Efficiency Of Feed Use Research Articles

A need for generating sound quantitative data at national levels for feed-efficient animal production

Increasing demand for livestock products will impose a huge demand on feed resources. Biophysical factors such as scarcity of land, soil and water, food–fuel–feed competition, ongoing global climate change and increasing competition for arable land and non-renewable resources such as fossil sources and minerals are challenging the sustainability of feed production systems. Efficient use of available feed resources is key to efficient animal production and food security. It is impossible to effectively manage a resource if its availability is not known. While Feed inventories or Feed assessments provide critical information on feed productive capacities and feed availability at a regional/country level, the sufficiency of the feed supply can only be gauged relative to demands for feeds. Essentially, this comparison between livestock requirements and feed supplies constitutes the Feed balance. In many countries Feed Balances are not usually available or accurate despite their strategic role for livestock development opportunities, for providing input data into country level food input-output analyses and for emergency prevention. Estimation of Feed Balance at a national level requires information on the amounts of feed resources available and their energy content, livestock population and herd structure. Likewise, reliable and harmonised herd structure data are also lacking. Information on what proportions of cereals being produced in a country that are diverted to feed production is critical for assessing food security situations in countries. In most situations these data are not available for most developing countries. Equally important is the information on the feeding systems i.e. how different feed resources are being fed to livestock. Assessment of environmental impacts of livestock and development of optimal feeding strategies rely on information about feeding systems and data on feed balance. Feed-use efficiency and decrease in release of environmental pollutants from livestock production systems hinges on feeding of balanced rations; and for their preparation, availability of reliable data on chemical composition and nutritional value of feed resources is a must. Also for reducing wastages, ensuring food safety through enhancing feed safety and promoting international trade, data on the presence of microbial contaminants including mycotoxins, heavy metals, antibiotic and pesticide residues must also be strengthened. Development of a National Feed Resource Information Systems linked to a Global Feed Resource Information Systems should be considered. Feed Inventories, Feed Balance, Feeding Systems, and Feed Quality including Feed Contaminants should be considered as integral components of an overall strategy or options that integrate technical (genetics, health and nutrition), policy and institutional interventions for using resources more efficiently to produce more food and feed. Both policy makers and animal feed and crop scientists have a role to play in making this possible.

Modelling pasture management and livestock genotype interventions to improve whole-farm productivity and reduce greenhouse gas emissions intensities

Livestock greenhouse gas (GHG) emissions form the largest proportion of emissions from agriculture. Here we seek intervention strategies for sustainably intensifying the productivity of prime lamb enterprises without increasing net farm emissions. We apply a biophysical model and an emissions calculator to determine the implications of several interventions to a prime lamb farm in south-eastern Australia. We examine the effects of lamb liveweight or age at sale, weaning rate, maiden ewe joining age, genetic feed-use efficiency, supplementary grain feeding according to green pasture availability, soil fertility and botanical composition. For each intervention, stocking rates were optimised to the lesser of a minimum ground cover threshold or a maximum supplementary grain feeding threshold. Total animal production of the baseline farm was 478 kg clean fleece weight plus liveweight (CFW+LWT)/ha.annum and ranged from 166 to 609 kg CFW+LWT/ha.annum for interventions that replaced existing pastures with annual ryegrass or increased soil fertility respectively. Annual GHG emissions intensity of the baseline farm was 8.7 kg CO2-e/kg CFW+LWT and varied between 7.7 and 9.2 kg CO2-e/kg CFW+LWT for interventions that reduced maiden ewe joining age or increased sale liveweight, respectively. Stocking rate primarily governed total animal production, and in many cases production drove emissions, so interventions that increased production did not always reduce emissions intensity. Indeed, replacing existing perennial ryegrass/subterranean clover mixed pastures with perennial legume swards caused large reductions in both production and emissions, and interventions that increased soil fertility via phosphate addition caused large increases in production and emissions; as a consequence, both strategies had little effect on emissions intensity. Implementing several beneficial interventions simultaneously further increased production and reduced emissions intensity relative to implementing individual interventions alone. Baseline production increased by 61% by increasing soil fertility, improving feed-use efficiency and reducing the joining age of maiden ewes, while baseline emissions intensity was reduced by 17% by improving feed use efficiency, reducing the joining age of maiden ewes and supplementary grain feeding. We demonstrate that imposing several strategies on existing sheep farming systems simultaneously is more conducive to sustainable agricultural intensification than is imposing any single intervention alone, provided individual strategies were beneficial in their own right. The best strategies for both sustainably increasing production and reducing emissions intensity are those that decouple the linkage between production and emissions such as interventions that shift the balance of the flock away from adults and towards juveniles while holding average annual stocking rates constant.

Evolution of the modern broiler and feed efficiency.

Although the chicken was domesticated during the Neolithic period, the development of the modern broiler is a recent event that has occurred within the past 100 years. The chicken's adaptability has allowed it to be grown globally under a range of husbandry conditions. That is, the same genetic stock may be found in a range of environments, where it is noted for rapid growth to market weight and efficiency of feed use, which has increased dramatically, mainly through genetic selection. Under good husbandry and a high-energy diet, at 35 days of age a 1.40-kg broiler required 3.22 kg of feed in 1985. Twenty-five years later, we have a 2.44-kg broiler produced on 3.66 kg of feed. This review attempts to address the history of factors contributing to these changes, obstacles that have had to be overcome, and future limitations.

EFFECTIVENESS OF USING POLYURETHANE FOAM TO REDUCE HEAT LOSS IN THE PREMISES FOR BREEDING

It is proved that the use of polyurethane foam insulation for the purpose of walling premises for breeding allows them to halve the deficit of heat in winter. Because of this more efficient use of feed, increases the intensity and the level of growth of young comprehensive energy transformation process in the energy of live weight gain of cattle while increasing the profitability of its cultivation for meat.

Dietary supplementation with N-carbamylglutamate increases the expression of intestinal amino acid transporters in weaned Huanjiang mini-pig piglets1

Weaning is associated with reduced intestinal absorptive capacity in piglets. Our previous study indicated that dietary supplementation with N-carbamylglutamate (NCG) enhanced growth performance and improved intestinal function in weaned piglets. The present study was conducted to test the hypothesis that dietary supplementation with NCG may increase the growth performance of weaned piglets by regulating the expression of intestinal nutrient transporters, thus enhancing nutrient absorption. Twenty-four Huanjiang mini-pig piglets weaned at 21 d of age (3.17 ± 0.21 kg average BW) were randomly assigned to 2 dietary treatments consisting of a basal diet and the basal diet with 0.1% NCG supplementation for a 14-d period with 6 pens per treatment and 1 male and 1 female per pen. On d 14, 1 piglet was randomly selected from each pen for blood and tissue sampling. Dietary NCG supplementation enhanced (P < 0.05) growth rate and the efficiency of feed use in weaned Huanjiang mini-pig piglets. The NCG-supplemented diet increased (P < 0.05) mRNA expression levels of Slc6a19, Slc7a9, and Slc1a1 and the protein abundance of ASCT2, B(0)AT1, b(0,+)AT, y(+)LAT1, and EAAC1 in the jejunum. Furthermore, the contents of low density lipoprotein, ammonia, urea nitrogen, and AA as well as the activity of alkaline phosphatase in plasma were all altered (P < 0.05) by supplementation with NCG. These findings indicate that dietary supplementation with NCG may improve intestinal absorptive function in weaned piglets by increasing the expression of AA transporters in the intestine.

Can carbon footprint serve as an indicator of the environmental impact of meat production?

The carbon footprint (CF), the amount of greenhouse gases (GHG) emitted during a product's lifecycle, was evaluated as an indicator of the wider environmental impacts of meat production using existing life cycle assessments of different types of meat (pork, chicken and beef). The CF generally acts as an indicator of acidification and eutrophication potential, since more efficient use of nitrogen leads to less eutrophying and acidifying substances being released to the environment and to lower GHG emissions in nitrous oxide form. GHG mitigation strategies based on more efficient use of feed can therefore also lead to decreased acidification and eutrophication potential. Decreased GHG emissions due to increased productivity mean less land is required for feed production, so CF can act as a proxy for land use. For the impact category primary energy use, apparent conflicts with CF were identified. Pasture-based beef production can be either very energy-efficient or energy-demanding, but both forms produce high CH4 emissions from enteric fermentation. For monogastric animal production, CF can function as an indicator of primary energy use, as both energy use and GHG emissions originate mainly from feed production. It is unclear how the biodiversity impact category correlates to CF. More intensive production can allow more land to be left in its natural state, but can involve increased use of pesticides and fertilisers and monocropping locally, threatening biodiversity. Using CF as an indicator of the environmental impact of meat can generate conflicts with other environmental categories in some cases. However, the risk of damaging other environmental areas when acting on CF must be weighed against the risk of further neglecting to act on global warming by failing to exploit the current market momentum of carbon footprinting.

Leptin in farm animals: where are we and where can we go?

Fat affects meat quality, value and production efficiency as well as providing energy reserves for pregnancy and lactation in farm livestock. Leptin, the adipocyte product of the obese (ob) gene, was quickly seen as a predictor of body fat content in animals approaching slaughter and an aid to assessing reproductive readiness in females. Its participation in inflammation and immune responses that help animals survive infection and trauma has clear additional relevance to meat and milk production. Furthermore, almost a decade of discoveries of nucleotide polymorphisms in the leptin and leptin receptor genes has suggested useful applications relating to feed intake regulation, the efficiency of feed use, the composition of growth, the timing of puberty, mammogenesis and mammary gland function and fertility in cattle, pigs and poultry. The current review attempts to summarise where research has taken us in each of these aspects and speculates on where future research might lead.

Re-defining efficiency of feed use by livestock

Livestock, particularly ruminants, can eat a wider range of biomass than humans. In the drive for greater efficiency, intensive systems of livestock production have evolved to compete with humans for high-energy crops such as cereals. Feeds consumed by livestock were analysed in terms of the quantities used and efficiency of conversion of grassland, human-edible (‘edible’) crops and crop by-products into milk, meat and eggs, using the United Kingdom as an example of a developed livestock industry. Some 42 million tonnes of forage dry matter were consumed from 2008 to 2009 by the UK ruminant livestock population of which 0.7 was grazed pasture and 0.3 million tonnes was conserved forage. In addition, almost 13 million tonnes of raw material concentrate feeds were used in the UK animal feed industry from 2008 to 2009 of which cereal grains comprised 5.3 and soyabean meal 1.9 million tonnes. The proportion of edible feed in typical UK concentrate formulations ranged from 0.36 for milk production to 0.75 for poultry meat production. Example systems of livestock production were used to calculate feed conversion ratios (FCR – feed input per unit of fresh product). FCR for concentrate feeds was lowest for milk at 0.27 and for the meat systems ranged from 2.3 for poultry meat to 8.8 for cereal beef. Differences in FCR between systems of meat production were smaller when efficiency was calculated on an edible input/output basis, where spring-calving/grass finishing upland suckler beef and lowland lamb production were more efficient than pig and poultry meat production. With the exception of milk and upland suckler beef, FCR for edible feed protein into edible animal protein were >1.0. Edible protein/animal protein FCR of 1.0 may be possible by replacing cereal grain and soyabean meal with cereal by-products in concentrate formulations. It is concluded that by accounting for the proportions of human-edible and inedible feeds used in typical livestock production systems, a more realistic estimate of efficiency can be made for comparisons between systems.

Effects of physically effective fiber on chewing activity, ruminal fermentation, and digestibility in goats1

The objective of this study was to evaluate the effects of physically effective NDF (peNDF) in goat diets containing alfalfa hay as the sole forage source on feed intake, chewing activity, ruminal fermentation, and nutrient digestibility. Four rumen-fistulated goats were fed different proportions of chopped and ground alfalfa hay in a 4 × 4 Latin square design. Diets were chemically similar but varied in peNDF content: low, moderate low, moderate high, and high. Dietary peNDF content was determined using the Penn State Particle Separator with 2 sieves (8 and 19 mm) or 3 sieves (1.18, 8, and 19 mm). The dietary peNDF content ranged from 1.9 to 11.7% using the 2 sieves and from 15.2 to 20.0% using the 3 sieves. Increasing forage particle length increased intake of peNDF, but decreased DMI linearly (P = 0.05). Ruminating and total chewing time (min/d) were increased linearly (P = 0.001 and 0.007, respectively) with increased dietary peNDF, resulting in a linear reduction (P < 0.001) in the duration of time that ruminal pH was less than 5.8 (10.9, 9.0, 1.2, and 0.3 h/d, respectively). Increasing dietary peNDF tended to increase the molar proportion of propionate linearly (P = 0.08) and decrease the molar proportion of butyrate (P = 0.09), but did not affect total VFA concentration. Increasing dietary peNDF linearly decreased the apparent digestibility of OM, NDF, and ADF in the total tract (P = 0.009, 0.003, and 0.008, respectively). This study demonstrated that increasing the dietary peNDF contained in alfalfa hay forage stimulated chewing activity and improved ruminal pH status, but reduced nutrient intake and efficiency of feed use.

Genetics of Residual Feed Intake in Cattle and Pigs: A Review

The feed resource for animals is a major cost determinant for profitability in livestock production enterprises, and thus any effort at improving the efficiency of feed use will help to reduce feed cost. Feed conversion ratio, expressed as feed inputs per unit output, is a traditional measure of efficiency that has significant phenotypic and genetic correlations with feed intake and growth traits. The use of ratio traits for genetic selection may cause problems associated with prediction of change in the component traits in future generations. Residual feed intake, a linear index, is a trait derived from the difference between actual feed intake and that predicted on the basis of the requirements for maintenance of body weight and production. Considerable genetic variation exists in residual feed intake for cattle and pigs, which should respond to selection. Phenotypic independence of phenotypic residual feed intake with body weight and weight gain can be obligatory. Genetic residual feed intake is genetically independent of its component traits (body weight and weight gain). Genetic correlations of residual feed intake with daily feed intake and feed conversion efficiency have been strong and positive in both cattle and pigs. Residual feed intake is favorably genetically correlated with eye muscle area and carcass weight in cattle and with eye muscle area and backfat in pigs. Selection to reduce residual feed intake (excessive intake of feed) will improve the efficiency of feed and most of the economically important carcass traits in cattle and pigs. Therefore, residual feed intake can be used to replace traditional feed conversion ratio as a selection criterion of feed efficiency in breeding programs. However, further studies are required on the variation of residual feed intake during different developmental stage of production.

Relating life cycle assessment indicators to gross value added for Dutch dairy farms

Sustainable dairy production requires farms that are economically viable, environmentally sound and socially acceptable. A low environmental impact of milk production is not necessarily associated with an economically viable farm. To gain insight into a possible “trade-off” between economic and environmental sustainability, the relation between the environmental and economic indicators of dairy farms was quantified, and farm characteristics that influence this relation were identified. Economic and environmental indicators were quantified for 119 specialized dairy farms in 2005, based on data from the Dutch Farm Accountancy Data Network (FADN). Economic indicators used were: gross value added expressed per kg fat-and-protein-corrected milk (FPCM) or expressed per unit of labour, i.e. labour productivity. Environmental indicators used were: land use per kg FPCM, energy use per kg FPCM, global warming potential per kg FPCM, eutrophication and acidification potential per kg FPCM or per ha of land. Environmental indicators were deduced from a life cycle assessment. High labour productivity on dairy farms was associated with low on-farm energy use, total and on-farm land use, total and on-farm global warming potential, and total and off-farm acidification potential per kg FPCM. High labour productivity, however, was associated also with high on-farm eutrophication and acidification potential per hectare. From partial least squares regression analysis, it was concluded that relations between economic and environmental indicators were affected mainly by milk production per ha, annual milk production per cow, farm size, and amount of concentrates per kg FPCM. An increase in annual milk production per cow, for example, not only increased labour productivity, reduced energy use and global warming potential per kg FPCM but also, in the case of an unchanged stocking density, increased eutrophication and acidification per ha. To be economically and environmentally sustainable, animal production in the Netherlands, therefore, should focus on high animal productivity, i.e. high annual milk production per cow and efficient use of feed per kg milk, and moderate stocking density, provided that a good animal welfare standard is guaranteed.

Physiological adaptation to the humid tropics with special reference to the West African Dwarf (WAD) goat

West African Dwarf (WAD) goats are widely distributed in the subhumid and humid zones of Africa but are particularly associated with less favourable environments. Adaptive features such as feeding behaviour, efficiency of feed use and disease tolerance enable WAD goats to thrive on natural resources left untouched by other domestic ruminants. In marginal environments this goat remains the only domestic species that is able to survive. Among its physiological features small body size and low metabolic requirements are important traits that enable the animal to minimize its requirements in area or season where food sources are limited in quality and quantity. Specialized feeding behaviour and an efficient digestive system enable the animal to maximize food intake. Coat colour plays an important role in the evolved adaptation of this goat type. Reproductive fitness as manifested by prolific breeding is a major factor of adaptation. Defence mechanisms against infectious agents enable this type to thrive well in the hot humid tropics. The mechanisms involved in the regulation of these physiological functions of WAD goat are discussed. An understanding of these mechanisms could result in the development of improved techniques for enhancing goat productivity in humid environments.

Genetic parameter estimates for serum insulin-like growth factor I concentrations, and body weight and weight gains in Angus beef cattle divergently selected for serum insulin-like growth factor I concentration1,2,3

Data for the current study were obtained from a divergent selection experiment in which the selection criterion was the average serum IGF-I concentrations of 3 postweaning blood samples collected from purebred Angus calves. Multiple-trait derivative-free REML procedures were used to obtain genetic parameter estimates for IGF-I concentrations and for BW and BW gains measured from birth to the conclusion of a 140-d postweaning performance test. Included in the analysis were 2,674 animals in the A(-1) matrix, 1,761 of which had valid records for IGF-I concentrations. Direct heritability estimates +/- SE for IGF-I concentration at d 28, 42, and 56 of the postweaning period and for mean IGF-I concentrations were 0.44 +/- 0.07, 0.51 +/- 0.08, 0.42 +/- 0.07, and 0.52 +/- 0.08, respectively. Heritability estimates for maternal genetic effects ranged from 0.10 +/- 0.05 to 0.20 +/- 0.06. The proportion of total phenotypic variance due to the maternal permanent environmental effect was essentially zero for all measures of IGF-I concentrations. Genetic correlations of IGF-I concentrations with weaning and post-weaning BW ranged from 0.07 +/- 0.12 to 0.32 +/- 0.11 and generally demonstrated an increasing trend during the postweaning period. Averaged across the various measures of IGF-I, the genetic correlation of IGF-I with preweaning gain was 0.14, whereas the genetic correlation with postweaning gain was 0.29. Genetic correlations between IGF-I and BW gain were positive during all time intervals, except between weaning and the beginning of the postweaning test and from d 84 to 112 of the postweaning period. Environmental and phenotypic correlations of IGF-I with BW and BW gains were generally positive, but small. These results indicate that postweaning serum IGF-I concentration is moderately to highly heritable and has small positive genetic, environmental, and phenotypic correlations with BW other than birth weight and with pre- and postweaning gain. Therefore, if IGF-I proves to be a biological indicator of an economically important trait (e.g., efficiency of feed use for growth) in beef cattle, it should be possible to rapidly change IGF-I concentrations via selection without significantly altering live weight or rate of gain.

Increasing the Physically Effective Fiber Content of Dairy Cow Diets May Lower Efficiency of Feed Use

Barley silages varying in theoretical chop length were used to evaluate the effects of physically effective (pe) neutral detergent fiber (NDF) content of dairy cow diets on nutrient intakes, site and extent of digestion, microbial protein synthesis, and milk production. The experiment was designed as a replicated 3×3 Latin square using 6 lactating dairy cows with ruminal and duodenal cannulas. During each of 3 periods, cows were offered 1 of 3 diets (low, medium, and high peNDF) obtained using barley silage that varied in particle length: fine (theoretical chop length of 4.8mm), medium (equal proportions of long and fine silages), and long (theoretical chop length of 9.5mm). The peNDF contents were determined by multiplying the proportion (dry matter basis) of feed retained on the 2 screens (8 and 19mm) of the Penn State Particle Separator by the NDF content of the diet, and were 10.5, 11.8, and 13.8% for the low, medium, and high diets, respectively. Increased forage particle length linearly increased intake of peNDF but intakes of dry matter, organic matter, starch, and N were highest for cows fed the medium peNDF diet. Digestibilities of organic matter, NDF, and acid detergent fiber in the total tract were linearly decreased with increasing dietary peNDF, although total digestibility of starch and N was not affected by the treatments. Nevertheless, decreased digestibility due to increased dietary peNDF did not reduce milk production or milk composition because the cows were in mid to late lactation. Ruminal microbial protein synthesis and microbial efficiency were numerically higher with the low peNDF than with the medium or high peNDF diets. These results indicate that increasing the peNDF content of a diet containing barley silage decreases fiber digestibility in the total tract and lowers microbial efficiency. Therefore, the benefits of increasing dietary particle size, expressed as peNDF, on reducing the risk of ruminal acidosis should be weighed against potentially negative effects on efficiency of feed use.

Major Advances in Applied Dairy Cattle Nutrition

Milk yield per cow continues to increase with a slower rate of increase in dry matter intake; thus, efficiency of ruminal fermentation and digestibility of the dietary components are key factors in improving the efficiency of feed use. Over the past 25 yr, at least 2,567 articles relating to ruminant or dairy nutrition have been published in the Journal of Dairy Science. These studies have provided important advancements in improving feed efficiency and animal health by improving quality of feeds, increasing feedstuff and overall diet digestibility, better defining interactions among feedstuffs in diets, identifying alternative feed ingredients, better defining nutrient requirements, and improving efficiency of ruminal fermentation. The publications are vital in continuing to make advancements in providing adequate nutrition to dairy cattle and for facilitating exchange of knowledge among scientists.Forages have been studied more extensively than any other type of feed. Cereal grains continue to be the primary contributors of starch to diets, and thus are very important in meeting the energy needs of dairy cattle. Processing of cereal grains has improved their use. Feeding by-products contributes valuable nutrients to diets and allows feedstuffs to be used that would otherwise be handled as wastes in landfills. Many of these by-products provide a considerable amount of protein, nonforage fiber, fat, and minerals (sometimes a detriment as in the case of P) to diets. The primary feeding system today is the total mixed ration, with still considerable use of the pasture system. Major improvements have occurred in the use of protein, carbohydrates, and fats in diets. Although advancements have been made in feeding practices to minimize the risk of metabolic diseases, the periparturient period continues to present some of the greatest challenges in animal health.Computers are a must today for diet formulation and evaluation, but fewer software programs are developed by universities. Several nutrition conferences are held regularly in the United States that are vital for transferring knowledge to the feed industry and the producers of food; the attendance at such programs has increased about 4-fold over the past 25 yr. More emphasis on animal welfare will direct some of the areas of nutrition research. Challenges ahead include having adequate funding for conducting applied nutrition research and for training of students as scientists and for employment in the feed industry.

Varying Protein and Starch in the Diet of Dairy Cows. II. Effects on Performance and Nitrogen Utilization for Milk Production

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on the lactational performance and use of N for milk production. Sixty multiparous Holstein cows were used in a 210-d lactational trial with a completely randomized design with a 2×3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary CP (means = 14.8, 16.8, and 18.7%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25.0% corn silage, 20.0% alfalfa silage, 10.0% cottonseed, 26.7 to 37.0% corn grain, and 4.8 to 13.5% protein supplement, plus minerals and vitamins. Across the 210 d of lactation, the productive response of dairy cows to the source of supplemental CP depended on the concentration of CP in the diet. At 18.7% CP, cows fed SBM consumed more DM and produced more milk, 3.5% fat-corrected milk, fat, and true protein, but had lower efficiency of feed use and body condition score than cows fed AMB. At 16.8% CP, cows fed AMB produced more 3.5% fat-corrected milk, fat, and true protein than cows fed SBM. At 14.8% CP, cows fed SBM consumed more DM but produced less true protein and had lower feed efficiency than cows fed AMB. Across CP sources, cows fed 14.8% CP produced less fat-corrected milk and true protein than cows fed 16.8 and 18.7% CP. Across CP percentages, cows fed AMB produced more fat-corrected milk per kilogram of DM consumed than cows fed SBM. Despite these interactions, improvements in the gross efficiency of N use for milk production were achieved through reductions in the intake of N independently of the source of CP. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650g daily if the source of RDP and RUP are properly matched with the source and amount of carbohydrate in the diet.

Strain differences in feed efficiency measured as residual feed intake in individually reared rainbow trout, Oncorhynchus mykiss (Walbaum)

The efficient use of feed for growth and meat production is important for all animal production industries including aquaculture. Residual feed intake (RFI) is an alternative measure of feed efficiency that has been widely used in livestock production. Residual feed intake was calculated as the difference between intake observed and intake predicted on the basis of a bioenergetics model; a low RFI indicates greater efficiency. Residual feed intake offers some advantages as a selection criterion for improving production efficiency over traditional feed efficiency statistics because it is not a ratio and it typically has a larger coefficient of variation. The RFI of individually reared rainbow trout progeny from six different genetic cross-types was examined for genetic variation. Proximate analysis and nitrogen retention were also evaluated to determine if differences in RFI correlate to differences in body composition and nutrient retention and varied by cross-type. Differences between cross-types indicated a genetic component for RFI, with the most efficient fish of approximately 160 g consuming 0.99 g less and inefficient fish consuming 0.05 g more feed per day than expected. Lower RFI was associated with higher growth rates (r=−0.38, P<0.05) and greater nitrogen retention (r=−0.82 P<0.001).

A review of the effects of dairy breed on feed conversion efficiency - an opportunity lost?

The efficiency of conversion of feed to milk is an important determinant of farm productivity. One factor that has received little attention is the effect of breed on efficiency of feed use. Experimental data that has compared breeds (Holstein, Friesian, Jersey and Holstein-Friesian x Jersey crossbred cattle) for feed efficiency are reviewed. This includes data from New Zealand, USA and Europe. Feeds offered ranged from grazed pasture to total mixed rations. Experiments included short term component studies that measured feed intakes and milk production for periods ranging from 2 weeks to 7 months, whole lactation studies, farm systems comparisons over 3 years and calorimetry experiments. Differences between breeds in feed intake capacity, efficiency of milk solids production, energy metabolism and digestive capacity are highlighted. Opportunities for utilising breed differences in efficiency are outlined and future research is suggested.

Genotype differences and their impact on digestive tract function of ruminants: a review

Physiological factors that cause between-animal variation in digestive function were evaluated as possible selection traits to achieve improved growth and feed-use efficiency by ruminants. Comparative studies of the digestive function of Bos taurus and Bos indicus cattle, as well as selection lines of dairy cows and sheep were reviewed to determine the scope and significance of diversity in rumen function. All investigations indicated differences in digesta retention time between genotypes. Therefore, the digesta retention time, either the total mean retention time (MRT) or the ruminal retention time (RRT), may be suitable selection traits for improving animal productivity.Differences in MRT and RRT may affect animal productivity by changing the number and diversity of rumen microorganisms, the volatile fatty acid (VFA) pattern, the composition and maintenance energy requirement of the microbes, and thus the energetic efficiency of microbial growth. Further effects associated with changed RRT include a possible reduction in methane production and increased long-chain fatty acid (LCFA) synthesis in the rumen, which may consequently affect the energetic efficiency of the ruminant. It is concluded that despite strong evidence of genetic diversity in gut function, the central role of MRT and RRT in digestive metabolism has not been fully appreciated, nor have their contribution to productivity differences among livestock of similar or divergent genotypes been adequately investigated.

Factors Affecting Reproductive Performance in the Nepalese Pakhribas Pig: Effects of Nutrition and Housing during Lactation

The effects of housing and nutrition on the performance of growing gilts of the Nepalese Pakhribas breed were investigated. A total of 36 pigs were allocated according to a factorial design with 3 levels of nutrition, provided to achieve a target growth rate of 200, 300 or 400 g/day, and two types of housing, traditional or improved. The growth rate and body composition were monitored during the growing period and subsequent pregnancy. There was a significantly higher growth rate (p<0.01), greater P2 backfat thickness (p<0.01), and greater eye muscle depth (p<0.01) at service in pigs given the higher level of nutrition. Similarly, there was a significantly higher growth rate (p<0.05), and greater eye muscle depth (p<0.10) with improved housing but no significant difference in P2 backfat thickness. The conception rate was 90% at first service, with no difference between treatments. Gilts from the high plane of rearing produced a mean litter size of one piglet greater than those on the low plane, but this was not significant with the limited numbers. However, both improved plane of nutrition and reduced climatic penalty by improving housing resulted in increased birthweight of piglets (p<0.05). It is concluded that improvement in housing can give benefits equivalent to at least a 7% improvement in efficiency of feed use under traditional Nepalese circumstances for pig rearing. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 1 : 72- 78)