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Some of the adaptations of ruminant livestock to climate and feed resources are discussed. 1. Physical. Various types of coat serve to protect animals from cold and from the sun’s heat. 2. Physiological. Large rumen volumes enables animals to consume large amounts of poor roughages; fat depots in distinct regions of the body allow them to withstand regulation and fluctuating supply of nutrients, seasonality of reproduction matches requirement to seasonal variation in food supply. 3. Biochemical. There are species differences in the ability to recycle N to the rumen (buffaloes) in the requirement for glucose to accommodate several days of fasting (camels), and in adaptation to low atmospheric oxygen tension (yaks). Such adaptations are important and should be considered when animals exported to areas where climates and feeds are different.

Browse plants play an important role in providing fodder for ruminants in most parts of the World. However, the presence of tannins and other phenolic compounds in a large number of these feed resources limits their utilization as animal feed. This paper presents the nutritive value of some browse species based on their chemical composition (nitrogen, polyphenolics and neutral detergent fibre (NDF) content), dry matter (DM) degradability in sacco and gas production in vitro including the effect of the phenolic binding compound, polyethyleneglycol-4000 (PEG 4000), on in vitro gas production. The browse species evaluated were Calluna vulgaris (heather), Sarothamnus scoparius (broom), Ulex europaeus (gorse) and Chamaecytisus palmensis (tagasaste). The crude protein (CP) content was highest (P < 0.05) in broom (189 g kg−1 DM) followed by tagasaste (175 g kg−1 DM) and gorse pre-flower (168 g kg−1 DM) and the lowest was in heather (98 g kg−1). Heather had the highest (P < 0.05) concentration of the phenolic compounds compared with all the other species. Gorse in-flower contained a higher concentration (P < 0.05) of total extractable phenols (TEPH), total extractable tannins (TETa) and NDF and a lower content of CP than gorse pre-flower which is a reflection of their stage of maturity. As a result, gorse pre-flower had a higher in sacco degradability and in vitro gas production than gorse in-flower. Heather had the lowest degradability values. The ranking order of the browse plants in gas production was gorse pre-flower > tagasaste > broom > gorse in-flower > heather which was similar to their in sacco degradability values. Increasing the amount of substrate incubated slightly depressed the amount of gas produced by the browse plants. The response to PEG treatment increased with increased concentration of phenolic compounds in the browse plants. Thus, in heather, gas production increased by 51% at 12 h of incubation as a result of PEG treatment while the response was zero in the species with a low content of phenolic compounds. The results show that the phenolic compounds depress in vitro gas production and that PEG treatment has a potential for improving gas production and fermentation of feedstuffs high in phenolics due to the binding of the phenolic compounds to the PEG.

Principles of supplementation are discussed in respect of both, their positive and negative effects on roughage digestion and utilization by ruminants. It is pointed out that negative effects mainly occur when excessively processed concentrate is given in large quantities two times per day. This lowers rumen pH which in turn depresses cellulose digestion and intake of cellulosic feeds, leading to problems of acidosis and secondary ketosis due to off-feed conditions. To a large extent, such problems can be overcome by limited processing and feeding the concentrate mixed with the roughage. Supplements can also have positive effects by alleviating deficiencies such as nitrogen or by providing easily fermentable fiber to increase microbes for attachment to roughages. Supplements can increase microbial protein production and undegraded protein supply. It is emphasized that proper use and management of supplements can make the difference between profit and loss for small farmers.

Publisher Summary The control of rate and extent to which dietary protein and amino acids are degraded in the rumen fermentation is a major determinant of the supply side of the equation. The possible ways of increasing the efficiency of the supply process are examined as well as strategies for correcting amino acid shortfalls. The control of rumen protein and amino acid degradation requires a thorough understanding of the degradative process, particularly peptide and amino acid metabolism. It helps in identifying ways to alter rumen microbial metabolism. Genetic selection or engineering has a bright future in the control of forage-protein degradation. Control of protein loss in the silo demands the attention of scientists where silages are extensively utilized. The current quantitative knowledge of the protein and amino acid needs of the host ruminants is inadequate. The impact of rumen-protected protein and amino acids and other manipulative strategies will be largely unpredictable until this deficiency is corrected.

The rates of disappearance (p) of protein from fish-meal, meat-and-bone meal, soya-bean meal, cottonseed meal, linseed-meal and groundnut-meal were described when nylon bags were incubated in the rumens of sheep and cattle given either barley or dried grass. The exponential equation p = a + b (1 − e−ct),where a, b and c are constants, e is the natural logarithm, and p the amount disappearing in time, t, was used. There was no consistent difference between the degradabilities determined with sheep and cattle. Degradation was finally combined with different outflow rate (k) and the effective degradability (P) was described as the equation P = a + (bc) (c + k) .

New systems for estimating the requirements of ruminants for dietary protein involve separate estimates of the extent to which microbial and undegraded dietary protein meet the animal's net requirements for amino acids. The paper provides a brief review of the factors influencing both the synthesis of microbial protein and the amounts of dietary protein that escape the rumen undegraded. Although quantitative data on many of these factors are now emerging, the extensive nature of most sheep-production systems makes their application in a precise quantitative manner difficult. It is suggested that considerable improvements in production could be achieved by using the principles in a qualitative sense. For low-producing animals such as dry ewes, pregnant ewes up to a few weeks before lambing, and ‘store’ lambs, microbial protein will meet the animal's net requirements for amino-acid nitrogen provided that the animals have not been previously subjected to a specific protein deficiency. In contrast, the maximal yield of microbial protein will not meet the net requirements of high-producing animals, such as young, fast-growing lambs, and ewes in the final few weeks of pregnancy and during early lactation. These animals require protein supplements which at least in part escape degradation in the rumen.

Samples of untreated (US) and ammonia-treated (AS) barley straw of the Corgi variety were either soaked with water, ensiled with grass silage, or treated with alkaline hydrogen peroxide. The degradability of dry matter (DM) in the treated samples and their respective controls was determined by measuring DM loss from samples incubated in nylon bags for various periods in the rumen of sheep. Responses were assessed by using the mathematical model p = a + b (1 − e − ct ), where p is DM loss, ( a + b ) is potential degradability, c the rate constant of DM loss and t is the time of incubation. Soaking and ensilage produced no significant alteration of degradation pattern of DM loss. Treatment of US and AS with alkaline hydrogen peroxide, however, increased potential degradability by 20 and 10 percentage units, respectively. The results show that alkaline hydrogen peroxide is effective in improving the degradability of cereal straws.

When excessively processed cereals are given to ruminants a vast surface area of highly fermentable substrate is exposed to the rumen microorganisms. The subsequent effect on digestion and metabolism will depend largely on whether the cereal based diets are fed as the main or sole part of the diet or whether they are given as supplements to roughage based diets. Given as sole feeds, excessively processed grains can give rise to alterations in carcass quality (soft fat) in lambs, and problems of acidosis and rumenitis. Given as supplements to diets based on roughage, excessively processed grains can seriously reduce the rate of cellulose digestion with a consequent decrease in roughage intake and digestibility. The optimum extent of processing appears to be the minimum required to avoid an unacceptably low digestibility. The processing required is different for small ruminants (e.g. sheep, goats and calves) than for large (e.g. cattle). For sheep, grain should be fed whole; in general, processing does not increase digestibility or food utilization and can result in depressed cellulose digestion and in soft fat. For cattle some processing is required to ensure adequate digestion but the optimum is that required to give entrance through the seed coats to microorganisms and digestive enzymes. New methods, such as chemical treatment of whole grain, have given promising results.

Summary The role of silicaceous spicules in the aetiology of rumenitis in cattle was investigated by feeding diets of pearl barley and cotton fibres, with and without screened debris from barley pearlings. Spicules from barley grain appeared to cause only minor physical damage to the ruminai mucosa. Minor damage is not necessarily negligible, but it is suggested that the findings do not justify the allocation of high priority rating to barley breeding programmes aimed at the elimination of rachilla and lodicule spicules. Multiple inflammatory lesions of the rumen wall were found in sheep fed on a diet of barley to which cut cattle hair had been added, but not in sheep fed on barley alone.

Summary When whole barley grains were incorporated into pellets rather than rolled barley the severity of the pathological changes in the rumen wall was reduced. When unprocessed whole barley was fed, the pH in the rumen was increased and no pathological changes occurred. The rumen walls appeared completely healthy, there was no reduction in the apparent digestibility of the barley and the animal’s performance was unaffected.