Br. vet.]. (1976), 132, go

SOURCES OF VARIATION IN THE MILK FLOW RATE AND ITS RELATIONSHIPS WITH MILK YIELD, MILK COMPOSITION, AGE AND STAGE OF LACTATION IN DAIRY COWS BY

A. K.

RATHORE

Dairy Research Centre, Richmond, N.S. W. SUMMARY

Twelve lactating cows were used to obtain average milk flow rate for a period of 2 weeks, during that period average milk flow rate and milk yield were recorded on individual cows at Friday and Tuesday afternoon milking and Saturday and Wednesday morning milking each week. Animal variations were significant at the I per cent level for milk flow rate, milk yield, milk fat and milk protein percentages. There were significant differences in the morning and afternoon milk flow rates, milk yield, and milk fat percentages. Milk flow rate was positively correlated with milk yield, and negatively correlated with age and somatic cells in the milk. Milk yield was negatively correlate-d with the somatic cells. INTRODUCTION

With increased competition for labour in the dairy industry, more emphasis is being placed on increasing the efficiency of the milking operation. One measure of milking efficiency is the number of cows milked per man-hour. This in turn is influenced by the milking rate of the cow. Rate of milk removal and time required to milk are of econmnic importance in relation to the amount oflabour required per unit of milk yield. To establish a sound procedure to possibly reduce the time required to milk, it is important to know the extent to which physiological and environmental factors are responsible for the wide variations among cows for milking rate. A controversy exists as to the relationship between rate of milking and the total lactation production, Whittlestone (I 946) found that the average rate of milk flow declined towards the end of the lactation period, but that the time required to milk did not vary. Dodd (I949) found that both the time required to milk and the milk flow rate declined with the progressive reduction in milk yield within lactation. Dodd & Foot (I 953) hypothesized that the faster-milking cows produce more milk than slower-Inilking cows and are more persistent in production. However, Sandvik (1957) reported that the rate of milking had no

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significant effect on lactation production or persistency. Brumby (I 956) found no relationship between rate of milking and lactation production. Dodd & Neave (I95I) reported that milking rate may be important because it is related to other factors such as susceptibility to udder infection. The aims of this study were: (I) to determine the variation in morning and afternoon milk flow rates; (2) to evaluate the relationships between milk flow rate, milk yield, and somatic cell count in the milk; and (3) to determine the effect of stage of lactation and the age of the cows on milk flow rate. MATERIALS AND METHODS

In this experiment twelve lactating cows at I09 to I99 days of lactation were used. The cows were fed protected-lipid-protein supplements. The age of the cows varied from 3 years through to I8 years. Age was calculated in years at the time the experiment was begun, which is different from most experiments where age is calculated at the time of calving. The trial lasted for 2 weeks. During the experimental weeks the following observations were made at Fridays p.m., Saturdays a.m., Tuesdays p.m., and Wednesdays a.m. milking. At each milking the cows followed a fixed routine. They entered the bail, had their udder washed, massaged and dried, within 20 s of the udder preparation the teat cups were put on.

(i) Milking time: The timing by stop watches was begun when the milk started flowing (after the let down) and was ended when the rate of the flow dropped below o·I4 kg/min and the teat cups were removed. (ii) Milk samples were taken separately for fat and protein percentages. Milk yield was recorded to the nearest o·I I kg using tru-test milk meters. (iii) Fore-milk samples were analysed for the somatic cell count, in the calculation average value of the four quarters was used. (iv) Milk flow rate (kg/min) was calculated by dividing the milk yield per cow by the total milking time. RESULTS AND DISCUSSION

Table I shows the analyses of variance for the milk flow rate, milk yield, milk fat, and milk protein percentages, animal variations were found to be highly significant for all the four variables. Week-to-week variations were significant for milk yield and milk fat percentage. Day-to-day variations were found to be highly significant for milk fat percentage. Morning and afternoon milkings varied significantly for the milk flow rate, milk yield, and milk fat percentage. Week X day X animal interactions were highly significant for the milk flow rate, milk yield, milk fat, and milk protein. Table II presents correlation coefficients of all the variables studied. Milk flow rate was correlated (I per cent level) with milk yield (0·499),

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TABLE I MEAN SQ.UARE FOR MILK FLOW RATE (MFR), MILK YIELD (11), MILK FAT PER CENT (MF), AND MILK PROTEIN PER CENT (liP) IN LACTATING COWS

Week Day Week X day Animal Week X animal Day X animal Week X day X animal Time Residual

I II II II

II 47

Meansqumu MF

MFR

M

0•0335 o·o646 o·o864 2•7221** o·I2I3 O·I3I3 0•3859** 2•7142** o·o8o4

I0·94** I•82 7·7o** 127•32** 3·4I* 1·12 6·25** 548•17** I•-t-8

Df

0·5I04* o·735o** 9·6267** 5·2249** 0•3293** o·I293 1·6g34** 3I·o891** o·o8gi

MP 0•0527 o·o677 0·9943** 0•5538** O•II25 o·II-t-8 0•34I5** 0•2450 o·og62

* Significant at 5 per cent level. **Significant at I per cent level. TABLE II BETWEEN-ANIMAL CORRELATIONS FOR MILK PLOW RATE, MILK YIELD, MILK PAT PERCENTAGE, MILK PROTEIN PERCENTAGE, AGE, STAGE OP LACTATION, AND SOMATIC CELL COUNT Milk (kg)

Milk flow rate Milk yield Milk fat(%} Milk protein (%)

0·499**

Milk Fat (%) -o·I2I -0·325**

Age

Stage of lactation

protein

Stage of Lactation

So111Jltic

Age

(%)

(years)

(weeks)

count

-O•I45 -0·264** o·I93

-o·585** -o·o87 -o·I37 -0·239*

-o·o41 -o·o-t-8 0·36o** 0•470** -o·36o**

-0·233* -o·387** -0•072 -0·347** o·6o3** o·075

Milk

cell

* Significant at 5 per cent level. * * Significant at I per cent level.

age of the animal (-0·585) and somatic cells in the milk ( -0·233, at 5 per cent level). Milk yield was significantly correlated with milk fat ( -0·325), milk protein (o·264) and somatic cells in the milk ( -0·387). Milk fat was significantly correlated with the stage of lactation. Milk protein was correlated with age of the .cow ( -0·239), stage oflactation (0·470) and somatic cells (-0·347). Age of the cow was highly correlated with stage oflactation ( -o·36o) and somatic cells in the milk (o·6o3). In this study, the morning milk flow rates were significantly faster than the afternoon, this is possibly due to the fact that a greater amount of milk was removed in the morning. The milk flow rate was highly correlated with the milk yield, this is in agreement with the hypothesis of Dodd & Foot (1953) that the faster-milking cows produce more milk than the slower-milking cows. The positive correlation between milk flow rate and milk yield would indicate that as the cows are selected for increased production they will have faster

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milking rates. Since the milk flow rates are highly repeatable from day to day and week to week, a few measures of flow rates per cow would be sufficient. Milk flow rate declined significantly as the cows got older, and faster-milking cows had significantly lower somatic cells in the milk. Increase in the milk yield led to reduction in the milk fat, and milk protein percentage is in agreement with the report by Rathore (1970). Stage oflactation had no effect on the milk flow rate and milk yield, but was significantly correlated with milk fat and milk protein percentage. As a long-term measure, and in case faster milking cows yield higher production with lower somatic cells in the milk, it may be advisable to select cows with fast milk flow rates in dairy cattle breeding programmes. REFERENCES

P. J. (I956). Proc. N.:(,. Soc. Anim. Prod. 16, 89. DoDD, F. H. (I949). N.I.R.D. Ann. Rep. Reading, 20. DoDD, F. H. & NEAVE, F. K. (I95I). J. Dairy Res. 18,240. DoDD, F. H. & FooT, A. S. (I953). J. Dairy Res. 20, I38. RATHoRE, A. K. (I970). Aust. J. Dairy Tech. liS, 106. SANDVIK, 0. (I957). J. Dairy Res. ll4t 3I6. WHITTLESTONE, G. (I946). N.:(,.J. Sci. & Tech. liB, I88. BRUMBY,

(Accepted for publication 22 October I974)

Sources de variation dans le regbne d'ecoulement da lait et ses relations avec Ia production, Ia coDlposltion da lalt, son lge, et Ia periode de lactation chez Ia vache laitiire (Ratbore)

ResiiDle. On choisit douze vaches en lactation pour obtenir le regime moyen d'ecoulement du lait pendant une periode de 2 semaines, et durant cette periode on enregistra le regime moyen d'ecoulement du lait et la production de lait pour des vaches individuelles au moment de Ia traite des vendredis et mardis a pres-midis et des samedis et mercredis matins, chaque semaine. On trouva une variation significative au niveau I pour cent pour le regime d'ecoulement du lait, la production de lait, Ia matiere grasse du lait et les proteines du lait. On trouva des differences significatives entre les regimes d'ecoulement du lait, sa production, et ses matieres grasses des matinees et des apre&-midis. 11 y avait une correlation positive entre le regime d'ecoulement du lait et la production, et une correlation negative entre le regime d'ecoulement et I'Age et les cellules somatiques du lait. 11 y avait une correlation negative entre Ia production de lait et les cellules somatiques. Ursachen von Variationen in der Mllchprodaktion bel Mllchldihen unci dle Beziehang zwischen Milchprodaktion, Zusammensetzang der Mllch, Alter und can StacliUJD der Laktation (Ratbore) ZusaDlDlenfassang. Von I 2 niihrenden Ktihen wurde die durchschnittliche Milchproduktion wahrend zweier Wochen dadurch bestimmt, dass am Freitag und Dienstag nachmittags der durchschnittliche Milchfluss und die Milchproduktion einzelner Ki.ihe notiert wurde und ebenso am Samstag und Mittwoch morgen. Es fanden sich entsprechend den individuellen Tieren Unterschiede von I Prozent hinsichtilich Milchfluss, Milchproduktion, Fettgehalt und Eiweissgehalt; desgleichen gab es diesbeztigliche signifikante Verschiedenheiten zwischen Morgenund Nachmittagmilch.

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Zwischen Milchfluss und Milchproduktion hestand eine positive Korrelation und eine negative hinsichtlich des Alters und des Zellgehalts in der Milch. Milchproduktion war negativ in Korrelation mit somatischen Zellen. Fuentes de variaci6u en Ia raz6u de ftujo de Ia lec:he y sus relacioues con Ia producci6u de Ia lec:he, coDlposici6u de Ia lec:he, edad y etapa de lactaucia de las vacas lec:heras (Rathore) ResUDlen. Se emplearon doce vacas lactante para obtener Ia raz6n media de flujo de leche por un perlodo de 2 semanas, en que se registraron las razones medias de flujo de leche y de producci6n de cada vaca de los ordeiios de las tardes del viernes y martes y de las mananas del sabado y miercoles de ambas semanas. Las variaciones entre los animales fueron significantivos al nivel dell por ciento en cuanto a los porcentajes de Ia raz6n de flujo de leche, de Ia producci6n, de Ia grasa lactea y de las proteinas Iacteas. Se dieron diferencias significativas entre los porcentajes de raz6n de flujo, producci6n y grasas lacteas entre los ordeiios de Ia manana y de Ia tarde. La raz6n de flujo se correlacion6 positivamente con Ia producci6n de leche, y se correlacion6 negativamente con Ia edad y las celulas somaticas de Ia leche. La producci6n de leche se correlacion6 negativamente con las celulas somaticas.

Sources of variation in the milk flow rate and its relationships with milk yield, milk composition, age and stage of lactation in dairy cows.

Br. vet.]. (1976), 132, go SOURCES OF VARIATION IN THE MILK FLOW RATE AND ITS RELATIONSHIPS WITH MILK YIELD, MILK COMPOSITION, AGE AND STAGE OF LACTA...
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