How has ruminant feeding changed in past?
Of the many advances in ruminant nutrition made in recent times the change from dilute roughage-based feeds to highly concentrated grain-rich diets has probably had the greatest single impact on ruminants and on their rate of production. This change has been associated with many new and unexpected nutritional problems. This article deals with the role and uses of the ionophores, the B-vitamins, buffers and branched-chain fatty acids in such concentrated production diets for ruminants. It is evident from this review that intensified animal production and factors such as the use of new drugs, feed additives and recent developments such as the greater use of bypass proteins have an important bearing on the ruminant’s requirement for nutrients. There is therefore a need to re-examine established nutrient standards and principles continually as further intensification of ruminant production will influence these requirements and interrelationships in currently unforeseen ways.
Recent advances in ruminant nutrition!
Recent advances in ruminant nutrition cover a wide range of topics. The widespread use of highly concentrated diets has resulted in a completely new set of nutritional issues and deficiencies. The scope of this review does not allow us to do justice to the numerous developments that have enabled and continue to enable us to improve the rate and efficiency of meat, milk, and wool production.
Polyether antibiotics, also known as ionophores, were widely used after it was discovered that they had such a profound effect on ruminant production. The effects of ionophores on microbial growth, microbial metabolism, nutrient digestibility, and nutrient utilisation are the main areas of ionophore activity in ruminants. The well-known increase in feedlot gain efficiency and better pasture-fed animal growth appears to be the net result of these many effects acting in concert.
Ionophores improve animal performance by favourably altering the growth of specific bacterial strains. Lasalocid is toxic to bacteria that produce lactate, butyrate, formate, or hydrogen as a major end product. Increased propionate production not only improves feed utilisation efficiency but because propionic acid is gluconeogenic, it is a more versatile energy source.
Biological effects of ionophores
- Greater rumina! propionate concentration
- Lower rumina! acetate concentration
- Lower rumina! butyrate concentration
- Lower ruminal lactate in stressed animals
- Higher ruminal pH in stressed animals
- Less ruminal methane production
- Decreased intake of grain diets
- Increased intake of forage diets
- Increased ruminal forage fill
- Decreased ruminal rate of passage
- Increased dry matter digestibility
- Increased protein digestibility
- Decreased ruminal deamination
- Decreased ruminal proteolysis
- Protein sparing effect
- Modified ruminal escape of protein
- Modified ruminal escape of starch
- Modified rumen microbial population
- Increased body glucose turnover
- Modified substrate gluconeogenesis
- Reduced 3-methylindole production
- Earlier puberty in heifers
- Reduced fly pupae in faeces
Ionophores give a slight to moderate increase in the digestibility of dry matter and/or starch under many conditions. Increases in nitrogen digestibility in animals fed both low and high-protein diets have been reported. Factors such as feed intake, rumen fill, and rate of passage may influence the results. Monensin reduces dietary protein breakdown significantly and allows more undegraded feed protein to bypass the rumen. Lower rumen ammonia levels reflect this decreased deamination. As a result, the total amount of amino acid nitrogen reaching the abomasum increases.
Mode of action of ionophores
The ability of ionophores to bind and facilitate the transport of ions across biological membranes is their primary mode of action. One unanswered question is whether ionophores affect the availability and uptake of ions from feedstuffs and mineral supplements. This is an important question in the context of trace elements, particularly those considered toxic. The normal uptake, transport, and utilisation of divalent minerals in the animal body is accomplished through a variety of endogenous ‘ionophore’ transport routes. Elsasser investigated the possibility that the exogenous ionophores lasalocid and monensin might alter the normal uptake of divalent metal ions (1984). These findings imply that the addition of these agents may alter bioavailability, gut uptake, and tissue deposition.
Potassium nutrition
The mineral potassium (K) is the third most abundant in the animal body. Until recently, its inclusion in ruminant diets was thought to be unnecessary. With the increasing use of grain or grain byproducts, these perspectives must be reconsidered. K supplementation in high-concentrate diets for beef and dairy cattle, as well as sheep, is gaining popularity. Stressed cattle-fed diets containing 1.4% K outperformed control groups fed diets containing only 1.0% K.
Cattle pre-fed on 55% concentrate diets responded to K much less in the subsequent feedlot adaptation period. Hutcheson concluded that for the first two weeks after arrival in the feedlot, shipped cattle should receive 24.7 g K/l00 kg body mass. This is 20% more than the requirement for non-transported animals.
For a long time, nutritionists took the K requirement of dairy cows for granted. Increased cow productivity and increased use of grain or rain byproducts have led to a re-evaluation of the need for K supplementation. In practice, borderline K deficiency causes appetite loss and reduced milk production. Under farm conditions, symptoms of Frank K deficiency such as a rapid decrease in feed and water intake, a drop in milk and blood plasma K levels, loss of vitality, pica, and death are unlikely to be seen.
Researchers from the University of Florida studied the effects of sodium (Na) and potassium (K) in the diets of shaded and unshaded dairy cows. Cows fed K-deficient rations had significantly lower milk yield and pica, which was quickly reversed by feeding adequate K (1,1%). There was a NaiK interaction, with 0.7% Na and 1,58% K producing the highest yields and feed conversion. Excessive levels of K, while not toxic, may reduce performance. Increasing K increased calcium and N absorption but phosphorus absorption was not affected. The largest decrease in magnesium absorption occurred when K levels increased from 1.2 to 4%.
B complex vitamins in cow nutrition
Until recently, it was thought that ruminants with a functional rumen did not require B-vitamin supplements. The observation by Theiler, Green, and Viljoen (1915) and subsequent studies showing that net B-Vitamin synthesis occurs in the rumen is the main reason for this belief. These responses, combined with known cases of specific vitamin deficiencies and the unknown effect of many modern feed additives on vitamin synthesis and metabolism, necessitate a reconsideration of the role of B Vitamin supplementation in ruminant diets.
Thiamine supplementation in cows and sheep (ruminants)
Since Davies, Pill, Collings, Venn, and Bridges first demonstrated that thiamine administration cures polioencephalomalacia, there has been a lot of interest in thiamine for ruminants. Thiaminase II simply cleaves the vitamin, producing thiazole and pyrimidine, whereas thiaminase I not only destroys the vitamin but also produces thiamine analogue. The analogue then inhibits one or more of the thiamine-requiring enzymes required for energy metabolism in the central nervous system in the presence of suitable cosubstrates. PEM can be treated with large intravenous thiamine injections if detected early enough. Thiamine supplementation of feedlot diets is frequently recommended in practical feedlot situations. Lusby and Brent used 150 mg thiamine per day to prevent PEM in lambs, but PEM developed shortly after thiamine withdrawal. This suggests that in the presence of thiaminase I, approximately 1 g thiamine/day is required to prevent PEM in cattle. According to Edwin and Jackman, the activity of thiaminase enzymes can be so high that it can destroy 1 mg thiamine per minute.
Feeding thiamine to prevent PEM does not appear to be very practical because such high levels of thiamine are required to compete with the inhibiting analogues. According to Brent and Bartley, high levels of thiamine in the diet will result in more thiamine circulating, and if the concentrations of thiaminase I and cosubstrate are not limiting the rate of thiaminase I reaction, feeding thiamine will increase thiamine analogue synthesis and could potentially precipitate PEM. Miller, Goodrich, and Meiske discovered that monensin reduces ruminal thiamine loss over time.
Niacin supplementation in cows
Niacin can be produced by rumen microorganisms and the animal itself from tryptophan. When niacin is supplemented at a rate of about 6 g per cow per day, most studies show a positive response in milk production (250- 300 p.p.m.). The response is higher in postpartum cows than in mid-lactation cows, and it is higher in cows fed natural protein than in cows fed urea. The effect of niacin on milk production and ketosis in dairy cows can be explained in part by its ability to increase blood glucose levels while decreasing plasma or serum concentrations of ketones and free fatty acids. Brent et al. hypothesised that heating soybean meal would reduce the availability of niacin or tryptophan to bacteria in the rumen. The addition of niacin increased bacterial protein synthesis by 10.9%.
Choline
Although choline is not a vitamin, it is an important source of biologically active methyl groups. Choline is gaining popularity among ruminant researchers due to its potential lipotropic effect in high-producing dairy cows. Butterfat test, feed intake, and fat-corrected milk production have all improved in cows fed choline-fed diets, according to research.
Buffers
The use of buffers in ruminant feeds has been extensively studied over the last 25 years. Saliva plays an important role in neutralizing the volatile fatty acids produced during rumen fermentation by providing buffers (sodium and potassium bicarbonates). High-grain, low-fibre diets result in low rumen pH values, which are linked to lower butterfat percentages in dairy cows. Any decrease in saliva efflux will result in a more acidic rumen. Concentrated diets also ferment faster and produce higher levels and concentrations of volatile fatty acids. These conditions not only cause rumen papillae clumping, parakeratosis, and liver abscesses but also lactic acidosis during the adaptation period following abrupt changes to more concentrated diets. Finally, high-grain, low-fibre diets that result in low rumen pH values are linked to lower butterfat percentages in dairy cows.
The response obtained from the feeding of buffers can be expected to be influenced by many factors, such as the kind of buffers in use (sodium bentonite, sodium bicarbonate, potassium bicarbonate, calcium carbonate, dolomitic limestone and magnesium oxide to mention but a few), the levels used the stage of production tested (such as early lactation, feedlot adaptation periods, etc.), the natural buffering capacity of the basal diet, the level of concentrate fed, the kind of animal fed, and whether or not silage is included in the feed.
Branched-chain fatty acids
Branched-chain fatty acids (isobutyric, isovaleric, and 2-methylbutyric) and valeric, a straight-chain acid, are essential bacterial nutrients that promote cellulytic bacteria growth. One or more of the following features were improved in the most of the trials involving these acids: feed intake, cellulose digestion, nitrogen retention, microbial growth, and mass gains. Earlier research on the effects of these acids on animal production focused primarily on steers, growing heifers, and sheep fed high-cellulose, urea diets. Earlier studies focused on the effects of single or limited combinations of these acids on rumen production and metabolism. Only recently has research on dairy cattle fed standard production rations been conducted. Effect of ammonium salts of branched fatty acids (AS- VFA) on dairy cows over a full lactation were investigated S-VFA consisted of a mixture of three C-5 volatile fatty acids namely isovaleric, 2-methylbutyric and valerie acids and ammonium isobutyrate fed at various blends. Cows receiving the optimum blend peaked higher, produced more milk and more 4% fat corrected milk, milk protein and total solids than control cows
