2 Planning your nutrition

Transcription

1 2 Planning your nutrition A detailed knowledge of rumen physiology and ruminant metabolism is not essential for improving herd performance through better feeding. However, a broad understanding of rumen fermentation, nutrient requirements, feed intake and utilisation, energy balance, milk production and fertility needs, metabolic disorders and feed resources is important for anyone wishing to make the most of the many opportunities available for nutritional improvement in the vast majority of herds. It establishes the fundamental basis for improvement; allows dairy feeding to be planned in the most efficient way to achieve the required economic, environmental and social objectives; and enables common nutritional pitfalls to be appreciated and avoided. What s in this section? Understanding ruminant digestion and nutrient requirements Appreciating the interactions of feed intake and energy balance Assessing milk production and fertility needs. 2 Planning your nutrition Contents Action plan Page 2:3 Ruminant physiology Page 2:4 Nutrient requirements Page 2:9 Feed intake and utilisation Page 2:16 Nutrition and milk production Page 2:21 Nutrition and fertility Page 2:23 Metabolic disorders Page 2:24 Feeding and breeding Page 2:25 Feed resources Page 2:27 Improvement through feeding 2:1

2 Summary It is vital to appreciate the dynamic state of the rumen environment and the extent to which changing feeds or feeding systems can alter rumen conditions for better or worse Cows require four main groups of nutrients to live, grow, produce and reproduce water, energy, protein and minerals and vitamins The challenge of feeding high yielding cows is underlined by the fact that in a single lactation they are likely to produce more dry matter in the form of milk than their body contains Body Condition Scoring is widely accepted as a practical way of assessing body fat reserves, providing a good measure of a cow s energy balance to inform feeding and management The levels and ratios of individual volotile fatty acids (VFAs) produced by the digestive system can have a marked influence on milk fat and protein Nutrition in general and energy nutrition in particular has a major effect on fertility The range of metabolic disorders affecting dairy cows can invariably be prevented by ensuring the best possible dietary balance and particularly careful management at drying off, during the dry period and in early lactation While different types of stock may be better suited to different production systems, regardless of breed, the key to cost-effective feeding is meeting the animals particular performance requirements within their specific intake capacities. See also... Section 3: Section 4: Section 5: Section 6: Planning your feeding Assessing your feed options Managing your forage feeds Managing your non-forage feeds Section 7: Managing your feeding Section 9: Section 11: Managing dry cow feeding Factsheet 1: Metabolic disorders Factsheet 2: Common feed analysis terms Factsheet 3: The Dietary Cation-Anion Balance (DCAB) system Factsheet 4: Body Condition Scoring Factsheet 5: Common ration ingredients 2:2 Improvement through feeding

3 Action plan To improve your feeding efficiency you must. 1. Understand ruminant digestion Understand the way the rumen works and the key factors determining the efficiency of ruminant digestion (Page 2:4). 2. Understand key nutrient needs Understand the critical water, energy, protein, mineral and vitamin needs that have to be met each day through your feeding (Page 2:9). 3. Understand feed intake and utilisation Appreciate the interactions affecting feed intake and nutrient utilisation and the vital importance of ensuring the right energy balance (Page 2:17). 4. Understand feeding consequences Understand the way in which feeding affects milk production, fertility and digestive health and efficiency (Page 2:22). The Pd+ programme provides practical advice on improving herd fertility. For detailed guidance on optimising feeding for fertility see Section 7. The Grass+ programme provides practical advice on making the most of grass. For detailed guidance on grazing supplementation see Section 6. The Breeding+ programme provides practical advice on improving through breeding. For detailed guidance on herd improvement priorities see Section Understand feed ingredients Understand the vast range of ingredients available for dairy feeding and the need to select them carefully (Page 2:28). Improvement through feeding 2:3

4 Ruminant physiology Ruminants are distinguished from other animals by having a four-compartment stomach, comprising rumen, reticulum, omasum and abomasum (Figure 2.1). Figure 2.1: The ruminant stomach Ammonia is used as a nitrogen source for microbial growth and VFAs absorbed from the rumen are a key energy source for the cow. The inside of the rumen wall is lined with small fingerlike papillae which increase its absorptive area, allowing VFAs, ammonia and water to move directly into the bloodstream. Rumen Reticulum The papillae shorten, decreasing the rumen s inner surface area, when a low energy diet is fed (during the early dry period, for example). Omasum Abomasum Located on the left side of the body, the rumen makes up over 65% of an adult cow s total stomach volume. It is, in effect, a huge fermentation vat containing a soup of around 130 litres of chewed-up feed with large amounts of saliva and micro-organisms primarily bacteria and protozoa. Floating on top of this soup is a fibrous mat of coarser solid material which acts as a filter. Feed particles are regurgitated and re-chewed until they are small enough to fall through the fibre mat into the rumen liquor below. The rumen liquor commonly contains between 10 to the power 9 and 10 to the power 11 bacteria per ml, together with 10 to the power 5-10 to the power 6 protozoa. These break down degradable feed materials to produce volatile fatty acids (VFAs), ammonia and a variety of long chain fatty acids. Increasing the rumen-available energy content of the diet in the form of sugar and starch stimulates papillae growth, improving VFA absorption. While rumen fermentation allows good use to be made of fibrous feeds that could not otherwise be digested, it does mean only around 70-85% of the energy in the feed is available to the animal 6-15% commonly being lost as gases (mainly methane) and 6-7% as heat. Small in comparison to it, the reticulum is a continuation of the rumen with a honeycomb structure. Microbial fermentation continues as the feed moves through the reticulum and into the omasum a globe-shaped structure containing page-like folds of tissue through which water and some nutrients are absorbed. Moving through the omasum, the mixture of feed and rumen micro-organisms becomes progressively drier. 2:4 Improvement through feeding

5 Excessive intake of minerals or low quality fibre (such as sunflower hulls) can cause compaction of the omasum. Finally the abomasum or true stomach secretes hydrochloric acid and digestive enzymes to begin breaking down feeds that have escaped microbial digestion, together with microbes excreted from the rumen. Displaced abomasum (or twisted stomach) occurs when this area of the stomach moves from the lower right side to the top and left side of the cow. From the stomach the digesta moves into the small intestine where most of the digestive enzymes are secreted to break down both feed and microbial nutrients into simpler nutritional building blocks. These are absorbed across the intestinal lining and into the bloodstream through small finger-like projections (villi) which increase its surface area in the same was as the papillae in the rumen. Few digestive problems occur in this area. Bacterial fermentation of some undigested feed occurs in the final section of the digestive tract the large intestine which also absorbs both VFAs and water. Factsheet 1 provides practical guidance on metabolic disorders. Cows commonly spend 8-10 hours/day ruminating, the extent of rumination depending on the roughage content of the diet. The cycle of rumination involves four distinct elements: Regurgitation coarse material (the scratch effect) at the upper end of the rumen stimulates a bolus of feed (cud) to be returned to the mouth. Chewing each cud of regurgitated food is chewed many times to grind it down into particles small enough to pass out of the rumen. Salivation chewing stimulates the secretion of buffercontaining saliva (as much as 75 litres/day) which is mixed with the cud to stabilise rumen ph. Swallowing once the coarse material has been ground down sufficiently by chewing, it is swallowed and sinks to the bottom of the rumen to pass into the reticulum. Rule of thumb When cows are resting (not eating or being milked) over 60% should be ruminating. If the diet contains adequate long fibre, cows should chew at least 30 times (ideally 60) before re-swallowing. Understanding rumen dynamics The contents of the rumen are continually mixed by the rhythmic contraction of its walls, a healthy rumen contracts around twice a minute. As well as bringing feed and bacteria into close contact with each other, the contractions move smaller, denser feed particles out of the rumen while bringing larger, lighter particles up to the fibre mat at the top surface for rumination. Understanding VFA production Volatile fatty acids (VFAs) produced from microbial fermentation of feed carbohydrates in the rumen are the primary source of energy for ruminants. Improvement through feeding 2:5

6 Three distinct volatile fatty acids are produced by rumen fermentation acetate, propionate and butyrate the balance primarily depending on the balance of nutrient sources in the diet (Table 2.1). Acetate represents 55-70% of total VFA production and is an important precursor in milk fat synthesis. Butyrate varies from 5-15% of VFA production and is also a milk fat precursor. Under optimal conditions the acetate:propionate ratio should be greater than 2.2 to 1. Propionate comprises 15-30% of the VFA production and is a key precursor in milk lactose synthesis. High levels of acetate indicate a high fibre/low starch ration, producing a generally slower, more stable fermentation. High levels of propionate indicate a high starch/low fibre ration producing a faster rate of fermentation which can lead to reduced rumen ph, depressed fibre digestion and even acidosis. Factsheet 1 provides practical guidance on metabolic disorders. Table 2.1: Diet, fermentation and VFA production Microbe Substrate Nitrogen requirement Main VFAs produced ph range Hours to double microbial population Fibre-digesting bacteria Cellulose Hemicellulose Ammonia Acetate Butyrate Starch and sugar-digesting bacteria Starch Sugar Ammonia Amino acids Propionate Lactate Protozoa Starch Sugar Amino acids Understanding rumen efficiency With fibre-digesting bacteria thriving best at ph and starchdigesting bacteria at , the best balance of fibre and starch digestion occurs at a rumen ph of around 6.0. Factors affecting rumen ph and fermentation efficiency include: Forage to concentrate ratio High forage diets stimulate higher rates of saliva production, better rumen buffering and greater acetate production which supports butterfat levels. Excessive amounts of concentrates, on the other hand, increase propionate production, decrease rumen ph, reduce feed intake and microbial production and depress butterfats. 2:6 Improvement through feeding

7 Rule of thumb A forage to concentrate ratio of 60:40 (on a dry matter basis) should be maintained wherever possible. Going below 50:50 is not advisable. Concentrate type Starch-based concentrates may depress rumen ph to a greater extent than those based on digestible fibre. Physical form of feeds Grinding, pelleting, chopping or over-mixing can reduce the particle size of feeds to a level at which the rumen mat cannot be maintained, depressing rumination, saliva production and ph. Finely ground concentrates increase microbial fermentation (favouring lactic acid-producing bacteria, in particular), reducing rumen ph and increasing the risk of acidosis. Feed intake levels Higher feed intakes mean more material available for bacterial fermentation and higher levels of VFA production. Degradable fat levels If they are available in the rumen, fatty acids in vegetable and fish oils can coat fibre particles, reducing their digestibility. They can also be toxic to fibre-digesting bacteria. Grinding or extruding oilseeds tends to make these effects worse by rupturing cell walls and releasing oil into the rumen, while feeding whole oilseeds can reduce this risk. Rule of thumb The amount of degradable fats in the ration should be limited to less than 4%. Feeding method Total mixed rations (TMR) can be beneficial in stabilising rumen ph, providing a balanced supply of nutrients for the most efficient bacterial fermentation, increasing dry matter intake and minimising feed selection (Section 3). When high levels of concentrates are included, however, rumen ph may still be below optimum and fibre digestion compromised. The amount of saliva produced per unit of feed dry matter may also decline, leading rumen ph to drop. Ration moisture content Wet feeds can reduce rumen ph because less saliva is needed to lubricate the feed for swallowing. Rumen ph can also be adversely affected with very dry diets because of low intake levels. Rule of thumb The optimum DM of the total ration is 45-55%. Improvement through feeding 2:7

8 If concentrates are fed separately, it is important to limit the amount to 3kg/meal and avoid high starch levels and finely processed grains to prevent large fluctuations in rumen ph (Figure 2.2). Figure 2.2: Rumen ph fluctuations on different feeding regimes 7 Parlour fed twice per day 6.5 High Forage TMR ph 6 Optimum ph 5.5 High Concentrate TMR 5 Time It is vital to appreciate the dynamic state of the rumen environment and the extent to which changing feeds or feeding systems can alter rumen conditions for better or worse. 2:8 Improvement through feeding

9 Nutrient requirements Cows require four main groups of nutrients to live, grow, produce and reproduce water, energy, protein, and minerals and vitamins. Appreciating water requirements Comprising 50-80% of a cow s body, depending on age and essential for all cellular functions as well milk production, the transport of nutrients and excretion of waste products, water is the single most important dairy nutrient. It is also vital to the regulation of body temperature. The amount of drinking water a cow requires depends on milk yield, the moisture (or dry matter) content of the feed and the ambient temperature (Table 2.2). Rule of thumb Salmonella and other coliform bacteria can survive for long periods in the environment and leach into otherwise clean water supplies from some distance. Poorly-sited wells or bore holes can lead to contamination from nearby slurry stores, septic tank outflows, carcase burial pits and even landfills. Cryptosporidia, leptospirosis and Johne s disease are a few of the serious pathogens that can be passed on from contaminated water. Water quality testing All non-mains water should be tested annually for ph, total dissolved solids, total coliform bacteria, faecal coliform bacteria, total plate count and key minerals (Table 2.3) using clean, sterile sample containers from a testing laboratory. Samples for bacteriological testing must be refrigerated, insulated, and delivered to the laboratory within six hours. Other samples can be delivered or mailed using a standard overnight service. Cows require at least 60 litres of water/ head/day and may need 100 litres or more depending upon yield. As cows tend to drink in groups it is vital to provide sufficient trough space to ensure good access for all (Section 7). Because cows have a good sense of smell and taste it is important to ensure water supplies are of sufficient quality as well as sufficiently available. Improvement through feeding 2:9

10 Table 2.2: Daily drinking water requirement (litres) Average daily milk yield 20 litres 30 litres 40 litres Temperature <16ºC 16-20ºC >20ºC <16ºC 16-20ºC >20ºC <16ºC 16-20ºC >20ºC Ration DM 30% % % % % Table 2.3 Water quality guidelines Chemical Desirable level (mg/l) Possible problem level (mg/l) ph 6.5 to 8.0 Under 5.5 or over 8.5 Total coliform bacteria <20,000* 50,000* Total dissolved solids < Sulphate < Fluoride < Calcium < Magnesium < Copper < Arsenic < Cadmium < Lead < Nitrate-nitrogen < Barium <5 10 * total per litre 2:10 Improvement through feeding

11 Appreciating energy requirements Some 50-80% of the energy cows require to power all their bodily functions comes from volatile fatty acids (VFAs) produced by the fermentation of feed carbohydrates in the rumen, with the remainder derived from carbohydrates, fats and proteins that escape rumen degradation. The extent and speed of carbohydrate degradation in the rumen varies with the maturity of forages, sources of carbohydrate and degree of feed processing (Figure 2.3 and Table 2.4). The balance of different carbohydrates in the feed is important in determining the efficiency of ruminant digestion and metabolism (Table 2.5). Ruminant energy requirements and feed energy supplies are generally expressed in terms of Metabolisable Energy (ME) the energy available to the cow after accounting for losses in digestion, gases and urine. Fermentable Metabolisable Energy (FME) is the proportion of the ME potentially available in the rumen. Factsheet 2 summarises the common terms used in feed analyses. Figure 2.3: Rates of rumen fermentation Rate of fermentation Soluble sugars Starches and dextrins Cell wall carbohydrates Time hours Dairy feeds comprise two main types of carbohydrate non-structural sugars and starch from the contents of plant cells and seeds and structural cellulose, hemicellulose and pectin found in plant fibres and seed coats. Although not strictly a carbohydrate and virtually indigestible, lignin is grouped with structural carbohydrates analytically. In analyses, acid detergent fibre (ADF) measures the cellulose, lignin and lignified nitrogen components while neutral detergent fibre (NDF) comprises these elements plus hemi-cellulose and represents the total fibre content of the feed. Table 2.4 : Digestibility and speed of digestion of common feeds Feed Digestibility (%) Rate of digestion (hours) Molasses Turnips/fodder beet Cereals Good grass Good clover Poor hay Straw Improvement through feeding 2:11

12 Table 2.5: Guidelines for ration energy requirements Energy component Content in ration dry matter Sugar 5-10% Starch Fibre (ADF) (NDF) Fat 15-20%, half in slowly rumen degraded form 18-25% minimum 30-35% minimum 6% maximum, with a maximum 4% in rumen degradable form Dietary fats triglycerides with three fatty acids attached to a glycerol molecule are very much a secondary source of energy for ruminants, being present only at modest levels (2-3%) in diets commonly fed to dairy cattle. As highly concentrated sources of energy, animal fats and vegetable oils can be particularly valuable in increasing the energy content of rations for high yielding cows, particularly if they are protected from rumen degradation. Since fatty acids can interfere with rumen fermentation and fibre digestion, the fat content of dairy rations should be limited to a maximum of 6% of the dry matter (Table 2.5). Imbalances of the main energy sources can cause the following problems: Sugar and starch Too high Risk of acidosis; fat cows Too low Risk of low milk protein; thin cows Fibre Too high Intakes drop Too low Risk of acidosis; displaced abomasums Fat Too high Poor fibre digestion and low intakes Too low Risk of low milk yield and butter fat Appreciating protein requirements Essential to every aspect of body maintenance, reproduction and milk production, so called Metabolisable Protein (MP) is supplied to the cow as a combination of microbial protein from the rumen and dietary protein that passes through it undegraded (Figure 2.4). Ruminant protein requirements and feed protein supplies are generally expressed in terms of Crude Protein (CP) which includes non-protein nitrogen as well as true protein. Bacteria cannot use either fermentation acids or fats/oils as an energy source, so the right balance of dietary sugar, starch and fibre is essential for efficient rumen function. Rumen Degradable Protein (RDP) describes the protein supply available to the rumen microbes, while Digestible Undegraded Protein (DUP) is the protein available from the feed which escapes rumen degradation. 2:12 Improvement through feeding

13 Figure 2.4 Protein metabolism DUP MP D. Mic. P Factsheet 2 summarises the common terms used in feed analyses. Mouth Feed CP UDP Rumen UDP Gut RDP ERDP Lost Ammonia Mic. P Faecal P Appreciating mineral and vitamin requirements Urine N UDP Undegradable Dietary Protein RDP Rumen Degradable Protein ERDP Effective Rumen Degradable Protein DUP Digestible Undegradable Protein Mic.P Microbial Protein D.Mic.P Digestible Microbial Protein About 60-70% of dietary protein is degraded by rumen microbes into peptides, amino acids or ammonia which they use as nitrogen sources. Rumen microbes incorporate these building blocks into microbial protein, the most important factor governing the efficiency with which rumen degradable protein is converted into microbial protein being the supply of readily fermentable energy. Unincorporated ammonia is absorbed across the rumen wall and into blood, converted to urea in the liver and recycled in saliva or excreted in urine and milk. Although not considered to be a reliable guide for fertility purposes, milk urea nitrogen (MUN) concentrations can provide useful indications of the efficiency with which protein is being utilised in the rumen (Section 7). Minerals are inorganic compounds needed for a whole host of regulatory and structural functions in the cow. They are provided in different quantities and at different availabilities by different feeds and are supplied in a range of feed supplements (Section 4). Macro minerals So-called macro minerals (required in relatively large amounts grams/cow/day and expressed as a percent of ration dry matter) include calcium, phosphorus, magnesium, potassium, sodium and sulphur (Table 2.6). Sodium, potassium and sulphur salts are ionic and affect the acid-base balance in cows, which is critical to the maintenance of many bodily functions. When dry cows are fed rations high in potassium (producing positively-charged ions), for instance, the availability and absorption of magnesium can be reduced, leading to milk fever type symptoms. There is good evidence that feeding anionic (negatively-charged) chlorine or sulphur salts using a Dietary Cation-Anion Balance (DCAB) approach helps prevent milk fever in these circumstances (Section 9). If dry cow rations contain potassium at over 2% in the forage DM, however, it is often better to change the forage rather than adding anionic salts, since their poor palatability can depress appetite dramatically at a time when intakes are already under severe pressure. Improvement through feeding 2:13

14 Factsheet 3 provides detailed information on the DCAB system. Table 2.6: Key macro mineral functions, deficiency symptoms and interactions Mineral Use Deficiency symptoms Interactions Calcium (Ca) Bone growth, enzymes, muscular and nervous system Rickets, milk fever, low milk yield Phosphorus, Magnesium, Vitamin D Phosphorus (P) Bone growth, energy metabolism Rickets, depraved appetite, poor fertility Calcium, Magnesium, Iron, Aluminium, Vitamin D Magnesium (Mg) Enzymes, muscular and nervous systems Staggers, convulsions Calcium, Phosphorus, Potassium Sodium (Na) Muscular and nervous systems, acid-base balance Poor appetite, low milk production, urine licking Potassium, Chlorine, Sulphur Chlorine (Cl) Acid-base balance, hydrochloric acid Poor appetite, urine licking Sodium, Potassium Potassium (K) Acid-base balance, nervous system Low feed intake, poor coat condition Sodium, Chlorine, Magnesium Sulphur (S) Acid-base balance, sulphur amino acids, B vitamins Poor appetite, reduced microbial growth Copper, Molybdenum, Nitrogen Factsheet 1 provides practical guidance on metabolic disorders The many interactions between minerals and the fact that some can be toxic at relatively low levels makes providing them in excess of requirements as harmful as failing to correct deficiencies. Trace elements Key trace elements (minerals only required in relatively small amounts and measured in milligrams/day) include cobalt, copper, iodine, iron, manganese, selenium and zinc (Table 2.7). They can be supplemented in either inorganic (eg zinc oxide) or organic (eg zinc methionine) forms. Inorganic minerals are most commonly used because they are less expensive and more concentrated than organic minerals. Common mineral ratios to avoid imbalances include: Zinc : Copper <6:1 Zinc : Manganese 1:1-1.5:1 Iron : Copper 40:1 Potassium : Magnesium <6:1 Copper : Molybdenum 6:1 Potassium : Sodium 3:1-7:1 Potassium : Calcium + Magnesium <5:1 Copper toxicity is something that is talked about when looking at mineral rates. In terms of toxic limits 2:14 Improvement through feeding

15 there is an EU regulation in place on inclusion rates, currently set as a maximum of 40mg/kgDM Vitamins Vitamins are organic compounds needed in small amounts for a variety of chemical reactions in the body (Table 2.8). Table 2.7: Key trace element functions, deficiency symptoms and interactions Mineral Use Deficiency symptoms Interactions Cobalt (Co) Microbes to make vitamin B12 Poor appetite, anaemia, rough coat Copper (Cu) Enzymes, muscular and nervous systems, blood Poor immune system, rough coat (red tint), diarrhoea Molybdenum, Sulphur, Iron Iodine (I) Synthesis of thyroxine Goitre, poor fertility Iron (Fe) Haemoglobin, enzyme systems, immune system Anaemia Copper Manganese (Mn) Growth, bone formation, enzyme system Skeletal abnormalities, poor growth, poor fertility Calcium, Phosphorus, Zinc, Iron Selenium (Se) Immune function, enzyme system, cell membranes Poor immune function, white muscle disease, mastitis, retained placenta Calcium, Sulphur Zinc (Zn) Immune function, enzyme system, tissue repair Parakeratosis of skin, mastitis, stiff joints, high cell count, hoof problems Iron, Copper, Manganese Table 2.8: Key vitamin functions, deficiency symptoms and interactions Vitamin Use Deficiency symptoms Interactions Vitamin A Immune system, vision Night blindness, skin problems, weak calves, poor fertility Vitamin D Bone growth, calcium and phosphorus metabolism Rickets, osteomalacia, milk fever Calcium, Phosphorus Vitamin E Antioxidant White muscle disease, mastitis, retained cleansings Selenium Fresh forages are good sources of fat soluble vitamins (such as Vitamin A, D and E) but dried, stored and ensiled forages have little vitamin content remaining so diets based upon them must generally be supplemented. Water-soluble B vitamins can be synthesised by rumen microbes to meet the requirements of most dairy cows. Cobalt is needed for rumen microbial synthesis of Vitamin B12. Improvement through feeding 2:15

16 There is some evidence to support supplementing biotin (Vitamin B7) at 20mg/day for improved foot health and milk yield and niacin (Vitamin B3) at 6g/ day before calving and 12g/day after calving to minimise ketosis especially in over-fat cows. Factsheet 1 provides practical guidance on metabolic disorders 2:16 Improvement through feeding

17 Feed intake and utilisation While the efficiency with which feeds are fermented and digested clearly has a major effect on nutrient supply, the most important factor governing the extent to which cows can meet their energy, protein and other nutrient needs is the amount of feed they consume. This is especially important in the early stages of lactation when the energy demand for production is higher than intake can support, creating an increasingly negative energy balance which cows have to meet from body reserves, milking off their backs. Understanding feed intake Feed consumption is generally expressed in terms of Dry Matter Intake (DMI) the weight of feed material consumed excluding the moisture it contains. A large number of different animal, food and management factors affect DM intake. Key animal factors affecting DMI include: Cow size Big cows eat more than small cows Cow breed Some breeds of cow eat more for their size than others Cow age Heifers eat less than mature cows Milk yield Higher yielding cows eat more than lower yielders Cow condition Fat cows eat less than thin cows Stage of lactation Early lactation cows eat less than those in mid and late-lactation. Key food factors affecting DMI include: Fibre content Cows eat less when fibre levels are too high Protein content Cows eat more when protein levels rise Processing Cows eat more when the feed particle size is smaller Moisture content Cows eat most at a ration DM of 45-55% Diet composition Cows eat less when rations are poorly balanced Digestibility Cows eat more when rations are more digestible. Key management factors affecting DMI include: Feed access Cows eat more when feed is available ad-lib Water access Cows eat more when palatable water is readily available Feeding frequency Cows eat more when fresh feeds are provided more frequently Ration palatability Cows eat more the tastier they find the feed Feed spoilage Cows eat less when feeds are spoiled by decay or contamination Ration changes Cows eat less when rations are changed abruptly Cow comfort Cows eat more when they are relaxed and comfortable. Substitution rates The clear limit to the amount of fibre (NDF) cows can consume in a day means intakes of low fibre feeds like wheat (12% NDF) are potentially four times those of higher fibre feeds like good quality silage (48% NDF). Improvement through feeding 2:17

18 As well as having important implications for overall intakes, this means cows will eat less forage when supplements are available, the extent of this substitution depending on the type of supplement. Concentrate feeds generally displace relatively small amounts of forage from the diet, so supplementation will generally allow daily DM intakes and performance to be increased. A kilogram of wheat (12% NDF) will, for instance, displace only 0.25kg of 48% NDF silage from the daily intake (12% 48% = 0.25 substitution). In contrast, higher fibre feeds have higher substitution rates a kilogram of sugar beet pulp (32% NDF) displacing 0.67kg (32% 48%) of the same silage. Over and above the nutrients required for maintenance, milk production receives the clear priority in early lactation, with shortages of nutrients from the diet made-up by the mobilisation of body reserves. Thereafter, there is a progressive re-ordering of priorities, with milk production declining and a greater proportion of nutrients being directed to rebuilding body reserves primarily fat. The challenge of feeding high yielding cows is underlined by the fact that in a single lactation they are likely to produce more dry matter in the form of milk than their body contains. When buffer feeding grazed grass, higher fibre feeds can lead to substitution rates of greater than 1.0, reducing daily intakes and compromising performance (Section 5). The Grass+ programme provides practical advice on making the most of grass. For detailed guidance on grazing supplementation see Section 6. This challenge is particularly intense in early lactation, as milk yields build rapidly to a peak about 4-8 weeks after calving, whereas maximum voluntary feed intake is only reached after around weeks (Figure 2.5). Ensuring high DM intakes as soon as possible after calving is a key priority if high levels of both production and fertility are to be achieved. The inevitable rise in energy demand for milk production ahead of energy intake in the first few weeks of lactation has not been found to cause problems as long as intake catches-up with production by around the sixth or eighth week of lactation, at which time the negative energy balance ceases and cows stop losing weight. Prioritising energy balance Nutrients absorbed from the gut are continually being partitioned within the cow to maintain its body functions and support the production of milk and body reserves. 2:18 Improvement through feeding

19 Figure 2.5: Energy demand and supply over the lactation Negative energy balance Milk yield (Energy demand) Once daily DM intakes of 24kg or more are required by yields much in excess of 40 litres/day, however, increasing problems arise, even with particularly high energy density diets and relatively high daily weight losses (Table 2.9). Milk yield and intake Feed intake (Energy supply) Stage of lactation (weeks) The fact that early lactation intakes have not risen in line with milk yields in recent years has meant increasingly deeper and longer periods of negative energy balance in excess of 20 weeks in studies with very high yielding herds. At peak milk yields of up to 40 litres/day most cows have relatively little difficulty consuming sufficient feed to support their production without drawing too heavily on their body fat reserves, providing their diets are sufficiently concentrated, palatable and available. Considerable research into nutrition and fertility performance has pinpointed more pronounced and protracted early lactation energy deficits as a major factor in the lower fertility experienced by many high yielding cows. Research and experience indicates a daily DM intake of 3.5% of body weight should be achieved by five weeks after calving for optimum performance in high yielding herds (Table 2.10). The Pd+ programme provides practical advice on improving herd fertility. For detailed guidance on optimising feeding for fertility see Section 7. Improvement through feeding 2:19

20 Table 2.9: The impact of yield on energy and DM intake requirements Annual milk yield (litres) Typical peak yield (litres/day) Intake requirement to support peak yield (kg DM/day) Total ration energy concentration (ME/kg DM) 11 MJ 12 MJ 13 MJ Weight loss (kg/day) Weight loss (kg/day) Weight loss (kg/day) , , , , Table 2.10: Dry matter intake targets for high concentrate systems (kg/day) Weeks after calving Heifers (2 years) Cows Since DM intake rises and milk production declines in mid-late lactation, achieving the correct balance between energy supply and demand becomes progressively easier; especially as cows should be safely back in calf by this time. Indeed, the primary challenge in later lactation nutrition tends to be to prevent cows putting on too much condition. Assessing cow condition Body condition scoring is widely accepted as a practical way of assessing body fat reserves, providing a good measure of a cow s energy balance to inform feeding and management. A semi-subjective assessment of condition scoring is best carried out by the same person on each occasion to eliminate operator differences (Section 7). 2:20 Improvement through feeding

21 As the change in condition score is more important than the absolute value, scoring should be undertaken regularly. A good routine involves scoring: At calving; 60 days post calving 100 days before drying off At drying-off. Rule of thumb Cows should: Maintain condition during the dry period; Lose no more than 0.25 Condition Score to 4 weeks post calving; and, lose no more than 0.25 Condition Score from 4 to 8 weeks post calving. Factsheet 4 provides practical advice on Body Condition Scoring Considerable research and practical experience has established the following ideal Body Condition Score targets for key stages in the lactation cycle: At calving: days post calving days before drying off At drying-off: Improvement through feeding 2:21

22 Nutrition and milk production Most of the major constituents of milk lactose, fat and protein are synthesised in the mammary gland from precursors selectively absorbed from the blood and transported either from the digestive system or from body reserves. Lactose is mainly synthesised from glucose which, in turn, is produced in the liver from the VFA, propionate, together with glycerol and fatty acids from the breakdown of dietary or body fat. Since the amount of water secreted by the mammary gland is directly related to lactose levels, lactose synthesis is the principal driver of milk volume. The primary building blocks of milk fat are the VFAs, acetate and butyrate, with glucose supplying the glycerol required. Milk protein primarily casein is produced from amino acids. Milk production always follows the same general pattern over the lactation, progressively declining from its peak 4-8 weeks after calving. However, the shape of the lactation curve will vary with the breed and age of cow, month of calving and, most importantly, the feeding regime. Some lactation curves show marked peaks with a more rapid initial rise and subsequent decline in production, while others are notably flatter, rising to less of a peak but maintaining production far better as the lactation progresses (Figure 2.6). Figure 2.6 Typical lactation curves. Daily yield Month of lactation Providing the same amount of milk is produced over the lactation, flatter curves stimulated by flatrate concentrate feeding can be advantageous because they mean lower peaks of energy demand and potentially lower early lactation energy deficits (Section 6). Influencing milk components The levels and ratios of individual VFAs produced by the digestive system can have a marked influence on milk fat and protein percentages. There are a number of ways of manipulating milk solids levels through feeding, although the costeffectiveness of ration adjustments always needs to be assessed against the specific milk contract. 2:22 Improvement through feeding

23 Milk protein percentages can best be increased by: Increasing the energy density of the ration Feeding high ME silages with good intake potential Increasing the protein content of the ration Feeding mixed forages Increasing the degradable starch content of the ration with ingredients such as rolled wheat Increasing the by-pass starch content of the ration with ingredients such as crimped maize Increasing the by-pass protein of the ration with ingredients such as protected soybean meal Using both protected starch and protein Feeding protected methionine Avoiding added fat (even protected fat) Calving cows in optimum condition. Protected fats Fats are protected from rumen degradation either by conversion into a rumen insoluble soap or naturally by virtue of a high melting point which makes them relatively inert in the rumen. The form of protection must, of course, ensure they are available for breakdown and absorption lower down the digestive tract. The fatty acids making up protected fats can be a relatively pure source of 16 carbon chain molecules palmitic acid (known as C16s) or a mixture of C14, C16 and C18 molecules (usually referred to generically as protected fats). C16 fatty acids can be directly converted into milk fat to boost butterfat percentages. Milk fat percentages can best be increased by: Increasing the forage to concentrate ratio Feeding high fibre forages Ensuring sufficient long fibre Feeding high digestible fibre concentrates Feeding concentrates little and often to stabilise rumen ph Avoiding high oil by-products such as distillers and brewers grains Avoiding whole oil seeds such as full fat soya and whole rape seed Avoiding fish oil products Feeding small amounts of a protected fat. Improvement through feeding 2:23

24 Nutrition and fertility Nutrition in general and energy nutrition in particular has a major effect on fertility. Cows in too much of a negative energy balance in early lactation tend to be difficult to get back in calf. Because higher insulin levels have a detrimental effect on embryo quality, however, cows subsequently need diets higher in saturated fat to stimulate progesterone production and lower in starch to minimise insulin production. This implies that feeding for fertility in this way is likely to require more complex grouping of stock than may be practicable for many. This results both from a delay in the resumption of normal oestrus cycling and a lower conception rate. Cows that are too fat at calving encounter particular problems since their early lactation appetites tend to be poor, resulting in excessive body fat mobilisation which can result in ketosis or fatty liver syndrome. For optimum fertility, cows should calve down at Body Condition Score and lose no more than half a condition score by service. Factsheet 4 provides practical advice on Body Condition Scoring. Feeding for fertility Nottingham University research suggests that different types of diets can be fed to influence ovarian activity and egg quality. Increasing starch and reducing fat supply, for example, has been shown to increase bulling activity and insulin levels. Excess protein is not, itself, a major cause of poor fertility. However, excess protein almost always exacerbates energy deficits as additional energy is required to get rid of it. There is some evidence that high blood ammonia reduces early embryonic growth which could lead to pregnancies being lost within the first 10 days. If fertility problems persist despite cows being in the correct body condition and rations being correctly balanced for energy and protein, it is advisable to check the mineral and vitamin status of both animals and rations. In view of the many interactions between different minerals, it is vital to analyse the mineral status of forages and seek specialist advice before undertaking additional supplementation. Minerals excesses can be as much of a problem as insufficiencies, so particular care is always essential in supplementation. 2:24 Improvement through feeding

25 Metabolic disorders A number of disorders linked to incorrect diet or feeding can have adverse effects on dairy cow health and welfare as well as productivity. The most common of these are: Acidosis Displaced abomasums (DA) Hypocalcaemia (milk fever) Metabolic disorders can invariably be prevented by ensuring the best possible dietary balance and particularly careful management of cows at drying off, during the dry period and in early lactation (Section 9). Hypomagnesaemia (grass staggers) Ketosis (acetonaemia) Fatty liver Laminitis Retained foetal membranes (retained cleansings). All the common metabolic disorders have a knock-on effect on fertility, since sick cows typically don t cycle. It can take many months for the reproductive system to recover from metabolic disorders. Factsheet 1 provides practical guidance on metabolic disorders. The Pd+ programme provides practical advice on improving herd fertility. For detailed guidance on optimising feeding for fertility see Section 7. Improvement through feeding 2:25

26 Feeding and breeding Opinion remains firmly divided over the relative merits of different dairy breeds and their suitability for different production regimes. There are clear differences between the breeds in their ability to produce milk and milk components which need to be accounted for in their feeding (Table 2.11). Table 2.11: Typical dairy breed liveweights and genetic production abilities Breed Weight kg/yr Fat kg/year Protein kg/year Fat % Protein % Holstein Shorthorn Ayrshire Jersey Guernsey Friesian Montbeliarde Brown Swiss Source: Current genetic base (PTA 2010) heifer equivalent production values of cows born 2005 by breed, DairyCo Breeding+ Equally, differences in bodyweights mean differences in daily dry matter intake capacities, although some breeds are recognised as having rather higher intake capacities for their size than others (Section 7). Some breeds are considered to be better at looking after themselves and replacing condition more easily than others, making them better suited to systems involving out-wintering or extended grazing. Lighter animals may be valuable for causing less poaching and deeper-bodied cows with larger rumen capacities better adapted to high forage grazing systems. Specific selection pressures (historically in New Zealand, for example and now in certain UK studs) are likely to produce bloodlines with better inherent grazing abilities than those selected under predominantly housed production regimes. Furthermore, long-term University of Edinburgh/ SAC investigations at Langhill demonstrate clear differences in the performance ability of different lines of cattle within the Holstein Friesian breed. Compared to their average genetic merit contemporaries, the Langhill studies show cows consistently bred from bulls with the highest weight of fat + protein proofs over 20 years: Produce markedly higher yields under both high and low input systems Need not necessarily produce lower fat or protein percentages Have higher intake capacities Are more efficient at converting feed energy into milk energy Generate substantially higher feeding margins. 2:26 Improvement through feeding

27 Overall, the animals bred for combined weight of fat and protein produced similar yields from 1 tonne of concentrates as their unselected contemporaries did from 2.4 tonnes, resulting in substantially higher margins. Cross breeding studies in New Zealand and North America have further highlighted the potential for improving overall dairy productivity particularly in terms of fertility, health and survivability by harnessing the power of hybrid vigour. While different types of stock may be better suited to different production systems, regardless of breed the key to cost-effective feeding is meeting the animals particular performance requirements within their specific intake capacities. The Breeding+ programme provides practical advice on improving through breeding. For detailed guidance on herd improvement priorities see Section 1. Improvement through feeding 2:27

28 Feed resources A wide range of forages, concentrates, moist feeds and supplements are available to meet dairy cow energy, protein, mineral and vitamin requirements (Section 4). These need to be selected and utilised on the basis of specific analyses and careful rationing to ensure the best balanced diets (Table: 2.12). Table 2.12: Typical dairy feeding sources Nutrient type Typical examples Energy sources Sugar Starch Fibre Grass, grass silages, molasses, lactose, whey Maize silage, wholecrop silage, cereals, peas, beans, maize meal, maize germ extract, biscuit meal, bread Straw, hay, silage, sugarbeet pulp, citrus pulp, soya hulls Protein sources Rumen Degradable Protein (RDP) Digestible Undegradable Protein (DUP) Red clover, lucerne, legume silages, peas, beans, lupins, soyabeans, cottonseed meal, rapeseed meal, distillers grains, maize gluten feed, sunflower meal, urea Soyabean and protected soyabean meal, maize gluten (prairie) meal Mineral & vitamin sources Calcium Phosphorus Magnesium Sodium Vitamins Limestone, dicalcium phosphate Mono- and dicalcium phosphate Magnesium oxide, calcined magnesite Ground rock salt Proprietary mixes Factsheet 5 sets out the key attributes of common ration ingredients. 2:28 Improvement through feeding