton DM and per ha rather than as kg BW/ha, the impact on the individual ADG decreased by 0.18 or 0.86 g per additional ton BW/ha, depending on the initial BW of the cattle. These results provide a better view of the potential performance and feeding of cattle in tropical grasslands. The results provide an improved quantification of the relationships between diet and performance, as well as the overall quantitative impact of SR and supplementation.

Influence of trough versus pasture feeding on average daily gain and carcass characteristics in ruminants: a meta-analysis.

Quantitative meta-analysis was run on 108 publications featuring 116 experiments and 399 treatments dealing with the effect of trough or pasture feeding environment (FE) on ruminant performances. The objective was to compare the effect of trough or pasture FE on ADG, diet OM digestibility (OMD), various carcass characteristics, and the interaction between FE and complementation modalities. Live weight was adjusted to compare results between species. Results showed that trough-fed animals had higher ADG (+17.89%; P < 0.001), hot carcass yield (HYield; + 2.47%; P < 0.001) and carcass fat content (+ 24.87%; P < 0.001) than pasture-fed animals but lower carcass muscle and bone percentages (-1.60% [P = 0.010] and -7.63% [P = 0.003], respectively). Feeding environment had no effect on diet OMD (P = 0.818), but the number of observations was low. After considering the addition or not of concentrate in the diet (addiCO), FE effect persisted on ADG (P = 0.024) and carcass fat content (P = 0.027) but not on HYield (P = 0.078) or muscle and bone percentages (P = 0.119 and P = 0.581, respectively). After considering the nature of the concentrate (natCO), FE effect persisted on ADG (P < 0.001) and HYield (P = 0.004). Considering the percentage of concentrate in the diet (PCO) erased FE effect on ADG (P = 0.891) and HYield (P = 0.128). In contrast, considering the quantity of concentrate(QCO) erased FE effect on ADG (P = 0.084) but not on HYield (P = 0.006) or on carcass fat and muscle contents (P = 0.040 and P = 0.040, respectively) although the FE effect on carcass bone content persisted (P = 0.550). Animal species and physiological stage had no effect on any of the variables studied (P > 0.05) but experiment did (P ≤ 0.001). The increase in ADG was positively correlated to HYield in cattle (P = 0.002) and small ruminants (P = 0.003) and positively linked to carcass fat content (P = 0.007) but not carcass muscle content, which actually decreased (P = 0.001). Overall, this meta-analysis confirmed previous reports of FE effects and revealed how the differences generally reported result from a confounding effect of FE and nature of the diet. Indeed, in most of the studies used, trough-fed animals were supplemented with concentrate whereas pasture-fed animals were not. This research also highlighted the fact that pasture-fed animals have the potential to achieve the same performances as trough-fed animals when fed a similar diet.

Mixed grazing systems of goats with cattle in tropical conditions: an alternative to improving animal production in the pasture.

Mixed grazing systems combining sheep and cattle have shown better growth performance for one or both species. This observation has been attributed to their complementary feeding behaviour and the reduced host infection by gastrointestinal nematodes. Less attention has been paid to mixed grazing systems combining goats and cattle. Here, continuously grazing goats mixed with cattle (M) were compared with control goats reared alone (C) under tropical conditions. The comparison was conducted with gastrointestinal nematode-infected (I) and non-infected (nI) goats. Thus, the four treatments were cattle with gastrointestinal nematode-infected goats (MI), gastrointestinal nematode-infected goats alone (CI), cattle with non-infected goats (MnI) and non-infected goats (CnI). Average daily gain (ADG, g/day) and grass production were measured for the four groups of animals (six goats and two heifers treated with MI or MnI) grazing for 3 months on 4 subplots. Monthly measurements were performed over 5-day periods. This pattern was replicated in space for a second set of four subplots and in time for six successive cohorts of animals (bands 1 to 6). The ADG of goats in mixed grazing conditions was higher than controls irrespective of the infection status (32.6 v. 18.4 g/day for MI v. CI; 44.2 v. 33.5 g/day for MnI v. CnI). Concomitantly, the average biomass was lower for mixed grazing animals compared with controls (174 v. 170 for MI and MnI; 235 v. 208 for CI and CnI, respectively), suggesting better use of the sward. For daily BW gain (g/kg DM), mixed grazing also yielded better results than the control (1.88 v. 0.52 g BW/kg DM per day for MI v. CI; 2.08 v. 1.47 g BW/kg DM per day for MnI and CnI). Mixed grazing of goats and heifers offers a promising alternative for increasing goat and overall animal production as well as improving the management of pastures.

Effects of feeding system and slaughter age on the growth and carcass characteristics of tropical-breed steers.

This study aimed to compare the growth performances and carcass characteristics of tropical-breed steers reared in 2 contrasted feeding systems (indoor vs. pasture) and slaughtered at different ages (early vs. late). A total of 309 Creole steers (growing at an initial BW of 173 ± 3 kg and an initial age of 252 ± 4 d) were used over a continuous 12-yr study. Indoor steers were housed in a cattle shed, fed fresh-cut grass plus concentrate, and slaughtered at 14.5 or 17.1 ± 0.1 mo of age. Pasture steers were pasture grazed without supplemental feed, and slaughtered at 17.6 and 21.2 ± 0.1 mo of age. Indoor-fed steers had a greater ADG (786 vs. 517 ± 29 g•d(-1); P < 0.0001) and more carcass fat (164 vs. 145 ± 4.5 g•kg(-1); P = 0.001) than pasture-fed steers. Late-slaughtered steers had decreased ADG (630 vs. 673 ± 27 g•d(-1); P = 0.001) but greater dressing percentages (hot dressing percentage = 55.7 vs. 54.7 ± 0.34%; chilled dressing percentage = 54.5 vs. 53.4 ± 0.34%; P < 0.0001) than early-slaughtered steers. The interaction between feeding system and slaughter age was significant for carcass tissue composition. Whole-carcass muscle content was greater in late-slaughtered steers than early-slaughtered steers, especially in pasture-fed steers (720 vs. 698 ± 6.0 g•kg(-1); P < 0.0001), but less so in indoor-fed steers (707 vs. 700 ± 5.9 g•kg(-1); P = 0.046). Furthermore, increasing slaughter age had no effect on carcass fat in indoor-fed steers (162 vs. 166 ± 4.8 g•kg(-1); P = 0.342), but decreased carcass fat in pasture-fed steers (150 vs. 140 ± 5.0 g•kg(-1); P = 0.014). The results showed that slaughter age and feeding system are 2 major factors that independently affect most of the growth and carcass traits of tropical-breed steers but jointly influence tissue deposition. Our study found that in tropical-breed steers that are grazing, late slaughtering grazing steers increased carcass muscle content without extra fat, thus yielding a carcass quality better suited to consumer choices.

Comparison of intake and digestibility of fresh Digitaria decumbens grass fed to sheep, indoors or at pasture, at two different stages of regrowth.

The effect of two feeding systems (indoors and at pasture) on intake and digestion of fresh grass was studied at two stages of regrowth (21 and 35 days of regrowth) in two parallel experiments. In Experiment 1, 10 adult Martinik rams weighing, on average, 50.5 (± 0.9) kg, including four fitted with rumen cannula, were randomly allocated to two groups according to a 2 × 2 Latin Square design. These rams consumed a 21-day regrowth of Digitaria decumbens grass diet during two successive 28-day periods, indoors (five rams) or at pasture (five tethered rams). In Experiment 2, 10 other Martinik rams weighing, on average, 45.5 (± 0.9) kg, including four fitted with rumen cannula, were randomly allocated to two groups according to a 2 × 2 Latin Square design. These rams consumed a 35-day regrowth of D. decumbens grass diet during two successive 28-day periods, either indoors (five rams) or at pasture (five tethered rams). For the indoors groups, in vivo organic matter digestibility (OMD) was measured by total collection of feces. In addition, OMD was estimated indoors and at pasture using the fecal CP (CPf) method (OMDCPf). Organic matter intake (OMI) was then estimated using OMDCPf and fecal organic matter output (OMICPf). Correlations of 0.49 and 0.77 were found between in vivo OMD and OMDCPf (P < 0.05) and between OMI and OMICPf (P < 0.001), respectively. OMDCPf was 1.8% (P < 0.05) and 2.7% (P < 0.01) lower indoors than at pasture at 21 and 35 days of regrowth, respectively, whereas OMICPf indoors was 1.1 and 1.16 times that registered at pasture at 21 and 35 days of regrowth, respectively. The higher OMDCPf at pasture was linked to the higher selective behavior of rams at pasture, whereas the differences in OMICPf between the two feeding systems were linked to differences in the total bulk density of the grass. These studies show that differences in OMDCPf and OMICPf exist between animals fed indoors and at pasture with the same forage and that these differences may vary according to the stage of regrowth of the grass offered.

The importance of grasslands for animal production and other functions: a review on management and methodological progress in the tropics.

The global importance of grasslands is indicated by their extent; they comprise some 26% of total land area and 80% of agriculturally productive land. The majority of grasslands are located in tropical developing countries where they are particularly important to the livelihoods of some one billion poor peoples. Grasslands clearly provide the feed base for grazing livestock and thus numerous high-quality foods, but such livestock also provide products such as fertilizer, transport, traction, fibre and leather. In addition, grasslands provide important services and roles including as water catchments, biodiversity reserves, for cultural and recreational needs, and potentially a carbon sink to alleviate greenhouse gas emissions. Inevitably, such functions may conflict with management for production of livestock products. Much of the increasing global demand for meat and milk, particularly from developing countries, will have to be supplied from grassland ecosystems, and this will provide difficult challenges. Increased production of meat and milk generally requires increased intake of metabolizable energy, and thus increased voluntary intake and/or digestibility of diets selected by grazing animals. These will require more widespread and effective application of improved management. Strategies to improve productivity include fertilizer application, grazing management, greater use of crop by-products, legumes and supplements and manipulation of stocking rate and herbage allowance. However, it is often difficult to predict the efficiency and cost-effectiveness of such strategies, particularly in tropical developing country production systems. Evaluation and on-going adjustment of grazing systems require appropriate and reliable assessment criteria, but these are often lacking. A number of emerging technologies may contribute to timely low-cost acquisition of quantitative information to better understand the soil-pasture-animal interactions and animal management in grassland systems. Development of remote imaging of vegetation, global positioning technology, improved diet markers, near IR spectroscopy and modelling provide improved tools for knowledge-based decisions on the productivity constraints of grazing animals. Individual electronic identification of animals offers opportunities for precision management on an individual animal basis for improved productivity. Improved outcomes in the form of livestock products, services and/or other outcomes from grasslands should be possible, but clearly a diversity of solutions are needed for the vast range of environments and social circumstances of global grasslands.

Cross-infection between tropical goats and heifers with Haemonchus contortus.

Developing effective biological control without the systematic use of anthelmintics is necessary to reduce the impact of gastrointestinal nematodes on small ruminants. Therefore, grazing management systems that use different host species to dilute nematodes in pasture appear to be promising for worm control. A trial was carried out to investigate the specificity of Haemonchus contortus for goats and cattle and to evaluate cross-infection between ruminant species. The effect of an experimental infection of 12 heifers by the free-living stages of H. contortus collected from goats (500 larvae per kg liveweight) was evaluated and compared to uninfected controls. After 28 and 35 days, egg excretion was measured. The experimental infection of heifers by H. contortus was not significant, with no egg excretion. These results, i.e., the lack of cross-infection of GIN between goats and cattle, suggest that integrated grazing using such animals could be employed for pasture dilution and decontamination.

Growth performance, carcass quality, and noncarcass components of indigenous Caribbean goats under varying nutritional densities.

Studies were conducted to determine the effects of feeding regimens on growth and carcass quality of the Creole goat, a genotype indigenous to the Caribbean. Forty kids weighing 9.0 +/- 1.2 kg of BW were reared indoors after weaning. Four supplement amounts were compared (10 kids per treatment): the G0 group received the basal diet (tropical forage, 8.8 MJ of ME and 108 g of CP/kg of DM) without concentrate, whereas the G100, G200, and G300 groups were offered 130, 230, and 310 g/d of concentrate (13.6 MJ of ME and 209 g of CP/kg of DM), respectively, in addition to the basal diet. The kids were slaughtered according to the standard procedure at 22 to 24 kg of BW for assessment of carcass traits and meat quality. Total DMI increased significantly, from 51 to 78 g/kg of BW(0.75), for G0 to G300 kids, whereas their ADG doubled from 42 to 84 g/d (P < 0.01; P < 0.01, respectively). The G:F values reached 125 to 130 for the G200 and G300 diets and were satisfactory compared with literature values. The carcass weight and dressing percentage (P < 0.01) increased from group G0 to G300, from 9 to 13 kg and from 42 to 51%, respectively. The proportions of the different cuts (related to the carcass weight) did not vary by diet. The conformation score increased significantly (P < 0.05) among the 4 groups from an average score of 3.2 to 4.0 (score/5). There was a significant effect (P < 0.01) of supplement amount on the accumulation of internal fat tissues: the kidney fat weight increased from 113 to 253 g from the G0 to the G300 group. Regardless of the feeding level and amount of internal fat, the carcasses had an acceptable fat cover score, which remained less than 2.6 (score/5). A significant effect was not observed for the ultimate pH and the main color variables of the meat. The cooking loss and the shoulder DM content varied (P < 0.05) with the supplement amount. By increasing the nutritional density of the diet, it was possible to obtain well-conformed and heavy carcasses, with no excessive fattening. Indigenous Creole goats have potential as meat animals when fed to gain more than 80 g/d. The optimal supplement supply with good-quality grass would be approximately 3.69 MJ of ME/d in our conditions. Further studies are required on meat sensory parameters and fatty acid profiles.

Influence of earthworms on development of the free-living stages of gastrointestinal nematodes in goat faeces.

With the important infection of small ruminants by gastrointestinal nematodes, and in the face of reduced efficacy of anthelminthic treatments, a search for other biological options is necessary. The effect of earthworms on the free-living stages of Haemonchus contortus and Trichostrongylus colubriformis in faeces from goats naturally infected in tropical pastures was evaluated. Two levels (0 vs 14 individuals per container) of indigenous earthworms (50% Pontoscolex corethrus and 50% Perionyx excavatus) were added to containers filled with soil and faeces collected from 20 grazing goats. After 1 week, the numbers of free-living stages of each infective larvae species was measured. The addition of earthworms reduced by 34% (P<0.006) the number of infective larvae recovered in the faeces of goats. The reduction was significant for both larvae species, 29% and 33% for H. contortus and T. colubriformis, respectively. The ratio of the two species of larvae, without or with earthworms, did not vary significantly (P>0.21). These results must be confirmed in experiments on pasture, with other ratios and combinations of earthworms.

Comparison of fecal crude protein and fecal near-infrared reflectance spectroscopy to predict digestibility of fresh grass consumed by sheep.

Organic matter digestibility (OMD), an essential criterion for the evaluation of the nutrition of ruminants, cannot be measured easily at pasture. Therefore, the objective of this study was to test and compare 2 methods of OMD prediction based on the fecal CP content (CPf) or near infrared reflectance spectroscopy (NIRS) applied to feces. First, published equations derived from fecal N (Eq. 1(CP), n = 40) and from fecal NIRS (Eq. 1(NIRS), n = 84) were used to predict OMD of an independent validation data set from which in vivo OMD, ranging from 58 to 74%, was measured for 4 regrowth stages of Digitaria decumbens. Second, to establish equations usable in grazing situations and to improve the efficiency of the predictions, new equations were calculated from a large data set (n = 174) using CPf (Eq. 2(CP)) or fecal NIRS (Eq. 2(NIRS)). By applying the CPf method, Eq. 2(CPf) (OMD, % = 88.4 - 263.9/CPf, % of OM; residual SD = 2.92, r(2) = 0.63) showed similar statistical parameters (P < 0.01) when compared with Eq. 1(CP) (OMD, % = 86.6 - 266.2/CPf, % of OM; residual SD = 2.95, r(2) = 0.79). When using fecal NIRS, Eq. 2(NIRS) showed decreased SE of calibration (SEC = 1.48) and of cross-validation (SECV = 1.75) and greater coefficient of determination of cross-validation (R(2)(CV) = 0.85) than the previously published Eq. 1(NIRS) (SEC = 1.78, SECV = 2.02, R(2)(CV) = 0.77). The validation of the 4 equations on the validation data set was satisfactory overall with an average difference between the predicted and the observed OMD ranging from 0.98 to 2.79 percentage units. The Eq. 2(NIRS) was nevertheless the most precise with a decreased residual SD of 2.53 and also the most accurate, because the SD of the average difference between predicted and observed OMD was the lowest. Therefore, fecal NIRS provided the most reliable estimates of OMD and is thus a useful tool to predict OMD at pasture. However, an adequate number of reference data are required to establish good calibration. Indeed, better calibration statistics were obtained by increasing the data set from 84 (Eq. 1(NIRS)) to 174 (Eq. 2(NIRS)). In contrast, using fecal N on a set of 84 or 174 points did not improve the prediction. Both methods are useful for predicting OMD at pasture in certain circumstances, using fecal NIRS when a large data set (n = 84 and n = 174) is available and fecal CP with smaller data sets (n = 40).