Managing dairy cows for optimal performance.

Abstract

33 Managing dairy cows for optimal performance D.E. Beever CEDAR_ADAS (Reading), Department of Agriculture, The University of Reading, Reading RG6 6AJ, UK d.e.beever@reading.ac.uk Summary Many factors affect the overall performance and hence profitability of dairying systems, with nutrition, genetics and animal environment being key determinants. This paper examines some of the issues that currently face dairying in developed countries and from this analysis some key factors are discussed in more detail. Of principal concern is that modern dairy cows have considerably greater milk yield potential than their ancestors. The rate of improvement in milk secretion has outpaced any increase in feed intake and failure of the cow to meet her nutrient requirements, especially energ y, in early lactation is giving rise to considerable loss of body condition and associated reductions in reproductive competence. Current knowledge is summarised to examine possible strategies for improving feed intake, aiming to reduce the energ y deficit, whilst recognising that grazed or ensiled grass are likely to make relatively small contributions to overall nutrient demands. The transition period from late gestation to early lactation is a period of considerable change within the cow. Research is currently active in this area and current knowledge is summarised to provide management guidelines to ensure successful lactations. The paper examines the potential of an alternative breed, emphasising the greater importance of milk solids output as the milk market moves to increased processing of milk with an associated increased demand for milk fat and protein. Brief reference is also made to the role of cross breeding and some caution is offered, suggesting that this current interest may be more directed towards overcoming problems than developing cows better fitted for the purpose, be it production of liquid milk or milk solids. Keywords: dairy cattle, energy metabolism, feed intake, transition management, dairy breeds consumers and the media, increasing demands are being placed on the dairy farmer as a producer of human food, and ultimately on the dairy cow. Evermore conscious of possible health issues associated with the consumption of animal products, the consumer stridently demands consistent products with respect to hygiene standards as well as auditable production systems, and payment schemes in many countries now reward milk of low somatic cell and total bacterial numbers. Similarly through health concerns along with increased knowledge and sophistication, consumer demand for alternative milk products is increasing as reflected in marginally more than 50% of UK milk being processed, over 50% of the liquid milk market being supplied as reduced fat content, and continued reluctance to purchase butter although cream and ice cream sales are buoyant. Inevitably, these issues make the milk processor more aware of the importance of milk composition (milk fat and protein levels) to optimise product yield per unit milk processed whilst recognising that product quality (e.g. cheese) may be affected when milk of substandard composition is used. With such issues, it is not surprising that many dairy farmers still see the production of milk and milk solids as the sole objectives of their business and base assessments of overall farm profitability on direct input costs in relation to volume of milk sold. This however is a gross oversimplification of milk production. Before producing any milk, the replacement heifer must be reared successfully to gain target weight and body condition for breeding at around 15 months of age to ensure that the animal will calve for the first time at 2 years of age. This represents an enormous overhead on the subsequent production of milk and must be covered by achieving a lifetime milk production commensurate with the animals genetic potential. Once lactating, the firstcalved heifer still has to achieve mature breed size and lactational performance with respect to milk volume and composition must be balanced against the achievement of this growth whilst ensuring a successful pregnancy if overall lifetime productivity is to be uninterrupted. Continuation of the Introduction The primary objective of keeping dairy cows remains the production of milk but with continuing pressure from Recent Advances in Animal Nutrition in Australia, Volume 14 (2003) 34 Beever, D.E. 365 d calving interval dogma necessitates that all newly calved cows become pregnant by day 90 of lactation. Most cows do not recommence cyclity until at least lactation day 2025, whilst farmers generally impose a voluntary waiting period of 60 d. This provides an optimal breeding period of only 30 d, a remarkably short period in which to establish a successful pregnancy. A further concern with the modern dairy cow is the control of body condition. Immediately post calving, feed intake increases at a slower rate than milk yield, the outcome being that total nutrient supply, particularly energ y, is not sufficient to meet the cows demands to support milk production for several weeks into the lactation. The cow responds by mobilising body tissue with commensurate losses of body condition which in turn may affect the cows subsequent fertility whilst heightening public concern over animal welfare. Periods of high body energy loss are invariably associated with compromised milk composition and may predispose the cow to nutritional disorders which can affect overall health, wellbeing and longer term productivity. Overriding all of these issues, the modern dairy cow is considerably different from those that existed only one or two decades ago. Through rigorous genetic selection, especially in the Holstein breed but now being pursued in other breeds, milk yield expectations are much higher as breeders and farmers have focused heavily on this as a main selection criterion, seen by many to be the best approach to improve financial returns. Such changes in emphasis however have not occurred without some costs. Average cow longevity remains relatively short, failure of animals to rebreed is now a major issue, and lameness and mastitis are increasing; excessive loss of body condition has already been cited. Many factors contribute to the overall productivity of dairy cows and introduction of improved genetics is of little value unless accompanied by appropriate management changes. In this respect greater attention must be given to matching cow and management type, whilst profitability from dairy cows will only be optimised through a fuller recognition of all factors involved during the cows lifetime, rather than being driven by milk yield and improved genetics alone. Consideration of many of these aspects is beyond the remit of this paper but based on some of the issues currently facing the Australian dairy industry, several key areas have been identified and will be considered in more detail. Recent efforts at the CEDAR laboratory have focussed on energy metabolism in high yielding cows and this paper will summarise current findings, focussing on the partitioning of energy between milk and body tissue synthesis which by implication can result in significant loss of body condition in early lactation. Having established the importance of achieving high levels of energy intake, the paper will attempt to examine issues associated with the inclusion of forages in the ration and assess the role of grazed grass in the ration of high yielding cows. The paper will then focus on some of the changes which occur during the periparturient period by reviewing current information on transition management. This is an important period within the annual life cycle of the cow and illustrative of the important physiological and metabolic changes which occur within the animal, thus allowing management systems to be developed to meet these additional demands. Finally the paper will briefly consider the role of alternative breeds, including the current interest being shown in cross breeding, conscious that continued Holsteinisation of the worlds dairy cow population may not represent the ideal route for efficient milk production for all situations. Energy metabolism Provision of sufficient energy to meet all production demands remains the principal driving force behind achieving satisfactory yields of milk and milk solids, and represents the major challenge to the satisfactory feeding of the modern Holstein cow. Calorimetric evidence presented by Sutton et al. (1991) for modest yielding Friesians and recent data for higher yielding Holsteins (Beever et al. 2001, 2002) provide a useful comparison of the consequences of increased genetic selection for milk production on the energy demands of the modern dairy cow. With daily feed dry matter (DM) intake and milk yields of 21 and 33 kg respectively, Friesians consumed 250 MJ/d metabolizable energ y (ME) and partitioned 105 and 130 MJ ME/d to milk and heat respectively, providing a residual sum (15 MJ/d), equivalent to 0.75 kg/d body tissue repletion. In contrast, Holsteins eating 26 kg feed DM/d and producing 52 kg milk/d consumed an additional 90 MJ gross energy/d, equivalent to an extra 45 MJ ME. In support of a higher milk output, 150 MJ ME/d was partitioned to milk with 160 MJ ME/d accounted for as heat, due to increased costs associated with higher levels of milk production and higher maintenance costs (Offer et al. 2002) given Holsteins tend to be larger than Friesians. In this respect, recent research in the UK (Kebreab et al. 2003) examined almost 700 individual calorimetric data sets for dairy cows and established that maintenance energy costs as proposed by AFRC (1993) were too low and should be increased by approximately 20 MJ/d for Holsteins. With an estimated energy output as heat and milk of 310 MJ/d there was a resultant loss of body energy of 15 MJ/d, or 0.75 kg body tissue/d. What is most striking is that the difference in body tissue repletion in Friesians and body tissue loss in Holsteins was relatively small (� 15 MJ/d), yet such differences can have major implications for overall lactational performance and is of major concern with respect to milk composition, cow fertility and reduced cow longevity. Several studies in this laboratory have reported excessive body tissue loss in the modern dairy cow when lactational demands are high. What was most interesting about these data was not only the depth of this energ y Managing dairy cows for optimal performance 35 loss, particularly in the immediate post calving period, but also its duration. Calorimetric studies showed body energy loss continued up to week 14 of lactation, an observation subsequently ratified by examination of body condition score change from calving to week 24 of lactation. Consistently it has been shown that body energy loss at week 6 of lactation may be as much as 40 MJ/d. Furthermore, if the data of Sutter and Beever (2000) which examined energy metabolism for each of the first 8 weeks of lactation, albeit with lower yielding cows, are extended to higher yielding Holsteins it can be estimated that body energy loss in high yielding cows may approach or possibly exceed 60 MJ/d in the immediate postcalving period. This equates to a daily loss of 3 kg body tissue, presumed to be mainly as fat. Interestingly, Gibb et al. (1992) who examined body compositional changes in modest yielding Friesians by serial slaughtering between calving and week 29 of lactation noted a body fat loss of 37 kg by lactation week 8. Of this, 24 kg body fat was lost within the first 2 weeks of lactation, equivalent to 1.73 kg fat/d. At the same time, loss of body protein by week 8 of lactation amounted to only 5 kg, with losses during the first 2 weeks being less than 3 kg. Based on the observation by Gibb et al. (1992) that body fat represents the major loss of body energy during early lactation, Beever et al. (2001) used calorimetric data to provide estimates of body fat loss in relation to stage of lactation. By lactation week 10, a body fat loss of 60 kg was estimated. The next 10 weeks was a period of little overall change (+ 5 kg), with cessation of body tissue mobilisation by week 14, followed by relatively small gains. Extending this analysis for a further 10 weeks, body fat gain approximated to 28 kg, indicating significant body repletion, presumably due to reducing lactational demands whilst levels of ME intake were still relatively high. Of greater interest, however, is that by lactation week 30 these cows still had a net body fat loss of more than 25 kg. Assuming some of these cows would be dried off at lactation day 305 provides a target for total body fat repletion between lactation week 30 and drying off of 0.3 kg/d, which must not be confused with body weight gain, which includes changes in gut fill and the developing foetus. Whether or not this rate of tissue gain can be achieved is open to conjecture, especially when feed intake will be declining, whilst many of these cows are still capable of producing significant quantities of milk. Evidence from geneticists at Scottish Agricultural Colleges who scored the body condition of high and low genetic merit cows over their first three lactations suggests that full body condition score repletion is not always achieved and represents an accumulating overhead as cows move to subsequent lactations (Coffey et al. 2002). To examine ways of manipulating nutrient partition during early lactation, Beever et al. (2002) considered feeding either increased dietary levels of starch or protein to high yielding cows for the first 20 weeks of lactation. Against a control total mixed ration containing 17% protein and 23% starch, protein or starch levels were increased to 20% and 28% respectively. A lactational study showed no overall effects between high protein and high starch rations in terms of feed intake, milk yield or milk protein content, but the high protein ration had significantly higher milk fat contents and a 14% improvement in milk fat yield. On the basis of calorimetric estimates of dietary ME contents, cows fed high protein were estimated to have a mean body energy loss during the first 20 weeks of lactation of 15 MJ/d compared with 5 MJ/d for cows fed high starch. Whilst this difference may appear relatively small, over 140 d it would amount to an increased loss of body fat of 35 kg for cows fed the high protein compared with high starch ration. Parallel calorimetric data with similar cows fed the same rations confirmed these effects. Measurements at 6 week intervals over the first 24 weeks of lactation indicated a milk yield response of 5 kg/d for high protein cows (51 vs 46 kg/d), more in line with normal expectations when feeding additional dietary protein. Milk fat content was unaffected but a substantial improvement in milk protein content was noted on the high starch ration (31.2 vs 29.0 g/kg). Overall production of milk protein as well as milk fat was however greater for high protein, equivalent to daily increases of 0.10 and 0.23 kg respectively. Measurement of ME intake showed no effect due to ration type (mean 284 MJ/d) from which it is concluded that the additional energy to support the increased output of milk solids (as expected milk lactose output was also increased on the high protein ration) was associated with increased mobilisation of body tissue. Cows fed high starch lost on average 0.4 MJ energy/d from calving to lactation week 24 while t hose fed high protein mobilised 12.6 MJ/d over the same period. Of greatest interest however was the extent of body tissue ener g y mobilisation measured at week 6 of lactation. Whilst high starch cows lost 12.1 MJ/d, those fed high protein mobilised 38 MJ/d. Similar responses to increased protein feeding during early lactation have been reported, albeit with lower yielding cows (�rskov et al. 1987) and suggest that whilst high protein feeding can be justified in relation to immediate lactational effects, when longer term effects are considered, namely control of body condition during early lactation, it may not be the most appropriate strategy for achieving the collective aim of high milk solids output and control over body condition score loss. Feed intake Whilst there have been only limited studies to examine feed DM intake in high yielding cows, Clarke and Davies (1980) reported a DM intake of 38 g/kg liveweight for cows yielding almost 40 kg milk/d whilst Chase (1993) suggested a level in excess of 40 g/kg was required for cows producing more than 10 000 kg milk per 305 day lactation. Of equal importance is the level of DM intake achieved during the first weeks after calving. Studies by Hattan et al. (2001) indicated week 36 Beever, D.E. 1 and 2 intakes equivalent to 0.76 of week 5 intake in high yielding cows, with a comparable value of 0.71 for lower yielding cows. In contrast Kertz et al. (1991) reported a value of 0.83 whilst Weiss (2001) found a value of only 0.67. Equally, Kertz et al. (1991) and Neilsen et al. (1983) reported maximum DM intake was not attained until week 8 to 15 of lactation, whilst Hattan et al. reported a value of 38.6 g/kg at week 6 with little evidence of any major increase thereafter. Comparable values for lower yielding cows in this study were 35.2 g/kg at week 6, declining marginally by weeks 18 and 24 (mean, 33.5 g/kg) in response to increased rates of body weight gain being noted in these cows. Appropriate strategies to improve feed intake are available. Alterations in the forage component of the ration can have marked effects on total intake as demonstrated by Phipps et al. (1995) who replaced 33% on a DM basis of the grass silage component of total mixed rations with either whole crop wheat silage, brewers grains, fodder beet or maize silage; in each case they noted significant improvements in total feed DM intake with commensurate improvements in milk yield, often with associated improvements in milk composition, especially milk protein. Whilst the studies of Phipps et al. (1995) were not designed to determine the mechanisms involved it is generally concluded that inclusion of other forages will alter the consistency of rumen contents, and in particular the physical characteristics of the digesta raft which in turn is believed to improve rumen function and promote rumination. The impact of feeding increased starch rather than protein in relation to the control of body condition score has already been discussed, whilst increasing the fat content of the ration appears to be a relatively easy option for increasing total ME intakes. However, this strategy does not always result in increased tissue energy repletion, with evidence that such diets may promote milk yield and thus exacerbate rather than alleviate the problem of compromised energy intake. Problems of feeding grass silage to high yielding cows have also been recognised and in the UK it is becoming increasingly common practice to remove all of the grass silage from high specification rations designed for high yielding cows. The study by Beever et al. (2002) provided some insight to this issue. Using high genetic merit multiparous cows, two experimental objectives were examined. Based on a ration of similar composition to those used previously for high yielding cows, containing 28% starch but no grass silage, the first objective was to determine the lactational response to increasing dietary starch content to 32%. In both rations, the forage component comprised of maize silage, dried lucerne and chopped grass hay but no grass silage. The second objective examined the incremental replacement of the forage component of the control ration with grass silage, whilst maintaining overall ration starch content. From calving to lactation week 20 control cows had a mean DM intake of 22.8 kg/d whilst higher starch inclusion increased feed DM intake to 24.4 kg/d. Grass silage inclusion at 20% of the total forage component was found to cause a small stimulation of feed intake compared with the control, although this difference was not statistically significant. Thereafter as an increasing proportion of the forage component was supplied as grass silage (40 and 60% respectively) the total DM intake declined to 21 kg/d, equivalent to 86% of that achieved on the increased starch ration which was more indicative of the feed intake that high yielding cows should be achieving. Such changes were associated with an overall decline in milk yield (6 kg/d) and it was concluded that grass silage inclusion in the ration of high genetic merit cows should not exceed 25% of the forage DM component or 12% of total ration DM. It was interesting to note however that milk fat content increased with increasing grass silage inclusion and overall milk fat yield was maintained whilst milk protein content was unaffected but a reduction in milk protein yield was inevitable. Whilst comparable data for high genetic merit cows grazing grass pasture are not available, feed intake from pasture is unlikely to sustain daily milk yields above 2527 kg. Accepting these data were obtained with modest yielding Friesians, it may be that such thresholds would be higher in genetically improved Holsteins. However it should be recognised that the rate of improvement in milk yield over the last decade in such cows has not been matched by a similar rate of increase in appetite. Cows grazing adequate pasture with daily yields of 27 kg milk of standard composition and not mobilising body tissue can be estimated to be consuming 200 MJ ME/d. Assuming genetically improved Holsteins may consume an additional 15% feed DM as grazed pasture, this increased intake of ME (+ 30 MJ/d) must be balanced against increased maintenance costs (Kebreab et al. 2003), whilst recognising that the energy cost of producing milk of lower constituent content, as often occurs with higher yielding cows, would be reduced. On this basis, it is concluded that grazed grass alone is unlikely to support more than 32 kg milk/d in Holsteins and achievement of this target would necessitate a fresh forage intake approaching 100 kg/d. Such levels of milk yield are considerably below expectations for many cows and is clear evidence of the limitations imposed on cows by the necessity to consume and process such large amounts of fresh forage within any one 24 h period. Based on the energ y requirements for lactation as recently recommended in the UK, the quantities of feed needed to support higher levels of milk production have been computed and are presented in Table 1. On the basis of the quantities of ME needed to support levels of milk production between 27 and 52 kg/d and known relationships between the intake of forage and concentrates (substitution rate), the data aim to determine the quantities of forage and concentrates needed to meet total energy demands for maintenance and lactation, assuming no change in body tissue mass. Assuming optimal forage quality (12 MJ ME/kg DM and low substitution rate), estimated ME Managing dairy cows for optimal performance 37 requirements for maintenance and a daily milk output of 27 kg could, on theoretical grounds, be met by consuming 17 kg DM/d as fresh forage. To sustain this level of performance both grass quality and availability must be optimised, especially when attainment of this level of forage DM intake is associated with a fresh weight intake approaching 100 kg/d. Increasing outputs of milk will require additional ME intake and even assuming a relatively low rate of forage substitution, the amount of concentrate required increases markedly to almost 10 kgDM/d whilst total forage intake was estimated to decline by only 2 kg DM/d. This resulted in an estimated total intake of feed of 25 kg DM/d with forage supplying only 60% of total nutrients, a level of consumption that can only be achieved only by using optimal feed ingredients. Maintaining the ME content of grazed grass at 12 MJ/kgDM throughout the whole season is virtually impossible and when a lower ME density (11.5 MJ/kgDM) was assumed (Option 2, Table 1) it was evident that with increasing milk yields, the contribution from grazed forage falls dramatically. The need for additional concentrates increased progressively to 13.6 kg DM/d, with forage now providing only 46% of DM intake (25.2 kg/d), and a total DM intake equivalent to 42 g DM intake/kg body weight which for high yielding Holsteins must be approaching maximum achievable level. The factors governing forage substitution rate are reasonably well understood and it is probably unwise to assume a value of only 0.2 kg/kg concentrate supplied when much higher values have been frequently reported. In the third option presented in Table 1, substitution rate was increased to 0.4 kg/kg and at this level the most serious consequences with respect to the potential contribution of grazed forage to the high yielding cow can be noted, with estimated concentrate requirement increasing to over 16 kgDM/d to meet the energy demands of cows yielding 52 kg milk/d. Meanwhile, forage consumption fell to 8.5 kg DM/d and contributed only 34% of total ration DM. Such findings question keeping such animals at pasture and expecting them to harvest their own food when at least 70% of total ME requirements are being supplied as concentrates. Furthermore, in many grazing situations, the daily concentrate allowance is often supplied only at milking. The wisdom of this practice, in which the high yielding cow is expected to consume in excess of 50% of total daily ME requirements in less than 2% of the whole day should be challenged, and may partly explain why the incidence of acidosis is increasing in such cows. Overall, it is therefore not surprising that many high yielding cows lose significant amounts of body condition whilst at pasture. However, dogma still exists in many parts of the world that grazed grass is the cheapest and most ideal feed for dairy cows, when clearly it has serious limitations and is probably the most significant reason why pasturebased high genetic merit cows have compromised lactations. Transition issues Whilst the practice of steaming up cows before calving has long been recognised, it is only over the last decade that scientific information has begun to replace anecdotal evidence. The period from drying off to calving is recognised as important in the annual cycle of milk production, through establishment of good appetites, acceptable milk yields and composition as well as minimisation of health and fertility problems. All are crucially important if profitable systems of milk Table 1 The effect of grazed forage quality, forage substitution rate and levels of milk production on the contributions of forage and concentrates required to meet total metabolizable energy requirements for maintenance and milk production, assuming zero body tissue change. A Forage options Milk yield kg/d 27 37 47 52 ME intake MJ/d 205 249 291 309 249 291 309 249 291 309 Grass DMI kg/d 17.0 16.2 15.3 15.0 14.5 12.4 11.6 11.4 9.3 8.5 ConcsB DMI kg/d 0 4.2 8.3 9.9 6.3 11.4 13.6 9.1 14.2 16.3 Total DMI kg/d 17.0 20.4 23.6 24.9 20.8 23.8 25.2 20.5 23.5 24.8 Forage content % total 100 79 65 60 70 52 46 56 40 34 1. Optimal forage quality 2. Reduced ME content 37 47 52 3. Reduced ME and intake 37 47 52 A B Forage options: 1. Grass ME 12 MJ/kgDM, optimal intake (no concs) 17 kg DM/d, forage substitution 0.2 kg DMI/kg conc DM fed 2. Grass ME 11.5 MJ/kgDM, optimal intake (no concs) 17 kg DM/d, forage substitution 0.4 kg DMI/kg conc DM fed 3. Grass ME 11.5 MJ/kgDM, optimal intake (no concs) 15 kg DM/d, forage substitution 0.4 kg DMI/kg conc DM fed Concentrate feed; 13 MJ ME/kgDM 38 Beever, D.E. production are to be achieved and a recent report from New York State, highlighting the incidence of production related diseases during the periparturient period, provided confirmatory evidence. Analysis of individual cow data from a number of herds identified seven important disease states, of which five had a median incidence day within 14 days of calving (Table 2). Retained foetal membranes and metritis were the highest risks during the periparturient period, whilst highest overall risks were for mastitis and ovarian cysts, albeit both had median incidence days later in lactation. Table 2 Incidence of major production_related diseases in Holstein cows. Disease Median incidence day 1 1 8 11 11 59 97 Assessment of lactational risk % 7.4 >5.0 >5.0 7.6 >5.0 9.7 9.1 Retained placenta Milk fever Ketosis Metritis Displaced abomasum Mastitis Ovarian cysts (from New York State survey) Feed intake and lactational performance From drying off until calving, primary management objectives consist of repletion of secretory and other metabolically active tissues, avoidance of peri parturient problems (diseases) and establishment of the subsequent lactation. It is advisable to complete body tissue repletion prior to drying off, as anecdotal evidence suggests achievement of body condition gain in non lactating cows is relatively difficult. This assumption does not however appear to have been adequately evaluated under rigorous experimental conditions and may be based on the belief that reduced feed intake at this time plus increasing foetal demands is likely to result in reduced partitioning of nutrients to body tissue repletion in favour of more demanding processes, which include tissue hypertrophy in preparation for the subsequent lactation. It is relatively clear that feed intake will be reduced once lactation ceases and unlikely to exceed 20 g DM/kg liveweight, of which at least half should be as reasonable quality forage. From drying off until approximately 7 days before expected calving, Burhans and Bell (1998) and others found appetite to be relatively constant and only seriously affected during the week prior to calving when intake reductions of >30% may be experienced. The most noticeable reductions occur on the day of calving and Grummer (1995) showed a strong relationship between DM intake achieved on the day prior to calving with that on day 21 after calving, stressing the importance of providing the periparturient cow an opportunity to maintain satisfactory levels of feed intake by providing palatable feeds that are both accessible and available in sufficient quantities. In most cows, feed intake increases quite rapidly in the immediate postcalving period although peak intake is unlikely to be achieved until week 8 of lactation or later. During this time nutrient demands to support milk production will exceed nutrient intake and body tissue mobilisation will be inevitable. Whilst this is an acceptable phenomenon in all lactating mammals, avoidance of excessive tissue loss is desirable through stimulation of feed intake. Burhans and Bell (1998) showed a strong inverse relationship between plasma nonesterified fatty acid (NEFA) concentrations and dry matter intake from 18 days prior until 18 days post calving with a pronounced increase in NEFA levels at day 6 prior to calving coinciding with detectable reductions in feed intake. NEFA levels peaked at day 4 postcalving but were reduced to 50% of peak values by day 18. To control such processes and prevent the accumulation of ketone bodies, indicative of compromised liver metabolism and possibly giving rise to sub clinical or even clinical ketosis, promotion of feed intake after calving is essential. Abrupt changes to the ration should be avoided and current practice recommends inclusion of part of the lactation ration in the total ration for approximately 2 to 3 weeks pr