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Comparison of Sumatra sheep and three hair sheep crossbreds. I. Growth, mortality and wool cover of F1 lambs
Small Ruminant Research EISEVIER
Small Ruminant Research 25 (1997) 1-7
Comparison of Sumatra sheep and three hair sheep crossbreds. I. Growth, mortality and wool cover of F, lambs R.M. Gatenby aTb* *, G.E. Bradford b, M. Doloksaribu a, E. Romjali a, A.D. Pitono a, H. Sakul b a Sub-Balai Penelitian Temak Sei Putih, P.O. Box 1, Galang 20585, North Sumatra, Indonesia b Department of Animal Science, Uniuersity ofCalifornia, Davis CA, 95616, USA Accepted 20 September 1996
Abstract Sumatra ewes were mated to give Java Fat-tail crossbred (E,), Virgin Island crossbred (H,) and purebred Sumatra (S) lambs, or were inseminated to give Barbados Blackbelly crossbred (B,) lambs. A total of 882 lambs were born to 407 ewes in 568 lambings. Average litter size was 1.55 and lamb mortality to weaning at 3 months was 22.5%. Weights of lambs averaged 1.83 kg at birth and 8.7 kg at weaning. For female lambs only, weights averaged 14.4 kg at 6 months and 17.9 kg at 9 months of age. At weaning the average increases in weight of the crossbreds above S were E, lo-13%, H 1 14-15% and B, 32%. At 3 months of age all breed groups had similar wool scores, but in older animals the ranking was B, (least wool) < H, < E, < S (most wool).0 1997 Elsevier Science B.V. Keywords: Sumatra; Java Fat-tail; Barbados Blackbelly: Virgin Island; Hair sheep: Growth
1. Introduction
The experiment reported here was part of a research program on the development of sheep production integrated with plantation crops, in this case rubber, in the humid tropics. The local sheep in North Sumatra are a thin-tailed type with small body size but high reproductive potential (Iniguez et al., 1991b). Most Sumatra sheep have a coarse kempy fleece. It has been suggested (Fitzhugh and Bradford, 1983) that hair sheep, i.e. those with little or no wool, are better adapted to a hot humid climate.
Several breeds of hair sheep are larger in body size than the Sumatra sheep, and their crosses might, therefore, be expected to grow more rapidly. The objective of this experiment was to compare the performance of Sumatra sheep with that of their crosses with three breeds of hair sheep in a humid tropical production system. In this paper we present the results of the first phase, namely lamb growth, mortality and wool cover.
2. Methods 2. I _ Location
Corresponding author at present address: Cherry Garth, Church Lane, Manby, Louth, Lincolnshire LNI 1 8HL. UK. Fax: +441507-327615; E-mail: [email protected] l
This
Research
experiment was carried out at the AARD Station for Animal Production in Sei Putih,
00921~4488/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. PII SO921-4488(96)00969-8
2
R.M. Gatenby et aL/SmaN
North Sumatra (3”N, 99”E). Altitude is about 50 m above sea level. Annual rainfall totals about 1800 mm, with rain in every month. Mean minimum temperature is 23°C and mean maximum temperature is 32”C, with little seasonal variation, 2.2. Breeds and mating program
The experiment was initiated by allocating ewes to rams of four breeds. The ewes were predominantly purebred Sumatra (S) ewes, with a mature weight for this flock averaging 22 kg. They were augmented by some Garut Strain of Java Thin-tail (JTT) X Sumatra F, ewes, designated G,, from the same flock; their mean mature weight was 25 kg. The JTT and S breeds are similar in many respects and are believed to have recent common ancestry, but the J’IT are larger, have longer tails and different colour patterns. Ewes of the two groups, S and G,, were allocated randomly to the four sire groups and the progeny of each of the four sire groups were considered as one population. However, dam breed group (S, G,) was included as a factor in the analyses. The four sire breeds were Sumatra (S), Java Fattail known in Indonesia as Ekor Gemuk (E), Virgin Island or St. Croix (H) and Barbados Blackbelly (B). The Java Fat-tail are found mainly in East Java; many of the adult sheep of this breed are free of wool (Mason, 1978; Iniguez et al., 1991a). The H and B groups originated in the Caribbean islands of St. Croix and Barbados, respectively (Devendra, 1972; Hupp and Deller, 1983), and are categorised as hair sheep breeds although each may have some wool breed ancestry. The flock of S sheep was established at the Sei Putih station from local sheep, starting in 1984. In 1986 seven rams and seven ewes of the H breed were brought to Sei Putih from the USA. These animals descended from a 1974 importation into the USA from St. Croix. In 1991, 15 rams and 35 ewes of the E breed were brought from East Java. The introduced H and E sheep were maintained as pure breeds under comparable management to the S flock. Also in 1991 frozen semen from 7 B rams was imported from the island of Barbados. Body weights of the S, E and H purebred mature ewes in the Sei Putih flock averaged 22 kg, 26 kg
Ruminant Research 25 (1997) 1-7
and 31 kg, respectively, at mating. No comparable data are available for B ewes in Sei Putih; weights of B ewes in the Caribbean average about 40 kg (Fitzhugh and Bradford, 1983). Matings for this experiment were made in October and November 1991 using five or six rams each of the S, E and H breeds, and semen from the seven B rams. In addition, natural matings using the first three breeds were repeated in January and April 1992. Natural matings were individually supervised following twice daily oestrus detection with vasectomised rams. A total of 407 ewes (312 S, 95 G,) lambed one or more times over the three seasons, 314 in March/April, 70 in June and 184 in September, for a total of 568 lambings. Lambs sired by S, E, H and B rams were designated S, E,, H, and B, , respectively. Ewes mated to rams of all four breed groups were treated as similarly as possible, except that the ewes inseminated with B semen were synchronised and inseminated in the week before the start of the natural matings with rams of the other breeds. Thus the B, lambs were born on average 2 weeks earlier than the S, E, and H, lambs. Unfortunately, there was no semen available to allow insemination to produce B, lambs in the subsequent seasons.
2.3. Animals and management
The sheep were housed in group pens in four large sheep houses with raised slatted floors. Ewes and suckling lambs were grazed from 08:OO h to 16:00 h daily in rubber plantations. Ewes with single lambs were given 250 g day-’ concentrate for only 2 weeks after lambing, while those with two or more lambs received concentrate for 6 weeks. All ewes were fed about 100 g day-’ molasses mixed with urea. Ewes were exposed to rams for 34-day periods four times a year, and lambs were weaned at exactly 3 months of age. Lambs aged 3-6 months were stall-fed with grass and concentrate (300 g day-’ ). From 6 months of age when the ewe lambs joined the main ewe flock for grazing, and until the age of 15 months, they were fed a small amount of concentrate (200 g day-’ >. The concentrate typically comprised rice bran (25%), cassava meal (25%), palm kernel cake
R.M. Gatenby et al./Small
(25.8%), molasses (20.7%), fish meal (1.4%), (1.1%) and minerals (1.0%).
3
Ruminant Research 25 (1997) l-7
Institute Inc., and mortality data using the CATMOD procedure of SAS Institute Inc. (SAS Institute Inc., 1988). The models used for birth weights of lambs are shown in Table 1. Interactions were not included as there were many factors in the models and we had little interest in investigating the well-known relationships among the effects of sex, type of birth, age of dam, etc. Heterosis could not be calculated, because of the absence of contemporary purebreds of all breeds. The models shown in Table 1 were also used for weaning weight, except that type of birth was replaced by type of birth and rearing (11, 2 1, 22 and 32). As there were very few lambs with type of rearing 31 and 33, these two categories were combined with Category 32. Analyses of 6- and 9-month weights were similar but included females only. The models used for wool score were identical to those for lamb weights, while those for mortality were similar but individual sire was excluded. The models for litter size included only breed group of dam, age of dam and season of birth.
lime
2.4. Data recorded Mating date and sire were recorded for all matings. Birth date, litter size and birth weight were recorded at lambing. All lambs were weaned and weighed at exactly 90 days of age. Weights of ewe lambs were also recorded at 6 and 9 months; weights taken within a few days of the exact age were adjusted to 182 and 274 days by linear interpolation. No data at 9 months of age were collected from lambs born in the third season (September). All deaths were recorded, and lamb mortality was summarised by three periods: (1) O-2 weeks of age, ‘Perinatal mortality’. Lambs born dead were included in this figure; (2) 2 weeks to 3 months of age; (3) 3-9 months of age, ‘Post-weaning mortality’. A wool scoring system was developed which included (i) the proportion of the body covered with wool and (ii) wool length, each on an arbitrary O-9 scale with 0 = no wool cover/shortest and 9 = complete wool cover/longest. The product of these two (range O-81) was calculated and is designated ‘wool score’. Lambs were scored at 3, 6 and 9 months of age.
3. Results 3.1. Litter size
2.5. Data analysis Two sets of analyses were done, one with the S, E, and H, breed groups in all three seasons (Analysis I), and one involving only the animals born in March 1992 with all four breed groups (Analysis II). Data on litter size, lamb weights and wool scores were analysed using the GLM procedure of the SAS
The percentages of litters of 1, 2, 3 and 4 lambs in the total data set were 54%, 38%, 7% and l%, respectively. These figures are almost identical to those reported by Iniguez et al. (1991b) for the same flock in 1985-1988. Overall litter size was 1.55. Litter size was affected by breed of dam (P < 0.001). but not by age of dam nor season of birth. Average litter size ( f SE) was 1.46 ( kO.04) for S and 1.78
Table 1 Statistical
are numbers of observations
models for analysis
of birth weights.
Analysis Breed group Sex Type of birth Breed group of dam Age of dam (years) Season of birth Sire within breed
Numbers
in parentheses
1 (three breed groups, three seasons)
S (255). E, (289), H, (255) M (412). F (387) 1 (282), 2 (400). 2 3 (117) S (585). G, (214) < 2 (167),2-3 (264). 3-4 (171),4-6 (138). March (406). June (103). September (290) (Individual sires)
Analysis 11 (four breed groups, March 1992)
> 6 (59)
S (123). E, (148), H, (135), B, (83) M (263), F (226) 1 (168). 2 (244). > 3 (77) S (359). G, (130) < 2 (162). 2-3 (1271, 3-4 (90),4-6 (Individual
sires)
(74). > 6 (36)
4
R.M. Gatenby et al. /Small
Table 2 Least squares means and standard errors (kg) for Iamb weights. Values for birth and 3 months are for both sexes; values for 6 and 9 months are for females only Birth
6 months
9 months
Analysis I: three breed groups, all seasons n 799 616 275 8.7 f 0.1 Overall mean 1.83 f 0.02 14.4kO.2
159 17.9kO.2
Breedgroup s El Hi Sex Male Female
3 months
** 1.71 *0.03a l.73f0.05a 1.95f0.0Sb
*** 7.8kO.2’ 8.6f0.3b 8.9f0.3b
I**
**
1.85kO.03 1.74*0.03
8.6kO.2 8.2*0.2
l
t**
*t*
12.8*0.4’ 14.3*0.5b 15.4f0.4b
17.0f0.6a 18.2hO.5’ 19.9 f0.5b
Breedofdam S G,
2.31 f0.04 1.75*0.03 1.33f0.05 * 1.68*0.03 1.92*0.04 l
** 1.53f0.04 1.75f0.03 1.88 f 0.04 1.95 f 0.05 1.88*0.06
Season of birth
ns
Sire within breed
16.3 *0.4 14.2kO.5 13.3*0.3 12.9f0.6
***
*t
l
Ageofdam <2years 2-3 years 3-4 years 4-6 years > 6 years
March June September
a**
11.0&0.2 8.2kO.3 7.5f0.2 6.9*0.3
l
7.7*0.2 9.1 kO.2 *** 7.4*0.2 8.750.2 8.8 f 0.2 9.2 f 0.2 7.9f0.3 l
13.6+0.3 14.8kO.5 ns 13.5f0.5 14.5rtO.3 14.7zbO.4 14.6kO.5 13.8*0.7 I..
El HI B,
(3)
19.8 kO.5 18.6f0.8 17.5f0.4 17.5&-0.9
Type of birth 1 2 3
**
***
*t*
4.6 10.2 23.1
6.7 15.0 17.1
11.3 25.2 40.2
ns 18.2*0.4 18.5*0.6
Breed of dam S
ns 17.7kO.6 18.6*0.5 18.5*0.6 18.250.7 18.8f0.9
Age of dam <2years 2-3 years 3-4 years 4-6 years > 6 years
ns 13.8 8.3 8.8 10.9 10.2
12.0 14.0 12.9 4.3 23.7
Season of birth March June September
is6 9.7 11.0
10.1 6.8 17.6
tt*
l
*
ns
Breed group S
G,
l
* 11.1 7.5
***
l
13.2 10.3 *
l
**
24.3 17.8 l
*t
25.8 22.3 21.6 15.2 33.9 l
*
19.7 16.5 28.6
Analysis II: all breed groups, March only 489 489 489 n 10.8 8.8 19.6 Overall mean Breed group
156 17.8&0.2 l
l
(1+2)
ns 21.4 23.8
ns
12.8kO.5’ 13.5*0.6ab 13.9f0.5Pb 14.7f0.5b
(2)
ns 12.9 11.9
ns
l
(1)
Analysis I: three breed groups, all seasons n 799 799 799 Overall mean 10.1 12.4 22.5
ns 8.5 11.9
ns
** 7.8*0.2a 8.8f0.4b 9.0f0.3b 10.3*0.3’
3-9 months
Sex Male Female
17.3*0.4 19.4kO.6
l
o-3 months
ns 24.7 20.8 22.3
13.1 f0.4 14.0&0.5 15.5 f 0.4
l
0.5-3.0 months
ns 13.3 10.0 14.1
8.550.2 8.6kO.3 8.1 f 0.2
* 1.71 kO.05’ 1.82&0.0Spb l.95f0.06b 1.97~t0.06~
O-14 days
ns 11.4 10.7 8.2
1.82+0.03 1.73ItO.05 1.85 *0.04
Analysis II: all breed groups, March only n 488 391 163 8.9 f 0.1 Overall mean 1.81 f 0.02 13.4*0.2 Breed group S
Table 3 Factors affecting lamb mortality (8) of three breed groups in all seasons. Values until 3 months are for both sexes; the final column is for females only
E, Hi
Type of birth (or birth and rearing) *** *I* 101) (21) 2 (22) 3 (32)
Ruminant Research 25 (1997) I-7
t*
16.6*0.6a 17.2&0.7p 19.0f0.5b 19.9f0.6b
*** P 0.05. Within each comparison, means with the same superscript different (P > 0.05). l
are not
13.8 8.8 6.7 16.9
S E, Hi Bl **
l
ns
P
* * P
* 8.1 8.1 14.1 2.4 * P
ns 21.9 16.9 20.7 19.3
183 13.1 ns 18.5 18.0 4.4
ns 10.9 14.4 13.3 ns 13.0 13.5 ns 11.3 15.4 21.6 4.0 6.2 ns 13.8 10.5
180 13.3
Et.9 17.0 5.4 11.4
ns, P>O.O5.
(kO.07) for G, dams. One possible explanation for the higher litter sizes of the G, dams is the higher frequency of the prolificacy gene (Bradford et al.,
R.M. Gatenby et al./Small
1991) in the Java Thin-tail breed, which sired the G, dams, than in the Sumatra.
Ruminant
Research 25 (1997)
Table 4 Least squares means and standard errors for wool scores. Values for 3 months are for both sexes; values for 6 and 9 months are for females only
3.2. Weights of lambs The analysis of three breed groups in three seasons, summarised in Table 2, shows that average weights were 1.83 kg at birth and 8.7 kg at weaning for lambs of both sexes. For female lambs only, weights averaged 14.4 kg at 6 months and 17.9 kg at 9 months of age. Lamb weights were affected by breed group, sex of lamb, type of birth, breed of dam, age of dam and season of birth. Individual sire within breed had no significant effect. Breed group means only are shown for Analysis II, with all four breeds in one season. Fixed effects of sex, type of birth and rearing, breed group of dam and age of dam were similar for the two analyses. Sire within breed was significant for birth and weaning weights in the four-breed comparison, but was not significant, possibly due to the smaller sample size, for 6- and 9-month weights. The average lamb weights for each breed group shown in Table 2 show that: (1) the ranking of average lamb weights was consistently S < E, < H, < B,; (2) in Analysis I weaning weights of E, and H, crossbred lambs were 10% and 14%, respectively, heavier than purebred S lambs. In Analysis II weaning weights of E,, H, and B, lambs were 13%, 15% and 32% heavier than S lambs. Weaning weights were higher for male than female lambs, for lambs born and reared in small litters, and for G, than S dams. Young ewes (age < 2 years) and old ewes (> 6 years) weaned smaller lambs than ewes aged 2-6 years. 3.3. Lamb mortality Table 3 shows that pre-weaning mortality averaged 22.5% (from birth to 3 months), and for females post-weaning mortality (3 to 9 months) averaged 13.1%. Mortality to weaning was affected by type of birth, breed of dam, age of dam and season
5
l-7
6 months
9 months
Analysis I: three breed groups, all seasons 515 276 n 51.6*0.2 60.5rtO.2 Overall mean
3 months
166 51.8kO.4
E, HI
ns 54.7 f l.4a 54.7+2.0a 55.9k2.1’
Sex M F
ns 54.4 f I .4 55.8f I.5
Breed group S
Type of birth and II 21 22 32 Breed of dam s G, Age of dam <2years 2-3 years 3-4 years 4-6 years > 6 years
rearing * * 57.2&- I.5 54.2f2.3 52.251.4 56.952.2
*t 52.3* I.3 58.0& I.9 t** 52.2+ 1.9 51.6f I.5 6l.lk I.8 57.3* 1.9 53.3 k2.7
***
*
68.0& 2.2b 64.9f3.2b 51.9*2.5a
68.7 f4.6b 61.1 +~4.4~~ 54.0~t4.3~
_
l
*
it
66.3*2.3 61.4*3.3 57.9k2.1 60.9k33.7
50.2f4.1 58.7k6.3 63.8&-3.2 72.4*7.1
ns 62.2k I.8 61.1 k2.8
67.4*3.3 55.1 f5.1
ns 63.6+3.0 64.3k2.1 64.8f2.7 62.2*3.1 53.2f4.3
65.9f4.7 57.2f4.2 69.2k5.2 51.2h5.7 62.8 *7.l
l
*
Season of birth March June September
*tt
*t*
**/
43.7k 1.4 55.7k2.3 65.9f I.5
54.352.1 71.4k3.2 59.2f2.3
43.4k3.3 79.1 54.9 -
Sire within breed
ns
ns
ns
Analysis 11: all breed groups, March only n 375 I64 42.1 kO.2 53.3f0.4 Overall mean Breed group S E, I-II Bl
ns 43.4& l.3a 42.8k2.0a 41.2*l.7a 41.4+ l.6a
163 41.4*0.4
*t*
***
64.4k4.5b 58.1 +5.1b 41.6h4.0’ 38.8f4.6a
52.3f5.4C 38.6f6.0b 34.3f4.7b 17.9~h5.5~
* * * P < 0.001; * * P < 0.01; * P < 0.05; ns, P > 0.05. Within each comparison, means with the same superscript significantly different (P > 0.05).
are not
6
R.M. Gaienby et al. /Small
of birth, but not by breed group nor sex. Post-weaning mortality was not affected by any of these factors. Pre-weaning mortality increased with litter size and averaged 1 l%, 25% and 40% for litter sizes of 1, 2 and 2 3, respectively. Mortality was highest for dams older than 6 years (34%) and younger than 2 years (26%), and was lowest for dams aged 4-6 years (15%). Analysis II showed that the mortality rates of B, lambs were similar to those of the other three breed groups. A substantial number of lambs were born dead. Post-mortem examination of still-born lambs which were superficially normal showed accumulation of fluid in the body cavity of the lamb. There were four main causes of death in lambs before weaning: (1) insufficient milk consumption which predisposed lambs to parasites; (2) worms, particularly Haemonchus contortus which caused severe anaemia. Worms were most obvious in the final weeks before weaning; (3) coccidia, which caused diarrhoea in lambs aged about 2 months; (4) pneumonia in ewes in December 1992 when there was prolonged rain. 3.4. Wool coat The effect of breed group on wool score is summarised in Table 4. Wool scores at 3 months of age were similar for all breed groups, but in older animals the scores were consistently B 1 < H, < E, < S. At 9 months of age wool scores for B, crossbred ewes were about one-third those of the S ewes. Seasonal effects on wool were quite large, with the June lamb crop having substantially higher wool scores than the March-born lambs at 6 and 9 months of age.
4. Discussion Average weights of lambs were 1.83 and 8.7 kg at birth and 3 months. Weights of females at 6 and 9 months averaged 14.4 and 17.9 kg. There was a consistent effect of breed group on lamb weight. At weaning E,, H, and B, crossbreds were 10-13, 14-15 and 32% heavier than Sumatra lambs. These differences can be partly attributed to differences in mature size of the sire breed, and there is possibly
Ruminant Research 25 (1997) 1-7
also an effect of hybrid vigour in the crossbred lambs. In Tobago, which has a similar climate to North Sumatra, a 6-year comparison showed that the growth of Barbados Blackbelly lambs to weaning was markedly superior to that of Virgin Island lambs (Rastogi et al., 1993). The young rams from this experiment were evaluated in a feeding trial (Pond et al., 1994) to examine the extent to which crossbred ram lambs require a higher quality diet to express their genetic potential. Groups of rams were fed either (i> a low quality diet of plantation grass ad libitum plus 400 g per head per day concentrate (11.6 MJ ME per kg, 11.8% CP) comprising locally available feedstuffs, or (ii) a high quality diet fed at 3.3% body weight containing concentrate (13.5 MJ ME per kg, 15.3% CP, given at 70% of DM intake) and Paspalum dilatatum grass (30% intake). On high quality diets when the rams could express their growth potential the average growth rates for S, E,, H, and B, rams were 125 g day-‘, 164 g day-‘, 161 g day-’ and 185 g day-‘, respectively. Thus the ranking of breed groups was B, > E, > H, > S, and the B, grew 48% faster than the S. On the low quality diet, where a limited amount of concentrate was fed on a per head basis not according to body weight, the S lambs outperformed the larger crossbreds; the breed group means were 86 g day-‘, 79 g day-‘, 78 g day-’ and 64 g day-’ for S, E,, H, and B,, respectively. Thus, where good quality diets are available, weaned crossbred lambs grow faster than purebred Sumatra lambs, but on poor diets there is no benefit of the superior growth potential of the crossbreds. Lamb mortality to weaning was 22.5%. This high value can be attributed to the high litter size and health problems associated with the hot humid climate. Mortality was not affected by breed group. Wool scores at 6 and 9 months of age showed an effect of breed group. The breed groups were ranked B, < H, < E, < S. One of the goals of crossing with hair sheep was to produce animals for this hot humid environment as free of wool as possible. Clearly the F, lambs were not wool-free at 3 and 6 months of age. However, by 9 months the B, crosses had very much less wool than the other groups. Also the variability within groups suggests that selection in the crossbred groups should lead to a reduction in
R.M. Gatenby et al. /Small Ruminant Research 25 f 1997) l-7
wool unless heritability is very low. Odenya (1982) obtained an estimate of 0.26 for heritability of wool cover in Dorper sheep.
5. Conclusion Growth rate was higher for each of the crossbred groups as expected from crossing with breeds with higher mature weights. Since there were no appreciable breed differences in viability, the higher weights of the crossbred lambs resulted in higher weight of lamb per ewe. The use of hair sheep, in particular the Barbados Blackbelly and, to a lesser extent, the Virgin Island St. Croix, resulted in lambs with less wool at 6 and 9 months of age.
Acknowledgements We thank Torop Siallagan, Pungu Nababan, Saleh and other staff of the animal houses for their care of the flock and record-keeping; and Leo P. Batubara, Director of SBPT Sei Putih, for support of this work. The research described in this paper was funded through the Small Ruminant Collaborative Research Support Program by USAID grant DAN 1328-G-000046-00.
References Bradford, G.E., Inounu, I., Iniguez, L.C., Tiesnamurti, B. and Thomas, D.L., 1991. The prolificacy gene of Javanese sheep. In: J.M. Elsen, L. Bodin and J. Thimonier (Editors), Proceed-
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ings 2nd International Workshop on Major Genes for Prolificacy in sheep. Institut National de la Recherche Agronomique, Paris, France, pp. 66-73. Devendra, C., 1972. Barbados Blackbelly sheep of the Caribbean. Trop. Agric., Trinidad, 49: 23-29. Fitzhugh, H.A. and Bradford, G.E., 1983 (Editors) Hair Sheep of Western Africa and the Americas. Westview Press, Boulder, Colorado, USA, 3 19 pp. Hupp, H. and Deller, D., 1983. Virgin Islands White hair sheep. In: H.A. Fitzhugh and G.E. Bradford (Editors), Hair Sheep of Western Africa and the Americas. Westview Press, Boulder, Colorado, USA, pp. 17 1- 175. Iniguez, L., Bradford, G.E., Komarudin, and Sutama, K., 1991a. The Javanese Fat Tail, an Indonesian sheep population with potential to produce hair sheep. In Wildeus, S. (Editor), Hair Sheep Research. Proceedings of a Symposium held in St. Croix, US Virgin Islands, June. University of the Virgin Islands Agricultural Experiment Station, St. Croix, USA, pp. 54-62. Iniguez, L., Sanchez, M. and Ginting, S.P., 199ib. Productivity of Sumatran sheep in a system integrated with rubber plantation. Small Rumin. Res., 5: 303-317. Mason, I.L., 1978. Sheep in Java. World Anim. Rev., 27: 17-22. Odenya, W.O., 1982. Relationship of coat cover and production traits in the Dorper breed of sheep. M.Sc. Thesis, University of California, Davis, USA, 74 pp. Pond, K.R., Sanchez, M.D., Home, P.M., Merkel, R.C., Batubara, L.P., Ibrahim, T., Ginting, S.P., Bums, J.C. and Fisher, D.S., 1994. Improving feeding strategies for small ruminants in the Asian region. In: Subandriyo and R.M. Gatenby (Editors), Strategic Development for Small Ruminant Production in Asia and the Pacific. Proceedings of a Symposium held in Conjunction with the 7th Asian-Australasian Association of Animal Production Societies Congress, July 1994, Denpasar, Bali, Indonesia. Small Ruminant CRSP, University of California, Davis, USA, pp. 77-97. Rastogi, R.K., Keens-Dumas, M.J. and Lauckner, F.B., 1993. Comparative performance of several breeds of Caribbean hair sheep in purebreeding and crossbreeding. Small Rumin. Res., 9: 353-366. SAS Institute Inc., 1988. SAS Procedures Guide, Release 6.03 Edition. SAS Institute Inc., Cary, NC, USA, 441 pp.
Small Ruminant Research 25 (1997) 1-7
Comparison of Sumatra sheep and three hair sheep crossbreds. I. Growth, mortality and wool cover of F, lambs R.M. Gatenby aTb* *, G.E. Bradford b, M. Doloksaribu a, E. Romjali a, A.D. Pitono a, H. Sakul b a Sub-Balai Penelitian Temak Sei Putih, P.O. Box 1, Galang 20585, North Sumatra, Indonesia b Department of Animal Science, Uniuersity ofCalifornia, Davis CA, 95616, USA Accepted 20 September 1996
Abstract Sumatra ewes were mated to give Java Fat-tail crossbred (E,), Virgin Island crossbred (H,) and purebred Sumatra (S) lambs, or were inseminated to give Barbados Blackbelly crossbred (B,) lambs. A total of 882 lambs were born to 407 ewes in 568 lambings. Average litter size was 1.55 and lamb mortality to weaning at 3 months was 22.5%. Weights of lambs averaged 1.83 kg at birth and 8.7 kg at weaning. For female lambs only, weights averaged 14.4 kg at 6 months and 17.9 kg at 9 months of age. At weaning the average increases in weight of the crossbreds above S were E, lo-13%, H 1 14-15% and B, 32%. At 3 months of age all breed groups had similar wool scores, but in older animals the ranking was B, (least wool) < H, < E, < S (most wool).0 1997 Elsevier Science B.V. Keywords: Sumatra; Java Fat-tail; Barbados Blackbelly: Virgin Island; Hair sheep: Growth
1. Introduction
The experiment reported here was part of a research program on the development of sheep production integrated with plantation crops, in this case rubber, in the humid tropics. The local sheep in North Sumatra are a thin-tailed type with small body size but high reproductive potential (Iniguez et al., 1991b). Most Sumatra sheep have a coarse kempy fleece. It has been suggested (Fitzhugh and Bradford, 1983) that hair sheep, i.e. those with little or no wool, are better adapted to a hot humid climate.
Several breeds of hair sheep are larger in body size than the Sumatra sheep, and their crosses might, therefore, be expected to grow more rapidly. The objective of this experiment was to compare the performance of Sumatra sheep with that of their crosses with three breeds of hair sheep in a humid tropical production system. In this paper we present the results of the first phase, namely lamb growth, mortality and wool cover.
2. Methods 2. I _ Location
Corresponding author at present address: Cherry Garth, Church Lane, Manby, Louth, Lincolnshire LNI 1 8HL. UK. Fax: +441507-327615; E-mail: [email protected] l
This
Research
experiment was carried out at the AARD Station for Animal Production in Sei Putih,
00921~4488/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. PII SO921-4488(96)00969-8
2
R.M. Gatenby et aL/SmaN
North Sumatra (3”N, 99”E). Altitude is about 50 m above sea level. Annual rainfall totals about 1800 mm, with rain in every month. Mean minimum temperature is 23°C and mean maximum temperature is 32”C, with little seasonal variation, 2.2. Breeds and mating program
The experiment was initiated by allocating ewes to rams of four breeds. The ewes were predominantly purebred Sumatra (S) ewes, with a mature weight for this flock averaging 22 kg. They were augmented by some Garut Strain of Java Thin-tail (JTT) X Sumatra F, ewes, designated G,, from the same flock; their mean mature weight was 25 kg. The JTT and S breeds are similar in many respects and are believed to have recent common ancestry, but the J’IT are larger, have longer tails and different colour patterns. Ewes of the two groups, S and G,, were allocated randomly to the four sire groups and the progeny of each of the four sire groups were considered as one population. However, dam breed group (S, G,) was included as a factor in the analyses. The four sire breeds were Sumatra (S), Java Fattail known in Indonesia as Ekor Gemuk (E), Virgin Island or St. Croix (H) and Barbados Blackbelly (B). The Java Fat-tail are found mainly in East Java; many of the adult sheep of this breed are free of wool (Mason, 1978; Iniguez et al., 1991a). The H and B groups originated in the Caribbean islands of St. Croix and Barbados, respectively (Devendra, 1972; Hupp and Deller, 1983), and are categorised as hair sheep breeds although each may have some wool breed ancestry. The flock of S sheep was established at the Sei Putih station from local sheep, starting in 1984. In 1986 seven rams and seven ewes of the H breed were brought to Sei Putih from the USA. These animals descended from a 1974 importation into the USA from St. Croix. In 1991, 15 rams and 35 ewes of the E breed were brought from East Java. The introduced H and E sheep were maintained as pure breeds under comparable management to the S flock. Also in 1991 frozen semen from 7 B rams was imported from the island of Barbados. Body weights of the S, E and H purebred mature ewes in the Sei Putih flock averaged 22 kg, 26 kg
Ruminant Research 25 (1997) 1-7
and 31 kg, respectively, at mating. No comparable data are available for B ewes in Sei Putih; weights of B ewes in the Caribbean average about 40 kg (Fitzhugh and Bradford, 1983). Matings for this experiment were made in October and November 1991 using five or six rams each of the S, E and H breeds, and semen from the seven B rams. In addition, natural matings using the first three breeds were repeated in January and April 1992. Natural matings were individually supervised following twice daily oestrus detection with vasectomised rams. A total of 407 ewes (312 S, 95 G,) lambed one or more times over the three seasons, 314 in March/April, 70 in June and 184 in September, for a total of 568 lambings. Lambs sired by S, E, H and B rams were designated S, E,, H, and B, , respectively. Ewes mated to rams of all four breed groups were treated as similarly as possible, except that the ewes inseminated with B semen were synchronised and inseminated in the week before the start of the natural matings with rams of the other breeds. Thus the B, lambs were born on average 2 weeks earlier than the S, E, and H, lambs. Unfortunately, there was no semen available to allow insemination to produce B, lambs in the subsequent seasons.
2.3. Animals and management
The sheep were housed in group pens in four large sheep houses with raised slatted floors. Ewes and suckling lambs were grazed from 08:OO h to 16:00 h daily in rubber plantations. Ewes with single lambs were given 250 g day-’ concentrate for only 2 weeks after lambing, while those with two or more lambs received concentrate for 6 weeks. All ewes were fed about 100 g day-’ molasses mixed with urea. Ewes were exposed to rams for 34-day periods four times a year, and lambs were weaned at exactly 3 months of age. Lambs aged 3-6 months were stall-fed with grass and concentrate (300 g day-’ ). From 6 months of age when the ewe lambs joined the main ewe flock for grazing, and until the age of 15 months, they were fed a small amount of concentrate (200 g day-’ >. The concentrate typically comprised rice bran (25%), cassava meal (25%), palm kernel cake
R.M. Gatenby et al./Small
(25.8%), molasses (20.7%), fish meal (1.4%), (1.1%) and minerals (1.0%).
3
Ruminant Research 25 (1997) l-7
Institute Inc., and mortality data using the CATMOD procedure of SAS Institute Inc. (SAS Institute Inc., 1988). The models used for birth weights of lambs are shown in Table 1. Interactions were not included as there were many factors in the models and we had little interest in investigating the well-known relationships among the effects of sex, type of birth, age of dam, etc. Heterosis could not be calculated, because of the absence of contemporary purebreds of all breeds. The models shown in Table 1 were also used for weaning weight, except that type of birth was replaced by type of birth and rearing (11, 2 1, 22 and 32). As there were very few lambs with type of rearing 31 and 33, these two categories were combined with Category 32. Analyses of 6- and 9-month weights were similar but included females only. The models used for wool score were identical to those for lamb weights, while those for mortality were similar but individual sire was excluded. The models for litter size included only breed group of dam, age of dam and season of birth.
lime
2.4. Data recorded Mating date and sire were recorded for all matings. Birth date, litter size and birth weight were recorded at lambing. All lambs were weaned and weighed at exactly 90 days of age. Weights of ewe lambs were also recorded at 6 and 9 months; weights taken within a few days of the exact age were adjusted to 182 and 274 days by linear interpolation. No data at 9 months of age were collected from lambs born in the third season (September). All deaths were recorded, and lamb mortality was summarised by three periods: (1) O-2 weeks of age, ‘Perinatal mortality’. Lambs born dead were included in this figure; (2) 2 weeks to 3 months of age; (3) 3-9 months of age, ‘Post-weaning mortality’. A wool scoring system was developed which included (i) the proportion of the body covered with wool and (ii) wool length, each on an arbitrary O-9 scale with 0 = no wool cover/shortest and 9 = complete wool cover/longest. The product of these two (range O-81) was calculated and is designated ‘wool score’. Lambs were scored at 3, 6 and 9 months of age.
3. Results 3.1. Litter size
2.5. Data analysis Two sets of analyses were done, one with the S, E, and H, breed groups in all three seasons (Analysis I), and one involving only the animals born in March 1992 with all four breed groups (Analysis II). Data on litter size, lamb weights and wool scores were analysed using the GLM procedure of the SAS
The percentages of litters of 1, 2, 3 and 4 lambs in the total data set were 54%, 38%, 7% and l%, respectively. These figures are almost identical to those reported by Iniguez et al. (1991b) for the same flock in 1985-1988. Overall litter size was 1.55. Litter size was affected by breed of dam (P < 0.001). but not by age of dam nor season of birth. Average litter size ( f SE) was 1.46 ( kO.04) for S and 1.78
Table 1 Statistical
are numbers of observations
models for analysis
of birth weights.
Analysis Breed group Sex Type of birth Breed group of dam Age of dam (years) Season of birth Sire within breed
Numbers
in parentheses
1 (three breed groups, three seasons)
S (255). E, (289), H, (255) M (412). F (387) 1 (282), 2 (400). 2 3 (117) S (585). G, (214) < 2 (167),2-3 (264). 3-4 (171),4-6 (138). March (406). June (103). September (290) (Individual sires)
Analysis 11 (four breed groups, March 1992)
> 6 (59)
S (123). E, (148), H, (135), B, (83) M (263), F (226) 1 (168). 2 (244). > 3 (77) S (359). G, (130) < 2 (162). 2-3 (1271, 3-4 (90),4-6 (Individual
sires)
(74). > 6 (36)
4
R.M. Gatenby et al. /Small
Table 2 Least squares means and standard errors (kg) for Iamb weights. Values for birth and 3 months are for both sexes; values for 6 and 9 months are for females only Birth
6 months
9 months
Analysis I: three breed groups, all seasons n 799 616 275 8.7 f 0.1 Overall mean 1.83 f 0.02 14.4kO.2
159 17.9kO.2
Breedgroup s El Hi Sex Male Female
3 months
** 1.71 *0.03a l.73f0.05a 1.95f0.0Sb
*** 7.8kO.2’ 8.6f0.3b 8.9f0.3b
I**
**
1.85kO.03 1.74*0.03
8.6kO.2 8.2*0.2
l
t**
*t*
12.8*0.4’ 14.3*0.5b 15.4f0.4b
17.0f0.6a 18.2hO.5’ 19.9 f0.5b
Breedofdam S G,
2.31 f0.04 1.75*0.03 1.33f0.05 * 1.68*0.03 1.92*0.04 l
** 1.53f0.04 1.75f0.03 1.88 f 0.04 1.95 f 0.05 1.88*0.06
Season of birth
ns
Sire within breed
16.3 *0.4 14.2kO.5 13.3*0.3 12.9f0.6
***
*t
l
Ageofdam <2years 2-3 years 3-4 years 4-6 years > 6 years
March June September
a**
11.0&0.2 8.2kO.3 7.5f0.2 6.9*0.3
l
7.7*0.2 9.1 kO.2 *** 7.4*0.2 8.750.2 8.8 f 0.2 9.2 f 0.2 7.9f0.3 l
13.6+0.3 14.8kO.5 ns 13.5f0.5 14.5rtO.3 14.7zbO.4 14.6kO.5 13.8*0.7 I..
El HI B,
(3)
19.8 kO.5 18.6f0.8 17.5f0.4 17.5&-0.9
Type of birth 1 2 3
**
***
*t*
4.6 10.2 23.1
6.7 15.0 17.1
11.3 25.2 40.2
ns 18.2*0.4 18.5*0.6
Breed of dam S
ns 17.7kO.6 18.6*0.5 18.5*0.6 18.250.7 18.8f0.9
Age of dam <2years 2-3 years 3-4 years 4-6 years > 6 years
ns 13.8 8.3 8.8 10.9 10.2
12.0 14.0 12.9 4.3 23.7
Season of birth March June September
is6 9.7 11.0
10.1 6.8 17.6
tt*
l
*
ns
Breed group S
G,
l
* 11.1 7.5
***
l
13.2 10.3 *
l
**
24.3 17.8 l
*t
25.8 22.3 21.6 15.2 33.9 l
*
19.7 16.5 28.6
Analysis II: all breed groups, March only 489 489 489 n 10.8 8.8 19.6 Overall mean Breed group
156 17.8&0.2 l
l
(1+2)
ns 21.4 23.8
ns
12.8kO.5’ 13.5*0.6ab 13.9f0.5Pb 14.7f0.5b
(2)
ns 12.9 11.9
ns
l
(1)
Analysis I: three breed groups, all seasons n 799 799 799 Overall mean 10.1 12.4 22.5
ns 8.5 11.9
ns
** 7.8*0.2a 8.8f0.4b 9.0f0.3b 10.3*0.3’
3-9 months
Sex Male Female
17.3*0.4 19.4kO.6
l
o-3 months
ns 24.7 20.8 22.3
13.1 f0.4 14.0&0.5 15.5 f 0.4
l
0.5-3.0 months
ns 13.3 10.0 14.1
8.550.2 8.6kO.3 8.1 f 0.2
* 1.71 kO.05’ 1.82&0.0Spb l.95f0.06b 1.97~t0.06~
O-14 days
ns 11.4 10.7 8.2
1.82+0.03 1.73ItO.05 1.85 *0.04
Analysis II: all breed groups, March only n 488 391 163 8.9 f 0.1 Overall mean 1.81 f 0.02 13.4*0.2 Breed group S
Table 3 Factors affecting lamb mortality (8) of three breed groups in all seasons. Values until 3 months are for both sexes; the final column is for females only
E, Hi
Type of birth (or birth and rearing) *** *I* 101) (21) 2 (22) 3 (32)
Ruminant Research 25 (1997) I-7
t*
16.6*0.6a 17.2&0.7p 19.0f0.5b 19.9f0.6b
*** P
are not
13.8 8.8 6.7 16.9
S E, Hi Bl **
l
ns
P
* * P
* 8.1 8.1 14.1 2.4 * P
ns 21.9 16.9 20.7 19.3
183 13.1 ns 18.5 18.0 4.4
ns 10.9 14.4 13.3 ns 13.0 13.5 ns 11.3 15.4 21.6 4.0 6.2 ns 13.8 10.5
180 13.3
Et.9 17.0 5.4 11.4
ns, P>O.O5.
(kO.07) for G, dams. One possible explanation for the higher litter sizes of the G, dams is the higher frequency of the prolificacy gene (Bradford et al.,
R.M. Gatenby et al./Small
1991) in the Java Thin-tail breed, which sired the G, dams, than in the Sumatra.
Ruminant
Research 25 (1997)
Table 4 Least squares means and standard errors for wool scores. Values for 3 months are for both sexes; values for 6 and 9 months are for females only
3.2. Weights of lambs The analysis of three breed groups in three seasons, summarised in Table 2, shows that average weights were 1.83 kg at birth and 8.7 kg at weaning for lambs of both sexes. For female lambs only, weights averaged 14.4 kg at 6 months and 17.9 kg at 9 months of age. Lamb weights were affected by breed group, sex of lamb, type of birth, breed of dam, age of dam and season of birth. Individual sire within breed had no significant effect. Breed group means only are shown for Analysis II, with all four breeds in one season. Fixed effects of sex, type of birth and rearing, breed group of dam and age of dam were similar for the two analyses. Sire within breed was significant for birth and weaning weights in the four-breed comparison, but was not significant, possibly due to the smaller sample size, for 6- and 9-month weights. The average lamb weights for each breed group shown in Table 2 show that: (1) the ranking of average lamb weights was consistently S < E, < H, < B,; (2) in Analysis I weaning weights of E, and H, crossbred lambs were 10% and 14%, respectively, heavier than purebred S lambs. In Analysis II weaning weights of E,, H, and B, lambs were 13%, 15% and 32% heavier than S lambs. Weaning weights were higher for male than female lambs, for lambs born and reared in small litters, and for G, than S dams. Young ewes (age < 2 years) and old ewes (> 6 years) weaned smaller lambs than ewes aged 2-6 years. 3.3. Lamb mortality Table 3 shows that pre-weaning mortality averaged 22.5% (from birth to 3 months), and for females post-weaning mortality (3 to 9 months) averaged 13.1%. Mortality to weaning was affected by type of birth, breed of dam, age of dam and season
5
l-7
6 months
9 months
Analysis I: three breed groups, all seasons 515 276 n 51.6*0.2 60.5rtO.2 Overall mean
3 months
166 51.8kO.4
E, HI
ns 54.7 f l.4a 54.7+2.0a 55.9k2.1’
Sex M F
ns 54.4 f I .4 55.8f I.5
Breed group S
Type of birth and II 21 22 32 Breed of dam s G, Age of dam <2years 2-3 years 3-4 years 4-6 years > 6 years
rearing * * 57.2&- I.5 54.2f2.3 52.251.4 56.952.2
*t 52.3* I.3 58.0& I.9 t** 52.2+ 1.9 51.6f I.5 6l.lk I.8 57.3* 1.9 53.3 k2.7
***
*
68.0& 2.2b 64.9f3.2b 51.9*2.5a
68.7 f4.6b 61.1 +~4.4~~ 54.0~t4.3~
_
l
*
it
66.3*2.3 61.4*3.3 57.9k2.1 60.9k33.7
50.2f4.1 58.7k6.3 63.8&-3.2 72.4*7.1
ns 62.2k I.8 61.1 k2.8
67.4*3.3 55.1 f5.1
ns 63.6+3.0 64.3k2.1 64.8f2.7 62.2*3.1 53.2f4.3
65.9f4.7 57.2f4.2 69.2k5.2 51.2h5.7 62.8 *7.l
l
*
Season of birth March June September
*tt
*t*
**/
43.7k 1.4 55.7k2.3 65.9f I.5
54.352.1 71.4k3.2 59.2f2.3
43.4k3.3 79.1 54.9 -
Sire within breed
ns
ns
ns
Analysis 11: all breed groups, March only n 375 I64 42.1 kO.2 53.3f0.4 Overall mean Breed group S E, I-II Bl
ns 43.4& l.3a 42.8k2.0a 41.2*l.7a 41.4+ l.6a
163 41.4*0.4
*t*
***
64.4k4.5b 58.1 +5.1b 41.6h4.0’ 38.8f4.6a
52.3f5.4C 38.6f6.0b 34.3f4.7b 17.9~h5.5~
* * * P < 0.001; * * P < 0.01; * P < 0.05; ns, P > 0.05. Within each comparison, means with the same superscript significantly different (P > 0.05).
are not
6
R.M. Gaienby et al. /Small
of birth, but not by breed group nor sex. Post-weaning mortality was not affected by any of these factors. Pre-weaning mortality increased with litter size and averaged 1 l%, 25% and 40% for litter sizes of 1, 2 and 2 3, respectively. Mortality was highest for dams older than 6 years (34%) and younger than 2 years (26%), and was lowest for dams aged 4-6 years (15%). Analysis II showed that the mortality rates of B, lambs were similar to those of the other three breed groups. A substantial number of lambs were born dead. Post-mortem examination of still-born lambs which were superficially normal showed accumulation of fluid in the body cavity of the lamb. There were four main causes of death in lambs before weaning: (1) insufficient milk consumption which predisposed lambs to parasites; (2) worms, particularly Haemonchus contortus which caused severe anaemia. Worms were most obvious in the final weeks before weaning; (3) coccidia, which caused diarrhoea in lambs aged about 2 months; (4) pneumonia in ewes in December 1992 when there was prolonged rain. 3.4. Wool coat The effect of breed group on wool score is summarised in Table 4. Wool scores at 3 months of age were similar for all breed groups, but in older animals the scores were consistently B 1 < H, < E, < S. At 9 months of age wool scores for B, crossbred ewes were about one-third those of the S ewes. Seasonal effects on wool were quite large, with the June lamb crop having substantially higher wool scores than the March-born lambs at 6 and 9 months of age.
4. Discussion Average weights of lambs were 1.83 and 8.7 kg at birth and 3 months. Weights of females at 6 and 9 months averaged 14.4 and 17.9 kg. There was a consistent effect of breed group on lamb weight. At weaning E,, H, and B, crossbreds were 10-13, 14-15 and 32% heavier than Sumatra lambs. These differences can be partly attributed to differences in mature size of the sire breed, and there is possibly
Ruminant Research 25 (1997) 1-7
also an effect of hybrid vigour in the crossbred lambs. In Tobago, which has a similar climate to North Sumatra, a 6-year comparison showed that the growth of Barbados Blackbelly lambs to weaning was markedly superior to that of Virgin Island lambs (Rastogi et al., 1993). The young rams from this experiment were evaluated in a feeding trial (Pond et al., 1994) to examine the extent to which crossbred ram lambs require a higher quality diet to express their genetic potential. Groups of rams were fed either (i> a low quality diet of plantation grass ad libitum plus 400 g per head per day concentrate (11.6 MJ ME per kg, 11.8% CP) comprising locally available feedstuffs, or (ii) a high quality diet fed at 3.3% body weight containing concentrate (13.5 MJ ME per kg, 15.3% CP, given at 70% of DM intake) and Paspalum dilatatum grass (30% intake). On high quality diets when the rams could express their growth potential the average growth rates for S, E,, H, and B, rams were 125 g day-‘, 164 g day-‘, 161 g day-’ and 185 g day-‘, respectively. Thus the ranking of breed groups was B, > E, > H, > S, and the B, grew 48% faster than the S. On the low quality diet, where a limited amount of concentrate was fed on a per head basis not according to body weight, the S lambs outperformed the larger crossbreds; the breed group means were 86 g day-‘, 79 g day-‘, 78 g day-’ and 64 g day-’ for S, E,, H, and B,, respectively. Thus, where good quality diets are available, weaned crossbred lambs grow faster than purebred Sumatra lambs, but on poor diets there is no benefit of the superior growth potential of the crossbreds. Lamb mortality to weaning was 22.5%. This high value can be attributed to the high litter size and health problems associated with the hot humid climate. Mortality was not affected by breed group. Wool scores at 6 and 9 months of age showed an effect of breed group. The breed groups were ranked B, < H, < E, < S. One of the goals of crossing with hair sheep was to produce animals for this hot humid environment as free of wool as possible. Clearly the F, lambs were not wool-free at 3 and 6 months of age. However, by 9 months the B, crosses had very much less wool than the other groups. Also the variability within groups suggests that selection in the crossbred groups should lead to a reduction in
R.M. Gatenby et al. /Small Ruminant Research 25 f 1997) l-7
wool unless heritability is very low. Odenya (1982) obtained an estimate of 0.26 for heritability of wool cover in Dorper sheep.
5. Conclusion Growth rate was higher for each of the crossbred groups as expected from crossing with breeds with higher mature weights. Since there were no appreciable breed differences in viability, the higher weights of the crossbred lambs resulted in higher weight of lamb per ewe. The use of hair sheep, in particular the Barbados Blackbelly and, to a lesser extent, the Virgin Island St. Croix, resulted in lambs with less wool at 6 and 9 months of age.
Acknowledgements We thank Torop Siallagan, Pungu Nababan, Saleh and other staff of the animal houses for their care of the flock and record-keeping; and Leo P. Batubara, Director of SBPT Sei Putih, for support of this work. The research described in this paper was funded through the Small Ruminant Collaborative Research Support Program by USAID grant DAN 1328-G-000046-00.
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