Last update: February 4, 2015 07:42:05 AM E-mail Print

 

PREDICTION OF LAMBING DATE BASED ON CLINICAL EXAMINATION PRIOR TO PARTURITION IN EWES

 

J.V. Viljoen

 

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

Email: Johan Viljoen

 

INTRODUCTION

Farmers who previously applied an extensive lambing system are now increasingly making use of the lambing pen system. Advantages of this system are that newborn lambs are less exposed to climate risks, fewer lambs are lost due to predation, improved care and observation of ewes and newborn lambs is possible during lambing. As a result, the weaning percentage can be increased.

 

The farmer, however, has to keep the ewes in the lambing pen for as short a time as possible. The main reasons for this are:

 

The gestation period varies from 140 to 155 days in domestic sheep breeds and can be up to 170 days in some wild breeds. Pregnancy is one to two days shorter if the ewe is carrying more than one lamb (Lynch et al., 1992).

Arnold & Morgan (1975) observed the lambing behaviour of seven breeds of domestic sheep and although there was considerable variation in the length of pre-parturient behaviours, the same behaviours were seen regardless of breed or age of the ewe. Pre-parturient behaviour of ewes includes alternately standing and lying down, walking in circles, sudden movement for about 10 meters, licking the lips or making a tongue movement into the air, licking the ground where amniotic fluid has been spilt, pawing the ground and making distress calls. An initial sign of imminent parturition is restlessness. This is shown by two-thirds of ewes and generally occurs within three hours of parturition. Another pre-parturient behaviour pattern is the interest shown in the newborn lambs and the amniotic fluid of other ewes. This behaviour, induced by elevated levels of oestrogen in the ewe from 12 hours before parturition, can also include attempts to foster another ewe’s lamb (Lynch et al., 1992, Florence, 2002).

 

From about day 135 of pregnancy, the following signs usually mean that delivery will be during the next 2 to 15 hours (Pearl et al., 1998): 

 

Some ewes show no or only a few of these signs.  An accurate set of flock records, including mating dates, is the most accurate indication that lambing is rapidly approaching. The practice of scanning the ewes to get an indication of the time of lambing depends on the experience and therefore the accuracy of the scan operator.

During the second half of gestation, changes occur in the pregnant ewe. Most signs of approaching parturition relate to changes in the pelvic ligaments, enlargement of the vulva, and mammary activity (Hafez, 1987). Some farmers separate the ewes that are closest to lambing by checking the udder size. About two to three weeks before the expected lambing commences, all the ewes that show udder development are put separately into a lambing camp. This practice continues regularly until the end of the lambing season.

The objective of this trial was to determine if clinical parameters could provide a basis for the prediction of a lambing date.

 

MATERIALS AND METHODS

GADI-Trial

The initial part of the trial was done in the lambing pens during the spring lambing season of 2010 at Grootfontein Agricultural Development Institute (GADI) near Middelburg in the Eastern Cape Province. Fifteen 8-tooth and fifteen 6-tooth ewes from the Dohne Merino flock at GADI were used for this trial.

The ewes were placed into the lambing pens (1.5 m x 1.5 m) about 10 days before the expected onset of lambing, where they were fed pellets and had ad libitum access to water. The pregnancy status of the ewes was confirmed by ultrasound and only single lambing ewes were selected for this trial. Data collection started the day after the ewes were placed in the pens and ended at lambing.

Various parameters were assessed twice daily at 08:00 and 15:00 for all ewes. The parameters and the scale of assessment are summarised in Table 1. The time of lambing was recorded to the nearest possible hour. The pens were again visited between 21:00 and 22:00 to record any lambing that had taken place.

 

On-farm trials

The results of the GADI trial were applied in follow up on-farm trials during 2011. Three parameters were identified that showed high R2 values, as well as appeared to be the best practical indicators of the lambing date. These parameters were udder size, udder tone and colostrum viscosity. The 2011 trials took place on three farms, namely Cypherwater (Richmond district), Elandsheuwel and The Willows (Middelburg district). Assessments were done on the ewes on a weekly basis. A decision was made to use a combined scoring system including udder size, udder tone and colostrum viscosity. At Elandsheuwel and Cypherwater, this combined scoring system was implemented and ewes with a combined score of nine or above were put into the lambing pens.

When the trial was done on the The Willows, and with input from the farmer, two other parameters were added. These were body shape and udder position relative to the ventral line of the abdomen. The assessment of these parameters is described in Table 2.

 

Table 1. Scale of assessment of parameters

Parameter

Scale of assessment

1

2

3

4

5

Udder size

One average man’s fist

1.5 fists

Two fists

2.5 fists

Three fists

Udder filling (indicated by area around teat that bulges)

No bulging out

Start to bulge

Moderate bulging

Even more bulging

Extensive bulging

Udder tone

No tone

 

Medium tone

 

Firm tone

Colostrum quantity

No colostrum

Colostrum in one half only or only a small quantity in both halves

Colostrum in both halves

 

Colostrum runs freely when milked

Colostrum consistency and viscosity

Greasy or sticky and glassy yellow

Hanging on a string when milked and appears more grey

Looks and runs like cold condensed milk

Looks and runs like warmed up condensed milk

“Ideal milk” like

Vulva colour

Pale pink

Light pink

Dark pink (congested)

 

 

Vulva consistency

Firm

Relaxed/pasty

Flabby and slightly swollen

Swollen

Highly swollen with oedematous edges of vulva

Vulva swelling

Normal

Slightly

Big swelling

Largely swollen (only with twins)

 

Vulva moistness

 

Dry appearance

Slightly moist

Moist

 

 

Double folds appearance (lateral of vulva)

No double folds

Folds getting bigger

Largely swollen

 

 

Perineum colour

Pale

Slightly pink

Very pink

 

 

Vaginal opening (dorsal to ventral)

One adult male finger fits in like a normal barren ewe

Two fingers fits in

2.5 fingers width

Three fingers

Four fingers

Mucous secretion / mucous plug

No mucous

Small amount of mucous

Mucous string hangs out/large amount

 

 

 

Table 2. Scale of assessment of additional parameters

Parameter

Scale of assessment

1

5

Body shape

Barrel shape

V-shape or triangular shape like a dairy cow

Udder position

Udder positioned high between the hind legs

Udder dropping until in horizontal line with ventral line of abdomen

 

During the 2012 lambing season these trials were repeated at GADI and The Willows on singleton ewes, and at Elandsheuwel on twin-bearing ewes. The ewes that were expected to lamb within the next seven days were put in a group in smaller paddocks separate from the rest of the flock.

 

Results and Discussion

GADI trial - 2010

The relationship between the different pre-partum indicators and time until lambing was determined by fitting a linear regression model for each trait. Only data recorded within the last seven days before lambing were used in the analysis. The relationship between the parameters and days before lambing, as well as the R2 values, are given in Table 3. For all parameters, there was a highly significant relationship with time, but the R2 values were low, ranging from 0.006 (mucous secretion) to 0.1660 (udder fill).

 

Table 3. Relationship between the parameters and days before lambing

Parameters

Equations

R2

Udder size

Y = -0.1638x + 4.7843

0.1088

Udder tone

Y = -0.0876x + 4.6187

0.0603

Udder fill

Y = -0.2240x + 2.7851

0.1660

Colostrum quantity

Y = -0.2899x + 4.0183

0.1161

Colostrum viscosity

Y = -0.3773x + 3.9635

0.1555

Vulva consistency

Y = -0.0500x + 3.2430

0.0245

Vulva swelling

Y = -0.0534x + 2.9297

0.0441

Vulva opening

Y = -0.0795x + 3.4627

0.0234

Double folds

Y = -0.0764x + 2.7110

0.0507

Vulva moistness

Y = -0.0606x + 2.5559

0.0632

Vulva colour

Y = -0.0535x + 2.7702

0.0505

Perineum colour

Y = -0.0404x + 2.5353

0.0262

Mucous

Y = -0.0134x + 1.1437

0.0060

Combined (udder fill, colostrum quantity and colostrum viscosity)

Y = -0.8294x + 12.7600

0.1772

 

In order to obtain a practical tool for on-farm implementation, various combinations of parameters were made. The combination that showed the highest R2 value, were udder fill, colostrum quantity and colostrum viscosity. The combined scores for these three parameters for the last seven days before lambing are depicted in Figure 1. It implies that if all ewes with a combined score of seven or more are put in the pens, they should lamb within the next seven days.

 

Figure 1. Combined values of udder size, colostrum quantity and colostrum viscosity

 

This concept was tested using the data collected during the GADI trial. A specific date during the first week was identified. A combined score of seven was taken as the cut-off point. All ewes with a combined score below seven, remained in the flock in the veld, while those with a combined score of seven or above, were put in the pens. Subsequently, the accuracy of this prediction was determined from the actual lambing dates. This was repeated for all four weeks of the lambing season. The results are summarised in Table 4.

 

Table 4. Accuracy of prediction of lambing within 7 days – GADI 2010

Ewes correctly included - Percentage of ewes that lambed within 7 days that were predicted to lamb within 7 days

50%

Ewes incorrectly excluded - Percentage of ewes that lambed within 7 days that were predicted not to lamb within 7 days

13%

 

From Table 4 it is evident that the prediction of which ewes will lamb within the next seven days was not very accurate, as 50% of the ewes that would have been put in the pens took longer than seven days before lambing, and 13% of the ewes that would have been left in the field, lambed within that week.


On-farm trials - 2011

With the extension of this trial into August 2011, a combination of udder size, udder tone and colostrum viscosity, was evaluated. The parameters that were selected for this combination were the ones that were quick and easy to assess when evaluation takes place on the farm. In order to make it practical for the farmer to apply, evaluation on the ewes was done on a weekly basis according to a combined score of the parameters. The ewes were divided into two groups according to the total combined values. Group 1 was put into the lambing pens as they were expected to lamb within the next seven days. Continuous observation was done on a daily basis on these ewes. Group 2 was put in a camp where less frequent observation took place during the week, as these ewes were not expected to lamb within the next week.

The condition of the ewes on the different farms, as well as their grazing and feeding patterns, varied and thus the total combined values for each group had to be adapted from farm to farm. Even the udder size and amount of milk in the udder at the same stage of pregnancy on the different farms varied. Thus the values determined for the different groups on the various farms differed. At Cypherwater the udders of the ewes were much bigger at the same stage of gestation than those at Elandsheuwel. Therefore a higher combined score was used as cut-off point. Group 1 had a score of ≥9 and Group 2 ewes had a score of  <9. The results are summarised in Tables 5 and 6 for Cypherwater and Elandsheuwel respectively.

 

Table 5. Accuracy of prediction of lambing within 7 days – Cypherwater 2011

Ewes correctly included - Percentage of ewes that lambed within 7 days that were predicted to lamb within 7 days

30%

Ewes incorrectly excluded - Percentage of ewes that lambed within 7 days that were predicted not to lamb within 7 days

28%

 

Table 6. Accuracy of prediction of lambing within 7 days – Elandsheuwel 2011

Ewes correctly included - Percentage of ewes that lambed within 7 days that were predicted to lamb within 7 days

46%

Ewes incorrectly excluded - Percentage of ewes that lambed within 7 days that were predicted not to lamb within 7 days

26%

 

The mating period at Elandsheuwel was 37 days, and closer to the end of the lambing season the prediction of lambing was less accurate on this farm. The percentage of ewes that had a much smaller udder (three according to assessment of udder size in Table 1) but with a tone score of four also started lambing within seven days closer to the end of the lambing season, which was not the case at the beginning of the season. This contributed to the overall lower accuracy of prediction at Elandsheuwel (Table 6).

Another factor that affects the accuracy of the prediction of lambing is the length of the wool, as it is more difficult to score the ewe when her wool is long. At Cypherwater, there were ewes with long wool and short wool in the same flock, compared to Elandsheuwel where all the ewes had short wool. Some other factors also affected the parameters that were evaluated to predict lambing date. These were age of the ewes, single or twin bearing ewes, the difference in milk production of the ewes, type of feed that the ewes received, condition of the ewes and the differences in udder size. Certain ewes have a smaller udder than others because of their genetics and sometimes they lamb before ewes with bigger udders. In the same way, some ewes have milk in their udders a week before lambing while the udders of their contemporaries get filled with milk only a day or two before lambing.

Ewes of different ages in the same flock complicated the prediction. The udders of older ewes expand much quicker towards the end, compared to younger ewes whose udders develop over a more extended period. The younger ewes keep the barrel body shape until right before lambing (Figure 2), whereas older ewes turn into the V-shape or triangular shape a few days before the due date (Figure 3), thus making it easier to predict the lambing date.

 

Figure 2. Barrel shaped body of younger ewe Figure 3. V-shape in ewe no. 7

 

At The Willows two additional parameters, namely body shape and position of the udder (in relation with the caudoventral line of the abdomen) in combination with the previous three parameters, were observed. These parameters are difficult to evaluate when the ewe is standing in a pen and are best evaluated from a distance. The results of the evaluation at The Willows are indicated in Table 7. Adding body shape and position of the udder increased the accuracy of prediction. However, the number of ewes incorrectly excluded, remained around 25%.

 

Table 7. Accuracy of prediction of lambing within 7 days – The Willows 2011

Ewes correctly included - Percentage of ewes that lambed within 7 days that were predicted to lamb within 7 days

88%

Ewes incorrectly excluded - Percentage of ewes that lambed within 7 days that were predicted not to lamb within 7 days

24%

 

 

Figure 4. Udder filling and position of udders

 

Figure 4 gives a view on the udder filling and udder position from behind the ewes that are at different stages of gestation. The ewe in the middle and on the right is about 24 to 48 hours away from lambing, whereas the ewe on  the left is more than seven days from lambing.

 

On-farm trials – 2012

The trials were repeated during the 2012 lambing season at GADI and Elandsheuwel. From the results in Tables 8 and 9 it is evident that accuracy of prediction is higher when combining udder size, udder tone, udder position, body shape and colostrum viscosity. However, there were still 20% ewes that lambed which were not predicted to lamb.

 

Table 8. Accuracy of prediction of lambing within 7 days - GADI 2012

Ewes correctly included - Percentage of ewes that lambed within 7 days that were predicted to lamb within 7 days

81%

Ewes incorrectly excluded - Percentage of ewes that lambed within 7 days that were predicted not to lamb within 7 days

19%

 

Table 9. Accuracy of prediction of lambing within 7 days - Elandsheuwel 2012

Ewes correctly included - Percentage of ewes that lambed within 7 days that were predicted to lamb within 7 days

67%

Ewes incorrectly excluded - Percentage of ewes that lambed within 7 days that were predicted not to lamb within 7 days

Not recorded

 

CONCLUSIONS

During the 2010 GADI trial, there was a significant relationship with time for all parameters, but the R2 values were low. The combination of the parameters udder fill, colostrum viscosity and colostrum quantity had the highest R2 values. With the follow up on-farm trials another combination of parameters were evaluated namely udder size, udder tone, udder position, body shape and colostrum viscosity and the subsequent accuracy of prediction was higher. However, there were still about 20% ewes that lambed which were not predicted to lamb.

Including more parameters in the evaluation process increased the accuracy of prediction of lambing within 7 days. This will contribute to farmers saving days in the pens. Keeping the ewes in the veld and only selecting the ewes that were within 7 days of lambing once a week to bring into the lambing pens or small camps would reduce the cost of extra feed and labour during the lambing season.

Farmers are increasingly using the lambing pen system or even small paddocks to lamb and this model will be of benefit to the sheep industry. The cost implication of penning the ewes at lambing is the main reason why farmers would like to keep the ewes in pens for as short a time as possible and this model could be a valuable tool in lowering the cost.

 

REFERENCES

Arnold, G.W. & Morgan, P.D., 1975. Behaviour of the ewe and lamb at lambing and its relationship to lamb mortality. Appl. Anim. Ethol. 2, 25-46.

Florence, R., 2002. Lambing FAQ: What special care do ewes require before lambing?

       http://www.sheepscreek.com/rural/lamb.html.

Hafez, E.S.E., 1987. Reproduction in Farm Animals, 5th Edition, pp. 229-258.

Lynch, J.J., Hinch, G.N. & Adams, D.B., 1992. The behaviour of sheep, Biological Principles and Implications for Production, CSIRO, pp. 126-152.

Pearl, R., Heckart, M. & Wehmer, C., 1998. The lambing process.

http://ag.ansc.purdue.edu/sheep/ansc442/Semprijs/lambing/lamb/html.

 

Published

Grootfontein Agric 15 (1) (42)