WHERE ARE WE NOW WITH BST ?

by

Gary F . Hartnell, PhD, PAS and Jorge Estrada, M SAnimal Sciences Division

Monsanto CompanySt . Louis, MO

Introductio n

Improving the profitability of the dairy enterprise is the goa lfor dairy producers to survive in today's markets . Over the year sdairymen have adopted new technologies such as milking machines, bul ktanks, milking parlors, group housing, and total mixed diets to hel pimprove their labor efficiency .

As each decade passes, laborefficiency increases so that more cows are milked per person . I naddition, dairymen have also realized that by increasing the productionoutput per cow, their profitability increases because they are reducin gthe maintenance cost per unit of milk produced . Therefore, dairymenhave adopted technologies such as artificial insemination usin gsuperior genetics, DHI, feed additives and good nutrition and healt hprograms to achieve more milk per cow . Since feed is a major cost i nthe production of milk, any improvement in the utilization of feed i nthe production of milk (increase in yield of milk and milk component sin relation to the nutritional cost of maintenance) offers another too lto improve profitability .

With the recent advent of recombinant bovine somatotropin (bST )technology, another method for improving productive efficiency is no wavailable because milk yield per cow is increased allowing a greate rproportion of the consumed nutrients to be used for milk production a scompared to maintenance . Never before has a product been so thoroughl yresearched prior to commercialization as bST . Over 1500 studies usingmore than 30,000 dairy cows throughout the world have been used . O nNovember 5, 1993, the Food and Drug Administration (FDA) approve dMonsanto's bST product (POSILA C' bovine somatotropin) . Since February4, 1994 POSILAC has been commercially sold in the United States . Thi spaper emphasizes what we have learned prior to and sinc ecommercialization of POSILAC (currently the only bST product approve dfor use in the U .S .) . In addition, the importance of nutrition andmanagement in optimizing the response of the dairy cow administered bSTis discussed .

U .S . Milk Consumption Since Approva l

•

BST approval has had virtually no impact on the consumer' s

®POSILAC is a registered trademark of Monsanto Company

buying decisions .

Consumer acceptance of milk has remained unchanged since earl y

February when POSILAC bovine somatotropin by Monsanto first went int o

commercial use on U .S . Dairy Farms according to February U .S .

Department of Agriculture milk consumption figures (1) . Despite

widespread media coverage which has resulted in consumer awareness o f

bST jumping from 28 to 63 percent (tracking studies conducted b yGallup) since FDA approval in November, the buying habits of consumer s

remained unchanged . Jim Barr, Chief Executive Officer of the Nationa lMilk Producers Federation, has reported similar findings with thei r

marketing and tracking data as compared to the Gallup survey (1) . Thi sis great news to the dairy industry which had expressed concern abou thow consumers would respond to this new technology .

Milk Yiel d

• BST adoption has had little impact on the total milk productio nin February .

• In the U .S . the milk response (lbs/cow/day) to POSILAC appear sto be independent of the rolling herd average .

In the U .S .commercial field trials, milk response to POSILAC range dbetween 5 to 15 lbs/cow/day . Reports from around the countr yindicate producers are getting responses similar to if no tbetter than these results .

USDA data for fluid milk sales nationwide actually showed a 0 .0 5percent increase over the same period in 1993 (1) . The Northeastbroke even, the Southeast increased 0 .3 percent, the Midwest droppedby 0 .8 percent, the Southwest increased by 2 .3 percent and the Wes tincreased by 2 .8 percent with February of 1993 . New York was theonly top-10 dairy state east of the Mississippi River that did not los eproduction, holding even with last year's levels (2) . Cropp predict shealthy milk prices for the year, with the worst-case scenario yieldin gan average M-W of no lower than $12/cwt (2) .

Administration of bST has resulted in a significant milk yiel dincrease in lactating dairy cattle (3) . Clinical studies evaluatin gthe efficacy of POSILAC bovine somatotropin in first calf heifers an dsecond lactation and older cows have shown milk responses averaging 8 . 5and 8 .8 lbs/cow/day, respectively (4) . Milk production increased withi nthe first week and remained above controls for the remainder of th elactation . When milk yield is plotted on a daily basis, the respons eto POSILAC bovine somatotropin reaches a peak about 8-9 days afte radministration and then declines until the next supplementation at day14 . In all cases the yield remained above the control level during th e14-day period . The maximum increase in milk yield occurs after 3 t o4 injections . Fat-corrected milk (3 .5%) response averaged 7 .7 and 10 . 2lbs/cow/day for first calf heifers and cows, respectively, in•thes esame studies .

Responses to 12 weeks of supplementation with POSILAC wer e

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evaluated in 29 commercial dairy herds (one Jersey, 28 Holstein )involving 2298 cows in 10 states (4) . Rolling herd averages for the28 Holstein herds ranged from 14,791 to 25,500 lbs . Administration o fPOSILAC resulted in a significant increase in milk yield (range : 5 . 7to 18 .5 lbs/cow/day ; mean : 11 .2 lbs/cow/day) . The magnitude of mil kresponse (lbs/cow/day) appeared to be similar regardless of the rollingherd average . Reports from around the country indicate similar toif not better than these results .

Milk Comoositio n

Composition of milk from cows supplemented with POSILAC bovin esomatotropin is similar to the milk composition of control cows .No effect of practical significance was observed regarding th enutritional and manufacturing properties of milk from cowssupplemented with POSILAC .

The concentration of milk fat and protein vary due to factor ssuch as genetics, breed, stage of lactation, environment, season o fthe year, milking management, cow age, health, diet composition, an dnutritional status . These same factors also affect the mil kcomposition of cows supplemented with POSILAC and the variation in th econcentration of milk nutrients are of the same magnitude as tha tnormally observed within the herd . One example of this is the impac tof nutritional status . In the early stages of POSILAC administration ,increases in milk fat and decreases in milk protein may occur wheneve rthe milk yield increases cause changes in energy and protein balanc ein the cow such that body fat and protein stores are mobilized to mee tthe increased nutrient demands . These changes in energy balance aresimilar to, but smaller than, the changes that normally occur at th eonset of lactation . With prolonged administration of POSILAC, cow sgradually adjust their feed intake to meet their increased nutrien trequirements, and nutrient balance is restored . In general, thepercentages of milk fat and protein were not different for POSILAC an dcontrol cows when POSILAC was administered over a full lactation (week s9 - 44 of lactation) . On a practical level, proper nutritiona lmanagement is essential for a sustained response to POSILAC and thi sresults in normal fat, protein and lactose content of milk .

Feed Intake

• Reports on the effect of POSILAC on feed intake has beenconsistent with previous studies .

• Feed intake increases gradually and by two to seven weeks afte rbST initiation extra nutrients are provided to meet the need sfor the increased milk production . POSILAC supplementatio nresults in an increased nutrient intake when cows respond wit han increase in milk production . Peak feed intake followed peakmilk yield by several weeks . The increase in intake associate dwith POSILAC supplementation occurred earlier for primiparou scows than multiparous cows . Nutrient balances when average dover the treatment period were unaffected by bST administration .

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• Overall, cows administered POSILAC generally adjust thei rvoluntary intake in a predictable fashion relative to the extr anutrients needed for the increased production . NRC guidelinescan be utilized .

In general, the increase in dry matter and energy intake matche sthe increase in that required for the extra milk produced (3,4) . Drymatter and net energy for lactation (NEL) intakes were greater for bot hfirst calf heifers and cows groups during the use of POSILAC for th e36 weeks of lactation . Overall, dry matter intake for first cal fheifers and cows administered POSILAC was increased by 3 .5 lbs/cow/da yand 3 .3 lbs/cow/day, respectively . As a rule of thumb, dry matte rintake is increased 1 lb for every 2 .5 to 3 .0 lbs of milk increase .Dry matter intake appeared to increase beyond the controls at about 2to 3 weeks and 6 to 7 weeks after administration of POSILAC in firs tcalf heifers and cows, respectively . Dry matter and NEL intake o fsupplemented cows peaked higher than the controls and remained highe rthroughout the supplementation period .

Enemy Balance, Body Conditio n

• Energy balance when averaged over the supplementation period an dmean body weight change were unaffected by POSILACsupplementation . Body fat mky decrease with the onset ofPOSILAC supplementation (if they are in a negative energybalance) until a balance of additional dietary energy i sprovided by the increase in DMI (3) . Cows in a positive energybalance after the initiation of POSILAC will maintain their bod ycondition until DMI increases . Regaining optimal body conditionmay take longer in cows administered bST .

• Cows administered POSILAC need to regain body condition over th elactation cycle just like cows not administered POSILAC .

Managing for proper body condition is very important . Failureto regain adequate body reserves before dryoff and the nex tcalving may suppress subsequent lactation performance regardles sof whether or not POSILAC is used .

Breeds

Similar milk yield responses to bST have been reported in al ldairy breeds .

Most research has been done with Holstein Friesians but response sof similar magnitude have also been reported for other dairy breed s(4) . . Dairy breeds included Holstein Friesian, Jerseys, Ayrshires ,Brown Swiss, British Friesians, Shorthorn, Shorthorn X Jersey, Jerse yX Aberdeen Angus, Shorthorn X Aryshire, Jersey X Ayrshire, Jersey XFriesian, Friesian X Shorthorn, Friesian X Jersey, Dutch Red andWhites, Fleckvieh, Jamaican Hope, New Zealand Friesian and German Blac kand White cows which have responded in a similar manner to bS Tadministration .

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Parit y

• Cows of all parities have been reported to respond wit hincreased milk yields .

• In general, second lactation and older cows had the same o rhigher milk production responses when administered POSILA Cbovine somatotropin as compared to first calf heifers . However ,this difference has not observed in all cases .

Parity can affect the magnitude of the milk response to bS Tadministration . Milk yield response to bST administration has oftenbeen shown to be greater in second lactation and older cows than i nfirst calf heifers . However, some studies showed first lactatio nanimals responding to a similar extent as cows . . This variable respons eto bST is likely related to differences in level of milk production ,differences in the shape of the lactation curve and/or differences i nthe extent to which primiparous cows need to divert nutrients fo rgrowth . The well-grown heifers appeared to respond in a similarmagnitude as the second lactation and older cows . Therefore, goo dheifer raising programs and managing first calf heifers groupe dtogether to optimize dry matter intake will become more important i nmaximizing the milk response to POSILAC .

Milking Frequency

• Cows milked two, three or four times-a-day respond with asimilar magnitude of milk increase in response to bSTsupplementation .

The mode of action of bST appears to be different from that o fincreasing the frequency of milk production . The response to bS Tsupplementation appears to be independent of the frequency of milking .No single dairy study has been conducted evaluating the effect o fmilking frequency and bST supplementation on milk response . However ,the magnitude of the milk response to bST supplementation was simila rwhen comparing responses across studies in which different milkin gfrequencies (2X, 3X or 4X) were used .

Environment

• Cows administered bST in warm or cold environments respon dsimilarly to those cows in a thermoneutral environment (5) . Themilk response to bST administration is not affected by hea t(5,6) . The same management of cows in heat stress situation swould also apply to the bST-treated cow .

• The effect of environmental conditions on feed intake ma ymodulate the magnitude of the milk response to bS Tadministration .

Milk yield, water and feed intake and heat production were

increased in bST-supplemented cows without adversely affecting the hea tbalance of the cow . Cows supplemented with bST produced more heat than

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control cows in hot, cold and thermoneutral conditions . The increasedheat production associated with somatotropin supplementation was als oaccompanied by increased heat losses so that no adverse heat balanc eproblems occurred . BST-treated cows under heat stress dissipate th eincreased heat load through increased respiratory and ski nvaporization . Rectal temperatures were slightly elevated independen tof environmental conditions . In short-term studies conducted i nArizona, California, Florida, Missouri, Southern California, Brazil an dZimbabwe and long-term studies in Arizona, Georgia, Israel and Mexico ,cows supplemented with bST under heat stress conditions responded withincreased milk yields as compared to controls . During the heat stres speriod, the magnitude of the DMI increase for the cows supplemente dwith POSILAC remained constant even though the DMI decreased for al lcows (5,6) . Body condition increased for both bST and non-bS Tsupplemented groups up to the heat stress period and then remainedconstant for both groups over the heat stress period (6) . Two Floridadairies were used to evaluate the milk response to POSILAC (Table 1) .The studies were started in the middle of July and continued for 1 2weeks . In one herd, about half the cows started in July and the othe rhalf started in October . The milk response for both the combine dstudies was 13 .2 and 9 .7 lbs of milk or 15 .6 and 11 .6 lbs of 3 .5 %fat-corrected milk for first lactation and second lactation or greater ,respectively (Table 2) . First lactation cows administered POSILAC i nthe summer responded to the same magnitude as those cows starting i nthe Fall (Table 3) . Second lactation and older cows tended to give ahigher milk response to POSILAC in the Fall as compared to the summer .During both summer and Fall, administration of POSILAC resulted i nsignificant increases in milk yield . The effect of the environmentalconditions on feed intake may modulate the magnitude of the mil kresponse to bST administration . Keeping feed intake up throug hmanagement and nutritional intervention (as currently recommende dduring periods of heat stress) such as providing plenty of cool water ,adding dietary potassium, and the use of low heat increment feed sduring periods of heat stress may become important in maintaining asuccessful response to bST as well as maintaining the level o fproduction in general .

NUTRIENT REQUIREMENTS AND MANAGEMEN T

• Cows fed diets meeting or exceeding Dairy NRC requirements ar eresponding well . Dairy cows fed total mixed rations, pasture ,forages fed separately from grain and protein supplements, etc .are responding in a similar fashion .

• Digestibility of dietary components and partial efficiencies o fnutrient utilization are not altered by bST administration . I naddition, cows administered bST respond to a similar extent t ocontrol cows when 1) fed diets containing supplemental fat ; 2 )forage to concentrate ratios in the diet were altered ; 3) usin gdifferent fiber and carbohydrate sources ; 4) fed buffers ; 5) feddiets containing different proportions of rumen undegradabl eprotein ; and 6) infused with supplemental levels of methionin eand lysine . bST-administered cows are metabolically similar t ountreated cows of equal production .

Therefore the curren t

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National Research Council listings of nutrient requirements fo rlactating dairy cows are applicable to the cow supplemented withPOSILAC .

At the onset of POSILAC administration, milk production increase srapidly whereas the change in dry matter intake is more gradual . . Thi ssequence of events is similar to that which normally occurs soon afte rcalving . The production by the bST-administered cow requires tha tadditional nutrients be supplied to the mammary gland to synthesize theadditional milk . In the early lactation cow, body reserves aremobilized to provide a temporary supply of nutrients . Milk productionwill continue to increase until the nutrient supply (dietary input plu sbody reserves) has become limiting . With onset of bST administration ,the increased nutrient supply comes from one or a combination of th efollowing : 1) a repartitioning of nutrients and increased flow to th emammary gland ; 2) increased mobilization of nutrients from bodyreserves ; and/or 3) increased intake (3) .

Studies have consistently demonstrated that bST administratio ndoes not alter the digestibility of dietary dry matter, energy (fat orcarbohydrate), protein, minerals or micronutrients . The underlyingassumptions used in determining the nutrient requirements fo rmaintenance and milk production appear to be unchanged for the bST -administered dairy cow . The increased milk yield resulting from th eonset of bST administration results from the mobilization of bod yreserves or reduced deposition of reserves to meet the nutrien trequirements not supplied via the dietary input . As the dietary inputincreases to meet requirements, the amount of body reserves mobilizeddecreases . This coordination of body metabolism and the use o freserves mimics those of the early postpartum cow .

Overall, the results demonstrate that the current Dairy NR Crequirements for maintenance and milk production are appropriate fo rdairy cows administered bST . Clinical trials in which the 1978 DairyNRC guidelines were followed demonstrated significant increases in mil koutput with administration of POSILAC bovine somatotropin when diet swere fed and managed based on the milk production level and bod ycondition of the lactating dairy cow .

Nutrient Density and Source s

With the continuing advances in genetic merit for milk yield an dthe drive to increase profitability by increasing the output of mil kper cow, the nutrient intake must also increase . The amount o fnutrients available to the animal depends on the nutrient density o fthe diet and the amount of dry matter consumed . Factors affecting drymatter intake are very important particularly during periods of hea tstress . Nutrient density of the diet may be increased by 1) increasingthe proportion of concentrate versus forage in the diet ; 2) selectingconcentrate ingredients of higher energy/protein content and quality ;and/or 3) adding fat sources such as animal fat, vegetable oils, oi lseeds, or inert/bypass fat sources . Decisions as to whether or no tthese ingredients should be used should be based on economic ,management and environmental considerations independent of the use of

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POSILAC . The milk production response from the use of POSILAC has no tbeen shown to be enhanced with the use of additional fat and/o rundegradable protein in the diet or changing forage to concentrat eratios . In general, the nutritional status of the animal ma yinfluence the magnitude of the milk response . Whenever, energy and .o rprotein is limiting or the cow is in a negative energy balance, th eIGF-I response is diminished . Therefore, nutrient insufficiency appear sto uncouple the bST mechanism for increasing milk yield (3) .

Pasture

Production responses of bST-treated cattle on pasture have bee nvariable . Cows will respond with increased milk yield when allowed t ograze pasture . The magnitude of the response will depend on th equality and quantity of the pasture available .

MANAGEMENT CONSIDERATIONS FOR USING POSILAC BOVINE SOMATOTROPI N

Quality of management and nutrition will be major factors i naffecting the magnitude and duration of the response to bST . It i sknown that different herds and cows within a herd respond differentl yto POSILAC . Reasons for the differential response are illusive . Apoorly managed dairy farm may expect to have diminished responses t obST supplementation because other factors will likely limit the abilit yof the cow to produce milk . The optimum response may be expected i nthose well-managed herds that have healthy well-fed cows . Many of thesame management factors that are needed to successfully switch from 2 Xto 3X milking or to successfully implement other technologies whic hincrease milk yield should also be employed for the successful use o fPOSILAC bovine somatotropin . The feeding program must be managed t ooptimize dry matter intake especially in periods of heat stres s

Body condition at the time of bST treatment may have an impacton the milk response . Because feed intake lags behind the mil kresponse, a cow with greater body reserves could mobilize morenutrients for milk production when supplemented with bST as compare dto the cow with less reserves .

The difference in body conditio nscores among the herd may reflect a difference in the quality o fmanagement . In contrast, Monsanto has summarized 23 studies usin gPOSILAC bovine somatotropin and did not find an association betwee naverage body condition score before the start of supplementation an dsubsequent response to POSILAC over a 12-week period . The primaryobjective is to have cows in the proper body condition by dryoff .However, if body condition has not been adequately regained by the endof lactation, then dry cows should be split into two groups . One grou pfed to replenish body condition and weight as much as possible withoutprecipitating peripartum problems . The other group should be fed t omaintain condition . All cows would be fed a transition diet prior t ocalving . Management emphasis must be on replenishing body conditio nover the lactation cycle .

Studies evaluating the use of bST have included total mixeddiets, flat-rate feeding, magnet or computer feeders and componentfeeding system and pasture . .

There appears to be no apparent

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difference in milk response to bST supplementation due to feedin g

system as long as good quality forage is available . However, feeding

grain separate from forage should be reassessed when large amounts o f

grain are fed in two meals per day . Since the increase in dry matte r

intake lags behind the milk response, one should be cautious i nimmediately increasing the amount of grain unless the amount of grai nis fed over more meals per day (up to six to eight lbs of grain pe rmeal) . Increasing grain according to yield prior to considering th eamount of grain fed per meal may result in the cow consuming the grai n

at the expense of the forage . If the cow is already borderline o nfiber, this additional grain may interfere with proper rume n

fermentation .

Altering feeding frequency, protein degradability, concentrat elevel in the diet, incorporating ruminally inert fat or buffers hav ehad little effect on the bST response . Optimize dry matter intake aswell as providing high quality forage is a proven strategy fo rincreasing milk yield independent of the use of bST . Other factor saffecting DMI include feeding a nutritionally balanced diet ad libitum,bunk space, feeding frequency, moisture content of the diet, mold-fre efeed and bunks, plenty of fresh clean water available, managing tim ecows are away from feed (time in holding areas prior to and afte rmilking, etc .), managing heat stress through the use of shades, prope rventilation, sprinklers, etc . Feeding a continuously available TM Rbalanced for the desired level of production may be one of the bestmethods to feed the cow supplemented with bST . Milk yield response t obST supplementation appeared to be greater when feed was available t ocows for at least 19 hours per day . Cows supplemented with bST shoul dbe managed and fed just like other high producing cows .

General Recommendation s

• Formulate and feed diets for body condition and performance o fthe cow following NRC guidelines . Dietary recommendation sshould result in cows attaining proper body condition at dryof fand at calving .

• No special requirements or feed additives are needed .

• Optimize dry matter intake .

• Feed high quality forages .

• Optimize cow comfort .

•

Feeding total mixed rations ad libitum:Keep cows in production groups based on milk yield an dbody condition .

• Component feeding where grain is fed based on milk yield an dforage is fed ad libitum:

Hold grain constant for about three weeks then adjus tslowly according to milk yield and body condition for

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consuming large amounts of grain . This will allow enough

time for the dry matter intake to maximally increase sothat a proper forage to concentrate ratio can b e

maintained . As a target, limit grain to a maximum of si x

to eight lbs per meal . Feed according to milk productio ntaking body condition into account for that stage o f

lactation .

Component feeding where grain is fed based on the dairyman' sperception of the cow's need and forage is fed ad libitum :

Feed grain according to body condition . As long as theforage is of good quality, dry matter intake will increas eto support the milk yield response . Recommend going o nDHIA or a similar milk recording program .

Pasture :Provide good quality pasture ad libitum and shade during period sof high temperature . Fresh clean water should be availabl enearby . Supplement feed according to milk production level andbody condition .

References

1.

Haworth, B . 1994 . Consumer Consumption of milk unaffected by BS Tdebate . Dairy Coalition BST Infoline . March 24, 1994 .

2.

So Far, BST Impact Minimal . Dairy Profit Weekly . Vol . V, No .11 ,March 21, 1994 .

3.

Bauman, D .E . and R . G . Vernon . 1993 . Effects of exogenous bovinesomatotropin on lactation . Ann . Rev . Nutr . 13 :437-461 .

4.

Hartnell, G .F . 1993 . Feeding and managing the bST-supplemente ddairy cow . Monsanto publication ASD-3078 .

5. Johnson, H .D ., R . Li, Manalu, K .J . Spencer-Johnson, A . AnnBecker, R .J . Collier, and C .A . Baile . 1991 . Effects ofsomatotropin on milk yield and physiological responses durin gsummer farm and hot laboratory conditions . J . Dairy sci .S4 :1250-1262 .

6. Lotan, E ., H . Struman, J .I . Weller, and E . Ezra . 1993 . Effect sof recombinant bovine somatotropin under conditions of hig hproduction and heat stress . J . Dairy Sci . 76 :1394-1402 .

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Table 1 .

Description of Two Commercial Florida Dairy Herds .

Herd A Herd B

North FL South FL

1438 900

1200 70 0

18,900 (3X) 14,500(2X)

Item

Locatio n

Total number of cow s

Number of cows milking

Rolling herd average, lbs

305 ME herd average, lbs

Number of cows on stud y

Date started on bST

Duration of administratio n

Dry lot - Shades

Parlor holding area

Feed description

17,844

139

6 injections - 12 weeks

Yes

Sprinklers and fans

TMR - Coastal hay, cottonseed hulls,corn whole cottonseed, soybean meal ,hominy, minerals and vitamins

July 19, 1988

17,435

46

Group 1 - July 22, 1988Group 2 - October 14, 1988

6 injections - 12 weeks

Yes - Feeding area is shaded

Sprinklers and fans

TMR - cottonseed hulls, wholecotonseed, hominy, soybean meal, mea tmeal, cottonseed meal, minerals an dvitamins, corn silage, coastal bermudagrass hay

Table 2 .

Effect of POSILAC Bovine Somatotropin on Milk yield, 3 .5% FCM, and Mil kComposition in Two Florida Dairy Herds .

Item Control POSILAC Difference

Fir

ctation

Number of cows 30 3 3

Milk, lbs/cow/day 475 60.7 13 .2 '

3 .5% FCM, lbs/ cow/day 46 .4 62 .0 15 .6'

Fat, % 3.47 3 .60 0.13

Protein, % 3.07 3.00 (0 .07)

Second lactation & olde r

Numbers of cows 58 64

Milk, 16s/cow/day 59.5 69 .2 9 .7•

35% FCM, lbs/cow/day 58 .7 703 11.6'

Fat, % 3.45 3 .67 0 .22

Protein, % 3.10 3 .07 (0.03)

. Difference was statistically significant at P< .05 .

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