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RESPONSE OF COWS MILK COMPOSITION TO CHANGES IN ENVIRONMENTAL TEMPERATURE A thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University Palmerston North DENNISTER DI~S B~NDhRANAY~KA 1971 I I 1 • 1 1 • 2 ( a ) (b) ( C) ( d) ( e) ( f) ( g) 1.3 1. 4 (a) CH:,PTER TWO 2.1 2.2 2.3 (a) (b) 2.4 2.5 2.6 (a) (b) TABLE OF CONTENTS CHJ~PTER ONE Introduction Thermoregulatory Responses of Cattle to Thermal Stress Cardiovascular Responses Respiratory Rate and Respiratory Evaporative Heat Loss Sweating Rate and Cutaneous Evaporative Heat Loss Food Intake and Digestion Water Consumption Engergy Metabolism Endocrine Responses Rumen Characteri s tics Productive Responses Milk Yield and Composition M .. TERL.,LS ,,ND METHODS f,n imals Housing and Management Feeding Feed Feeding During the Experimental Period Measurement of Respiratory Rate and Rectal Temperature Milking Sampling and Tests Milk Composition Cell Content Page No. 2 4 6 7 8 10 12 15 17 19 19 26 27 28 29 29 31 33 34 35 35 35 ( C) Osmolarity ( d) Fatty :,cid Compos ition of Milk Fat 2.7 Sampling Ru men Liquor and Tests ( a ) pH (b) Concentration of Volatile Fatty ,·,cids (c) Proportions of Volatile Fatty :.cids 2.8 Statistical i,nalys i s of Data CH, ,PTER THREE RESULTS 3 . 11 3 .1 2 3 . 13 3 0 14 3 .17 3 . 18 3.20 3 .21 Respiratory Rate Rec tal Temperature Food Intake Vater Consumption Rumen Characteris tic s Milk Yield Fat Percentages , Yield of Fat and Molar Percentages of Mil k Fatty ~cids Protein Pe rcentages and Yield Lactose Percentages and Yield Osmolarity Cell Content of Milk Body Weight Changes CH~PTER FOUR DISCUSSION 4.1 Thermoregulatory Responses 4.11 Rumen Characteristic s 4.12 Milk Yield 4. 13 Milk Composition Page No. 38 41 42 43 44 45 46 48 55 57 62 65 67 68 69 70 71 74 77 Page No. ( a ) Fat 78 (b) Protein 82 ( C) Lactose 84 ( d ) Os molarity 85 ( e) Cell Content 86 Summa ry 87 Conclu s ions 88 Bibliography Table 1 1 • 11 1. 1 2 1. 13 1 . 14 1 . 15 1. 16 1 . 17 1 . 18 1 . 19 1 . 20 1. 21 1 . 22 1.23 1 . 24 1 . 25 1 . 26 1.27 1 . 28 L1ST OF' T:,BtES Respiratory Rates Daily Rectal Temperatures Intake of Dry Matte r Lb . Dai ly ~ater Consumption Lb. Daily ~ate r Consumption Lb . Pr el i mina ry-Experi mental Period Means Rume n pH Changes in Rumen pH Prel iminary- Experimental Perio d Means Mo l a r Proportions of Vo l atile Fatty ,.ci ds of Rumen Li qu or Changes in Molar Pr oportions of Volatile Fatty ~cids of Rumen Liquor Preliminary- Experimental Period Means Mo l a r Concentrations of Volatile Fatty ~cids of Rumen Liquor Changes in the Molar Concentration of Volatile Fatty ~cids of Rumen Liquor Preliminary- Experimental Period Means Da i ly Milk Yi eld Da ily Fat Corrected Milk Yield Decline in the Da ily Milk Yi e ld Preliminary-Experimental Period Means Decline in the Daily Fat Corrected Milk Yield Lb Prel iminary - Experimental Period Means Fat Percentage Cha nge in the Fat Percentage Preliminary­ Experimental Period Means Daily Fat Yield Lb. Decline in Daily Fat Yield Lb. Preliminary-Experimental P eriod Means Page No. 43 44 45 46 47 48 50 50 51 52 53 54 55 56 57 58 58 59 1 . 29 1. 30 1. 32 1.33 1 . 34 1 . 35 1 . 36 1 . 37 1. 38 1 , 39 1 . 40 1 . 41 1042 Molar Percentages of Milk Fatty ~cids Changes in the Molar Percentages of Milk Fatty hcids . Preliminary- Experimental Period Means Protein Percentage Fat Free Serum Decline in Protein Percentage F~t Free Serum . Preli minary - Experimental Pe riod Means Daily Protein Yield Lb . Declines in Daily Protein Yield Lb . Preliminary-Experimental Period Means Lactose Percentage Fat Free Serum Daily Yield of Lactose Lb . Decline in Lactose Percentage Fat Fr ee Serum Preliminary- Experimental Period Means Declin e i n Daily Lactose Yield Lb . Preliminary - Experimental Period Means Osmol arity of Daily ~ . M. and P . M. Milk Samples . Miliosmoles/Lit. Decline in Osmolarity of Daily Milk Samples . Preliminary- Experimental Period Means Cell Content of Milk In CM . Body Weight Changes Lb . Page No. 60 61 62 63 63 64 65 65 66 66 67 67 68 69 Appendix I Appendix II Appendix IlI Appendix IV Appendix V Appendix VI Appendix VII Appendix VIII Appendix IX Appendix X , ,ppendix XI /,ppendix XII i,ppendix XI I I 1\ppendix XI V APPENDICES Daily Water Consumption - Analysis of Variance Rumen pH Ze ro Hours Post Feeding - Analysis of Variance Acetic tc id Nilimoles % - Analysis of Variance Propionic Acid !iilimoles % - Analysis of Variance Bu tyric Acid Milimoles % - Anal ys is of Variance A. M. Fat Pe r centage - Analysis of Vari ance P . G. Fat Percentage - Analysis of Var i ance Daily Fat Yield - Analys is of Variance Molar ~e ~centa~es cf_c 6 - c14 Milk Fatty ,~cids - ,,nalysis of Variance Molar Percentages of c,B : O + c, 8 : 1 + c ,8 : Z + c, 8 : 3 - Analysis of Variance Molar Percentage of C 8 Milk Fatty Ac id .. 1 - lnalysis of Variance l . M. Protein Percentage - ~nalys i s of Variance P . M. Protein Percentage - l nalysis of Variance Osmolarity of Milk Miliosmoles/Lit - ~nalysis of Varian c e ACJrnOWLEDGEMENTS It is indeed a pleasure to thank Professors I.L . Cmpbell Dean of the Faculty of hgriculture and Horticulture , D. S . Flux Head of the Department of Dairy Hysbandry and R . E . Munford for their inva luable help and advice . I am d eeply indebt e d to my Supervisor Dr C . W. Holmes of the Depa rtment of Dairy Husbandry for his continual interest invaluable help and guidance . I wish to thank Mr A. D. F . Davey for permission to use his unpublished data , Mr 0 . B. Currie and Mr ~ . ½. F . Davey a lso of the Depa rtment of Dairy Husbandry for their advice and help . For the grant offered by the New Zealand Government through the Colombo Plan for Technical Co - operation in South and South East ~s ia I am v~ry grateful . I also wish to thank Syliva, Graham Juke , the staff of the lnimal Physiology Unit , Miss Campbell and the staff of Massey University Library for their valuable assistance . To Elaine Ross for the typ i ng of the script at such short notice I am very thankful . 1 CHAPTER ONE 1 . 1 Introduction 1 . 2 Thermer egulatory Responses of Cattle to Thermal Stress (a) Cardiovascular Responses (b) Respiratory Ra te and Respira tory Evaporative Heat Loss (c) Sweat i ng Rate a nd Cutaneous Evaporative Heat Lo ss (d) Food Intake and Diges tion (e) Wat e r Consumption (f) Energy Metabolism (g) Endoc rin e Responses 1 . 3 Rumen Char3c t eristics 1 . 4 Productive Responses (a ) Milk Yjeld &nd Composition 1 • 1 Introduction The need for greater production of animal proteins in the developing countries stems from two factors . Protein deficier.cy among growing populations due to a wide gap between production and c onsumpt ion and the continuing demand for the conventional proteins despite the availability of synthetic substitutes French 1970. Studies with re rard to the nutritional properties of dairy products Henry 1957; McGillivray and Porter 1960 . McGillivray and Gregory 1962 showed that the (prot ein ) fraction of milk v.ras well balanced in the essential amino acids enchancing their nutritive value . Milk production at the desired levels has not been possible in humid and arid regions of the world due to a variety of technical problems chief of which have been the choice of dairy breeds and the availability of good quality pas ture , Payne 1957. Cattle breeds indigenous to these regions are poor milk producers. They are slow developing, late maturing animals with short lactatious, long dry periods and poor milk let down; factors which probably contribute to their higher heat tolerance , a character incompatible with high milk yields Mahadevan and Marples 1961 . In the United States of America Red Sindhi and Brahman breeds were used in cross breeding programmes aimed at evolving a heat tolerant high producing dairy breed for the gulf coast areas . The first generation Jersey Sindhi and Jersey Brahman crosses not only produced less milk than thei r contemporary pure Jerseys , but also lacked persistency and a suitable dairy temperament; which were in fact heritable. Brandon McDowel l and Brown 1966 . These observations do not preclude however the 2 advantages of cross breeding for higher milk production in the tropics Legates 1966; Salazar 1968 . Although early ventures using temperate 3 breeds of cattle for milk production in the tropics have shown results of a disappointing nature Payne 1957, given near temperate conditions fou n d in tropical uplands these breeds could respond well . }968 ; Yung Chen Chia 1968 . Tra il Tl1e pr oblems associa ted with feeding in the trop i cs are reviewed by Payn e 1966 , Citing Hardison 1966 , Mi lford and Minso n 1963-64 . Payn e pointed out that tropical pas ture s pecies mature fast and thus . . contain a hi gh crude f ibre co n tent which be~6m~s a di~~dvaritage t o c~ttle und er a certain de gree of thermal st r ess . Fe e d i ng practices have to take in t o account a n animal ' s heat tol e r a nce , and wh ere productive animals have to be kept on high planes of nu trit i on , r at ions low in crude fibre but high in crude protein , together with frequent fe e ding throughout the twenty four hours have been emphasized . 1 , 2(a) Thermoregulatory Responses of Cattle to T~ermal Stress Card iovascular Respons~s Changes in heart r ate varied with the thermal intensity to wh ich cattle were exposed. A decline in heart rate was observed under conditions of prolonged exposure to mild heat Worstell and Brody 1953 . Exposure to severe heat however increased the heart rate of calves Bianca and Findlay 1962 , Ingr am and Wh ittow 196~ . Heart rate was pos itively correlated with the metabolic rate Kibl e r and Brody 1942, Blaxter and Wood 1951 . Cons equent ly changes in the he a rt rate under various degrees of thermal stress could be attributed to this r e l ationship , Bianca 1958 suggested that an increase in r espi ratory rate might be a contributory cause to an increase in the heart rate. In view of an increase in the excretion rate of nor adrenaline consequent to an increase in its secretion rate under thermal stress (Alv~ez and Johnson 1970) it might appear as if this catecho~m~e by its direct action on the heart cause cardiac acceleration . The blood volume of lactating cows Dale Bourge and Brody 1956 and of calves Bianca 1957 showed significant increases under thermal s tress. Murti and Mullick 1961 reported seasonal variation in the blood volume of I ndian buffaloes , In summer the blood volume was greater than in wi nter . Blood flow to skin a r eas where there were more arteriovenous anastamoses increased under high ambient temperatures Beakley and Findlay 1955, Wh ittow 1962 . It is however not known whether mammary blood flow is alter ed due to an increase in blood flow to peripheral areas . A decrease in blood flow to the mammary gland would reduce the inflow of metabol ites which would in turn r esult in an alteration in milk synthesis . 4 5 Th e changes that occur in the comp os ition of blood under thermal st ress are listed below . (1) A decl i ne in the haemo to c ri t val ue due to hae modilution McDowell , Moody , Van Soest , Lehman and ford 1969 ( 2 ) A decline in blood acetate med i ated t hrough a decline in blood thyroxine Yousef and Jo hnson 1965 (3 ) A decline in plasma protein McDowell et al . 1969 (4) A decreas e in blood i nsu lin Kamal , I brahim , Seif and Johnson, 19 70 (5) A de c r ease in blood glucose Rouss e l Beatty, Uhoulson , Pinero a nd Waters 1971 ( 6) Changes in p lasma free animo acids Kamal , Ibrahim, Seif and Johnson 1970 . Pr ec ursors of a l most al l the milk const i tuents are taken up by the lactating mammary gland from the b l ood , Linzell 1968 . Glucose and acetate fulfill two important functions in the mammary gland. They are partly metaboli zed , and the bal an c e used up by the udder for the synthes i s of a ll of l actose , a part of glycerol a nd short chai n f a tty acids . Annison and Linzell 1964 . Amino acids a r e inco r po r ated into milk proteins . It i s not surprising to find changes i n milk proteins , fat and lactose consequent to c hanges i n their precursors in blood . 6 1.2 ( b) ;~~s_--ej.r_,_!-._:_:~y _ _ 'fate a nd _K_':_':'_p~r<'.'tO_!'Y Evaporative Heat Loss The firs t ~eact ion obse~vad i n cattle exposed t o a h i gh amb ient temperatur e is ~hermal po l ypn oeu , Karnal 1964 . It is an i mm ediate ;·espo~.se t'.) r'.ir,~;ip:: te excess 1:Joc y l:wc, t, being initiated b y the st i mulatio~ of J8~ .• p h e r 2l tje~m~l rec&pto~s Bligh 1957 a n d probabl y cf deer, body rec e 1Jtors Rai;so:.1 . .:-'lu ick anc: _ Coughlin ~ S'69 . 1-ie'..-;·iratcr .- r2-tes cf Jersey 1 Ho l st ei :, and Bro·,:n S1.·; i E:.c; cows 2n1 that of ~rehman scw3 at 24°c Jorstell and _!:'.fod~y 1).~)3; wh i le re s_pirni:;e,ry r a.ts-c .:_:s }1 i gr! 2.s 200 per mi nut ~~ in Respiratory ventilation inc reases due to the :..~espirutory ::~.te oxceec.ling c:1a:ctges i n the tic1 -". l vol:J.me , Bi ::i.r:, ca a n <'\ ?indle~r 1952_ . Since respiratory vaporization depends partly on the r.1ovemc-, ·,:·, ·:; of ,n ;~ ··.·i th i n the resp i ;:-·a to r y ·trac t an increase in r "::f;pir1·:; or:- ventil -~t i 0.n j:'.'lsr ' 'l,ses respir 2. tory evaporative heat losses . Ki b l er C. ' 1d B:..·o dy showc>d tha'c: respi£ato r y va~ori z~tion rates vcried 2 ~ :f'r o n 50grr/m /hr for tern1w r ate '-:. ee ds to 30gm/mc./hr for t ro p ic a l bre~ds of c~t tle . Hyp c rvPnt i lation has been sh o wn to wash out excess:'. vc am'.)u·,ts of' c a r bon di '•Xic.e leadi ng to respiratory a l kalosi,s i acc omu~n i e~ by~ r i se in t he p H of uri ne . Dale and Brody 1952, 7 1 . 2(c) Sweating Rate and Cutaneous Evaporative Heat Loss It has been proved that cattle sweat actively when under thermal stress, Knapp and Robinson 1954 , Mc Lean 1963; from sweat glands cf an apocri n e nature Findlay and Yan~ 1950, Hafez, Eadreldin and Shafe i 1955 , which in the main h&d a thermoregulato r y function , Fergusson and Dowling 1955, McDowell , McDani ~l, Ba rrada an d l ee 1961, At 0 96 F the skin temperature of calves decreased consequent to sweat gland cctivity Klemm and Robinson 1955 , The contribution of cutaneous vaporization to total vaporization was 80% while that of respiratory vaporization ¼as 20%, Yeck and Stewart 1959 . The amount of heat dissipated consequent to cutaneous vaporization therefore makes it the major avenue fo r dissipation of extra body heat in cattl e under th e rmal stress . Sweat gland secretions we re h i ghly alkaline , and the i r concentra tions of reducing sugars , lactic ac i d , inorganic phospherous , total protein and non-protein nitroge n were higher than for blood . Under conditions of the r mal stress and thus of act ive sweat ing protein losseE could be fairly high , Joshi 1 Joshi , McDowell and ~ahu 1968 . Al tho ugh sweat gl ands serve a use ful thermoregul a tory f u nction , they cou ld to a certain degree affect p r oduction under the r mal st r ess . ./ 1 . 2(d) Food Intake and Digestion High amb i ent t emperatures had a depressing effect on the voluntary int ~ke of all breeds of cattle . The temperatures at which thi s effect was manifested varied with different breeds, Wo r stell and Brody 1953; Davis and Meril ~n 1960, Robinson and 8 Klemm 1953 . Field observations showed that high am b ient temperatures reduc ed the g r az i n6 time of beef cattle, Bonsma , Shchultz and Badenhorst 1940, Seath and Mill er 1946 . Worst ell and Brody 1953 found tha t the decline in voluntary intake coincided with the rise in body temperature implying that Brobeck ' s 1948 thermost at ic theory on food intake was applicable to rumina nts ac well . Baile and Mayer 1968; Dinius Kavanaugh and Baumgardt 1970 experimenting with goa ts obtained data contrary to those of Worstell and Brody, and in fact contradicated Brobeck ' s theory . The rumen temperature being higher than the rectal temperature was suggested as a factor limiting intake by Brody, Dale and Stewart 1955. Temperature mediated decline in voluntary int a ke in ruminants has not been elucidated. There is evidence to show that lact a ting cows respond better to diets containing a lower percentage of fibre under thermal stress . Stott and Moody 1960 obtained a significant cow response in the fat corrected milk yields by decreasing hay and increasing concentrates in the diet. Respiratory rates and body temper atures declined as well . Similar observations were made by Lei ghton and Rupel 1956 and 1960 , with diets low in fibre but high in proteins, and Breidenstein , Johnston, Hindery and Rusoff 1960 with diets containing 22 and 32% crude fibre at ambient temperatures 0 of 23 . 9 and 35 C. Evidence to the contrary were obtained by 9 Rogerson 1960 and by Wayman , Johnson, Meril an and Berry 1962 . Where the composition of the r a tion i s conce rned those with the l east heat increment per 100 Kcal digested appear to give the best response at high ambient temperatur es . Armstrong and Blaxter 1956 contended that the heat incr ement was greater when the propo r tion of acetic acid increased in the ru men . Rations containing a high pe r centage of crude fibre resulted in a h i gher proportion of acet ic acid . Evidence in support of this cont ent i on was advanced by Shaw , Ensor , Telleghea and Lee 1960 , Armst ro ng , Bl axter, Graham and Weinman 1958 , Graham 19 6 4 , Leighton 1965 . Digest ibility has been found to increase under hot environmental conditions , Blaxter and ~einman 1961 , Davi s and ~erilan 1961 . The apparent digestibility of prote i ns d i d not change in steers with elevated rectal temperatures , Vercoe 1969 , McDowell et al . , 1969 suggested that a dec r ea se in the intake of digestible ener gy par tly accounted for the increase in digestibil it y , whi le an increase in concentrates to roughage also contributed to the tota l digestibility of a mixed roughage and concentrate diet. Wayman et al ., 1962 , Kibler , J ohnson and Berry 1966, Johnson , Kibl er , Berr y , Wa yman and Merilan 1966 demonstrated that the decline in voluntary intake of nutrients accounted fo r more than half the decline in mi lk y i e ld unde r the r mal stress . Ur>"• QY M/,,..,.. · L . .. :::::S!TY 10 1 . 2(e) Water Consu~ption The amount of dry matter eaten and the severity of th ermal stress seemed to govern the water consumpt ion of cattle, Yousef , Hahn and Johnson 1968. Calves consumed more water at 27° than at 10°c, Johnson Ragsdale and Yeck 1960. Lactating cows consumed more water at a high ambient temperature, Ragsdale , Worstell , Thompson and Brody 1949. Und er graz ing conditions ambient temperature and water consumption were significently correlated, Harbin , Ha rbough, Neeley a nd Fine 1958 . A decrease in water consumption with increas ing ambient temperatures Ragsdale , Worstell , Thompson and Brody 1949; Ragsdale, Thompson , Worstell and Brody 1951, was explained by the fact that the decline in in take of dry ma tter and the concurrent decrease in the milk yield collectively reduced water requirements for metabolism . Although there was ~n increase in the requirements of water for thermoregulation, this was offset by a decrease in the water requirements for metabolism . An increase in the c rude protei~ content of the diet increased th e water consumption in cattle. Payne 1963. Roge r son 1963 , found that a reduction of 12 to 4% crude protein in the diet decreased the intake of digestable energy by 60% , and heat production by 20% p r ovided water was withhe l d . Water turnover of grazing cattle was greater in summer than in wint er, MacFarlane and Howard 1966, Siebert and MacFarlane 1969 . Since wate r turnover depends on the water actually consumed , water produced by metabolism , a nd the loss of water in urine, f aeces and sweat , the increased water turnover in summer would result from an increase in water loss and to a compensatory increase in water consumed. Whereas requirements of water in temperate climates mainly stem from metabolic demands , in tro p ical climates they arise primarily from thermoregulatory demands , Bi anca , Findlay and McLean 1965 ~ 11 1. 2(f) Energy Metabolism Heat product ion in l actating cows declin ed by 30 - 40% when ei t her exposed to ambient temperatures varying from 80 - 100°F or wh en their rectal temperatures increased from 10 1 - 106°F , Kib l e r 1 2 Brody a nd Worstell 1949, The decline in heat production was closely &sso ciated with a rapid decline in voluntary intake, followed by a decline in milk yield and possibly to a decreas e in thyroid activity . ( 0 . d A gradually incr easing amb ient temperature 50 - 90 F over a perio of two months ) decreased the oxygen consumption of calves from 110 to 85 litr es pe r hour . Th e oxygen consumption of normally fed calves increased f ro m 83 to 107 litres/hr and that of f as ting calves from 69 to 87 litres/hr when th e ambient t emperature was suddenly incr eased to 100°F , Kibler 1960 . Blaxter and \i ainman 1961 found an incr ease in heat production when two s te e r s were suddenly exposed to an amb i ent t e mperature of 35°c. Low metabolic heat production assoc iated with prolongect exposure to elevated &mbient temperatures was due to a decline in oxygen consumption , Kible r 1960, and to a decline in thyroid activity , Blincoe a nd Brody 1955, Yousef, Kible r and Johnson 1967 . Apparently all the following factors, a decline in voluntary intake, a decline in oxygen consumption , a decrease in thyroid act ivity and a. decline in milk production seem to of_fset heat production by increased respiratory muscular exertion , Kamal 1964. However when the respiratory rates of cattle remain e l evated, _respiratory muscular activity would be expected to utili ze some part of the tot a l intake of energy despite a decline in heat production consequent to the factors considered above. A significant decrease in the utilization of feed energy for productive purposes and an increase in the utilization of feed energy for heat production were observed in ad libitum fed lactating cows a t 31°c , Kibler, Johnson and Berry 1966. McDowell et al., 1969 contended tha t the energy r equirements of cattle increased under thermal stres5, due to an increase in the expenditure of energy . The authors cited Consalazio and Shapiro 1964 in thi s r ecard who found that an extra expenditure of energy occurred under thermal stress concequent to heat transport by blood , increased sweat gland activity and an increased metabolic rate . Under thermal stress the energy intake of ad libitum fed cows decreased due to a decline in intake of dry matter and acco rdin r to Kibler et al. , 1966 and McDowell et al ., 1969 an increa8ed proportion of this was utilized for non p roductive purposes . The efficiency of utilization of energy for productive pu rpos es then declined . When lactating cows were maintained at hich ambient temperatures on th e same l evel of gross energy that they voluntary took under normal ambient temperatures the decl ine in milk yield was markedly less, Kibler et al ., 1966. This i mplied that ma in- t ain ini them on the same l evel of energy did not stress them further , and allowing energy for non product ive purposes , more energy was available for production . However under these circumstances force fed cows gained body weight , which meant that of the energy available for production a greater proportion was used for gains in body we ight. Such a sh i ft in intermediary metabolism seems possible in the ligh t of ev i dence by Weldy , McDowell , Van Soest and Bond 1964; Gengler Martz , Johnson, Krause and Hahn 1970 who showed that the acetate to propionate ratio in the rumen declined under thermal stress . The general opinion i s that a change in rumen metabolism favouring a decrease in the acetate to propionate ratio favours b ody weight gains r athe r than milk with a high fat content . For a discussion reference i s 14 made to the review by Van So es t 1963 . The observation s of Kibler et al ., 1966 tend to support this shift in that force fed cows under conditions of thermal stress showed gains in body we ight. Subsequent investigations however tend to show increased lipolysis under thermal stress due to dec lin es in blood glucose and plasma insulin ( See 1 . 2 ( a)) and to an i ncreased secretion of corticoids . (Se e 1 . 2 (g)). The animals used by Kibler et al ., 1966 consumed more water under cont r ol feeding , and could have increased their body wate r cont en t, and probably gut fill as wel l. Under theGe circumstances the body W8 i ght changes could have occurred consequent to a higher body water content , a greater gut fill and to a retention of ene rgy due to lipogonesis offsetting lipolysis in the adipose tissue . 15 1 . 2(g ) Endocrine Responses Thyroid activ ity was negatively correlated with the ambient t emper2.ture . A ri se in th e ambient temperature low e r e d thyroid activity , Bl incoe and Brody 1955 , Johnso n and Ra~sdale 1960 , Lu ndgren and Johnson 1964. Whereas thyroid secr.-,tion and turnover r a tes Jecreascd , plas ma 17 hydrox y corticosterone increased in heat stressed cows , Thompson , JohnstcG , Br e id ~nstein , Guidry , Banerj ee and Barnett 1963 . Subsequently i(otby and Johson 1967 shov;ed that ACTF increas ~,a it::: rned ia tely on exposure to 90°F , but declin e d on p r olonged exposure . hegner and Stott and ~crsma and Stott 1969 r eport ed findings contrary to thos e of Kotby and Johnson 1967 . They found AC TH to be elevated over~ period of 2 - 3 months of hea t expos ur e . During this period blood progesterone l e v e l was high and l0ucocytes in the milk increased . Similar changes were observed vi i th par,.:;nteral FJ.dminiG tra ti on of ACTH . Ne ither blood l evel s of somatotrophin nor of prolact in of l ac tating cows exposed to high ambient temp e ratur es have been meas ured . Proppe and Gale 1970 found a decline in serum samatotrophin assoc i ated with other thcrmore~ulatory respo nses such as cutaneous vadodilatation and a fall in oxygen consumption in baboons whose preoptic and a nt e rior hypothalamic r eg ions in the brain were heat e d . Blood insulin declined at high ambient ternp E:- ratures, Kamal, et al ., i 970. Thyroxine somotot roph in a n d adrenal corticoids i ncreased under co ld s tr ess . Cold acclimation r esulted in an increase in thyrox ire and adr enaline enh anced the calorigenic ac t ion of thyroxine, Swanson 1965. The . 131 r elease of I increased toge t her wi t h it s per i pher a l ut ili zati on , adrenals hyphertroph i ed increasing the sec r etion of corticoids and pituitary ACTH remained e l evated i n cold a cclimation . Endocrine 16 adjustments of guinea pigs expos e d to moderately cold temperatur es was charac:teriz t: d by a sustained a ugmentation of pituitary , thyroid and ad r enal functions , D'Ange lo 1960 . Thyroxine metaboli~.m was slow and decr eased progr ess iv e ly in cattle exposed to h igh amb i ~nt t emperature s , Yousef a nd Johnson 1966 a . Th e authors 1966 (b) su gges ted t hat th e c ~l or i genic action of somatotr oph i n was enhanc ed by thyroxine . a & b Yousef , Kibler and Johnson 1967 contended that the ca l origeni c effect of th yr oxin e somatotrophi n and a dr enal corticoids d ecl ine d in cows ex posed to h i gh ambient temperatures , r re s umably due to a decline in all the hormones and a lack of sync r g icism necessary for calorigenes is when compared with cold expos ur e . 17 1 • 3 Rumen Characteristics The concent ration of volatile fatty acids of thermally st ressed cows declined . A dec l ine in acetic acid largely account ed for the total decline in the volatile fatty acids of th e r mall y stressed cows under conditions of uncont r olled f eed ing, ~cldy 2 McDowell , Van Soest and Bond 1964 , ~hile acetic and propionic acids accounted for a d ecline in controlled fed cows , Kell~ Martz and Johnson 1966 . A rise in the rumen temp~rature decreased the pe rc entage of acetic ac id and i ncreased that of propionic and butyric acids , Gengler , Martz, Johnson , Kr ause and Hahn 1969 . Th e decrease in the concentration of volatile fatty ac ids was however due to thermal stress rather than to an increase in the ru men temperature . Di ets lacking in physical fibrousness (more concentrates to roughage , chopped or pelleted r oughage) p r oduced more propionic ac i d when compared with acet ic and butyric a cids . Starry and Rook 1966 , Starry a nd Sutton 1969. Under these coni tions rumen pH decreased , together with the digestion of cellulos e , Sterry and Sutton 1969 . Sterry 1970 suggested that an initial decrease in the flow of saliva to the ru me n r e duce d its pH , du e to a d ec r ease in the buffer ing action in the rumen. An acid pH s u bsequ ently reduced th e cellu~.yt ic organisms in the rum en . Cows that were expos e d to a high amb i en t t empe r ature showed lowe r values for rumen pH, Misra , Mar tz, Stanl ey , J ohnson , Campb ell a nd Hilderbrand 1970 . A d e cline in the voJ.r:me of saliva en t ering the r ume n may be suggested as being the contributory cause for a decline in rumen pH under thermal stress simply be caus e cat t l e salivate under thermal stress and this sal i va i s subsequently lost . Consequ ently th e change in rumen fermentation will be similar to that which oc curs on d i ets lacking physical 18 fib rousness , The oxidation reduction protential which was a measure of th e activity of rumen micro-orga n is ms decrease d under the r mal stress , L'lJ-sr~ e t al ., 1970 and would in all p robability have decreased th e conc entrat ion of volatil n f atty acids . An increase in lactic acid a,,.<1 -: i'e: d ecrc2,sc. in volatile fatty ac ids vie r :.: h i gh l y ind ic at ive of a p r e-0 r ential gro wth of a mylolytic organisms to cellulyti c organisms consequ ent to changes i n the ru men pH und e r th e r mal stress . (hera&s t ~e concentrat i o n of hmmo ni a in the rumen was indep e nd en t of ambi ent temperatures, th e decline i n its concentration pos t f ee ding tended to be slow e r und e r thermal stress , Mi s r 2 e t a l., 1970 , The nut h ors citing the evidence of Eloomf i e ld, Kear l e y, Creach and Muhre r /1c,-;--,, '"uc.· r,-e" teri •• :::: O.J (-i t.) 0 I • that the slow rat e of d ec line post feeding un de r thorm2l str ess nas du e to a slow rat E of abso rpt ion in an a cid med iu m. l sl ow ra te of dec l ine of ,_rnrnon i a post feeding may also mean that its u~ilization for protein synth es is by the rumen micro - or gan isms has decl ined -~ l~ th e cellulose digest ing bac teria utilized ammonia in p ref e r en c e to ~-:.. c;f0nr.ed aCJ ino acids for protein s ynth es is, Bl ackburn 1965. 1, 1~cr~2s c in ce:lu l yt ic organ isms in the rumen would at l eas t in part ,. :~c.- ; ·1 a r-:l ow decline in arnnonia post f eeding unclGr th e rma.l .stress. fhe circumstantial e videnc e point s out to t he fact that th e r e might be ~ G~CPt0 r 7 oss of dietary proteins and a gr eater decrease in bac terial J~o t ains , brinejng about a n overall decreas e in the a vai l ab ility of protejn to th e a nimal. When viewed with proteolysis, a nd subsequent ~:S8~ a protein deficiency un de r therm~l s tress might be expected with , -~' :..· c-nt c.ecr easP., of :;?r::>tein in products like milk~ 1.4(a) Productive Res pons es Milk Yield and Composition / The secreting bovine mammary gl and i s extremely compl e x in its synthetic pro c esses such that optima l conditions are a pr e r equisite 19 for maximal yields with least chang e s in th e composition . Data from perfusion experiment s with caprine mammary glands h ave shown th e importance of flow r a t e of metabolites to th e gland . For both yield a nd composit i on to be norma l in pvr f used mamm~r y g lands the rate of flow of metabolites had to be th e snme as in the int a ct gland, Hardwick and Linz ell 1960, Hardwick , Li nzell and Pric e 1961 . Th e metabolism of th e who l e body is gear e d to a id th e secreting mammary g l and . Under diff~rent phys i ological condit ions mi lk yi eld a nd composition devi a te from the normal , Lin zell 1968 . In view of optima l conditions bei n g a pr erequis it e to t he l ~ctat ing mammary gland , chang es in rum en metaboli sm , int e rm e diatry me tabolism, cardiovascul a r system, blood composition a nd endocrine balance conseq uent to th ermal stress must n e c essarily bring about concurr ent cha nges in milk yi eld and composition Kamal 1964 . Ea rly findings on the dir e ct e ff ec ts of th e clima tic environme nt on milk yi e ld and co mpos ition are r e viewed by Payne 1954. Data from the Missouri climatic laborato ry up to 1953 have been summarized by Dorst ell nnd Brody 1953 . Studies at the Missour climatic laboratory have examined th e e ff ects of each clima tic var iabl e on milk yield. The milk yield of all br eeds of cows us e d in th e tri a ls declined under conditions of a constant wet bulb temp er a ture but elevated dry bulb temp eratures . However the effective temperatures va ried from temperate to tropical breeds. ~thigh ambient temperatures the decline in milk yield of early lactation was rel n tively greater tha n tha t o f l a te lacta tion , Johnson, Kibl er, Ragsdale and Shanklin 1960 . ~l s o th e d ec line in high produ c ing cows wes gr ea t e r than in low p rodu c ing co r·s , Jo h nson , Ha hn 1 Kibl e r and Meril a n 1962. Dith 20 ide ntic a l twins , f e d th e s a me r n tions, but man~ge d und er two differ e nt clima tic e nvironme nts , Pa yn e a nd Hancock 1957 s howed tha t th e set of t wins ma nag e d und e r hot e nviro n ment a l conditions, produced on an averag e less milk, butt e rfa t and s olids not fat . Climatic physiological s tudies in Tas mRnia, Re es 1964, s how e d th e s a me effects on milk yi e ld and comp osition in a ddition to d e pr es s ions in total acidity and fr ee zi n g point d epr ess ion. D~ t a of Hces 1964 have be en obtained from ve ry short exposure p e riods to va rying a mbi e nt t ~mp c r a tures with- out int c rv ~ning control p e rio ds . Cons equ en tly c a r r y ov e r e ffects could h ~v e be e n int e r p r e t ed R S tr eD tm e nt e f f ects. Th e eff e cts of humidity on milk yi e ld we r e only manifest e d at ambi ent temperatures above 24°c , when an incr eas e in humidity result e d in gr e ,1ter declines in th e milk yi e ld, Ye ck a nd St ewart 1959, Johnson Ragsdal e , Berry and Shanklin 1963. Milk yi e lds of Holstein , Jersey and Brown Swiss cows d e clin e d by 32 , 18 and 15% r espectively on increasing the humidity from 40 to 90% at 29°c, Yeck and Stewart also found tha t the decline in milk yield was less a t high wind velocities when compared with low wind velociti e s at the same ambient temp erature . Brody , Ragsdale , Thompson and Worst ell 1954 cont ended that high yielding l2rge dairy cows benefitted more from the effects of high wind velocities under thermal stress. Analys i s of dat a from trials at Missouri by Cobble and Herman 1951 showed the following changes in milk yield and compos ition due to thermal stress. ' ,, decline in milk yield. 0 ,. decline in the fat perc entage up to 90 F , and an increase abov e 90°F . i. dec r ease in SNF and totc1l nitrogen . .. de cr ease in lactos e . ,.n increas e in chloride No change in the freezing point . 21 Ch~nges in the fatty acids of milk fat were chara cterized by a decline in sho r t chain a cids c4 - c12 , and un increase in c16 and c1B:o· Th e incr e~sc in c18 : 0 resulted in a decline in c18 : 1 Ric h ardson , Johnson, Gehrke and Goerlit z 1961 . High ambient temperatures caused d eclines in total phosphorous , and m~gnesuim . Citric ac id declined only during early l acta tion . Th o ch~nges in sodium or sodium to potassium ratio we re not significant, Kamal , Johnson a nd Ra gsdale 1961 . The depressing effect of h igh amb i e nt temperatures a nd humidit i es on milk product ion has still not been solve d fully. Experim ental findings of 1iayman et al . , '1962 , Johnson et a l., 1966 implied that the prim ry e ff ec t of therm~l stress W3S mediated through a decline in intake a nd ther e fore due to und erf eLd ing e ffects. When the intake of gross energy was maintaine d under the rmal stress the decline in milk yi e ld w~.s smuller when compc'.red ,\'i th ad libitum feeding . However the milk yields of cont rol fed cows were below their y i eld under normal ambient temp eratures, wh ich a lso impli ed that temp erature mediated changes in the endocr ine balance by their effects on metabolism or on golactopoesis or both account ed for the balance . In view of thes e observat ions under- feeding effec ts , and endocrine effects on metabolism and galactopoesis have to be considered to explain the overa ll changes in milk yield a nd compos ition unde r th ermal stress . Da t a on underfeeding cows after calving by Flux and Patchell 1954 on milk yield a nd composition are cons ide r ed , bec ause of t he ir r e l evance t o studi es with hi gh ambient t emperatur es wh i ch i n the main used cows with al r eady establi s h e d lactation s . Un de r feed i ng afte r calv i ng caused a d e cline in milk y i eld , fat y i e ld and SNF% . A d ec r ease in t he SNF% was du e t o 22 - d eclines i n b o t h p r ote i n% and lac t ose% . The chan ges unde r t he r mal stress are s i mila r to those of underfee ding . As seen earli e r 1 . 2 ( g ) the changes in th e endoc r ine balance we r e an i ncrease i n AC TH and adrenal cort i cori ds , a dec r Lase in t hyr ox i ne , p r obabl y f r om u nder­ feeding effects , Bl i ncoe and Brody 1955 , Ki bl e r 1960 or f r om di r ec t effects , Lundgr en and Johnson 1964 , and i nsulin , Kum2 b et. al . 2 1970 A probable dec rease in soma t otroph i n , Proffe and Gal e 1970 and a n inc rease in nor a drenaline, Al v c:re z antl John£;on 1970 . The poss i ble effects of endocrine changes together with othe r changes such as a dec line of blood glucose and ace t ate on metaboli sm and udde r me t abolism a r e summari sed . ( 1 ) An i ncrease in c o r t i cori ds , c atec h o l am i nes a n d a decr ease in i nsulin f a vou r 1 i polys i s in adipose ti ssu e , with a r e l ease of l ong cha i n f atty aci ds , which wou ld be i nc orp ora t e d in milk f a t incr eas ing the long c ha i n f a tty acids . (2 ) An inc r eas e in c or t icorids woul d inc r ease g lucone o g enes i s a nd decrea se p ro t ein precursor s to th e gland with a concurrent decline in milk protein . Regan and Richardson 193B observed a decline in c as ein under th ermal stress . (3) A d e cline in glucos e and ac e tate would r e duce udder met a bolism , r e duce l a ctos e synth esis a nd th e synthesis of short chain f atty acids . The decreas e in a cetate may arise due to changes in the rumen, a decline in thyroxine, Yousef and Johnson or t o both . 23. The possible effects on golactopoesis are based on the findings of Cowie and Tindall 1961, Cowie , Knaggs and Tindall 1963 . Da ta on hypophysectomized goats showed that prolactin tri - iodothyronine i nsulin and dexameth a sone restored milk yields to normal level s . These ho r mones were considered essential for golactopoes is . Presuming that the Eame h0rmones ~re essent i a l for th e bovine , under the r mal stress gal actopoesis could be affected by a decline in insul in somatotrophin and thyroxine a nd e11hanced secretion of ACTH which has be en s hown to d ecreas e milk yield , Flux, Folley and Rowlands 1955 , 24 This experiment was carried out to examine some of the r esponses in cows milk yield and composition due to an e l evated dry bulb temp e rature . Responses examined were rectal temp e r ature and r e~ piratory rate as measures of thermal stress , water intake , milk yield and composition, cel~in milk and osmolarity , rumen character ­ istic s with regard to pH and volatil e fatty acids, and changes in the composition of milk fat . Sinc e the responses were to be examined cit a constant level of intake cows were paired and the control cows with ­ in pairs were controlled fed to ensure the same l eve l of intake , see 2 . 4 Wayman , et al . , 1962, Kibler 1966 , Johson , et al ., 1966 compared the reuponses in milk yield of cows on·two levels of intake at the sarne hie~ nmb i e nt t emperatur e . The ir resul ts proved that the decline in milk y i el d was due to a decline in voluntary intake and to other factor s , and that the former accounte d for more than half the decline . In this experi ment a comparision of the responses was made on cows maintaiPed on the same l eve l of intak e but at two different ambient temp e r atur es , and consequently examining whether the cows exposed to the high ambient temperature showed a greater decline in milk yield and changes in composition due to changes other than a decline in voluntary intake. 0ater intake and osmolarity were measured to examine possible effects of haemodilution on the water content of milk . Since changes in rumen fermentation are r efl ected in milk yiel d and composition, particularly the fat moiety and body ½~ight changes , rumen pH and volatile fatty acids were examined with a view to relating any a lterations to possible changes in the compos ition of milk fat. Daily AM and PM milk samples were subject to the Wisconsin Mastitis Test in order to observe cha nges in the cells in milk and thus cor tico rid act ivity and the ir related effects on milk composition. 25 CHAPTER TWO Materials and Methods 2 . 1 Animals 2 . 2 Housing and Management 2 , 3(a) Feed ( b) Feeding During the Experimental feriod 2 . 4 ~easurement of Respiratory Rate and Rectal Temperature 2 . 5 Milking 2 . 6 Sampling and Tests (a) Milk Composition (b) Cell Content (c) Os~olarity (d) Fatty Acid Composition of Milk Fat 2 . 7 Sampling Rumen Liquor and Tests ( a) pH (b) Concentration of Volatile Fatty Acids (c) Pr oportions of Volatile Fatty Ac i ds 2 . 8 Statistical Analysis of Data 26 27 2 . 1 Animals Four lactating non pregnant cows from Massey University dairy herd which had been fitted with rumen fistu l ae in the previous year were used in the experiment . Porticulers of the cows are given in the table below . - I •• * * Cow No . Br eed Body~eight Stage of Lactation 8 FRxJ 783 Lb 16 weeks post Partu~ 77 J 732 9 we eks post Partu m 121* J 791 9 weeks post Partum 122* J 842 15 weeks post Partum * Monozygous Twins ** At beginning of experiment Th e four cows we re divided into two groups, and to mai ntain the same level of intake during the experimental period see 2 . 3(b) cows in the two g roups were paired . The use of a pair of monozygous twins in the experiment r esult ed in the other two cows be ing r and omly paired . GROUPS EXPERIMENTAL CONTROL 8 77 ,, J PAIR I ¥1 PAIR II ¥2 ·' 2 . 2 Both groups of cows we re initi a lly kept in two temp erature c ont r olled roo ms ( + 1°c ) in i ndiv i dual cow s t ands fitted with fo od bins and wa t er troughs . At th e end of a prelimina ry pe riod of 29 days the r oom tempe r atur e of the experiment a l gr oup was 0 increased to 30 C. 0 was returned to 15 C, 0 It remai ned at 30 C unti l day 54 , when it Measuremen t s continued until day 62 28 D~Y 55 TO D~Y 62 ·---····------------ Coctr oJ. E:xn...: rinent,>. l G:co up GToup 1 5°C ----·· ------ -~------ ConGrol Grouri 15° C ,__ _______ -·---- Con t rol B:;:-perir.~en ta.l Grou11 Group 15°C 29 2 . 3(a ) Feed Cows were fed dried grass from day 0 through to day 64 of the experiment . A proximate analys i s of a sample of the dri ed grass is s i ven belov: . Ac i d Detergent fibre Crude Protein Ether Extract Ash 28 . 1;~ 9 -z.nl • :;,a Ni trogen Free ExtrRct (By difference ) 34 . 2% An apparent d i gestibilit y of 73 . 0 ( A. ½. Davey u n published data) was obtained using four sheep . Particulars are given below. No . of Sheep Intake Di gestib ility 10 1245 gm 73 . 4 2 1157 gm 70 . 0 A 1245 gm 74 . 7 13 945 gm 73 .3 The digestible organic matter calculat ed from the above figures for organ ic matt er and diges tibility was 63 . 2% Using the approximation tha t 1 g ram of digestible organic matter is equivalent to 3 , 6 Kcal of metabolizable energy, and maintenence requirements under stall feeding conditions at 11500 Kcal of metabolizable energy Blaxter 1964 , the requirements of dri ed grass for maintenence were estimated a t 7 . 0lbs . 30 Requirements for production were estim3ted by assuming that 0 . 351b of digestible organic matter was required to produce one pound of fat corrected milk . The cows were fed 1 pound in excess of their requirements thus estimated . No 8 and 121 , 301b and no 77 and 122 291b of dried grass respectively . Approximately half of the daily ration was offerred to each cow at 600 hrs , and the balance at 1600 hours before milking . 31 2 . 3(b) F ee ding During the Experimental Pe riod During the experimental per iod the c ows we r e fed in pairs and the intake of the Pai r controlled at the l eve l consumed by the membe r with the lowest voluntary intake . Pair 1 i s taken as an exampl e and pair feeding is i l lust r ated in the table given below . EXPERIMENTAL COW No . 8 DAY 0 301b of dried g r ass were weighed at 1800 hrs f or day 1 DAY I Appr oximately half of the dried grass we i ghed on Day 0 was offered at 600 h r s before mi lking . Bal a nc e of t he gr ass was of f e red at 1600 hrs before milki ng . 301b of dri ed gr ass were we ighed n t 1800 hrs for Day 2 DAY 2 Grass refused from day 1 was weighed at 5 . 30 hrs. Four 50 gm samples from the refusals were placed in the oven. Approximately half of the g r ass weighed on day 1 CONTROL COW No . 77 DAY 0 291 b o f dried grass were weighed at 1800 hrs for day 1 DAY I Arproximetely half of the dried gr ass weighed on Da y 0 ~as offered at 60C hrs , before mil k ing . Bal ance of the grass was off ered at 1600 hrs before milking . 291 b of dried grass were weighed a t 1800 hrs fo r Day 2 DAY 2 Approximately h a lf of the dried grass we i ghed on day 1 was offered at 600 hrs before milking . Four 50 gm samples from the balance were placed in the oven. The dry matte r was offered at 600 hrs before The dry matter percentage of the four 50 gm sampl es was determined at 1500 hrs and the d ry matter refused from day 1 was determined . The balance grass was offered at 1600 hrs befo re milking . 301b of grass were we i ghed at 1800 hrs fo r day 3 32 percentage of the four 50 gm sample was determined at 1500 hrs. Using this dry matter percentage the weight of gr ass equivalent to the dry matte r refused by 8 was determined. This weight of grass was deducted from the balance of the grass offered at 1600 hrs before milking . 291b of grass were we ighed at 1800 hrs for day 3 The quantity of dry matter refused by experimental cow no 8 an day 1 was deducted from the dry matter offered to control cow no 77 on day 2. Cow 77 was consequently a day behind 8 in the intake of the same quant ity of dry matter. 2.4 Measurement of Re s piratory Rate and Rectal Temperature Rectal temperatures were measured twice daily a t 5 . 45 hrs and 15 . 45 hrs before feeding using a th ermister (Thermophil Ultrakust Co. ½est Germany) . This was c2librated again~a mercury in glass thermometer ( ± 0 . 05°c ) Respirato ry rates were recorded at 5 .45 and 15 . 45 hrs on several days , dur ing the preliminar y, experimental and pos t experimental periods . The respir&tory rate was measured by observing the movements of the right flank . 33 2. 5 Milking The cows were milked twice daily at 600 and 1600 hrs using a portable bucket ty,e milking mach in e , and the weight of the milk from each cow recorded at each milking . • 37 Nitrogen flow 25 ml/min Hydrog