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Animal’s feed efficiency in growing cattle (i.e. the animal ability to reach a market or adult BW with the least amount of feed intake), is a key factor in the beef cattle industry. Feeding systems have made huge progress to understand dietary factors influencing the average animal feed efficiency. However, there exists a considerable amount of animal-to-animal variation around the average feed efficiency observed in beef cattle reared in similar conditions, which is still far from being understood. This review aims to identify biological determinants and molecular pathways involved in the between-animal variation in feed efficiency with particular reference to growing beef cattle phenotyped for residual feed intake (RFI). Moreover, the review attempts to distinguish true potential determinants from those revealed through simple associations or indirectly linked to RFI through their association with feed intake. Most representative and studied biological processes which seem to be connected to feed efficiency were reviewed, such as feeding behaviour, digestion and methane production, rumen microbiome structure and functioning, energy metabolism at the whole body and cellular levels, protein turnover, hormone regulation and body composition. In addition, an overall molecular network analysis was conducted for unravelling networks and their linked functions involved in between-animal variation in feed efficiency. The results from this review suggest that feeding and digestive-related mechanisms could be associated with RFI mainly because they co-vary with feed intake. Although much more research is warranted, especially with high-forage diets, the role of feeding and digestive related mechanisms as true determinants of animal variability in feed efficiency could be minor. Concerning the metabolic-related mechanisms, despite the scarcity of studies using reference methods it seems that feed efficient animals have a significantly lower energy metabolic rate independent of the associated intake reduction. This lower heat production in feed efficient animals may result from a decreased protein turnover and a higher efficiency of ATP production in mitochondria, both mechanisms also identified in the molecular network analysis. In contrast, hormones and body composition could not be conclusively related to animal-to-animal variation in feed efficiency. The analysis of potential biological networks underlying RFI variations highlighted other significant pathways such as lipid metabolism and immunity and stress response. Finally, emerging knowledge suggests that metabolic functions underlying genetic variation in feed efficiency could be associated with other important traits in animal production. This emphasizes the relevance of understanding the biological basis of relevant animal traits to better define future balanced breeding programmes.

Over the past 20 years, substantial progress has been made in improving feeds and feeding technologies for most aquaculture species. Notable improvements in feed conversion efficiency (through a better understanding of requirements and improved feed management) and ingredient sustainability (through increased capability to use a wider range of ingredients) have been achieved. While advances have been made in understanding the requirements of many of the main aquaculture species, there is still much to be done in defining requirements, especially for many of the species being farmed in the developing world. Gains in the efficiency of feeds are slowing for developed species, but potential gains are still appreciable for less developed species. There is a growing need to more precisely prescribe the required levels of essential nutrients and various additives in the diet based on age, genotype, environment, and immune status to deliver a “precision nutrition” approach to farming aquaculture species. There is still further need to diversify our ingredient options to provide greater resilience, as the sustainability of different feed ingredient sources, including possible climate change impacts, is becoming a growing issue. There is a growing demand for biocircularity in our feed ingredient supply chains. Ultimately, what is needed to sustain future feed ingredient needs are sustainable sources of cost‐effective protein, some essential amino acid additives, some omega‐3 fatty acid resources, and various minerals and vitamin additives. The increasing use of new and varied resources will ensure that food safety remains an important issue throughout the world. Feed manufacturing has evolved from a simplistic exercise to a highly complex science with state‐of‐the‐art engineering, but its application is not consistent across all sectors, as there is still widespread use of pelleting, mash, and trash fish feeding in the developing world. Similarly, feed management has also dichotomized between the developed and developing world, with a high reliance on manual skilled labor in the developing world, whereas more advanced aquaculture systems are becoming increasingly reliant on automated computer‐controlled feeding systems.

The increase in the consumption of animal products is likely to put further pressure on the world's freshwater resources. This paper provides a comprehensive account of the water footprint of animal products, considering different production systems and feed composition per animal type and country. Nearly one-third of the total water footprint of agriculture in the world is related to the production of animal products. The water footprint of any animal product is larger than the water footprint of crop products with equivalent nutritional value. The average water footprint per calorie for beef is 20 times larger than for cereals and starchy roots. The water footprint per gram of protein for milk, eggs and chicken meat is 1.5 times larger than for pulses. The unfavorable feed conversion efficiency for animal products is largely responsible for the relatively large water footprint of animal products compared to the crop products. Animal products from industrial systems generally consume and pollute more ground- and surface-water resources than animal products from grazing or mixed systems. The rising global meat consumption and the intensification of animal production systems will put further pressure on the global freshwater resources in the coming decades. The study shows that from a freshwater perspective, animal products from grazing systems have a smaller blue and grey water footprint than products from industrial systems, and that it is more water-efficient to obtain calories, protein and fat through crop products than animal products.

Major feed ingredients, like maize and soya, and land resources are used by both humans and animals, causing competition and affecting costs. To make the poultry industry profitable, it is important to prevent wastage of feed, and feed efficiency is therefore important. Residual feed intake (RFI) and feed conversion ratio (FCR) are two measures of feed efficiency used to assess production efficiency. This review describes a different aspect of feed efficiency measures and how their correlated traits affect poultry production. Bird selection, based on RFI and FCR at the 5th week or market age, is effective since both are low to moderately heritable (heritability estimates of RFI and FCR are 0.21-0.49 and 0.11-0.44 respectively). Both RFI and FCR selection results in reduced feed intake without compromising growth rate. Selection based on RFI is better in comparison to FCR for improving feed efficiency, as it is a trait independent of the maintenance energy requirement of an individual bird. Bird with low RFI value can be expected to have better feed efficiency and can be helpful in lowering the cost of poultry production.

Chromium (Cr) is a trace element and plays a significant role in fish nutrition and physiology. An experiment was designed to know the effects of Cr addition in the diets to growth and feed utilization in striped catfish (Pangasianodon hypophthalmus). Four diets with Cr (0, 2, 4, and 8 mg kg−1) were fed to striped catfish in aquaria with triplicate groups for 60 days. Survival, growth parameters (weight gain, WG; %WG; specific growth rate, SGR), and feed utilization (feed intake, FI; feed efficiency, FE; protein efficiency ratio, PER; feed conversion ratio, FCR) were calculated at the end of the feeding trial. Several hemato-biochemical parameters, such as hemoglobin (Hb), red blood cell (RBC), white blood cell (WBC) and glucose level, and frequency of micronucleus (MN) formation in erythrocytes, were analyzed. The growth parameters (WG, %WG, and SGR) and feed utilization (FE and PER) increased significantly in the fish fed with 2 and 4 mg kg−1 Cr supplemented diets. On the other hand, the growth parameters suppressed in the fish fed with 8 mg kg−1 Cr-based diet. The polynomial regression analysis based on WG showed that 2.82 mg kg−1 Cr supplementation in the diet is optimum for the tested fish species. The values of Hb (g/dL), RBC (×106/mm3) and blood glucose (mg/dL) significantly decreased in the fish fed with the highest (8 mg kg−1) Cr-based feed. Conversely, MN frequency was significantly increased in the fish fed with 8 mg kg−1 Cr-based diet. Overall, 2.82 mg Cr kg−1 can be added to the diets of striped catfish for its better growth with maximum utilization of feed.

We present a unique, biologically consistent, spatially disaggregated global livestock dataset containing information on biomass use, production, feed efficiency, excretion, and greenhouse gas emissions for 28 regions, 8 livestock production systems, 4 animal species (cattle, small ruminants, pigs, and poultry), and 3 livestock products (milk, meat, and eggs). The dataset contains over 50 new global maps containing high-resolution information for understanding the multiple roles (biophysical, economic, social) that livestock can play in different parts of the world. The dataset highlights: (i) feed efficiency as a key driver of productivity, resource use, and greenhouse gas emission intensities, with vast differences between production systems and animal products; (ii) the importance of grasslands as a global resource, supplying almost 50% of biomass for animals while continuing to be at the epicentre of land conversion processes; and (iii) the importance of mixed crop–livestock systems, producing the greater part of animal production (over 60%) in both the developed and the developing world. These data provide critical information for developing targeted, sustainable solutions for the livestock sector and its widely ranging contribution to the global food system.

The beef cattle industry represents a significant portion of the USA’s agricultural sect, with beef cattle accounting for the most red meat consumed in the USA. Feed represents the largest input cost in the beef industry, accounting for approximately 70% of total input cost. Given that, novel methods need to be employed to optimize feed efficiency in cattle to reduce monetary cost as well as environmental cost associated with livestock industries, such as methane production and nitrogen release into the environment. The rumen microbiome contributes to feed efficiency by breaking down low-quality feedstuffs into energy substrates that can subsequently be utilized by the host animal. Attempts to manipulate the rumen microbiome have been met with mixed success, though persistent changes have not yet been achieved beyond changing diet. Recent technological advances have made analyzing host-wide effects of the rumen microbiome possible, as well as provided finer resolution of those effects. This manuscript reviews contributing factors to the rumen microbiome establishment or re-establishment following rumen microbiome perturbation, as well as host-microbiome interactions that may be responsible for possible host specificity of the rumen microbiome. Understanding and accounting for the variety of factors contributing to rumen microbiome establishment or re-establishment in cattle will ultimately lead to identification of biomarkers of feed efficiency that will result in improved selection criteria, as well as aid to determine methods for persistent microbiome manipulation to optimize production phenotypes.

Zinc (Zn) is an important dietary nutrient for the optimum growth performance, feed efficiency, normal metabolism, and fish health. Unfortunately, Zn requirement for mori (Cirrhinus mrigala) is not available. This experiment was designed to assess the impacts of Zn-gluconate levels on growth performance, feed utilization, mineral composition, and enzyme activities of mori and determines the optimum requirement of Zn-gluconate for this species. For this purpose, seven isonitrogenous (29.18%) and isolipidic (10.71%) purified diets were formulated with graded Zn-gluconate levels (0, 10, 20, 30, 40, 50, and 60 mg/kg). A total of 525 juveniles (4.30 ± 0.13 g) were distributed in 21 tanks. All treatments were assessed in triplicates. At the end of the trial (90 days), a progressive increase in final weight (FW) was observed in mori fed with 0–40 mg/kg of Zn-gluconate, remained constant at 50 mg/kg of Zn-gluconate, and significantly decreased at 60 mg/kg of Zn-gluconate. Similarly, weight gain and specific growth rate followed a similar pattern, while weight gain% increased till 40 mg/kg of Zn-gluconate. However, further increase (40–60 mg/kg) had a non-significant effect on weight gain%. Diet supplemented with 40 mg/kg of Zn-gluconate resulted in optimum values for feed intake and feed conversion ratio. Supplementation of Zn-gluconate did not affect dry matter, crude fat, and crude ash at all graded levels. However, whole body crude protein was significant in response to Zn-gluconate supplementation. Furthermore, Zn-gluconate absorption enhanced from 0 to 40 mg/kg of Zn-gluconate and remained constant afterward. Whole body mineral activity also followed a similar pattern. Overall, Zn-gluconate supplementation enhanced (P < 0.05) mineral activity in all parts of the tested parts of mori, including bones, scales, skin, eyes, heart, liver, and kidney. Moreover, the highest (P < 0.05) mineral activity in the skin, heart, liver, and kidney was observed in 60 mg/kg of Zn-gluconate. Supplementation of Zn-gluconate significantly increased the activity of alkaline phosphatase while it reduced thiobarbituric acid reactive substance contents of mori. The optimal dietary requirement of Zn-gluconate was recorded as 43.86 mg/kg through broken-line regression for maximum weight gain% of mori juveniles. Conclusively, 40 mg/kg of Zn-gluconate supplementation significantly enhanced the health of C. mrigala. However, a further increase in Zn-gluconate supplementation from 40 to 60 mg/kg did not significantly improve the above-mentioned parameters.

The objective of this work was to evaluate the effect of semi-purified glycerin added to the feed of pregnant and lactating sows on performance including dorsal diameter, body condition, daily weight gain, feed intake, and feed conversion rate. Growth and feeding parameters were evaluated in born piglets: litter average, survival, daily weight gain, feed conversion rate, and daily milk consumption. Pregnant sows (n = 60; initial weight 180 ± 22 kg) were randomly assigned to the Control or Glycerin group (2%). Semi-purified glycerin was supplied from the beginning of gestation until farrowing. The inclusion of semi-purified glycerin did not affect any of the parameters evaluated in sows during gestation. The inclusion of semi-purified glycerin had a significant effect (p = 0.04) on the body condition of sows at weaning and appeared to have a negative effect on piglet survival. However, semi-purified glycerin caused no negative effects on milk production during lactation and did not affect piglet performance parameters. The addition of semi-purified glycerin as a caloric source could be an economically viable alternative to be implemented in feeding pregnant and lactating sows. However, additional tests are suggested.

Aquaculture activity is affected by various environmental factors, including water salinity and high temperatures. The present study investigated the impact of using varying water salinity (0, 5, 10, 15 and 20 ppt) on the growth behavior, immune responses and antioxidative responses of common carp. Fish were raised under optimal conditions except for water salinity for 8 weeks; fish were then subjected to high-temperature stress (32 °C) for 48 h. The results indicated a reduced final weight (FBW), weight gain (WG), specific growth rate (SGR), condition factor (CF), feed intake and feed efficiency ratio (FER) in common carp reared in 15 and 20 ppt (p < 0.05). The lowest FBW, WG, SGR, CF, feed intake and FER values were observed in fish reared in 20 ppt water salinity (p < 0.05). In gills, the superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were markedly decreased, but malondialdehyde (MDA) levels increased in fish challenged with 15 and 20 ppt before they were subjected to heat stress (p < 0.05). After heat stress, the SOD, CAT and GPx were decreased, and the MDA increased in fish reared in varying salinity levels (p < 0.05). Before heat stress, the intestinal SOD, CAT and GPx markers were decreased by 15 and 20 ppt, while the MDA level was increased by 15 and 20 ppt (p < 0.05). Generally, heat stress lowered the SOD, CAT and GPx activity in the intestines and liver tissues but increased MDA levels in common carp stressed by varying salinity levels (p < 0.05). The most decreased lysozyme activity, SOD, CAT and GPx and increased MDA levels were observed in common carp exposed to 20 ppt before and after heat stress (p < 0.05). After heat stress, fish exposed to 15 and 20 ppt had lower NBT than the remaining groups, and fish exposed to 20 ppt had the lowest values (p < 0.05). Overall, the heat stress markedly suppressed the antioxidant and immune responses of common carp reared in hypersalinity conditions.