Review: New feeds and new feeding systems in intensive and semi-intensive forage-fed ruminant livestock systems

Abstract

The contributions that ruminant livestock make to greenhouse gas and other pollutant emissions are well documented and of considerable policy and public concern. At the same time, livestock production continues to play an important role in providing nutrient-rich foodstuffs for many people, particularly in less developed countries. They also offer a means by which plants that cannot be digested by humans, e.g. grass, can be converted into human-edible protein. In this review, we consider opportunities to improve nutrient capture by ruminant livestock through new feeds and feeding systems concentrating on intensive and semi-intensive systems, which we define as those in which animals are given diets that are designed and managed to be used as efficiently as possible. We consider alternative metrics for quantifying efficiency, taking into account resource use at a range of scales. Mechanisms for improving the performance and efficiencies of both individual animals and production systems are highlighted. We then go on to map these to potential changes in feeds and feeding systems. Particular attention is given to improving nitrogen use efficiency and reducing enteric methane production. There is significant potential for the use of home-grown crops or novel feedstuffs such as insects and macroalgae to act as alternative sources of key amino acids and reduce reliance on unsustainably grown soybeans. We conclude by highlighting the extent to which climate change could impact forage-based livestock production and the need to begin work on developing appropriate adaptation strategies.

Keywords: Animal production; Meat; Methane; Milk; Nutrient use efficiency.

Fig. 1

Mapping of the central components of alternative ruminant livestock systems to definitions of ‘intensive’, ‘semi-intensive’ and ‘extensive’ production; where temporary leys are <5 years old, and permanent pasture are >5 years old.

Fig. 2

Relationship between diet ratio of water-soluble carbohydrate (WSC) and nitrogen (N) concentrations and the proportion of feed N intake excreted in urine in dairy cows fed fresh ryegrass-based diets. Dots represent the mean values for individual animals measured and the solid line represents a split line regression (R² = 0.77) with the breakpoint of 8.94 g WSC/g N in the complete diet (Moorby, 2014).

Fig. 3

Mean amino acid profiles of CPs (g/g total amino acids) from insects (Rumpold and Schlüter, 2013a), macroalgae (seaweeds) (Makkar et al., 2016), soybean meal (Feedipedia, 2020b) and pea seeds (Feedipedia, 2020a). The mean sum of amino acids in CPs was 78.4, 75.0, 86.1 and 83.9 g/100 g for insects, macroalgae, soybean meal and pea seeds respectively.