Production responses of two genetic different types of Merino
sheep subjected to different nutritional levels
T.S. Brand
*, F. Franck
Elsenburg Agricultural Research Centre, Private Bag X1, Elsenburg 7607, South Africa
Accepted 5 October 1999
Abstract
The primary selection objective in the South African Mutton Merino is meat production, while wool plays a secondary role. The Merino, on the other hand is selected for wool production. Respectively 20 and 23 of each genetic different type of ewes were used in a 15-week indoor study to quantify the in¯uence of nutrient intake on certain production traits when fed at different levels of their respective requirements during late pregnancy (last 6 weeks) and lactation (®rst 6 weeks). Results were used to provide production parameters for the two types of ewes and their lambs at different levels of nutrition. Lambing percentage (per ewe lambed) of SA Mutton Merino ewes was 171% compared to 135% for Merino ewes. Live weight gains for meat-wool and wool-type ewes during late pregnancy amounted to 15.9 and 21.9%, with corresponding live weight losses of
ÿ8.3 andÿ1.1% during the ®rst 6 weeks of lactation. Greasy wool production during the last 9 weeks of pregnancy and the ®rst 6 weeks of lactation amounted to 1.57 kg eweÿ1 (meat-wool type ewes) and 2.84 kg eweÿ1 (wool-type ewes). Milk
production 17 days post partum was 2.33 kg/day and 1.84 kg/day for the two types of sheep. Lambs of the meat-wool type ewes had a mean birth weight of 4.1 kg and an average daily gain (ADG) of 270 g/day to 42 days of age. Lambs of the wool-type ewes had a mean birth weight of 4.9 kg and a 42-day ADG of 192 g/day. There were clear differences in production traits of the two types of Merino sheep, which were in accordance with their genetic differences. The study gave practical production norms for meat-wool and wool-type Merino ewes and their lambs when subjected to different nutritional levels. #2000 Elsevier Science B.V. All rights reserved.
Keywords:Merinos; Sheep; Production norms; Nutrient intake
1. Introduction
Adequate feeding of the reproducing ewe is of the utmost importance, since under-feeding of the ewe may cause short-term problems like pregnancy
tox-emia (Reid, 1963), a reduction in lamb birth weight, resulting in low survival levels (Schinckel, 1963), low ewe milk production (Alexander et al., 1956), poor lamb growth rate (Stephenson et al., 1981) and a reduced wool production (Allden, 1979). Inadequate feeding, however, may also limit the lifetime produc-tion and reproducproduc-tion of ewes and their lambs (Gunn, 1983). Conversely, high levels of feed may jeopardize lamb survival by a greater incidence of dystocia, in addition to being costly (Curll et al., 1975).
*Corresponding author. Tel.:27-21-8085225;
fax:27-21-80855185.
E-mail address: [email protected] (T.S. Brand)
During the last 8 weeks of pregnancy, the fetus gains 85% of its ®nal birth weight (Robinson, 1983). Nutrition during this stage largely determines the viability and early neonatal progress of lambs (MLC, 1988). Nutrition after lambing, on the other hand, has a major effect on milk production and hence on lamb growth rate (MLC, 1988).
We conducted an experiment to quantify the in¯u-ence of feeding level on some important production parameters of ewes of two genetic different types of Merino sheep and their growing lambs. The primary selection objective in the SA Mutton Merino is meat production, while wool plays a secondary role. The Merino, on the other hand, is selected for wool production. Du Plessis and De Wet (1981) detected differences between these two differently selected Merino types of sheep in the partitioning and utiliza-tion of nutrients for the producutiliza-tion of mutton and wool.
2. Material and methods
2.1. Outline of experiment
A total of 25 SA Mutton Merino and 25 Merino ewes were used in the study. Estrus was synchronised by treatment with Repromap(R) sponges. Ewes were joined from 24 December with rams of the same breeds. On 18 March ewes were strati®ed according to live weight and age and randomly allocated to ®ve experimental groups within breeds. Ewes were housed in individual pens and had free access to water at all times. The groups of ewes were randomly allocated to ®ve experimental treatments within breeds. They received 50, 75, 100, 125 and 150% of their daily requirements (NRC, 1985) for mid-pregnancy, late pregnancy (last 6 weeks of pregnancy) and lactation. The lambs did not have access to feed during lactation. Individual feeding of ewes ceased after 15 weeks (30 June). The ewes and their lambs then grazed lucerne and oat pasture as a single ¯ock.
2.2. Procedures with sheep
The ewes were weighed every 3 weeks. Lambs were weighed at birth, at 42 days in the pens, and at 100 days of age on the pasture. Live weight changes of ewes were determined during the 105-day pen feeding
experimental period, the last 6 weeks of pregnancy, and the ®rst 6 weeks of lactation. This ®gure included the live weight loss at parturition. The ewes were shorn on entering the differential feeding period and again at the end to determine total wool production. Lambs were shorn once at approximately 4.5 months of age. Milk production of the ewes was determined 17 days after lambing. Ewes were separated from their lambs and the live weight of the lambs was determined every 3 h before and after suckling over a 24 h period. The total milk production of the ewes was then calculated (Barnicoat, et al., 1949).
2.3. Analytical procedures
The diets were analyzed for dry matter (DM), organic matter (OM) and crude protein (CP) (AOAC, 1985). In vitro digestibility of organic matter (IVDOM) was determined as described by Tilley and Terry (1963). Acid detergent ®ber (ADF) and neutral detergent ®ber (NDF) contents were also determined (Van Soest, 1963; Van Soest and Wine, 1967).
2.4. Statistical analysis
Large differences in DMI between individual ewes, especially in the high intake groups occurred. Dry matter intake values were therefore regressed on dependant variables (ewe production or lamb perfor-mance) regardless of class.
Regressions of the production data on mean dry matter intake (DMI) for either the pregnancy, lacta-tion, or the total period were ®tted within breeds. Only data of lambed ewes were considered in the analysis. The effect of number of lambs born or suckled on production of ewes types was ignored, as a higher rate of twin births of SA Mutton Merino ewes is considered as a breed characteristic relative to Merinos. Differ-ences between regressions obtained for the two breeds were tested for signi®cance by comparing the regres-sion coef®cients of the linear regresregres-sion (yabx), using the standard error of the difference (SED) where:
S1SE of regression coefficient for SA Mutton Merino ewes
The difference between regression coef®cients was compared against two times the SED (approximately signi®cant at 5% level of probability). These proce-dures were described by Snedecor and Cochran (1980).
3. Results and discussion
3.1. Composition of diets
The CP contents of the experimental diets were 10.3% and 13.7% for the periods of late pregnancy and lactation, respectively (Table 1). The IVDOM of the diets were 53.2 and 64.4%, respectively. Calculated intake values to meet requirements were approxi-mately 1 800 g DM/day during late pregnancy, and 2500 g DM/day during lactation for SA Mutton Mer-ino ewes. The corresponding intake values for MerMer-ino ewes were approximately 1700 g DM/day, and 2300 g DM/day.
3.2. Production of ewes
Lambing percentage (expressed per ewe lambed) of Merino ewes was 135 and 171% for SA Mutton
Merino ewes. This was slightly higher than the gen-erally accepted production parameters for the respec-tive breeds (120% for Merino and 150% for SA Mutton Merino ewes) (Brand and De Villiers, 1989). Scatterplots and regression equations of the live weight changes of the ewes of the two types of sheep (n20 for SA Mutton Merino ewes andn23 for Merino ewes) during late pregnancy (last 6 weeks), early lactation (®rst 6 weeks) and the total experi-mental period (15 weeks), as well as the graphic illustration of the absolute live weights of ewes when fed to meet requirements are presented in Fig. 1. No signi®cant (P> 0.05) differences were observed among types of sheep for the regression coef®cients, although a tendency (P0.10) towards a difference was detected in the intercepts of the regression equa-tions for live weight change during late pregnancy. Calculated values of the production parameters of ewes and lambs, when ewes were fed to meet require-ments, are presented in Table 2.
Positive relationships (P0.001) were observed between DMI and live weight change of the ewes during late pregnancy and over the total experimental period. Correlation coef®cients exceeded 0.74 in all cases (Fig. 1). Live weight change during early lacta-tion also tended (P0.10) to be in¯uenced by DMI. The calculated live weight gain (Table 2) during late pregnancy for adequately fed SA Mutton Merino ewes (11.2 kg) and Merino ewes (12.1 kg) was similar, while the live weight loss of SA Mutton Merino ewes (ÿ7.3 kg) exceeded the value for Merinos (ÿ1.8 kg) during lactation. Adequately fed SA Mutton Merino ewes gained 15.9% and Merino ewes 21.9% of initial live weight during the last 6 weeks of pregnancy. These values were in the same range, although slightly higher than the proposed live weight gain of 10 to 18% found by Russel (1984) for Merino ewes. The live weight change of ewes during the ®rst 6 weeks of lactation, was ÿ8.3% and ÿ1.1% for SA Mutton Merino and Merinos, respectively, when fed to meet requirements. Although the live weight loss for ade-quately fed Merino ewes was lower than for SA Mutton Merino ewes, Merino ewes already gained weight 6 weeks into lactation, while SA Mutton Merino ewes were still losing weight (Fig. 1). The NRC (1985) suggested a live weight loss of 2.3% for lactating ewes with singles and 5.5% for ewes with twins on adequate levels of nutrition.
Table 1
Composition of the experimental diets
Experimental diets
Composition on a DM basis (%)
Dry matter 91.2 90.3
Ash 5.9 5.3
In vitro organic matter digestibility 53.2 64.4
Crude protein 10.3 13.7
Fig. 1. Live weight changes of SA Mutton Merino (±) and Merino (- - -) ewes at different levels of nutrition during pregnancy and lactation.
Table 2
Calculated production norms for reproducing meat-wool (SA Mutton Merino) and wool-type (Merino) ewes (respective lambing percentages of 171 and 135%) when fed at levels to meet requirements
Production parameter Breed
SA Mutton Merino Merino
y Syx y Syx
Ewes n20 n23
Live weight change during the last 6 weeks of pregnancy, kg 11.2 2.2 12.1 2.7 Live weight change during the last 6 weeks of pregnancy, % 15.9 3.4 21.9 5.2 Live weight change during the first 6 weeks of lactation, kg ÿ7.3 6.5 ÿ1.8 5.2 Live weight change during the first 6 weeks of lactation, % ÿ8.3 7.9 ÿ1.1 8.0
Wool production for 15 weeks, kg greasy woola 1.57 0.34 2.84 0.41
Milk production 17 days post partum, kg/day 2.33 0.70 1.84 0.45
Lambs n29 n24
Birth weight, kg 4.1 0.9 4.9 0.8
Live weight at 42 days of age, kg 15.4 3.5 12.6 2.5
ADG at 42 days of age, g/day 270 71 192 54
Live weight at 100 days of age, kg 27.9 5.5 20.6 3.6
ADG at 100 days of age, g/day 236 50 154 30
Wool production for 4.5 months, kg 0.85 0.25 1.25 0.29
Dry matter intake signi®cantly (P0.05) affected greasy wool production in Merino ewes, and tended (P0.07) to affect greasy wool production for SA Mutton Merino ewes (Fig. 2). The greasy wool pro-duction (Table 2) for adequately fed ewes of the two different breeds for the 105-day experimental period
was 2.84 kg (Merino ewes) and 1.57 kg (SA Mutton Merino ewes). It is well known that wool production is reduced under poor feeding conditions (Kelly and Ralph, 1988). Merino ewes produced approximately 80% more wool over the experimental period, which accentuated breed differences (Du Plessis and De Wet, 1981).
Milk production of both types of ewes was posi-tively related to DMI, although correlation coef®-cients were low, and only a tendency (P0.10) was observed in the case of the milk production of SA Mutton Merino ewes to be affected by DMI. Earlier studies indicated that nutrition affects milk yield of the ewe (Jordan and Mayer, 1989). The calculated milk yield of adequately fed SA Mutton Merino ewes 17 days post partum was approximately 30% higher than for Merino ewes.
The birth weight of Merino lambs was signi®cantly (P0.001; r0.57) affected by DMI of the ewes (Fig. 2), while no relationship was found in case of the SA Mutton Merino lambs (P> 0.05). Calculated mean birth weight for the two breeds (Table 2) was 4.1 kg (SA Mutton Merino) and 4.9 kg (Merino). The lower birth weight for SA Mutton Merino, compared to Merino lambs, is due to a higher rate of multiple births. The lack of response in the birth weight of SA Mutton Merino lambs in relation to DMI, as compared to Merino lambs, is dif®cult to explain. Production traits, like wool growth, presumably have a lower priority for available nutrients than for foetal development or milk production (Hawker and Ken-nedy, 1978). It may only be speculated that, due to genetic differences, the SA Mutton Merino ewes possibly partitioned more nutrients to foetal develop-ment than the Merino ewe. This speculation is sup-ported by the observations of McRabb et al. (1992) that maternal live weight, possibly body reserves not even quanti®able by condition score, protects and even enhances placental growth during a period of maternal undernutrition. There were very few data points for Merino ewes that ingested more than 1500 g DM/day during late pregnancy. It can be concluded that Merino ewes had dif®culty in maintaining DMI that met nutrient requirements. Since estimated birth weight was extrapolated beyond the data points, it may possibly be biased upwards for Merino lambs. Hey-denrych and Meissenheimer (1979) and Cloete (1993) found a mean birth weight of 3.95 kg (Merino lambs)
and 4.1 kg (SA Mutton Merino lambs) for lambs of free-grazing ewes.
3.3. Production of lambs
Growth data of the lambs (n29 for SA Mutton Merino andn24 for Merino lambs) of the two types of sheep are presented in Fig. 3. A positive relation-ship between the DMI of ewes during lactation and the daily gain of lambs was observed for both types. Dry matter intake during lactation, affected the average daily gain (ADG) of SA Mutton Merino lambs sig-ni®cantly at both 42 days of age (P0.03) and at 100 days of age (P0.04). With Merino lambs, the effect was signi®cant (P0.04) only at 42 days. Dry matter intake of ewes was unrelated to wool growth of the lambs, although a tendency towards signi®cance (P0.08) was observed in the case of SA Mutton Merino lambs (Fig. 3). Lambs of adequately fed SA Mutton Merino ewes (Table 2) grew 41 and 53% faster than Merino lambs at 42 and 100 days of age. Wool production, on the other hand, was 48% higher for Merino lambs compared to SA Mutton Merino lambs. These production ®gures of lambs are in accordance with selection objectives in the types of sheep. Du Plessis, 1974 found that 61% of retained nitrogen was utilized for body protein synthesis and 16% for wool production in SA Mutton Merino lambs. In Merino lambs, the corresponding ®gures were 19 and 49% indicating the difference in nutrient partitioning between these breeds due to genetic difference in body growth and wool production potential.
The positive relationships of DMI of ewes during lactation with the live weight of lambs were expected. The 42-day body weight of lambs was highly corre-lated (0.70±0.95) with maternal milk production (Bar-nicoat et al., 1949; Burris and Baugus, 1955). Although lambs have the ability to compensate in live weight after an initial period of undernourishment (Greeff et al., 1986), it seemed in this experiment that at 100 days of age the ADG of the lambs was still affected by the DMI of their dams. This observation was supported by the fact that the lamb's growth is largely dependant on the ewe's milk production during the ®rst three months of life (MLC, 1988). Lamb wool production is also affected by nutrients provided to the ewe during pregnancy and lactation, and to lambs during their early post-natal life (Corbett, 1979).
4. Conclusions
It is clear from the study that there are large differences in production traits between the two genetic different types of Merino sheep. South African
Mutton Merino ewes were subjected to larger changes in live weight, due to level of nutrition, compared to Merino ewes. This is due to the higher absolute live weights of SA Merino ewes. SA Mutton Merino ewes produced more milk, while their lambs grew faster than that of Merino ewes. Merino ewes and lambs, on the other hand, produced more wool. Production parameters were mostly positively related to an increase in DMI by ewes during pregnancy and lacta-tion, as expected. The study gave practical production norms for meat-wool and wool-type Merino ewes and their lambs when subjected to different nutritional levels.
Acknowledgements
Mr S.W.P. Cloete for help with the statistical ana-lysis of the data.
References
Alexander, G., McCance, I., Watson, R.W., 1956. The relation of maternal nutrition to neonatal mortality in Merino lambs. Proc. III. Int. Cong. on Anim. Reprod. Cambridge, UK, pp. 5±7. Allden, W.G., 1979. Feed intake, diet composition and wool
growth. In: Black J.L., Reis, P.J. (Eds.), Physiological and Environmental Limitations To Wool Growth. University of New England Publishing Unit. Armidale, Australia, pp. 61± 78.
AOAC 1985. Of®cial Methods of Analysis 13th (Ed.). Association of Of®cial Analytical Chemists, Arlington, VA, pp. 129± 145.
Barnicoat, C.R., Logan, A.C., Grant, A.I., 1949. Milk secretion studies with New Zealand Romney ewes. J. Agric. Sci. (Camb.) 39, 237±248.
Brand, T.S., De Villiers, T.T., 1989. Production norms and techniques for adapted sheep breeds under dryland conditions in the western and southern parts of the Cape, Department of Agriculture: Western Cape, Private Bag, X1, Elsenburg 7607, South Africa, pp 221±225 (in Afrikaans).
Burris, J., Baugus, C.A., 1955. Milk consumption and growth of suckling lambs. J. Anim. Sci. 14, 186±191.
Cloete, S.W.P., 1993. Observations on neonatal progress of Dormer and South African Mutton Merino lambs. S. Afr. J. Anim. Sci. 23, 38±42.
Corbett, J.L., 1979. Variation in wool growth with physiological state. In: Black J.L., Reis, P.J., (Eds.), Physiological and Environmental Limitations To Wool Growth. University of New Zealand Publishing Unit, Armidale, Australia, pp. 79±98.
Curll, M.J., Davidson, J.L., Freer, M., 1975. Ef®ciency of lamb production in relation to the weight of the ewe at mating and during pregnancy. Aust. J. Agric. Res. 26, 553±565. Du Plessis, J.J., De Wet, P.J., 1981. Nitrogen utilization by sheep. 1.
Nitrogen utilization weaned lambs of a wool-mutton and mutton-wool breed for wool and body protein formation. Agroanimalia 12, 21±27.
Greeff, J.C., Meissner, H.H., Roux, C.Z., Janse van Rensburg, R.J., 1986. The effect of compensatory growth on feed intake, growth rate and ef®ciency of feed utilization in sheep. S. Afr. J. Anim. Sci. 16, 162±168.
Gunn, R.G., 1983. The in¯uence of nutrition on the reproductive performance of ewes. In: Haresign, W. (Ed.), Sheep Production. Butterworths, London, pp. 99±110.
Hawker, H., Kennedy, J.P., 1978. In¯uence of season and reproductive status of wool growth of Merino ewes in an arid environment. Aust. J. Exp. Agric. 18, 648±652.
Heydenrych, H.J., Meissenheimer, D.J.B., 1979. Sex differences in the heritabilities of economic traits in South African Merino sheep. S. Afr. J. Anim. Sci. 9, 69±72.
Jordan, D.J., Mayer, D.G., 1989. Effect of udder damage and nutritional plane on milk yield. Aust. J. Exp. Agric. 29, 315± 320.
Kelly, R.W., Ralph, I.G., 1988. Lamb and wool production from ewes fed differently during pregnancy. Proc. Aust. Soc. Anim. Prod. 17, 218±221.
McRabb, G.J., Egan, A.R., Hosking, B.J., 1992. Maternal under-nutrition during mid-pregnancy in sheep: variable effects on placental growth. J. Agric. Sci. (Camb.) 118, 127±132. MLC 1988. Feeding the ewe. Sheep improvement services. Meat
and Livestock Commission. P.O. Box 44, Winterhill House, Snowdown Drive, Milton Keynes MK 6 1AX, UK, 78 pp. NRC 1985. Nutrient Requirements of Domestic Animals. National
Academy Press, Washington, 99 pp.
Reid, R.L., 1963. The nutritional physiology of the pregnant ewe. J. Aust. Inst. Agric. Sci. 29, 215±223.
Robinson, J.J., 1983. Nutrient requirement of the breeding ewe. In: Haresign, W. (Ed.), Recent Advances in Animal Nutrition. Butterworths, London, pp. 143±161.
Russel, A.J.F., 1984. Means of assessing the adequacy of nutrition of pregnant ewes. Livest. Prod. Sci. 11, 429±436.
Schinckel, P.G., 1963. Nutrition and sheep production: a review. Proc. World Conf. Anim. Prod. 1, 199±248.
Snedecor, G.W., Cochran, W.G., 1980. Statistical Methods 7th ed. The Iowa State University Press, Ames, IO, USA, 593 pp. Stephenson, R.G.A., Edwards, J.C., Hopkins, P.S., 1981. The use of
urea to improve milk yield and lamb survival of Merinos in a dry tropical environment. Aust. J. Agric. Res. 32, 497±509. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in
vitro digestion of forage crops. J. Brit. Grassl. Soc. 18, 101±104. Van Soest, P.J., 1963. Use of detergents in the analysis of ®brous feeds. II. A rapid method of determination of ®bre and lignin. J. Assoc. Off. Agric. Chem. 46, 829±835.
