Troubleshooting Milk Fat Challenges On Commercial
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1. 1 Factors that affect substrate supply and availability Given that the fatty acid isomers that cause MFD are intermediates in the pathways of ruminal biohydrogenation it is logical that the amount of initial substrate linoleic acid and perhaps lino lenic acid may be related to the amount of the key fatty acid intermediates that are produced and hence are subject to passage from the rumen As indicated above linoleic acid is the predominant long chain fatty acid in corn and corn byproducts Estimates of linoleic acid intake using CPM Dairy in herds in the Northeastern US in which corn silage comprises the majority of the forage 21 base in the ration and oilseeds are essentially the sole source of added dietary fat can approach or exceed 400 to 500 g d Furthermore ready availability of corn byproducts e g distillers grains at low cost in the feed industry can result in substantial inclusion of these byproducts in least cost rations Commonly book values are used for the fat content of distillers grains in ration formulation however interaction with a number of feed industry professionals suggests that the fat content of distillers grains can vary widely Furthermore the fatty acids in wet distill ers grains likely are more rapidly available than in dry distillers grains which further affects the dynamics of fatty acid biohydrogenation in the rumen Based upon general survey of the litera ture an effect of grain pr2. 46 Propionate 21 46 Butyrate 11 9 Acetate propionate 3 2 1 0 Ruminal VFA production moles d Acetate 29 4 28 1 Propionate 13 3 31 0 Whole body entry of butyrate moles d 7 0 9 1 1 Data compiled from Davis et al 1967 Bauman et al 1971 Palmquist et al 1969 Adapted from Bauman and Grii nari 2001 Table 2 Range of positional and geometric isomers of trans 18 1 and conjugated linoleic acids CLA and their ruminal outflow g d in lactating dairy cows Trans C18 1 Conjugated Linoleic Acids Ruminal Outflow Ruminal Outflow poner Min Max PENA Min Max Trans 4 0 4 2 0 trans 7 cis 9 lt 0 01 0 01 Trans 5 0 4 3 4 trans 7 trans 9 lt 0 01 0 02 Trans 6 8 0 4 16 2 trans 8 cis 10 lt 0 01 0 3 Trans 9 1 4 13 1 trans 8 trans 10 lt 0 01 0 10 Trans 10 1 5 114 0 cis 9 trans 11 0 31 2 86 Trans 11 17 0 148 0 trans 9 trans 11 0 14 0 29 Trans 12 1 9 20 8 trans 10 cis 12 0 02 1 84 Trans 13 14 4 2 60 3 trans 10 trans 12 0 05 0 23 Trans 15 2 0 29 0 cis 10 trans 12 0 08 0 29 Trans 16 2 3 18 2 cis 11 trans 13 0 01 0 33 trans 11 cis 13 lt 0 01 0 46 trans 11 trans 13 0 09 2 02 cis 12 trans 14 0 12 0 85 trans 12 trans 14 0 07 0 19 1 Adapted from Bauman and Lock 2006 Data were derived from five studies where samples were collected from either the omasum or duodenum of lactating dairy cows Piperova et al 2002 Shingfield et al 2003 Qiu et al 2004 Loor et al 2004 2005 pr November 13 14 Grantville PA
3. Brown 1970 Low fat milk syn drome In A T Phillipson Ed Physiology of Digestion and Metabolism in the Ruminant pp 545 565 Oriel Press Limited Newcastle upon Tyne UK de Veth M J J M Griinari A M Pfeiffer and D E Bau man 2004 Effect of CLA on milk fat synthesis compari son of inhibition by methyl esters and free fatty acids and relationships among studies Lipids 39 365 372 Duffield T F and R Bagg 2000 Use of ionophores in lactating dairy cattle A review Can Vet J 41 388 394 Duffield T R Bagg D Kelton P Dick and J Wilson 2003 A field study of dietary interactions with monensin on milk fat percentage in lactating dairy cattle J Dairy Sci 86 4161 4166 Fellner V F D Sauer and J K G Kramer 1997 Effect of nigericin monensin and tetonasin on biohydrogenation in continuous flow through ruminal fermenters J Dairy Sci 80 921 928 Griinari J M and D E Bauman 2006 Milk fat depression concepts mechanisms and management In K Sejrsen T Hvelplund and M O Nielsen Eds Ruminant physiol ogy Digestion metabolism and impact of nutrition on gene expression immunology and stress pp 383 411 Wageningen Academic Publishers Wageningen The Netherlands Griinari J M D A Dwyer M A McGuire D E Bauman D L Palmquist and K V V Nurmela 1998 Trans octadecenoic acids and milk fat depression in lactating dairy cows J Dairy Sci 81 1251 1261 Har
4. E C L Davis and H F Bucholtz 1971 Propionate production in the rumen of cows fed either a control or high grain low fiber diet J Dairy Sci 54 1282 1287 Bauman D E and J M Griinari 2001 Regulation and nutritional manipulation of milk fat low fat milk syn drome Livestock Prod Sci 70 15 29 Bauman D E and J M Griinari 2003 Nutritional regula tion of milk fat synthesis Ann Rev Nutr 23 203 227 Bauman D E and A L Lock 2006 Concepts in lipid digestion and metabolism in dairy cows Proceedings Tri State Nutr Conf Ft Wayne IN in press Baumgard L H B A Corl D A Dwyer A Saebo and D E Bauman 2000 Identification of the conjugated linoleic acid isomer that inhibits milk fat synthesis Am J Physiol 278 R179 R184 Bernal Santos G J W Perfield H D M Barbano D E Bauman and T R Overton 2003 Production responses of dairy cows to dietary supplementation with conjugated linoleic acid CLA during the transition period and early lactation J Dairy Sci 86 3218 3228 24 Castaneda Gutierrez E T R Overton W R Butler and D E Bauman 2005 Dietary supplements of two doses of calcium salts of conjugated linoleic acid during the transition period and early lactation J Dairy Sci 88 1078 1089 Davis C L 1967 Acetate production in the rumen of cows fed either control or low fiber high grain diets J Dairy Sci 50 1621 1625 Davis C L and R E
5. E Brown and D S Sachan 1969 Availability and metabolism of various substrates in ruminants V Entry rate into the body and incorporation into milk fat of D B hydroxybutyrate J Dairy Sci 52 633 638 Perfield I J W and D E Bauman 2005 Current theories and recent advances in the biology of milk fat depression Proc Cornell Nutr Conf Feed Manuf Cornell Univ Ithaca NY pp 95 106 Perfield H J W G Bernal Santos T R Overton and D E Bauman 2002 Effects of dietary supplementation of rumen protected conjugated linoleic acid in dairy cows during established lactation J Dairy Sci 85 2609 2617 Perfield II J W A L Lock A S b J M Griinari and D E Bauman 2005 Trans 9 cis 11 conjugated linoleic acid CLA reduces milk fat synthesis in lactating dairy cows J Dairy Sci 88 Suppl 1 211 Abstr Peterson D G L H Baumgard and D E Bauman 2002 Milk fat response to low doses of trans 10 cis 12 conju gated linoleic acid CLA J Dairy Sci 85 1764 1766 Piperova L S J Sampugna B B Teter K F Kalscheur M P Yurawecz Y Ku K M Morehouse and R A Erdman 2002 Duodenal and milk trans octadecenoic acid and conjugated linoleic acid CLA isomers indicate that postabsorptive synthesis is the predominant source of cis 9 containing CLA in lactating dairy cows J Nutr 132 1235 1241 Qiu X M L Eastridge and J L Firkins 2004 Effects of dry matter intake a
6. Linolenic Acid Linoleic Acid cis 9 cis 12 cis 15 Cig 3 cis 9 cis 12 Cig 0 cis 9 trans 11 cis 15 C4s 3 cis 9 trans 11 CLA trans 11 cis 15 C4s 2 trans 15 or cis 15 Cig trans 11 Cis Stearic Acid C4s 0 Figure 1 Generalized scheme of ruminal biohydrogenation of linoleic and linolenic acids to stearic acid Adapted from Harfoot and Hazlewood 1997 linoleic acid cis 9 cis 12 18 2 e Altered fermentation conjugated linoleic acid conjugated linoleic acid cis 9 trans 11 CLA trans 10 cis 12 CLA trans 11 18 1 trans 10 18 1 stearic acid 18 0 stearic acid 18 0 Figure 2 Generalized scheme of ruminal biohydrogenation of linoleic acid under normal conditions and during diet induced milk fat depression dotted line Adapted from Griinari and Bauman 1999 2007 Penn State Dairy Cattle Nutrition Workshop Hi 27
7. Passage to the intestine of as little as 1 5 to 2 grams per day of this fatty acid isomer would be sufficient to reduce milk fat syn thesis by 10 to 15 which is within the magnitude of MFD that has economic consequences for dairy producers in North America Although the potent effects of trans 10 cis 12 CLA on milk fat synthesis are the most well characterized it is likely that other related fatty acid isomers have effects on milk fat synthesis As mentioned above advances in analytical techniques have enabled the characterization of a large number of isomers of trans C 18 1 and CLA Table 2 the specific biological functions if any of many of these isomers remain uncharacter ized Recently Perfield et al 2005 showed that trans 9 cis 11 CLA caused a reduction in milk fat synthesis and another report indicated that the cis 10 trans 12 CLA also reduced milk fat syn thesis in lactating dairy cows S b et al 2005 It is likely that further research and advances in analytical techniques will identify other biologi cally potent fatty acid isomers that are produced during ruminal biohydrogenation of long chain unsaturated fatty acids Application of the Biohydrogenation Theory to Troubleshooting Diet induced MFD on Commercial Dairy Farms The biohydrogenation theory provides an attrac tive unifying conceptual framework for trouble shooting milk fat issues on commercial dairy 2007 Penn State Dairy Cattle Nutrition Works
8. Troubleshooting Milk Fat Challenges On Commercial Dairy Farms Thomas R Overton Dale E Bauman and Adam L Lock Department of Animal Science Cornell University Ithaca NY Department of Animal Science University of Vermont Burlington Introduction Although the topic of milk fat depression MFD is not a new topic in the dairy industry both industry and research interest in MFD in North America has intensified dramatically during re cent years Most pricing systems in the U S are now based on yields of milk components with greater value placed upon yields of milk fat and milk protein Recent data summaries indicate that approximately 38 of herds shipping milk into the Mideast Federal Order 33 primarily Indiana Michigan Ohio and Pennsylvania experienced a short term one to three month period in any year decrease more than 1 SD decrease below the mean milk fat test lt 3 46 in milk fat test Bailey et al 2005 Until recently milk pro duction quotas tied to milk fat yield in Canada resulted in perceived economic advantages in decreasing milk fat percentage while increasing kilograms of milk protein sold per cow However recent changes in guidelines for milk composi tion in Canada have dictated a minimum ratio of milk fat to milk protein in milk sold effectively eliminating the economic advantage of purposely producing milk with lower milk fat percentage During the past decade substantial evolution ha
9. ave been discussed include acetate insufficiency beta hydroxybutyrate BHBA insufficiency and the glucogenic insulin theory of MFD Approximately 50 of milk fatty acids are synthesized de novo from acetate and BHBA formed from butyrate produced in the rumen in the mammary gland these typically are the short and medium chain fatty acids and approximately half of the 16 carbon fatty acids Bauman and Griinari 2001 Although the sub strate supply theories are attractive e g acetate and butyrate are required for fatty acid synthesis by the mammary gland therefore a deficiency of ruminal production of these VFA in scenarios of low ruminal fiber digestion must cause MFD and are still referred to in the dairy industry it is unlikely that they explain MFD This argument 19 is summarized in Table 1 Concurrent with the substantial decrease in milk fat yield when a high grain low forage diet was fed was a substantial decrease in the molar percentage of acetate and a small decrease in the molar percentage of bu tyrate in ruminal fluid The molar percentage of propionate was increased sharply resulting in a dramatic decrease in the acetate to propionate ratio in ruminal fluid These types of approaches continue to be used commonly by researchers and others to imply that a change in molar percentage of a VFA in ruminal fluid must reflect a change in production rate However if we refer to data for ruminal production measured us
10. d therefore passage of fermentation acids from the rumen Salt also promotes water consumption however it is un likely that these factors will be of consequence unless unusually large amounts of free choice salt or sodium bicarbonate are consumed at the herd level 23 Summary Low milk fat percentage and yield is an impor tant economic issue to dairy farms across North America Research conducted during the past decade has markedly heightened our understand ing of the etiology of milk fat depression and this understanding can be translated into conceptual approaches for troubleshooting milk fat issues on commercial dairy farms Ongoing university and industry based research will further enhance our ability to diagnose the causes of milk fat issues on individual farms and to provide detailed guide lines for preventing or troubleshooting milk fat problems on dairy farms References AbuGhazaleh A A and Jenkins T C 2004 Short commu nication docosahexaenoic acid promotes vaccenic acid accumulation in mixed ruminal cultures when incubated with linoleic acid J Dairy Sci 87 1047 1050 Allen M S 1997 Relationship between fermentation acid production in the rumen and the requirement for physi cally effective fiber J Dairy Sci 80 1447 1462 Bailey K W C M Jones and A J Heinrichs 2005 Eco nomic returns to Holstein and Jersey herds under multiple component pricing J Dairy Sci 88 2269 2280 Bauman D
11. ddition of buffer and source of fat on duodenal flow and concentration of conjugated linoleic acid and trans 11 C18 1 in milk J Dairy Sci 87 4278 4286 Russell J B and J M Chow 1993 Another theory for the action of ruminal buffer salts Decreased starch fermentation and propionate production J Dairy Sci 2007 Penn State Dairy Cattle Nutrition Workshop W 7176 826 830 S b A P C S b J M Griinari and K J Shingfield 2005 Effect of abomasal infusions of geometric isomers of 10 12 conjugated linoleic acid on milk fat synthesis in dairy cows Lipids 40 823 832 Shaver R D 2005 Feeding to minimize acidosis and laminitis in dairy cattle Proc Cornell Nutr Conf Feed Manuf Cornell Univ Ithaca NY pp 49 60 Shingfield K J S Ahvenjarvi V Toivonen A Arola K V V Nurmela P Huhtanen and J M Griinari 2003 Effect of dietary fish oil on biohydrogenation of fatty acids and milk fatty acid content in cows Anim Sci 77 165 179 Von Keyserlingk M A G and T J DeVries 2005 The un explored frontier A perspective on how feeding behavior may change our understanding of dairy cattle nutrition Proc Cornell Nutr Conf Feed Manuf Cornell Univ Ithaca NY pp 71 82 25 Table 1 Acetate and butyrate shortage theories and milk fat depression Item Normal diet High grain low forage diet Milk yield No change Milk fat g d 683 363 Ruminal VFA molar percentage Acetate 67
12. foot C G and G P Hazlewood 1997 Lipid metabo lism in the rumen In P N Hobson and C S Stewart Eds The Rumen Microbial Ecosystem pp 382 426 Chapman amp Hall London UK Harvatine K J and M S Allen 2006 Fat supplements af fect fractional rates ofruminal fatty acid biohydrogenation and passage in dairy cows J Nutr 136 677 685 Lock A L K J Harvatine I R Ipharraguerre M E Van Amburgh J K Drackley and D E Bauman 2005 The dynamics of fat digestion in lactating dairy cows what does the literature tell us Proc Cornell Nutr Conf Feed Manuf Cornell Univ Ithaca NY pp 83 94 November 13 14 Grantville PA Loor J J K Ueda A Ferlay Y Chilliard and M Doreau 2004 Biohydrogenation duodenal flow and intestinal digestibility of trans fatty acids and conjugated linoleic acids in response to dietary forage concentrate ratio and linseed oil in dairy cows J Dairy Sci 87 2472 2485 Loor J J K Ueda A Ferlay Y Chilliard and M Dor eau 2005 Intestinal flow and digestibility of trans fatty acids and conjugated linoleic acids CLA in dairy cows fed a high concentrate diet supplemented with fish oil linseed oil or sunflower oil Anim Feed Sci Technol 119 203 225 McGuire M A J M Griinari D A Dwyer and D E Bau man 1995 Role of insulin in the regulation of mammary synthesis of fat and protein J Dairy Sci 78 816 824 Palmquist D L C L Davis R
13. he amount of chewing and salivary buffer produced per unit of rumen fermentable organic matter RFOM consumed decreases as RFOM increases This has implica tions for the risk of higher producing cows who also have higher DMI to have lower ruminal pH or different dynamics of ruminal pH during any 24 h period In addition to factors associated with diet formulation practicing nutritionists are well aware of the on farm factors related to feeding management DM changes variation in mixing and measurement of ingredient quantities that affect the translation of the ration on paper to the ration in the feedbunk Finally other aspects re lated to management or the environment feeding frequency stocking density heat stress among others can have marked effects on meal patterns of dairy cows and hence the dynamics of ruminal pH in any 24 h period reviewed by Shaver 2005 Von Keyserlingk and DeVries 2005 Despite our general understanding of these factors the degree and duration of low ruminal pH required to cause sufficient flux of linoleic acid through alternative pathways of ruminal biohydrogenation is not known Although the implications of low ruminal pH for production of the MFD causing intermediates have been well considered it is not known which other factors can also cause changes in the ru men bacteria population resulting in an increased flow of fatty acids through alternate pathways of ruminal biohydrogenation We hyp
14. hop WwW farms for several reasons First changes in milk fatty acid profile caused by infusion of trans 10 cis 12 CLA into the abomasum are consistent with common dietary situations high grain low forage high unsaturated oil intake that cause MFD and are unlike the changes in milk fatty acid profile caused by glucose or insulin infusion as described above Second this theory helps reconcile prob lems with low milk fat percentage absent overt signs of ruminal acidosis e g by conventional evaluation on a dairy farm rumen health seems excellent yet the herd has low milk fat test Third it enables us to conceptualize the potential roles of known modifiers of the ruminal environment e g monensin in interacting with other factors of the ruminal environment to result in MFD in some cases Finally field experience troubleshoot ing milk fat issues on dairy farms suggests that MFD occurs as a result of several concurrent diet or management factors rather than as a result of a single factor and our understanding of the biohy drogenation theory offers many opportunities for interactions of diet and management components to result in MFD We can divide the factors that can contribute to MFD into four general categories 1 Factors that affect substrate supply and availability 2 Factors that result in an altered ruminal environment 3 Factors that influence biohydrogenation rate and 4 Factors that influence rate of passage
15. ing isotopic ap proaches of VFA from cows fed these two types of diets at the bottom of Table 1 it is evident that the changes in molar proportions of VFA in the top part of the table were driven only by substan tially increased production of propionate and that production rates of acetate and butyrate were not affected by diet The increased molar percentage and production rate of propionate when a high grain low forage diet was fed that is depicted in Table 1 led some to consider the glucogenic insulin theory of MED This theory suggests that large amounts of propionate produced in the rumen result in pro duction of large amounts of glucose by the liver and subsequently increased circulating insulin concentrations The mammary gland is considered to be somewhat insensitive to insulin compared with tissues such as adipose tissue and muscle therefore it was proposed milk fat synthesis de creases due to a competition among tissues for substrates for milk fat synthesis with diets that increase circulating insulin causing a preferen tial channeling of substrates to non mammary However cows subjected to a long term hyper insulinemic euglycemic clamp experimental technique in which the effect of insulin can be determined without the confounding effects of hypoglycemia did not decrease milk fat synthesis compared to control cows McGuire et al 1995 in fact insulin or glucose infusion results in very different profiles of mi
16. ith MFD led Bauman and Griinari 2001 to evolve the trans theory of MFD into the biohydrogena tion theory through which they hypothesized that under certain dietary conditions the pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates which are potent inhibitors of milk fat synthesis Research conducted before the development of the biohydrogenation theory of MFD and that conducted during the past few years since it was advanced suggest that this theory represents a unifying theory for diet induced MFD The most well studied altered pathway of ruminal biohy drogenation of linoleic acid is depicted in Figure 2 in which under situations of altered ruminal fermentation commonly low ruminal pH linoleic November 13 14 Grantville PA acid C18 2 is first isomerized to trans 10 cis 12 conjugated linoleic acid CLA and then reduced to trans 10 C18 1 before being further reduced to stearic acid C18 0 Using pure isomers of CLA infused into the abomasum Baumgard et al 2000 determined that trans 10 cis 12 CLA was a potent inhibitor of milk fat synthesis In contrast infusion of cis 9 trans 11 CLA the CLA isomer produced through normal ruminal biohydrogena tion Figure 1 into the abomasum did not affect milk fat synthesis In subsequent experiments it was found that the response of milk fat to infusion of trans 10 cis 12 CLA was dose dependent de Veth et al 2004
17. lk fatty acids compared to diet induced MFD Bauman and Griinari 2001 20 suggesting that this mechanism does not explain diet induced MFD The second category of theories for the cause of MFD relates to the production of specific fatty acids in the rumen in situations of diet induced MFD that directly inhibit milk fat synthesis in the mammary gland Davis and Brown 1970 observed that MFD commonly was associated with increased concentrations of trans fatty acids in milk fat Trans fatty acids are produced in the rumen as intermediates of the biohydrogenation of linoleic and linolenic acids to stearic acid Figure 1 Linoleic and linolenic acids represent a large percentage of the fatty acids found in most forages and other plant based feedstuffs fed to dairy cattle cereal grains oilseeds etc Biohydrogenation of these fatty acids in the rumen by rumen bacteria is extensive and most of the linoleic and linolenic acid consumed by cows is biohydrogenated fully to stearic acid before leaving the rumen Lock et al 2005 however advances in analytical tech niques during the past few years have led to the determination that varying quantities of a large number of trans C18 1 monoenes and conjugated linoleic acids pass from the rumen to the lower tract for absorption Bauman and Lock 2006 Table 2 These findings coupled with the finding that only certain trans fatty acids and isomers of conjugated linoleic acid are associated w
18. n and as a result the rumen outflow of trans fatty acids increases Bauman and Griinari 2003 In vitro studies with mixed cultures of rumen bacteria have established that docosahexaenoic acid one of the long chain omega 3 fatty acids in fish oil is are responsible for this effect AbuGhazaleh and Jenkins 2004 4 Factors that influence rate of passage A fourth area that influences the likelihood that biohydrogenation intermediates responsible for MFD may pass from the rumen to the lower tract is rate of passage This has been less well characterized than the other factors but the possibility is logical As described above cows consuming greater amounts of RFOM have less chewing activity and buffer production per unit of RFOM than cows consuming smaller amounts of RFOM Cows that are consuming larger amounts of RFOM are those cows with higher DMI hence those cows also will have greater rates of passage from the rumen This simply means that those cows or herds with higher DMI likely will be more at risk for MFD and thus the margin of error is smaller in those herds In addition to DMI another factor that may be related to rate of passage particularly liquid rate of passage is consumption of buffer salts or salt particularly in free choice form These have not been studied in a controlled manner however Russell and Chow 1993 suggested that sodium bicarbonate may increase ruminal pH in part by increasing water intake an
19. ocessing in addition to potentially impacting the ruminal environment may be to increase fatty acid availability in the rumen in some situations 2 Factors that result in an altered ruminal environment These factors adhere most closely to those tradi tionally considered when troubleshooting MFD on dairy farms although it is likely that some factors not commonly considered also may interact with diet formulation to produce an altered ruminal environment leading to the production of trans 10 cis 12 CLA or related biohydrogenation inter mediates One major factor that leads to flux of fatty acids through alternate pathways of ruminal biohydrogenation is low ruminal pH Ruminal pH is thought to represent the balance between acid production from ruminal fermentation of carbohy drates buffer production from salivary and dietary sources and the rate of removal of fermentation acids from the rumen by absorption or passage Allen 1997 Dynamic interactions of these fac tors can result in marked changes in ruminal pH through any 24 h period These factors have been well reviewed Shaver 2005 and include dietary carbohydrate profile and rates of degradation of these carbohydrate fractions as affected by source processing and moisture physically effective NDF peNDF supply as affected by source and 22 particle size and production of salivary buffers as a function of peNDF supply and source Shaver 1995 also illustrated that t
20. ot appear to have marked effects on milk fat during early lacta tion Duffield and Bagg 2000 these data are consistent with those that suggest that milk fat is refractory to the effects of low doses of trans 10 cis 12 CLA until several weeks into lactation Ber nal Santos et al 2003 Castaneda Gutierrez et al 2005 During established lactation monensin supplementation can result in decreased milk fat percentage and yield Duffield and Bagg 2000 likely as a result of interactions with other dietary or management factors that predispose cows to experience MFD Duffield et al 2003 reported that both increasing dose of monensin and low particle size in the TMR were risk factors for MFD They also reported that component fed herds and herds feeding higher concentrations of nonstructural carbohydrates were at lower risk for low milk fat test when monensin was fed We currently are conducting a large field study using herds in the Northeast and Upper Midwest in which we are relating dietary factors including fatty acids and management factors to milk fatty acid composition in order to learn more about the interactions of monensin with other factors and subsequent MFD on dairy farms 2007 Penn State Dairy Cattle Nutrition Workshop WwW Dietary components can also have effects on specific steps in the biohydrogenation process For example fish oil affects those rumen bacteria catalyzing the terminal step in biohydrogenatio
21. othesize that factors such as ensiled feeds with abnormal fer mentation profiles particularly high acetic acid corn silages or moldy feeds may also cause the changes in biohydrogenation required to cause MFD however these factors remain unstudied in a controlled manner 3 Factors that influence biohydrogenation rate It is also logical that factors that affect the rate of biohydrogenation of fatty acids in the rumen November 13 14 Grantville PA may change the likelihood that intermediates responsible for MFD will pass from the rumen to the lower tract where they can be absorbed and directly inhibit milk fat synthesis in the mammary gland Harvatine and Allen 2006 It is important to think of these factors as not being causative for MFD rather they interact with a predisposing condition e g altered ruminal environment to accentuate the effects on milk fat Although it is likely that other factors exist that affect biohydrogenation rates of fatty acids the effects of monensin are among the more well characterized Monensin increases maintenance requirements of gram positive bacteria in the ru men by altering ion channels which renders these bacteria less competitive in the ruminal environ ment Duffield and Bagg 2000 The net result is changes in the ruminal bacterial population that appear to decrease rates of biohydrogenation of linoleic acid in the rumen Fellner et al 1997 Monensin supplementation does n
22. s occurred in our understanding of the etiology of MED As will be discussed below we do not fully understand all of the ruminal conditions that can result in predisposition for MFD however this new understanding of the mechanisms for MFD has facilitated our ability to troubleshoot milk fat problems on commercial dairy farms These mechanisms and the reasons why previously held theories for MFD likely are not applicable will be reviewed briefly in this paper however the reader is referred to other recent reviews that describe 2007 Penn State Dairy Cattle Nutrition Workshop WwW these in more detail Bauman and Griinari 2001 2003 Perfield and Bauman 2005 Bauman and Lock 2006 The subsequent emphasis of this paper will be to discuss dietary and management factors that affect the predisposition of cows and herds to MFD Our understanding of many of these remains conceptual we expect that after research conducted during the next few years is summarized our recommendations will be more quantitative Theories of Milk Fat Depression In general theories of the cause of MFD can be divided into two broad categories those sug gesting that substrate supply for milk fat synthesis is limiting in situations in which MFD occurs and those suggesting that MFD is caused by direct inhibition of milk fat synthesis in the mammary gland Bauman and Griinari 2001 Theories relating to substrate limitation of milk fat syn thesis that h
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