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AN INVESTIGATION INTO THE RELATIONSHIP BETWEEN MATERNAL

BREEDING VALUES AND MILK PRODUCTION IN AFRINO SHEEP

 

MA Snyman , J.J. Olivier & J.A.N. Cloete*

Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg Cape, 5900, South Africa

* Carnarvon Experimental Station, Carnarvon, 8925, South Africa

 

 

 1. Introduction

 

The availability of modern statistical software, able to partition variance into components resulting from either direct or maternal effects, caused a general tendency to include estimated maternal breeding values for weaning weight of the sire in the selection programme. These estimated maternal breeding values are assumed to be an indication of the milk production potential of the daughters of the sire. The objective of this study was to investigate the relationship between milk production and estimated maternal breeding values for weaning weight in Afrino sheep.

 

2. Material and methods

 

Fifty-two young Afrino ewes from the Carnarvon Experimental Afrino flock were synchronised with intra-vaginal sponges and hand mated two days after sponge withdrawal, to ensure that the lambs would be born within a week of each other. Milk production of these ewes were determined four, eight and twelve weeks after parturition by means of the oxytocin technique 1,7.

 

Ewes were given 1 cc oxytocin i.m. at 8:00 and the udders were milked out. At 12:00, a second dose of 1 cc oxytocin were administered and the ewes milked again. The milk production of this second milking were recorded in millilitres. This procedure was repeated the following day and the average milk production over these two days were used in the calculations.

 

Correlations of milk production (measured at four, eight and twelve weeks after parturition) with estimated maternal breeding values for weaning weight of the young ewe herself (MBV-WW) and for her sire (MBV-WWS), as well as estimated breeding values for total weight of lamb weaned for the young ewe herself (predicted from her parents' performance; EBV-TWW18), estimated breeding value for total weight of lamb weaned over her dam's lifetime in the flock (EBV-TWWD) and total weight of lamb weaned (TWW) 8 by the young ewe at the first parity (during which the milk production was recorded) were calculated by means of the PROC CORR procedure of SAS 5. Milk production at four, eight and twelve weeks were corrected for age of lambs and birth status of lambs before inclusion in the analyses.

 

3. Results and discussion

 

The mean and standard deviation for milk production (over a 24 hour period), as well as minimum and maximum values for MBV-WW, MBV-WWS, EBV-TWW18, EBV-TWWD and TWW are presented in Table 1, while the estimated correlations are summarised in Table 2.

 

Estimated maternal breeding value for weaning weight of the sire of the young ewe had a negative relationship with milk production measured at four, eight and twelve weeks after parturition. The relationship between estimated maternal breeding value for weaning weight of the young ewe with her own milk production measured at four and eight weeks are also negative, but it became positive at twelve weeks after parturition. This could be ascribed to the fact that milk production becomes less important relative to direct growth as the lamb/s grew older. From these results it is evident that the practise of selecting breeding sires on the basis of estimated maternal breeding values for weaning weight should be viewed with caution.

 

Estimated breeding values for total weight of lamb weaned had a low positive relationship, which also increased from four to twelve weeks after parturition, with milk production. As expected, total weight of lamb weaned by the young ewe had a significant positive relationship with her own milk production. This is in accordance with the positive correlations reported for beef cows 2,3.

 

Table 1. Mean, standard deviation, minimum and maximum values for the traits

 

  Mean SD Minimum Maximum
Milk production Week 4 2152 ml 585 ml 968 ml 3932 ml
Milk production Week 8 1515 ml 332 ml 834 ml 2428 ml
Milk production Week 12 1563 ml 436 ml 794 ml 2483 ml
TWW 48.36 kg 14.48 kg 27.6 kg 79.4 kg
MBV-WW     -0.06 1.74
MBV-WWS     0.37 1.69
EBV-TWW18     2.08 14.97
EBV-TWWD     -6.32 13.44

 

Table 2. Correlations between milk production and estimated maternal breeding values for weaning weight and estimated breeding values for total weight of lamb weaned

 

  MBV-WW MBV-WWS EBV-TWW18 EBV-TWWD TWW

Milk production

Week 4

-0.14

(0.33)

-0.13

(0.36)

0.09

(0.53)

0.05

(0.76)

0.53

(0.00)

Milk production

Week 8

-0.08

(0.56)

-0.17

(0.23)

0.10

(0.47)

0.14

(0.32)

0.51

(0.00)

Milk production

Week 12

0.13

(0.35)

-0.13

(0.35)

0.17

(0.23)

0.17

(0.22)

0.43

(0.00)

TWW

0.30

(0.03)

0.06

(0.69)

0.36

(0.01)

0.26

(0.06)

 

 

 

Conflicting findings regarding the covariance between direct and maternal effects on weaning weight in sheep have been reported 8. A negative relationship between the weaning weight of a heifer and her subsequent mothering ability has also been observed 4. Meyer 6, reporting no such adverse relationship, attributed the negative relationships reported by other workers to the lack of bias due to an unaccounted for negative direct-maternal environmental covariance. From this it can be concluded that the models separating direct and maternal effects are complicated. It is therefore imperative that the correct model be specified for use in analysing the effects contributing to variance in weaning weight, as well as for the resulting estimated breeding values, before these estimated maternal breeding values on weaning weight are made available to the industry. As far as the Carnarvon Afrino flock is concerned, it seems as if the models applied to estimate maternal breeding values for weaning weight were not the optimum models.

 

4. Conclusion

 

From these results it is evident that a further in depth investigation regarding the relationships between milk production, maternal breeding values for weaning weight and total weight of lamb weaned should be done before maternal breeding value for weaning weight could be recommended as a possible criterion in the selection programme of breeding sires.

 

5. References

 

1 ABOUL-NAGA, A.M., EL-SHOBOKSHY, A.S. & MOUSTAFA, M.A., 1981. Milk production from subtropical non-diary sheep. 2. Method of measuring. J. Agric. Sci. Camb. 79 : 303-308.

 

2 BEAL, W.E., NOTTER, D.R. & AKERS, R.M., 1990. Techniques for estimation of milk yield in beef cows and relationships of milk yield to a calf weight gain and post partum reproduction. J. Anim. Sci. 68 : 937.

 

3 CLUTTER, A.C & NIELSEN, M.K., 1987. Effect of the level of beef cow milk production on pre and post weaning calf growth. J. Anim. Sci. 64 : 1313.

 

4 JOHNSON, I.D. & MORANT, S.V., 1984. Evidence of a negative relationship between heifer growth and first calf weaning weight in commercial beef herds. Aust. J. Exp. Agric. Anim. Husb. 24 : 10.

 

 5 LITTELL, R.C., FREUD, R.J. & SPECTOR, P.C., 1991. SAS-system for linear models, 3rd Ed. SAS Institute. Inc. Cary, NC.

 

6 MEYER, K., CARRICK, M.J. & DONNELLY, B.J.P., 1994. Genetic parameters for milk production of Australian beef cows and weaning weight of their calves. J. Anim. Sci. 72 : 1155-1165.

 

7 MOORE, R.W., 1962. Comparison of two techniques for the estimation of the milk intake of lambs at pasture. Proc. Aust. Soc. Anim. Prod. 4 : 66-68.

 

8 SNYMAN, M.A., 1996. An investigation into selection for production and reproduction in Afrino sheep. Ph.D.- dissertation, University of the Orange Free State.

 


 

Published

Proceedings 35th SASAS congress, Nelspruit, 1-3 July