MILK DEVELOPMENT COUNCIL

Transcription

1 MILK DEVELOPMENT COUNCIL Economic Feeding for High Fertility Project No. 99/T2/17

2 ADAS BRIDGETS RESEARCH CENTRE STUDY 99/T2/17 (XCAAX) Economic Feeding for High Fertility Report prepared by Miss Helen Biggadike, Mr Richard Laven and Mr Robert Bull ADAS Bridgets Martyr Worthy Winchester Hampshire SO21 1AP Report prepared for Milk Development Council Stroud Road Cirencester Gloucestershire GL7 6JN Date of issue of report June 2001 h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 1of 38

3 CONTENTS 1 EXECUTIVE SUMMARY 3 2 FARMER RECOMMENDATIONS 4 3 AIMS AND OBJECTIVES 5 4 INTRODUCTION 6 5 ENERGY Introduction What is negative energy balance? What happens to a cow in negative energy balance Why and when does negative energy balance occur Effects of negative energy balance on reproduction How to avoid or lessen the effects of negative energy balance Summary References 14 6 BODY CONDITION SCORE Introduction BCS and genetics The effect of BCS at drying off, calving and insemination The effect of change in BCS Targets Summary References 21 7 DIETARY PROTEIN Introduction Protein requirements Rumen degradable protein Defining excess protein Increasing protein intake - results from research How does increased protein intake affect fertility? Site of effect Timing of effect Summary References 30 8 MINERALS AND TRACE ELEMENTS Introduction Effects on reproductive performance Diagnosis Estimating requirements Method of supplementation The form of supplementation Summary 33 9 ECONOMIC IMPLICATIONS Introduction The cost of extended calving intervals Example of energy requirement, intake and change in BCS Increasing energy fed, energy density Increasing dry matter intake Summary References ACKNOWLEDGEMENTS AUTHENTICATION 38 h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 2of 38

4 1 EXECUTIVE SUMMARY Scientific evidence relating to nutrition and fertility in high yielding dairy cows was reviewed: High genetic merit Holsteins will produce milk at the expense of body tissue. Negative energy balance (NEB) occurs when energy intake is insufficient to meet the requirements of maintenance and production and it is unavoidable in high production cows. The largest NEB usually occurs between 1 and 8 weeks post calving at the time of peak milk yield. Loss in body condiction score (BCS) is a good indicator of NEB and metabolic profiles can provide useful additional detail. NEB is made worse by disease, poor diet formulation and sub-optimal feeding facilities. Fat cows at drying off and calving make NEB worse High genetic merit cows fit best in a system with high feed inputs in keeping with their production potential. Improved management can help control body weight changes, e.g. feeding for a flatter lactation curve with a lower peak. Future improvements in selection criteria will help, e.g. using changes in BCS as a selection parameter as an indicator of fertility aiming to select animals with high milk production potential that are capable of preserving their body condition. There has been a trend to increase dietary protein for high production potential cows. Increasing dietary protein concentration results in increased milk yield and often in an increase in body tissue mobilisation. Feeding excess protein when energy supply is inadequate makes the negative effects of energy deficiency worse. In commercial practice, cows fed the highest protein diets are likely to be early lactation, high yielding cows, which are also most likely to be in a situation of energy deficiency. High protein diets are often wrongly blamed for causing poor fertility: - herds with high urea can still have good fertility. - blood or milk urea increases if rumen energy falls not only if protein intake increases. - urea is easy to measure and alter whereas the real effects of high protein on poor fertility are often difficult to identify. There is limited evidence to support the belief that there is a direct effect of excess dietary protein intake on fertility that is unrelated to energy deficiency. Energy sources are generally cheaper and excess energy can be effectively and efficiently turned into protein by the rumen. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 3of 38

5 Mineral or trace element deficiencies can result in poor fertility, but other causes should be eliminated first, before a conclusion of a mineral or trace element deficiency is made. In the UK, except in specific well-known situations, mineral or trace element deficiency is much less important as a cause of poor fertility than inadequate energy and protein intake. In an attempt to improve the utilisation of trace elements fed to cows, various chelated minerals (sometimes described as organic trace elements) are now available. Chelation is the bonding of trace minerals to organic compounds, which may make the minerals more available to the cow. A general improvement in the bioavailability is reported, but evidence that performance and reproduction is improved is still lacking. Nutrition related changes in reproductive performance are due to the influence of nutrition on metabolic hormones such as GH, insulin and the IGF system. NEB is believed to result in fewer large follicles developing, fewer follicles ovulating and reduced early embryo survival DAISY data show an average UK calving interval of 400 days and a barren culling rate of 18%. Despite increasing milk yields, the economic optimum still appears to be a calving interval of 365 days and a barren culling rate of 7%. It still appears to be economically worthwhile inseminating cows of average yield up to approximately 266 days post-calving and high yielding cows until 290 days post-calving. A cow with a 10000kg milk yield fed a 12.5 M/D diet and a maximum DMI of 24kg will be in energy deficit for approximately 100 days and is likely to lose 2 BCS points over this time. 1 BCS point is equivalent in energy terms to approximately 1680 MJ ME. In situations where cows are losing in excess of 1 BCS in early lactation the relationship between feed costs, reduced loss of body condition and improved fertility indicate substantial economic benefits of reducing loss of BCS by increasing energy intake. 2 FARMER RECOMMENDATIONS Aim to reduce the magnitude ( a maximum loss of 1 BCS) and duration (no more than 42 days) of negative energy balance (NEB) in early lactation. Body condition score cows at key times and set targets: Target body condition score Max./Min BCS Drying off max. Calving max. First insemination 2 to 2.5 (gaining condition) 1.5 min (must be gaining) Mid lactation 2.5 to 3 3 max. The early lactation diet should provide sufficient energy to reduce loss of condition to a maximum of 1 BCS point. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 4of 38

6 Use change in BCS information to assess energy status of the herd and make dietary changes to minimise excessive loss in early lactation or unwanted gain at the end of lactation. Aim to maximise DMI this generally has the biggest potential for controlling energy balance. Avoid overweight cows and heifers. Do not rely on making changes in body condition during the dry period. Ensure that feed is accessible, palatable, consistent and available ad-libitum to maximise intake. and avoid sudden changes in feeding. Forages need to be of high quality and consistent. Grassland management for grazing must be excellent to be successfully included in the diet of high production cows. Beware of lower than predicted intakes from grazed grass. High protein feeds tend to be expensive. Avoid feeding excess protein when energy supply is inadequate as this makes the negative effects of energy deficiency worse. Before increasing dietary protein concentration ensure an ample supply of energy, energy sources being generally cheaper and more efficient feeds for dairy cows. Follow the current AFRC allowances and recommendations for minerals and trace elements, it is then unlikely that you will have any mineral or trace element related infertility. Supplementation of minerals and trace elements is best provided in feed or possibly in water, free- access minerals are not generally recommended. In situations where cows are losing in excess of 1 BCS in early lactation the relationship between feed costs, reduced loss of body condition and improved fertility indicate substantial economic benefits of reducing loss of BCS by increasing energy intake. Judge the success of rations by cow performance and profitability, which includes reproductive performance and health as well as milk production and quality. 3 AIMS AND OBJECTIVES OF THE REVIEW An examination of scientific evidence relating to nutrition and fertility was undertaken with the overall objective of producing a review of key factors in nutritional related infertility and to highlight nutritional strategies to improve reproductive performance in high yielding Holstein dairy cows. The review is presented in five main sections as follows: 1) Energy 2) Body Condition Score 3) Protein 4) Minerals and Trace Elements 5) Economic Implications h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 5of 38

7 4 INTRODUCTION Reproductive performance of dairy cows in the UK is declining in a similar way to that seen in the US. This decline is related, in part, to the dramatic increase in milk yields, which has occurred over the same period, and the consequential increase in nutrient demands which we currently find difficult to fully satisfy. Excellent nutrition is a requirement of good reproductive performance, and this includes milking cow, dry cow, transition cow and heifer rearing diets. The fundamental requirements remain provision of sufficient energy and protein, and the correct balance between the two. The much greater requirements of high production cows make economic ration formulation more complex and dry matter intake often becomes a crucial, limiting factor. Normally the keep increase in energy requirements can be met by a combination of increased ration energy density and increased dry matter intake. However, as a ceiling is reached on dry matter intake, the challenge becomes one of increasing dietary energy density without compromising rumen function or reducing diet palatability. Some of the key requirements for rationing each of the categories are summarised below: Dry Cow Transition Cow Early Lactation Cow Encourage high DMI DMI will reduce Maximise DMI Low quality/energy density (e.g. straw/hay) Include main components of Highly palatable milking diet including forage Ensure good rumen fill Energy density must increase High quality components (including forage quality) Adequate energy supply Feed 2-3 weeks pre calving High energy density Correct energy:protein balance Dry cow mineral supplementation Dry cow mineral supplementation Correct energy:protein ratio Milking cow mineral supplementation Sufficient fibre 5 ENERGY 5.1 Introduction The most common and most important nutritional cause of reproductive failure in dairy cows is the inability of the diet to supply sufficient energy for maintenance and milk production (McClure 1994). An excessive or prolonged period of energy deficiency (i.e. total loss exceeding 1 body condition score or extending beyond 42 days post partum), is usually quoted as the main cause of poor pregnancy rates in dairy cows 5.2 What is Negative Energy Balance (NEB)? Energy balance is defined, as energy intake minus energy output and an animal will be in NEB if energy intake is insufficient to meet the requirements of maintenance and production. The terms metabolic load and metabolic stress are also sometimes used in relation to energy balance and can be defined as follows: Metabolic load = the burden imposed by the synthesis and secretion of milk; Metabolic stress = that amount of metabolic load that cannot be sustained, such that some energetic processes, including those that maintain general health, must be down regulated (Collard and others, 1999). h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 6of 38

8 Summary - Negative energy balance (NEB) occurs when energy intake is insufficient to meet the requirements of maintenance and production. 5.3 What happens to a cow in NEB? A cow in NEB has to find the energy to meet the deficit by mobilising body reserves. Thus, cows in NEB tend to lose body condition and liveweight, with cows that are more energy deficient tending to lose weight and condition at a faster rate. However, not all cattle in NEB will show significant falls in weight and condition. Thus changes in liveweight and body condition score (BCS) are only indicators of energy deficiency and are best used on a herd or group basis to identify NEB. Measuring both liveweight and BCS is a better indicator of NEB than measuring just weight or condition. If only one is measured, then BCS is better than liveweight. Changes in liveweight without supporting BCS data can be misleading due to changes in gut fill. Summary - On the farm, loss in body condition score (BCS) and/or liveweight are good indicators of NEB -, if they are used on a herd or a group of cows. Energy is absorbed from the diet via the rumen, as volatile fatty acids, and, via the small intestine, as amino acids (from proteins) and fatty acids (from fats). These compounds can be divided into two groups based on their role in the metabolism of the cell: 1) Gluconeogenic: These can be used to produce glucose, which in-turn can be either used to produce other carbohydrates, such as the milk sugar, lactose and the storage carbohydrate, glycogen, or can be broken down to produce CO 2 and water releasing energy 2) Ketogenic: These can be used to create fats, but not glucose. They too can be broken down to produce CO 2, water and energy, but only if there is sufficient glucose. The dairy cow absorbs very little glucose directly, because virtually all of the digestible carbohydrate is converted to fatty acids in the rumen.. Therefore, most of the glucose required by the dairy cow has to be produced from gluconeogenic compounds, primarily propionate and some specific amino acids. Thus blood glucose is very tightly controlled and is significantly lower than in non-ruminants. When a cow breaks down its body reserves, storage carbohydrates and some proteins are used to produce glucose but the fat reserves, the major energy stores, are primarily ketogenic and cannot be used to make glucose. Glucose is thus required for the cow to make efficient use of its fat reserves. In cows with prolonged or severe NEB, fat is broken down but the lack of available glucose means that not all the breakdown products can be used. These products are converted to ketones, which can be used to partly replace glucose by some tissues. However, this process is inefficient and slow, and if the NEB gets more severe or more prolonged, these compounds accumulate in the blood, milk or urine. If the concentration of ketones increases high enough, the cow develops the disease known as ketosis (acetonaemia, slow fever). As the utilisation of body reserves results in changes in blood and milk biochemistry, blood sampling can be used to identify animals in NEB: Glucose Blood glucose concentration is commonly used as an indicator of energy status. However, because blood glucose is very tightly controlled, large changes in glucose supply and utilisation only result in small changes in blood glucose. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 7of 38

9 5.3.2 Non-esterified free fatty acids (NEFAs) The concentration of NEFAs in the blood is closely related to the rate of fat breakdown. The more severe theneb the higher theconcentration of NEFAs, with a plasma concentration of >600µmol/l indicating that a cow is in severe NEB Beta-hydroxybutyrate (BHB) BHB is a ketone and is thus produced when there is insufficient available glucose to mobilise the fat breakdown products efficiently. BHB is used as a predictor of NEB as it is the most common ketone and is a stable compound. BHB plasma concentrations of >0.9 mmol/l are usually taken as indicating significant energy deficiency. Ward (1999) analysed blood for metabolic profiles from 15,000 cows managed under varying regimes in the UK. Blood concentration of BHB was above the standard of 0.9 mmol/l in 34% of cows calved for less than 6 weeks, this fell to 26% in cows calved between 6 and 17 weeks. These results suggest that a high proportion of dairy cows in the UK are energy deficient in the early part of lactation. BHB and other ketones can also be measured in milk, which is easier to obtain than blood. The concentration in milk is closely related to that in blood, and it is likely that the development of in-line sensors for milk ketones will be a significant advance in the detection of energy deficiency Insulin and insulin-like growth factor (IGF-1) Blood concentrations of these hormones decrease significantly in animals in NEB. Although rarely measured, the effect of NEB on these hormones is probably more important than the effect of NEB on NEFAs or BHB, as it is probably the reduction in insulin and IGF that results in the poor fertility associated with NEB. Summary - Examination of metabolites in blood and/or milk can be useful indicators of energy status. A range of tests (often called a metabolic profile) will always be more useful than a single test, and results from a group of cows will always be more useful than results from a single cow. 5.4 Why and when does NEB occur? Increased energy output Dairy cows are good at adjusting to short-term imbalances in nutrient supply. However, in early lactation when dietary intake is often unable to meet the demands of milk production, most cows enter a period of NEB, resulting in a substantial mobilisation of body reserves. The largest NEB is likely to coincide with peak milk yield, i.e. anywhere between 1 and 8 weeks post calving. The duration of NEB is variable but it is generally recognised that zero or positive energy balance has been restored when the cow is seen to be in a state of stable or increasing body condition. This often occurs between 8 and 12 weeks after calving. One of the greatest metabolic demands on the cow is the synthesis of lactose from glucose. On a typical high production dairy cow diet a huge dry matter intake (28+ kg DM) is required to supply enough propionate for glucose synthesis to support a 50 kg daily milk yield (Beever and others,, 2001). Alderman and Blake (1995) reported the ME and MP requirements, calculated for milk yields up to 70 kg/day, according to AFRC Table 1 summarises the calculated energy requirements for a 650 kg cow with a milk butterfat of 4%, milk protein of 3.4% and milk lactose of 4.8%. These calculations indicate that to support a 70kg milk yield, feeding a diet with an overall energy density of 13 MJ/kg DM, intake needs to increase to almost 28 kg DM/day and liveweight loss is predicted to be approximately 3kg/day. Although it does happen in some very high yielding herds, few cows can achieve intakes above 25 kg h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 8of 38

10 DM and few herdsmen would be happy with cows losing 3 kg/day liveweight even for a short period of time. Table 1 Estimated metabolisable energy (ME) requirements of high genetic merit dairy cows calculated in accordance with AFRC (1993). Milk yield (kg/day) Assumed dietary M/D (MJ/kg DM) Calculated liveweight change (kg/day) Assumed energy deficit (MJ ME/day) ME required (MJ/day) Calculated dry matter intake (kg/day) (After Alderman and Blake, 1995) Summary - a period of NEB invariably occurs in high production cows in early lactation regardless of diet and management. For example, to support a 50kg daily yield, AFRC 1993 calculations indicate that a cow will mobilise 2kg body weight/day in addition to consuming 22.4 kg DM of a 12.5 M/D ration Increasing genetic merit The highest levels of energy deficit tend to occur in high genetic merit cows which partition available nutrients favourably towards milk production at the expense of body reserves. The cows ability to increase feed intake has not kept pace with her ability to increase milk output hence high genetic merit cows find themselves in a state of increasing energy deficiency as yield potential increases. It appears that nutrition and management have failed to keep pace with genetic progress and the increased demands of the high genetic merit cow. Summary - The largest NEB is likely to occur between 1 and 8 weeks post calving coinciding with peak yield. The cows ability to increase feed intake has not kept pace with her increase in milk output and nutrient partitioning, which favours milk production in high genetic merit cows, and this has resulted in more severe and more prolonged periods of NEB Insufficient energy input Severe energy deficiency can also occur even in cows of modest yield due to inappropriate diet formulation or poor management of cows and feeding facilities. Herd managers should aim to provide a diet containing appropriate, balanced nutrients in a quantity and manner that allows cows to maximise intake during early lactation. NEB does not occur below a critical DMI or diet energy content norr above a specified milk yield. It is not an absolute input or output, but the balance between the two, which is important in determining when NEB occurs. Ward (1999) reported that there was no clear correlation between milk yield and BHB or glucose concentration indicating that higher yields alone do not necessarily result in greater energy deficiency. For example, variation in dry matter intake potential can have a huge influence on an individuals ability to meet the energy demands at a given milk yield. Summary - Higher milk yields do not necessarily result in greater energy deficiency, dry matter intake potential has a big influence on the relationship between yield and energy status. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 9of 38

11 5.4.4 Disease Diseases such as hypocalcaemia may induce or exacerbate NEB due to impaired rumen function in the form of reduced frequency of rumen contractions (Jonsson, 1999). Similarly, any condition, which reduces the cows desire or ability to consume large quantities of food in early lactation, will result in an increase in the magnitude or duration of NEB. In the long term cows try to adjust their energy intake in an attempt to keep levels of body energy reserves constant (Webb 1999). Summary - NEB will be made worse by diseases such as hypocalcaemia or by poor diet formulation, feeding facilities or management. 5.5 Effects of NEB on reproduction General effects of NEB The main physiological response of the cow to metabolic imbalance is to down-regulate reproductive function (Knight and others, 1998). Nutritional influences on fertility are likely to be multi-factorial and complex and may occur at several stages of the reproductive cycle. For example, underfeeding is generally believed to delay the occurrence of puberty in heifers, delay the recurrence of oestrus cycles/ovulation after calving and reduce pregnancy rates in early lactation. More specifically nutrition may influence follicular growth, corpus luteum (CL) function, oocyte quality, uterine environment or embryo survival and growth. Research from the USA (Butler, 2001) suggests that the scale of the NEB in the first 3 to 4 weeks post calving is highly correlated with the interval between calving and first ovulation. As NEB increases the interval to first ovulation increases along with a significantly reduced pregnancy rate after first insemination. Animals in NEB have a significantly increased risk of non-reproductive diseases such as mastitis and, lameness (Collard and others, 1999), which can then indirectly affect fertility. Energy deficiency can also increase the incidence of reproductive disease, Cook (1999) reported that subclinical ketosis was associated with a significant increase in metritis and cystic ovaries Summary - Energy deficiency has a wide range of effects on fertility, affecting the resumption of normal reproductive cycles after calving, reproductive tract health, ovulation, conception and embryo survival Effects on metabolic processes The actual requirements for energy and protein of an oocyte or embryo are tiny compared to the requirements of the cow. Reproductive changes due to nutrition are therefore not likely to be due to an inability to supply the nutrients required by the oocyte or embryo but to the influence of nutrition on metabolic hormones such as growth hormone (GH), insulin and the IGF system (Garnsworthy and others, 2000). Under-nutrition results in an increase in circulating concentration of GH decreases in liver GH receptors, circulating concentration of insulin, circulating concentration of IGF-1 and reduced IGF binding protein in the liver (Webb, 1999). Factors such as GH, insulin and IGF-1 are involved in the regulation of metabolic processes and have an influence on ovarian follicle development and the IGF system is important in embryo development (Wathes and others, 1998; Garnsworthy and Webb 2000). For example, cows fed diets to induce a low plasma insulin concentration took longer to resume ovarian activity after calving compared to cows fed diets, which induced high insulin concentrations (Webb, 1999). Growth hormone plays an important role in partitioning nutrients away from the deposition of body reserves towards milk production. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 10of 38

12 Plasma GH is found in higher concentrations in higher yielding cows and is positively correlated with changes in milk yield. Summary - Reproductive changes due to nutrition are not due to an inability to supply the nutrients required by the oocyte or embryo but due to the influence of nutrition on metabolic hormones Effects on pituitary function The pattern of luteinising hormone (LH) secretion is affected by nutrition with generally lower LH concentration recorded in cows during periods of energy deficiency (Webb, 1999). In addition, the response of the ovary to LH is reduced in cows in NEB. If energy supply is increased this effect is reversed with an increase in LH secretion, an increase in LH receptors and hence an improved response to the LH Effects on the ovaries Butler (1999) suggested that there was a strong link between energy availability and ovarian activity. Regardless of energy status, ovarian follicles start to develop 5 to 7 days after calving. However the fate of the dominant follicle that develops varies, it can ovulate as normal, it can fail to ovulate and regress followed by further follicle development or it can fail to ovulate and become cystic. Successful ovulation of the follicle depends on adequate follicle growth and on the ability of the follicle to produce sufficient oestradiol. Dominant follicles, which develop during a period of NEB produce less oestradiol and are less likely to ovulate compared to follicles developing when energy supply is adequate (Butler, 2001). During the post partum period cows in lower energy balance have fewer large ovarian follicles but more smaller follicles. The growth rate of the follicle before ovulation is slower in cows fed low energy diets compared to similar cows fed a high energy diet (Webb, 1999). It is likely that the metabolic stress in high yielding dairy cows in early lactation alters the pattern of ovarian follicle growth and development resulting in reduced reproductive function (Webb, 1999). Summary - In situations of NEB fewer large follicles develop and fewer follicles ovulate resulting in poorer fertility Effects on oocyte quality and embryo survival Oocyte quality and embryo survival are affected by energy status, as energy supply directly affects IGF-1 concentration. IGF-1 influences ovarian development directly and embryo survival indirectly by altering the metabolic and secretory activity of the uterus. As energy intake does not seem to affect fertilisation rate, the effect of NEB on pregnancy rate is probably on embryo survival (Sreenan and others, 2001), with most being lost between 8 and 16 days after insemination, before the maternal recognition of pregnancy. Summary - Energy deficiency reduces embryo survival Effects on progesterone Cows in NEB have lower blood progesterone concentration (Villa-Godoy and others, 1987), progesterone is important in the development of the early embryo. Dairy cows with abnormal oestrous cycles have more severe NEB than cow with normal cycles (Pushpakumara and others, 1999), probably because of the reduced IGF-1 in energy deficient cows Summary - Progesterone concentration is reduced in cows in NEB. Lower progesterone concentrations are associated with reduced reproductive performance. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 11of 38

13 5.6 How to avoid or lessen the effects of NEB Managing body condition score (BCS) Many dry cows are too fat, a factor known to exacerbate early lactation loss of body condition and energy deficit. Attempts to overcome the problem of early lactation energy deficiency by increasing the condition of cows at calving (BCS >3.5) usually results in lower feed intakes post calving and an even greater energy deficiency. Cows that are too thin (BCS <1.5) do not have enough body reserves and cannot overcome NEB Summary - Avoid fat and thin cows at drying off and calving Fitting the management system to the cows A recent SOAEFD funded study (Knight and others, 1998) assessed metabolic stress and its consequences in cows of different genetic merit managed for different levels of output. This study concluded that metabolic stress is not restricted to high genetic merit cows nor is it a consequence of absolute input or output but that it occurs as a result of an imbalance between input and output. For this reason, high genetic merit cows in low input systems are at greatest risk of disease and require the most careful management if they are to remain healthy. One of the key recommendations from this research was that the feeding of high genetic merit cows should match their production potential. Knight and others, (1998) concluded that low input systems should not be used with high genetic merit cows. They also suggested that management systems, which encouraged a lower peak but more sustained lactation curve, might reduce metabolic stress and thus improve fertility. Breeding programmes are beginning to address these issues. Summary - High genetic merit cows fit best in a system with high feed inputs in keeping with their production potential, it may be desirable to avoid low input systems with high genetic merit cows Diet formulation and feeding The relationships between different dietary constituents and reproductive performance are very complex and it is essential that diets for high genetic merit animals are formulated to optimise reproduction as well as lactation. For example, extra fat is often added to the diet of high yielding cows to increase energy intake and there is some evidence that dietary fat is beneficial to fertility due to effects on follicle growth, steroid hormone production and the ability of the uterus to respond to oxytocin (Garnsworthy and others, 2000). Dry matter intake (DMI) is a critical factor in controlling early lactation NEB. In order to maximise DMI, diet dry matter content (diet DM of 45% to 55% max is considered likely to maximise intake) palatability, smell, texture and consistency are all important. It is also important to provide plenty of feeding space at minimum walking distance from lying areas, supply fresh feed on a regular basis (once or twice a day) and make sure feed is truly ad-libitum (for a total mixed ration approx. 5% should remain uneaten at the end of each 24h period). Producing sufficient high quality, consistent forages is also a huge asset in the successful and economic rationing of high production cows. Consistent, high quality forage enables the ration to include healthy proportions of forage for rumen function while maintaining the M/D of the diet. Judge the success of your rations by cow performance and profitability, which includes reproductive performance and health as well as milk production and quality. Summary - Diets for high genetic merit animals should be formulated to optimise reproduction as well as lactation. Forage needs to be of high quality and consistent. Maximise dry matter intake (DMI), review diet dry matter content and palatability, h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 12of 38

14 provide plenty of accessible feeding space and offer fresh feed regularly on an ad-lib basis Changing diet It is well recognised that a period of poor fertility is often associated with radical changes in diet, and this is especially marked with turning cows out to spring grazing. Many problems seen in association with grazing, in particular the period following turnout to spring grazing, are likely to be due to an increase in energy deficiency due primarily to lower than predicted intakes. Summary - Avoid sudden drastic changes in feeding for example at turnout or to meet end of year targets at times critical to fertility. Achieving high intakes at grazing requires excellent management of grass and cows and may not be suitable for cows of very high yields due to the difficulty of predicting and achieving high forage intakes Flatter lactations Feeding and breeding to encourage a flatter lactation curve in high production cows would help enable the provision of adequate energy in early lactation. There is some circumstantial evidence that reducing the protein content of diets in early lactation (maybe to as low as 16%) followed by an increase in dietary protein content after approximately 6 to 8 weeks could encourage a flatter lactation curve without reducing total lactation production. As yet, however, there are no scientific reports to support this theory although research funded by MAFF and BOCM/PAULS is currently underway in the UK to investigate dietary manipulation of the lactation curve Breeding As yield increases it becomes harder to meet cows dietary needs, when dietary intake of nutrients does not meet requirements of output mobilisation of body reserves occurs. Due to the inadequacies of diet, the increased yield of high genetic merit dairy cows is often related at least in part to increased mobilisation of body reserves. However, this is not a consistent effect, some cows yield more but have a lower NEB and vice-versa. This is a genetic effect, and this relationship between yield and NEB after calving is likely to form the basis for future breeding plans, with selection aimed at lines that have high yields but minimise NEB. 5.7 Summary NEB occurs when energy intake is insufficient to meet the requirements of maintenance and production and it is almost unavoidable in high production cows in early lactation. The herd managers job is to reduce the magnitude ( a maximum loss of 1 BCS) and duration (no more than 42 days) of NEB.. On the farm, loss in BCS is a good indicator of NEB. Metabolic profiles can provide useful additional detail. The largest NEB is likely to occur between 1 week and 8 weeks post calving at the same time as peak milk yield. NEB will be made worse by disease, poor diet formulation and sub-optimal feeding facilities. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 13of 38

15 Nutrition related changes in reproductive performance are due to the influence of nutrition on metabolic hormones such as GH, insulin and the IGF system. Progesterone concentrations are also reduced. NEB is believed to result in fewer large follicles developing, fewer follicles ovulating and reduced early embryo survival Fat cows at drying off and calving will make NEB worse High genetic merit cows fit best in a system with high feed inputs in keeping with their production potential. Feed must be accessible, palatable, consistent and available ad-libitum to maximise intake. Avoid sudden changes in feeding. Forages need to be of high quality and consistent. Beware of lower than predicted intakes from grazed grass. Grassland management for grazing must be excellent to be successfully included in the diet of high production cows. Feeding and breeding to achieve a flatter lactation curve may be a future option. Judge the success of your rations by cow performance and profitability, which includes reproductive performance and health as well as milk production and quality. 5.8 References Alderman, G. and Blake, J.S. (1995) The energy and protein requirements according to AFRC (1993) of high genetic merit dairy cows. BSAS Occasional Publication 19: Beever, D.E., Hattan, A. and Reynolds, C.K. (2001) Nutrient supply to high yielding cows. BSAS Occasional Publication 26(1): Butler, W.R. (2001) Nutritional effects on resumption of ovarian cyclicity and conception rate in postpartum dairy cows. BSAS Occasional Publication 26(1): Collard, B.L., Boettcher, P.J., Dekkerst, J.C.M., Petitclerc, D. and Schaeffer, L.R. (1999) Relationship between energy balance and health traits of dairy cattle in early lactation. J. Dairy Sci. 83: Cook, N.B. (1999). Milk metabolic profiles in dairy cows and fertility. Cattle Practice 7(3): Garnsworthy, P.C. and Webb, R. (2000) Nutritional influences on fertility in dairy cows. Cattle Practice 8(4): Jonsson, N.N (1999) The effects of subclinical hypocalcaemia on postpartum fertility. Cattle Practice 7(3) h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 14of 38

16 McClure T.J. (1994) Nutritional and Metabolic Infertility in the Cow. CAB International Pushpakumara, P.G.A., Gardner, N.H., Reynolds, C.K., Beever, D.E. and Wathes, D.C. (1999) BSAS Proceedings of Occasional Meeting, Fertility in the high-producing dairy cow, 44. Sreenan, J.M., Diskin, M.G. and Morris, D.G. (2001) Embryo survival rate in cattle: a major limitation to the achievement of high fertility. BSAS Occasional Publication 26(1) Villa-Godoy, A., Hughes, T.L., Emery, R.S., Chapin, L.T. and Fogwell, R.L. (1988) Association between energy balance and luteal function in lactating dairy cows. J. Dairy Sci. 71: Ward, W.R. (1999) Effects of dietary energy and protein on the fertility of high yielding dairy cows. Cattle Practice 7(3): Wathes, D.C., Reynolds, T.S., Robinson, R.S. and Stevenson, K.R. (1998) Role of the IGF system in uterine function and placental development in ruminants. J. Dairy Sci. 4: Web, R. (1999) The influence of nutrition on fertility. Cattle Practice 7(3): BODY CONDITION SCORE 6.1 Introduction Dairy cows in early lactation, particularly high yielders, cannot match their energy and protein requirements from food alone, and thus use their body reserves to meet the energy and protein gap, resulting in a loss of body condition and liveweight. It is important that we can assess the body reserves available to a dairy cow. Currently the best technique for assessing body reserves is body condition scoring (BCS) which measures fat cover. It was developed at the National Institute for Research in Dairying and uses an 11 point scale of half points between 0 (very thin) and 5 (grossly fat) (MAFF 1986). It is a fairly objective technique, which means that although different assessors may give different scores these differences are unimportant as long as each assessor is consistent. BCS is assessed around the tailhead and over the loins as illustrated in Figure 1. BCS is a very useful score as it is closely related to body composition and is thus a useful tool in assessing carcass composition (Wright and others, 1984). Change in BCS is also closely linked with cumulative energy deficit, cows in more severe energy deficit or energy deficit for a longer period lose more body condition. (Ferguson and Otto, 1989). There is no simple relationship between BCS and liveweight for a group of cows, but as a rule of thumb, a loss of one point in BCS is equivalent to a loss of typically between 50 and 60kg or approximately 10% of liveweight.. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 15of 38

17 Figure 1 Illustrations of BCS Figure 1a Body condition score 1.0 (tailhead), deep cavity around tailhead with no fatty tissue between skin and pelvis Figure 1b Body condition score 1.5 (loin), depression in loin clearly visible, ends of transverse processes feel slightly rounded but upper surfaces easily felt. Figure 1c Body condition score 3.0 (tailhead), fatty tissue felt over tailhead area, skin smooth but pelvis can still be felt. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 16of 38

18 Figure 1d Body condition score 4.0 (tailhead), tailhead well completely filled, folds of fatty tissue present. Figure 1e Body condition score4.5 (loin), transverse processes cannot be felt, no depression visible in loin between backbone and hip bones. Summary - Learn how to body condition score your cows and use it as an indicator of changing body reserves and nutritional requirements, one BCS is equivalent to between 50 and 60kg (10% of liveweight). 6.2 BCS and genetics Genetic merit plays a significant part in the changes in liveweight and BCS seen during lactation. For years, the selection of dairy sires has focused on milk production potential. Increasing milk production potential relies on the fact that the higher genetic merit cows tend to have higher intake potential, partition nutrients favourably toward milk production and unless intake can keep pace with output, also tend to mobilise more body weight to support the higher level of production. Good management, particularly feeding and nutrition, can go a long way towards preventing excessive changes in liveweight and BCS but cannot prevent it completely. The two lines of cows at Langhill, Selection (high genetic merit) line, and Control line, are not different in yield-adjusted BCS at calving but as soon as they start lactating, differences appear. The higher yielding Selection line cows lose more body condition than Control cows some losing up to 100kg despite a high concentrate diet. Even within the two groups, cows that lose more condition, on average, yield more milk (a decrease in BCS of 1 being equivalent to about 2kg/day more milk). However, this is not a consistent effect, some cows are thinner and lose more weight even though they don t yield more, and vice-versa. This is a genetic effect, and change in BCS after calving is likely to form the basis h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 17of 38

19 for future breeding plans, with selection aimed at lines that have high yields but maintain BCS. Summary - High genetic merit cows will tend to lose more condition but look for lines of cows that have high yields but also maintain BCS post calving, this is what geneticists are currently trying to do. 6.3 The effect of BCS at drying off, calving and insemination Over-conditioned (fat) cows Fat cows are problem cows. Attempting to overcome the effects of energy deficiency in early lactation by increasing body condition at calving makes the energy deficiency worse. Fat cows eat less, mobilise more body tissue, lose more weight, and body condition than cows that calve in moderate condition (Garnsworthy and Webb 2000). Fat cows also have a significantly increased risk of disease at calving and for the following lactation. Digestive, metabolic, reproductive, infectious and systemic problems are all increased in fat cows (McClure, 1994). Fat cows have fat deposits in the pelvis, which reduces pelvic area, especially in first lactation heifers. This greatly increases the risk of calving problems. Cows with problems at calving have reduced productivity and a greater risk of reproductive problems, impaired fertility, and risk of being culled (Gearhart and others, 1990). Cows that are fat (BCS > 3.5) at drying off are 3 times more likely to develop reproductive problems in the next lactation than dry cows in good condition (BCS 2.5 to 3.5) (Gearhart and others, 1990). These problems include cystic ovaries (Gearhart and others, 1990), metritis and delayed return to oestrous activity (Titterton and Weaver 1999), The optimum BCS for post partum reproductive performance is 2.5 to 3. Summary - Over fat cows at drying off and calving will have significantly more problems during calving and re-breeding as well as having reduced milk production capabilities Under-conditioned (thin) cows Poor condition at calving or at insemination may lead to poor fertility (McClure, 1994). At Langhill genetic correlations of BCS and angularity with calving interval showed that thinner and more angular cows had longer calving intervals. These data also showed that BCS recorded 1 month after calving had the largest genetic correlation with calving interval in first lactation heifers (Price and others, 2000). In beef cows an increased period of anoestrus has been reported in cows that were thinner at calving, associated with reduced peaks in luteinising hormone, a hormone that plays an important role in controlling the activity of the ovary (Wright and others, 1992). However, a survey of 2000 high yielding cows in the UK (Garnsworthy and Webb, 2000) demonstrated that neither condition score at calving nor at service affected pregnancy rate to first service except when cows were very thin, condition score below 1.0. Summary - Very thin cows have longer periods between calving and the resumption of ovarian activity and longer calving to conception intervals h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 18of 38

20 Summary - Extremes of body condition, <1.5 or >4, will reduce reproductive performance h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 19of 38

21 6.4 The effect of change in BCS Change in BCS is a very good indicator of energy status in dairy cows (Garnsworthy and Webb, 2000) and can be used to assess nutritional status of the herd. Monitoring the recovery of the cow in the period after calving is vital. Condition scoring cows at drying off, calving and insemination is a highly effective method of assessing nutrition and energy balance on a herd basis (Sheldon, 1999). The change in BCS over the first 10 weeks of lactation is a useful tool in estimating likely herd fertility (Price and others, 2000). Minimising change in body condition will maximise fertility (Tables 2 and 3). Table 2 Relationship between BCS and fertility - summary of research findings Effect on fertility Associated change in body condition Reference Impaired fertility and high incidence of metabolic disorders Rapid loss of body condition after calving Gearhart and others, 1990 Low pregnancy rate Big loss (>10%) of weight in early lactation McClure, 1994 Low pregnancy rate Still losing weight (>1%/week) at time of AI McClure, % pregnancy rate Loss of 0.5 to 1.0 BCS points from calving to AI Domecq and others, % pregnancy rate Loss of > 1 BCS point from calving to AI Domecq and others, 1997 Reducing pregnancy rate Increasing loss of BCS in 1st month post calving (10,500kg, multiparous cows) Domecq and others, 1997 No effect on pregnancy rate Increasing loss of BCS in 1st month post calving (high yielding primiparous heifers) Domecq and others, 1997 Poorest pregnancy rate in highest genetic merit cows Highest genetic merit cows lost most BCS Garnsworthy and Webb, 2000 Lowest pregnancy rate Cows losing > 1.5 BCS points from calving to AI Garnsworthy and Webb, days increase in calving interval Cows losing 1 BCS point in early lactation Dairy Farmer, days longer to show oestrus Cows losing 1 BCS point in early lactation Dairy Farmer, 2000 Poorer pregnancy rates Cows losing 1 BCS point in early lactation Dairy Farmer, 2000 Table 3: Relationship between change in BCS and reproductive performance Loss in Body Condition Score (weeks 1-5 post partum) 0.5 or less 0.5 to or more Number of cows Days to 1st ovulation 27 a 31 a 42 b Days to 1st AI 48 ab 41 a 62 b 1st AI pregnancy rate (%) 65 a 53 a 17 b a,b means within rows with different superscripts differ (P<0.05) (Guthrie L.D. and West J.W. Web Nutrition and reproduction interactions in dairy cattle). h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 20of 38

22 Summary - Loss of body condition > 1.0 BCS point in early lactation, or continued loss of body condition around the time of insemination, will significantly reduce fertility 6.5 Targets As a minimum, animals should be scored at calving, in advance of first service, in mid lactation and at drying off. Target condition scores for Holsteins are 3 at calving, 2 to 2.5 at first insemination and 3 at drying off. The aim must be to dry cows off in the correct condition for calving. Scoring in mid lactation gives time for adjustments in feeding to be made to achieve this and avoids the need to take fire-brigade action during the dry period. 6.6 Summary Body condition score cows at key times and set targets: Target body condition score Max./Min BCS Drying off max. Calving max. First insemination 2 to 2.5 (gaining condition) 1.5 min (must be gaining) Mid lactation 2.5 to 3 3 max. Use change in BCS information to assess energy status of the herd and make dietary changes to minimise excessive loss in early lactation or unwanted gain at the end of lactation. Do not rely on making changes in body condition during the dry period. Avoid overweight cows and heifers. Minimise severity and duration of body condition loss in early lactation. High genetic merit Holsteins will produce milk at the expense of body tissue. NEB in early lactation is virtually inevitable. Improved management can help control body weight changes, e.g. feeding for a flatter lactation curve with a lower peak. Future improvements in selection criteria will help, e.g. plans include using changes in BCS as a genetic selection parameters as an indicator of fertility aiming to select animals with high milk production potential that are capable of preserving their body condition. h:\data\dairy\livestoc\cows\nutfert\finalrep.doc Page 21of 38