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LACTATION CURVES OF WOOL SHEEP EWES UNDER

DIFFERENT GRAZING CONDITIONS

 

M.A. Snyman1# & S.W.P. Cloete2


1 Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900

2 Institute for Animal Production: Elsenburg, Private Bag X1, Elsenburg, 7607 

# E-mail: Gretha Snyman

 


 

INTRODUCTION

In many sheep breeding enterprises, being it wool or mutton sheep, early growth is one of the most important traits contributing to income of a specific enterprise. The earlier market weight is reached, the more ewes can be kept on a specific farm. Factors influencing early growth of a lamb are the lamb’s own additive genes for growth, as well as the milk production and general maternal ability of its dam. It therefore follows that selection should be based on growth rate or body weight and on maternal traits (milk production and general maternal behaviour).

 

Body weight has always been one of the important traits considered during selection of both replacement ewes and rams in many wool and mutton sheep breeding enterprises. Using body weight as the sole selection criterion for improved early growth rate in lambs could, however, have the following detrimental effects:

Firstly, overall efficiency of pre-weaning growth could be negatively influenced due to a possible negative genetic relationship between additive direct and additive maternal components of traits affected by both direct and maternal effects. Early growth traits in sheep all fall within the latter category.

 

Secondly, as body weight at all ages is highly genetically correlated, increasing body weight at an early age will also increase mature body weight. This will have a negative effect on overall profitability of the enterprise, if the increase in body weight is not accompanied by an increase in lambing percentage or a net increase in income from wool production.

 

Maternal breeding values for early growth traits have been estimated for numerous sheep breeds and flocks over the past decade. Few, if any, of these studies have led to the implementation of breeding plans incorporating maternal breeding values in sheep. In beef cattle breeding, maternal breeding values for birth and weaning weight are readily used as selection criteria. Maternal effects might be more important in sheep than in cattle, as milk represents a larger component of pre-slaughter nutrition in lambs.

 

It is therefore important that selection emphasis should be shifted from body weight to include some measure of maternal performance as well, be it direct maternal breeding values for early body weight, such as weaning weight, or milk production potential of the ewe. Meyer et al. (1994) reported that milk production of the dam is the main determinant of maternal effects on growth of beef calves. Furthermore, it has also been reported that differences in milk production of beef cows affect weaning weight of their calves (Minick et al., 2001). Expected differences in milk production of progeny of sires accurately predicts differences in actual milk production of their daughters and weaning weight of the daughters’ calves, and can be used in a selection programme (Diaz et al., 1992; Minick et al., 2001; Baker et al., 2003). 

 

The use of maternal breeding values for early body weight and expected progeny differences in milk production, hold possibilities for implementation in the sheep breeding industry. This is especially true in flocks where an increase in body weight could not be accompanied by an increased lambing percentage, due to the specific flock already having a high lambing percentage. No literature references on the relationship between maternal breeding values for early growth traits of sires and milk production of their daughters could be found for sheep. This relationship should therefore be investigated in various sheep flocks before recommendations as to its implementation in practice could be made.

 

A project was implemented with the aim to determine milk production of individual ewes in four wool sheep flocks under different grazing conditions, in order to evaluate the use of maternal breeding values for early growth traits as alternative or additional selection criterion for improved growth efficiency in slaughter lamb production enterprises.

 

Differences in total milk production as well as the shape of the lactation curve have been reported for various sheep breeds (Corbett, 1968; Torres-Hernandez & Hohenboken, 1979; Reynolds & Brown, 1991; Snowder & Glimp, 1991; Sakul & Boylan, 1992; Ramsey et al., 1998; Cardellino & Benson, 2002). It is therefore necessary to determine the shape of the lactation curve in the experimental flocks in order to determine the most suitable time as well as number of measurements needed for recording of data on milk production of ewes. Therefore, during the first year of the project, repeated milk recordings were done on a selected sample of each ewe flock, in order to obtain the average shape of the lactation curves for the ewes in each of the four flocks. These lactation curves, total milk production and milk composition over the lactation period are reported in this paper.

 

MATERIAL AND METHODS

Animals of the Afrino flock at the Carnarvon Experimental Station, Dohne Merino flock at Grootfontein Agricultural Development Institute, Fine wool Merino stud at Cradock Experimental Station and ewes from the high and low reproduction lines of the Merino flock at the Elsenburg Agricultural Development Institute were included in this study.

 

Experimental ewes were selected from the ewes that lambed during the second week after lambing commenced. It was planned to include at least five ewes suckling single lambs and five ewes suckling twin lambs in each of three ewe age groups (two, three and four to six years of age), totalling 30 ewes per flock. Unfortunately, no 3-year old ewes with single lambs were available in the Afrino flock. Four Afrino ewes also died due to plant poisoning during the seventh week of lactation. No 3-year old Fine wool Merino ewes were available either, while only those Elsenburg ewes as summarised in Table 1, were available for milk recordings.

 

Table 1. Experimental layout for obtaining lactation curves for ewes in the four flocks

Number of suckling lambs

Afrino (n=25)

Age of ewe (years)

2

3

4-6

Single

6 (Group 1)

 

5 (Group 5)

Twins

5 (Group 2)

5 (Group 4)

4 (Group 6)

 

Dohne Merino (n=30)

Age of ewe (years)

2

3

4-6

Single

6 (Group 1)

2 (Group 3)

8 (Group 5)

Twins

3 (Group 2)

6 (Group 4)

5 (Group 6)

 

Cradock fine wool Merino (n=20)

Age of ewe (years)

2

 

4-6

Single

6 (Group 1)

 

5 (Group 3)

Twins

4 (Group 2)

 

5 (Group 4)

 

Elsenburg Merino (n=17)

Age of ewe (years)

2

 

4-6

Single (Low line)

3 (Group 1)

2 (Group 2)

 

Single (High line)

3 (Group 5)

 

5 (Group 4)

Twins (High line)

 

 

4 (Group 3)

 

Milk production of the ewes was determined at 7, 14, 21, 28, 35, 49, 63, 77 and 98 days after lambing, as well as at weaning, through the oxytocin technique (Gardner & Hogue, 1964; Corbett, 1968; Doney et al., 1979; Torres-Hernandez & Hohenboken, 1979, 1980; Reynolds & Brown, 1991; Bencini et al., 1992; Ramsey et al., 1998; Cardellino & Benson, 2002). On the day of milk recording, the lambs were removed from the ewes at 08:00. Each ewe was injected intramuscularly with 10 IU of oxytocin (Fentocin®, Virbac). The ewes were hand milked immediately after injection, until no more milk could be withdrawn from the udder. This milk was discarded and the time recorded. After a three-hour period, during which the lambs were still kept away from the ewes, the ewes again received a 10 IU oxytocin injection. They were hand milked again until no more milk could be withdrawn from the udders. This milk was recorded in millilitre. During the second milking, the ewes were milked in the same order as during the first milking, to ensure a three-hour inter milking period for each ewe.

 

Milk samples were collected from each Afrino, Dohne and Elsenburg ewe at each milking in standard milk sampling bottles obtained from the Milk Recording Scheme. Milk fat, milk protein and lactose were determined on each sample at Lactolab at Irene.

 

Calculation of daily and total milk production

Daily milk production (DMP) was calculated by multiplying the 3-hour milk production by 8 for each milking recorded. Daily milk production for the weeks when actual milk production was not recorded (Weeks 6, 8, 10, 12 and 14 to 16) was calculated by obtaining the average production of the two adjacent weekly values. Where there were two or three weeks between adjacent recordings, weekly milk production was obtained by intrapolation.

 

Total milk production per week over the lactation period (TMP1 to TMP17) was calculated by obtaining the average production of the two adjacent DMP weekly values, multiplied by 7. The first week’s TMP1 was obtained by multiplying DMP1 with the actual days of lactation of each ewe. Total milk production and average milk production per day (MP_DAY) over the 17-week lactation period, were also calculated.

 

RESULTS AND DISCUSSION

The average daily milk production over the 17 weeks of lactation is presented in Table 2 for the Afrino, Dohne, Fine wool and Elsenburg ewes respectively. The total milk production over the lactation period (TMP) is given in Table 3.

 

Table 2. Daily milk production (ml ± s.e.) of ewes over the 17-week lactation period

Week

Afrino

Dohne

Cradock fine wool Merino

Elsenburg Merino

DMP1

1242±368

1922±526

2261±689

 

DMP2

1089±422

1699±436

2316±882

1579±304

DMP3

1170±288

1907±427

2346±683

1592±487

DMP4

1371±293

2000±363

2159±905

1444±347

DMP5

1131±328

1718±522

1860±739

1095±340

DMP6

1116±232

1809±377

1776±555

1098±455

DMP7

1102±236

1581±259

1692±587

1143±478

DMP8

948±177

1354±310

1495±367

1126±360

DMP9

794±212

1245±244

1298±377

1109±289

DMP10

745±156

1136±291

1366±407

1047±201

DMP11

696±195

949±197

1434±582

984±189

DMP12

706±145

763±157

1277±435

873±190

DMP13

715±166

703±142

1120±404

761±218

DMP14

662±147

642±142

999±332

665±182

DMP15

608±142

582±155

876±304

570±152

DMP16

554±152

522±178

757±331

474±134

DMP17

500±175

462±209

636±401

379±131

MP_DAY

912±146

1260±162

1555±368

965±177

* DMP1 = Daily milk production during Week 1 of lactation, etc.

   MP_DAY = Average milk production per day over the 17-week lactation period

 

Differences between Afrino groups were only observed for DMP3, DMP7, DMP13, DMP14, DMP16 and DMP17. No group differences in average milk production per day, or in total milk production over the lactation period, were recorded for the Afrino ewes. This is in contrast with data recorded in 1995 on the same flock, where ewes rearing twin lambs had higher milk production. The very dry and poor grazing conditions during the current recording period, most probably accounted for the fact that no differences were observed. Significant differences between the different Dohne groups were recorded over most of the lactation period. Young ewes and older ewes with single lambs produced significantly less milk than 3-year old and older ewes rearing twins. Differences between Cradock fine wool Merino groups were only observed for weeks one to nine. Group differences in average milk production per day and in total milk production over the lactation period were recorded, where young ewes and single rearing ewes produced less milk than older and twin rearing ewes. In the Elsenburg Merino flock, differences among groups in the weekly milk productions were observed from weeks two to five, and again from weeks 10 to 17. In terms of average and total milk production, single rearing young ewes of both the low and high reproduction lines produced less milk than the older and twin rearing groups.

 

Table 3. Total milk production (ml ± s.e.) of ewes over the 17-week lactation period

 

Afrino

Dohne

Cradock fine wool Merino

Elsenburg Merino

Group 1

106 750±7 176

133 415±7 939 (4,6)

162 991±18 045 (2)

86 819±12 294 (3, 4)

Group 2

105 796±7 861

141 223±11 227 (4,6)

229 943±22 101 (1, 3)

108 584±15 056

Group 3

 

152 823±13 750

154 779±19 768 (2, 4)

142 639± 10 646 (1, 5)

Group 4

116 910±7 861

171 503±7 939 (1,2,5)

212 056±19 768 (3)

129 668±9 522 (1, 5)

Group 5

112 810±7 861

139 689±6 875 (4,6)

 

90 561±12 294 (3, 4)

Group 6

104 797±8 789

171 846±8 696 (1,2,5)

 

 

Average

109 491±17 577

151 185±19 445

186 595±44 202

115 777±21 293

1,2,3,4,5,6 = Values differed significantly (P<0.05) from those groups indicated in the superscripts

 

Cradock fine wool Merino and Dohne ewes produced more milk per day and in total than the Afrino and Elsenburg ewes, indicative of the better grazing conditions at Cradock and Grootfontein during the recording periods.

 

Lactation curves

Total weekly milk production was used to obtain lactation curves for the various flocks. The lactation curves for all the ewes (data pooled per flock) are illustrated in Figure 1 and the equations summarised in Table 4. When comparing milk production of the different ewes, large differences in the shape of the lactation curves of individual ewes, within groups and breeds, were observed.

 

 

Figure 1. Lactation curve of Afrino ewes

 

Table 4. Lactation curves for Afrino, Dohne, Fine wool and Elsenburg ewes over the 17-week lactation period

Flock

Lactation curve

R2

Afrino

y = 0.5495x2 – 372.32x + 9733.8

0.9249

Dohne

y = -22.427x2 – 310.32x + 14041

0.9480

Fine wool

y = 7.7916x2 – 896.65x + 18228

0.9783

Elsenburg

y = -3.9343x2 – 433.1x + 11789

0.949

 

 

Milk composition

The percentages of fat, protein and lactose recorded in milk samples taken over the lactation period are presented in Table 5 for the Afrino, Dohne and Elsenburg ewes. Only the averages for all ewes are presented, as there were generally no significant differences among groups with regard to any of the milk composition traits.

Table 5. Milk composition (± s.e.) of Afrino, Dohne and Elsenburg Merino ewes over the lactation period

Afrino

 

W1*

W2

W3

W4

W5

W7

W9

W13

 

Fat (%)

7.95±1.23

7.34±1.27

6.41±1.29

6.13±1.73

6.46±1.49

5.91±1.14

5.56±1.75

6.20±2.70

 

Protein (%)

4.46±0.43

4.26±0.31

4.07±0.35

4.07±0.87

4.25±0.28

4.58±0.44

4.39±1.04

4.86±1.73

 

Lactose (%)

4.93±0.26

5.07±0.24

4.95±0.16

4.82±1.00

4.85±0.23

5.08±0.21

4.88±1.03

4.27±1.60

 

Dohne

 

W1*

W2

W3

W4

W5

W6

W8

W10

W12

Fat (%)

7.79±2.11

6.69±1.18

6.75±1.17

5.28±2.88

6.56±1.20

5.95±0.80

5.95±1.62

6.86±1.20

7.38±1.39

Protein (%)

4.72±0.39

4.23±0.31

4.43±0.33

3.52±1.65

4.26±0.23

4.89±0.34

4.57±0.98

5.19±0.41

5.75±0.62

Lactose (%)

4.91±0.27

5.40±0.14

5.33±0.17

4.40±2.04

5.27±0.12

5.36±0.15

4.86±0.92

4.93±0.13

4.87±0.18

Elsenburg Merino

 

W2

W3

W4

W5

W6

W7

W9

W11

W13

Fat (%)

7.55±1.25

7.25±1.44

8.06±1.42

8.44±2.61

8.00±2.63

7.17±1.35

7.61±1.60

7.16±1.45

7.79±1.22

Protein (%)

4.35±0.56

4.25±0.47

4.29±0.59

4.38±0.69

4.84±0.39

4.96±0.39

5.50±0.51

5.79±0.57

5.76±0.66

Lactose (%)

4.99±0.59

5.07±0.44

5.16±0.36

4.95±0.70

4.77±0.49

5.00±0.30

4.84±0.37

4.69±0.61

4.50±0.51

* W1 = Week 1 of lactation, etc.

 

CONCLUSIONS

There are two aspects of the lactation curve that determine total milk production over the lactation period. These are peak milk production and lactation persistency. DMP3 serves as an indication of the first, while DMP12 can be regarded as giving an indication of the latter. Therefore, for the purpose of predicting total milk production, the milk production during the third and twelfth weeks of lactation will be recorded for all the ewes in these flocks for a 10-year period.

 

ACKNOWLEDGEMENTS

The authors wish to convey their sincere appreciation to all the people at the various Experimental Stations for their valuable assistance in the execution of the project.

 

REFERENCES

Baker, J.F., Boyd, M.E., Brown, A.H., Franke, D.E. & Thompson, C.E., 2003. Evaluation of maternal performance of daughters from high and low milk EPD sires. J. Anim. Sci. 81, 1406-1413.

Bencini, R., Martin, G.B., Purvis, I.W. & Hartmann, P.E., 1992. Use of oxytocin to measure milk output in Merino ewes and its effect on fat content. Aust. J. Exp. Agric. 32, 601-603.

Cardellino, R.A. & Benson, M.E., 2002. Lactation curves of commercial ewes rearing lambs. J. Anim. Sci. 80, 23-27.

Corbett, J.L., 1968. Variation in the yield and composition of milk of grazing Merino ewes. Aust. J. Agric. Res. 19, 283-294.

Diaz, C., Notter, D.R. & Beal, W.E., 1992. Relationship between milk expected progeny differences of polled Hereford sires and actual milk production of their crossbred daughters. J. Anim. Sci. 70, 396-402.

Doney, J.M., Peart, J.N. & Smith, W.F., 1979. A consideration of the techniques for estimation of milk yield by suckled sheep and a comparison of estimates obtained by two methods in relation to the effect of breed, level of production and stage of lactation. J. Agric. Sci. Camb. 92, 123-132.

Gardner, R.W. & Hogue, D.E., 1964. Effects of energy intake and number of lambs suckled on milk yield, milk composition and energetic efficiency of lactating ewes. J. Anim. Sci. 23, 935-942.

 

Published

Grootfontein Agric 8 (1)