Milking characteristics of dairy goats

H. Ilahia, P. Chastina, F. Bouvierb, J. Arhainxa, E. Ricarda, E. Manfredia,*

aINRA, Station d'AmeÂlioration GeÂneÂtique des Animaux, BP 27, 31326 Castanet-Tolosan Cedex, FrancebDomaine INRA de Galle, 18520 Avord, France

Accepted 10 May 1999

Abstract

The objectives of this study were to de®ne and to describe sources of variation and relationships among milking traits of goats.

Two data sets collected at the INRA Experimental Station of Bourges (France) were studied: 51 milkings of 30 goats were

measured using an experimental automated milk jar which records the volume of milk at each second (data set 1), and 1596

milkings of 133 goats were measured routinely using an automated milk recording system (12 milk jars working

simultaneously), recording milk volume every 15 s (data set 2). The analysis of data set 1 indicated that traits associated with

milk ¯ow were closely correlated. In particular, the milk collected during the ®rst minute of milking (MF1), traditionally used

for characterizing milking ability, was highly correlated with the maximum milk ¯ow (MAMF), the average ¯ow during

milking (AMF) and during milk emission (AMFE) (0.92, 0.85 and 0.85, respectively), these last two traits representing the

entire milking (milking time and milk emission). MF1 includes a `latency interval or reaction interval' between the setting-up

of teat cups and the beginning of milk emission. By using the experimental automated milk jar, three candidate traits were

measured and the `latency interval' was estimated: the time at the arrival of milk at the milk claw (TMC), at the test jar (TTJ)

and at the recording of the ®rst quantity of milk in the test jar (TR1). These traits were highly correlated with each other, and

partially correlated with those traits associated with milk ¯ow and milking time (total milking time (TMT) and milking

emission time (MET)). TR1, easily and routinely measured via automated milk recording, can be used to classify animals

according to their `latency interval'. Concerning the data set 2, the correlations between the total milking time (TMT) and the

other milking characteristics were low due to overmilking which may have occurred in routine milkings. MF1 was highly

correlated with MAMF (0.80) while TR1 was negatively correlated with MF1 and MAMF (ÿ0.79 and ÿ0.58, respectively).

The age of female, the lactation stage, the milking time and the random effect of female within year of production had a highly

signi®cant effect on all characteristics of milking, while litter size had no signi®cant effect. Within lactation, repeatabilities of

milking traits were high, in particular for MF1 and TR1. # 1999 Elsevier Science B.V. All rights reserved.

Keywords: Dairy goat; Milking; Milk ¯ow; Milking time; Latency interval; Repeatability

1. Introduction

Milking characteristics of dairy goats have been

measured for optimization of milking operations (Lu

et al., 1991) and physiological studies (Bruckmaier

et al., 1994). In these situations, experimental equip-

ments are used to collect data under controlled con-

ditions. For genetic studies, larger numbers of animals

are usually measured, not only in experimental sta-

tions but also in farms that vary in management

conditions. In this case, it is important to de®ne

Small Ruminant Research 34 (1999) 97±102

*Corresponding author. Tel.: +33-5-61-28-51-87; fax: +33-5-61-

28-53-53

E-mail address: manfredi@germinal.toulouse.inra.fr (E. Manfredi)

0921-4488/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.

PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 0 5 7 - 7

routinely measured traits which describe milking

characteristics adequately. The use of automated milk

recording devices allows routine measurement of

milking traits while reducing milk recording costs

and avoiding errors of measurements due to milker

intervention (Ricard et al., 1994).

The objectives of this study were to de®ne milking

characteristics of goats, easily measured in routine,

and to describe their sources of variation and the

relationships among them. In particular, previous

publications (Ricordeau et al., 1990; Le Roy et al.,

1995; Ilahi et al., 1998) reported high genetic varia-

bility for the quantity of milk collected during the ®rst

minute of milking (MF1) used as an estimate of milk

¯ow and milking speed. In this article, we study the

relationship of this trait with other characteristics of

milking: milking time, latency interval and milk ¯ow.

2. Materials and methods

2.1. Data

All data used in this study were collected at the

INRA Experimental Station of Bourges (France)

which has a rotational milking parlour equipped with

12 stalls and 12 claws. Milking of Alpine goats was

conducted at a vacuum level of 38 kPa, pulsation rate

of 90 pulses/min and pulsation ratio of 2/1. Two data

sets were used in this study.

Data set 1 corresponded to 51 morning milkings of

30 goats whose milking characteristics where col-

lected using an automated experimental jar able to

record milk volume at each second. The goats had

been previously selected for divergent milking speed

and they were milked one at a time to avoid over-

milking. This experimental jar allowed the recording

of the following measures: total quantity of milk

(QM); quantity of milk collected at the ®rst minute

of milking (MF1); time separating the setting-up of

teat cups and the arrival of milk at the milk claw

(TMC); time separating the setting-up of teat cups and

the arrival of milk at the test jar (TTJ); time separating

the set up of teat cups and the recording of the ®rst

quantity of milking the test jar (TR1); and total

milking time (TMT). These measurements allowed

the computation of: maximum milk ¯ow (MAMF);

milking emission time (MET � TMT ÿ TMC); aver-

age ¯ow during milking (AMF � QM/TMT); and

average ¯ow during milk emission (AMFE � QM/

MET).

The second data set corresponded to routine milk-

ings measured by an automated milk recording system

designed by INRA for on-farm applications. This

portable system is composed of 12 test jars which

work simultaneously and allows the measurement of

the quantity of milk collected every 15 s. Data from

the 12 test jars are then transferred and stored in a

computer. Each test jar, having a capacity of 4.5 l, is

equipped with a reed sensor and a ¯oat with a magnet.

The ¯oat and magnet, jointly, are sensitive to the milk

level and provoke the commutation of the reed sensor.

The quantity of milk necessary to induce the ®rst

commutation of the reed sensor is ca. 0.3 kg. This

data set included 1596 milkings corresponding to 133

Alpine goats measured on both, morning and evening

milkings between March and September 1996. The

traits recorded in data set 2 were QM, MAMF, MF1,

TR1 and TMT. Goats were milked routinely; over-

milking was not monitored.

Data set 1 was used to compare exhaustive with

routine milking measurements: TR1 vs. TMC and TTJ

(for latency interval); MAMF and MF1 vs. AMF and

AMFE (for estimates of milk ¯ow). Also, relation-

ships between milking time and other milking char-

acteristics were studied in the absence of overmilking.

Data set 2 was used to describe the relationships

among routinely measured milking traits and their

sources of variation, in particular the variability

among animals.

2.2. Analysis model

The traits QM, MF1, MAMF and TR1 of data set 2

were analyzed with the following mixed model:

Yijklm � �� Chi � ASj � Lsk � Tl � eijklm

where Yijklm is the observation corresponding to the ith

female on the jth age of the female within lactation

stage, the kth litter size and the lth time of milking, m

the population mean, Chi the random effect of female

(133 goats), ASj the age of the female within lactation

stage (four age classes and 11 stages, 28 days per

stage), Lsk the litter size (1, 2, 3 and more), Tl the time

of milking (morning or evening milking), and eijklm a

random residual.

98 H. Ilahi et al. / Small Ruminant Research 34 (1999) 97±102

Effects in the model and variance components for

the female (�ch2) and the residual (�e

2) terms were

estimated using SAS MIXED procedure. Repeatabil-

ities were computed as:

rp � �2ch

�2ch � �2

e

The female variance includes the genetic and the

permanent environmental effects.

3. Results and discussion

3.1. Milking characteristics

Means and standard deviations for each trait in data

set 1 are summarized in Table 1 and the corresponding

correlations are given in Table 2. The correlations

among traits measured in routine (data set 2) are

presented in Table 3.

Estimates of latency interval show a large varia-

bility which depended on the different methods of

measurement. Estimates varied from 3 s for TMC to

45 s for TR1 (Table 1). TMC is the closest to the real

Table 1

Means and standard deviations for each trait (data set 1)

Traits Mean SD

QMa (l) 1.489 0.578

MAMFb (l/min) 0.902 0.497

MF1c (l/min) 0.650 0.364

AMFd (l/min) 0.429 0.222

AMFEe (l/min) 0.433 0.223

TMCf (s) 3.2 3.3

TTJg (s) 12.8 10.2

TR1h (s) 44.7 31.0

METi (s) 236.3 95.5

TMTj (s) 239.6 97.2

a QM, total quantity of milk (l).b MAMF, maximum milk flow (l/min).c MF1, quantity of milk collected at the first minute of milking (l/

min).d AMF, average flow during milking (l/min).e AMFE, average flow during milk emission (l/min).f TMC, time separating the set up of teat cups and the arrival of

milk at the milk claw (s).g TTJ, time separating the set up of teat cups and the arrival of milk

at the test jar (s).h TR1 time separating the set up of teat cups and the recording of

the first quantity of milk in the test jar (s).i MET, milking emission time (s).j TMT, total milking time (s).

Table 2

Correlations between quantity of milk, latency intervals, milking flows and milking times (data set 1)

Traitsc MAMFd MF1e AMFf AMFEg TMCh TTJi TR1j METk TMTl

QMc 0.42b 0.25 0.49b 0.48b ÿ0.34a ÿ0.38b ÿ0.41b 0.18 0.17

MAMFd 0.92b 0.89b 0.89b ÿ0.52b ÿ0.62b ÿ0.67b ÿ0.54b ÿ0.55b

MF1e 0.85b 0.85b ÿ0.45b ÿ0.75b ÿ0.89b ÿ0.52b ÿ0.52b

AMFf 0.99b ÿ0.59b ÿ0.66b ÿ0.70 ÿ0.62b ÿ0.63b

AMFEg ÿ0.58b ÿ0.66b ÿ0.70b ÿ0.63b ÿ0.63b

TMCh 0.93b 0.89b 0.52b 0.54b

TTJi 0.98b 0.58b 0.61b

TR1j 0.62b 0.64b

METk 0.99b

a p < 0.05.b p < 0.01.c QM, total quantity of milk (l).d MAMF, maximum milk flow (l/min).e MF1, quantity of milk collected at the first minute of milking (l/min).f AMF, average flow during milking (l/min).g AMFE, average flow during milk emission (l/min).h TMC, time separating the set up of teat cups and the arrival of milk at the milk claw (s).i TTJ, time separating the set up of teat cups and the arrival of milk at the test jar (s).j TR1 time separating the set up of teat cups and the recording of the first quantity of milk in the test jar (s).k MET, milking emission time (s).l TMT, total milking time (s).

H. Ilahi et al. / Small Ruminant Research 34 (1999) 97±102 99

latency interval while TR1 is a poor estimate of

latency interval because it includes the initial milk

¯ow necessary to reach 0.3 kg of milk collected in the

jar. TTJ is intermediate between both measures,

though closer to TMC. Means of the three traits are

very different but highly correlated (0.89, Table 2).

Although TR1 is not as good as the two other estimates

of latency interval, it can be measured readily in

routine milkings.

Estimates of milk ¯ow (MAMF, MF1, AMF and

AMFE) were variable since milk ¯ow is not constant

during milking time (Table 1). MF1, the trait used to

characterize the milking ability in dairy goats, is lower

than MAMF because it includes two underlying com-

ponents: the real latency interval, without milk emis-

sion, and the milk emission between the beginning of

milk emission and 1 min of milking. MF1, however,

was highly correlated with MAMF (0.92 in data set 1;

0.80 in data set 2), AMF (0.85) and AMFE (0.85). The

last two traits represent the entire milking (milking

time and milk emission).

Relationships between TMC (the measurement of

latency interval which was less confounded with milk

¯ow) and MAMF (a measurement of milk ¯ow which

is not confounded with the latency interval) was about

ÿ0.52 (Table 2). This result suggests the existence of

common biological mechanisms regulating the begin-

ning of milk emission and the subsequent milk ¯ow,

probably depending on the teat characteristics and the

level of intra-mammary pressure. Correlations among

other estimates of, on one hand, milk ¯ow and, on the

other, latency interval ranged from ÿ0.45 to ÿ0.89

(Table 2). In particular, MF1 and MAMF were nega-

tively correlated with TR1 (ÿ0.89 and ÿ0.67, respec-

tively; Table 2). This association between milk ¯ows

and TR1 may be explained, on one hand, by the

characteristics of milking of each animal having an

in¯uence on both the traits (milk ¯ow and latency

interval) and, on the other, by the in¯uence of milk

¯ow on TR1.

Relationships between milk ¯ows, latency intervals

and milk yield showed that QM was moderately

correlated with MF1 and MAMF (0.25 and 0.42,

respectively, in Table 2; 0.32 and 0.48, respectively,

in Table 3). These correlations are higher than the

correlation between MF1, measured at a single milk-

ing, and milk traits calculated on a total lactation basis

(Ilahi et al., 1998). Milk yield (QM) was negatively

correlated (ÿ0.14) with latency interval (TR1) in data

set 2 (Table 3) and in data set 1 (ÿ0.34 to ÿ0.41

between latency intervals (TMC, TTJ and TR1) and

QM in Table 2). The quantity of milk collected

between 1 min and the end of milking (QM ÿMF1),

was highly correlated with the total quantity of milk

QM (0.90) but negatively correlated with MF1

(ÿ0.11). This is because MF1 includes the underlying

component `latency interval' (not shown).

In Table 2, milking times (MET and TMT) were

moderately correlated with milk ¯ows (MAMF, MF1,

AMF and AMFE) and with latency intervals (TMC,

TTJ and TR1), because in data set 1 overmilking was

avoided. For the data set 2, Table 3 shows that the

correlations between the total milking time TMT and

the other milking characteristics were low. These low

correlations possibly arose from overmilking, because

TMT depended not only on the characteristics of milk

emission of each animal, but also on the milker. These

results were similar to other observations reported by

Blanchard (1994) in dairy cattle.

3.2. Factors affecting milking characteristics

In data set 2, the time of milking (morning or

afternoon milkings) was an important source of var-

iation for all characteristics of milking (p < 0.01). The

morning milking presented a higher production level

than the afternoon milking. Correlations between

Table 3

Correlations between quantity of milk, latency interval, milk flows

and milking time (of 1596 milkings measured in the context of

milk recording at Bourges for both morning and evening milkings;

data set 2)

Traits MAMFd MF1e TR1f TMTg

QMc 0.48b 0.32a ÿ0.14 0.38a

MAMFd 0.80b ÿ0.58b 0.05

MF1e ÿ0.79b 0.06

TR1f 0.04

a p < 0.05.b p < 0.01.c QM, total quantity of milk (l).d MAMF, maximum milk flow (l/min).e MF1, quantity of milk collected at the first minute of milking

(l/min).f TR1 time separating the set up of teat cups and the recording of

the first quantity of milk in the test jar (s).g TMT, total milking time (s).

100 H. Ilahi et al. / Small Ruminant Research 34 (1999) 97±102

morning and afternoon characteristics (QM, MAMF,

MF1 and TR1) were over 0.65.

The age of the female, the lactation stage and their

interaction had a highly signi®cant effect on MF1,

MAMF and TR1 (Figs. 1±3). For all age categories

and for all milkings, both the traits associated with

milk ¯ow (MF1 and MAMF) decreased during the

lactation, while the latency interval TR1 increased.

The same relation between milk ¯ow and lactation

stage was observed by Bruckmaier et al. (1994).

Milk ¯ows (MF1 and MAMF) were higher in

second lactations (L2 > L1 > L3 > L4 and more),

Fig. 1. Effects of parity and lactation stage on the quantity of milk

collected at the first minute (MF1). Fig. 2. Effects of parity and lactation stage on the maximum milk

flow (MAMF).

Fig. 3. Effects of parity and lactation stage on the time separating the setting-up of teat cups and the recording of the first quantity of milk in

the test jar (TR1).

H. Ilahi et al. / Small Ruminant Research 34 (1999) 97±102 101

whereas the latency interval TR1 was higher for adult

goats (L4 and more > L3 > L1 > L2). Adult goats

presented a higher production level than primiparous

goats but a lower milk ¯ow and a longer latency

interval. This might be explained by the interaction

between milk secretion level and the development of

the mammary gland and by a possible decrease in

udder wall and muscle tonicity during the productive

life of the dairy goat.

There was no signi®cant effect of the litter size on

any characteristic of milking. This observation is

coherent with that reported by Peris et al. (1996). A

complementary analysis including the interaction of

litter size and lactation stage indicated that litter size

signi®cantly affected QM, MF1, MAMF and TR1

during the beginning of the lactation (stages 1±3).

Estimated variances for the `female effect' and

corresponding repeatabilities within lactation for the

four analyzed traits are given in Table 4. The different

estimates of repeatabilities within lactation were

high, in particular for MF1 and TR1 (0.71 and

0.63, respectively). These last two traits are highly

repeatable and are easily measured during routine

automated milk recording. Therefore, they can be

used to characterize milk emission in dairy goats

for selection purposes.

4. Conclusion

Estimated latency interval (TR1) and estimated

milk ¯ow (MF1) are useful measurements to charac-

terize milking characteristics in dairy goats. These

measurements are readily obtained in routine auto-

mated milk recording. Data collected in this way

permit adjustment for important factors of variation,

such as lactation stage, time of milking (AM, PM) and

age. Genetic parameters reported in this and in pre-

vious studies indicate that individual effects can be

exploited in selection programs for milk ¯ow, if this

trait is not antagonistic with other important traits,

such as udder characteristics and health.

Acknowledgements

The authors acknowledge ®nancial support of the

Ministry of Agriculture of Tunisia and the Animal

Genetic Department of INRA.

References

Blanchard, M., 1994. Le deÂbit maximum d'eÂmission du lait au

cours de la traite (eÂvolution et preÂdiction pour la vache laitieÁre),

conseÂquences pour les compteurs aÁ lait. Milk and Beef

Recording. Proceedings of the 29th Biennial Session of the

International Committee for Animal Recording (ICAR).

Ottawa, Canada. EAAP Publication No. 75, 1995. pp. 53±59.

Bruckmaier, R., Ritter, C., Schams, D., Blun, J., 1994. Machine

milking of dairy goats during lactation. J. Dairy Res. 61, 457±

466.

Ilahi, H., Chastin, P., Martin, J., Monod, F., Manfredi, E., 1998.

Genetic association between milking speed and milk produc-

tion in dairy goats. Proc. 6th World Congr. Genet Appl. Livest.

Prod., Armidale, NSW, Australia, vol. 24. pp. 216±219.

Le Roy, P., Elsen, J.M., Ricordeau, G., Bouillon, J., Manfredi, E.,

Chastin, P., Monod, F., 1995. Mise en eÂvidence d'un geÁne

majeur influenc,ant le deÂbit de traite des cheÁvres. Renc. Rech.

Ruminants 2, 177±180.

Lu, C.D., Potchoiba, M.J., Loetz, E.R., 1991. Influence of vacuum

level, pulsation ratio and rate on milking performance and

udder health in dairy goats. Small Rumin. Res. 5, 1±8.

Peris, S., Such, X., Caja, G., 1996. Milkability of Murciano±

Granadina dairy goats. Milk partitioning and flow rate during

machine milking according to parity, prolificacy and mode of

suckling. J. Dairy Res. 63, 1±9.

Ricordeau, G., Bouillon, J., Le Roy, P., Elsen, J.M., 1990.

DeÂterminisme geÂneÂtique du deÂbit de lait au cours de la traite

des cheÁvres. INRA Prod. Anim. 3(2), 121±126.

Ricard, E., Arhainx, J., Guillouet, P., Bouvier, F., Jacquin, M.,

Chastin, P., Astruc, J.M., Lagriffoul, G., Manfredi, E., Barillet,

F., 1994. On farm test of portable electronic jars for

automatized milk recording of sheep and goats. Proceeding of

29th Session of ICAR Ottawa, Canada. EAAP Publication No.

75, 1995. pp. 47±51.

Table 4

Estimates of variances and within lactation repeatabilities

Traits Phenotypic

variance

Residual

variance

Repeatability

QMa 89221.7 38380.8 0.57

MAMFb 76784.4 34690.7 0.55

MF1c 38376.8 11095.0 0.71

TR1d 222.0 82.5 0.63

a QM, total quantity of milk (l).b MAMF, maximum milk flow (l/min).c MF1, quantity of milk collected at the first minute of milking

(l/min).d TR1, time separating the set up of teat cups and the recording of

the first quantity of milk in the test jar (s).

102 H. Ilahi et al. / Small Ruminant Research 34 (1999) 97±102