Puberty and early mating performance in subtropical fat-tailed sheep and their crosses

Ferial Hassan¹, M.T. Mousa¹, A.M. Aboul-Naga², F. El-Hommosi³ and G. Abd El-Hafez³

¹Animal Production Research Institute, Ministry of Agriculture, Dokki, Cairo, Egypt
²Agricultural Counsellor, Embassy of Egypt in Rome, Via Salaria 267, 00199 Rome, Italy
³Faculty of Agriculture, University of Assiut, Assiut, Egypt

Abstract
Introduction
Materials and methods
Results
Discussion and conclusions
References

Abstract

In a crossbreeding trial of both Ossimi (O) and Awassi (A) with the highly prolific Chios (C) subtropical fat-tailed sheep, crossbred ewe lambs exhibited their first oestrus at a significantly (P<0.05) younger age than the purebred parents. They also had a higher (P<0.05) conception rate at yearling. C ewe lambs exhibited their first oestrus at the youngest age (230 days) and had the highest conception rate at one year of age. Season of lambing had little effect on age at puberty of either purebred or crossbred ewe lambs.

Crossbred ram lambs performed better in pubertal age than purebred parents. Semen quality at first ejaculation had poor quality, while it was good at 80% semen motility score.

Puberté et premières performances de reproduction chez des moutons à queue grasse des régions subtropicales et chez les produits de leur croisement

Résumé

Dans des essais de croisement entre des moutons de race Ossimi (O) et Awassi (A) avec des moutons à queue grasse très prolifiques de race Chios (C), les agnelles métisses avaient leurs premiers oestrus à un âge significativement moins avancé (P<0,05) que leurs parents de race pure, et un taux de conception à l'âge de 1 an également plus élevé. Les agnelles Chios affichaient l'âge au premier oestrus le plus précoce et le taux de conception à l'âge de 1 an le plus élevé. La saison d'agnelage avait très peu d'effet sur l'âge à la puberté des agnelles de race pure ou croisées.

Les performances à la puberté des agneaux mâles croisés étaient supérieures à celles de leurs parents de race pure. Le premier éjaculat était de qualité médiocre mais présentait une bonne note sur le plan de la motricité du sperme (80%).

Introduction

The Mediterranean subtropical Chios (C) sheep are known for their high prolificacy, early sexual maturity and good milk production. Their usefulness for improving sheep production in the subtropics where prolific temperate breeds performed poorly as purebreds has been reported (Aboul-Ela and Aboul-Naga, 1987). A crossbreeding programme was carried out by the Ministry of Agriculture in Egypt between the imported C sheep from Cyprus and both Ossimi (O) and Awassi (A) sheep. Production performance of these breeds and their crosses has been described by Mousa (1991). The present study reports on the puberty and early mating performance of the crosses and compares it with that of their purebred parents.

Materials and methods

An experiment was conducted at Mallawi Research Farm, Ministry of Agriculture, Upper Egypt between January and September 1987.0 and A ewes were mated to C rams to produce the F1 CO and CA lambs together with their parental groups. Lambs were kept with their dams up to weaning at eight weeks of age. There was a gradual introduction of pelleted concentrate mixture plus Berseem hay into their diets. From December till May, the flock grazed on Egyptian clover (Trifolium alexandrinum). In the summer the flock grazed on crop residues and green fodder when available. Grazing was supplemented with pelleted concentrate mixture.

Puberty performance was studied in both ewe and ram lambs born in the lambing season of May/June 1987 and in ewe lambs born in January/February 1988, starting from four months of age. Behaviourial oestrus was detected by active rams twice daily at 800 and 1600 hours. The first incidence of heat symptoms was recorded and the lambs were weighed. Conception rate among yearlings was tested by putting a fertile ram with each group of ewe lambs for a period of 35 days.

The ram lamb's ability to ejaculate in an artificial vagina was considered as a puberty criterion. The date of first ejaculation was recorded and the lambs were weighed. Semen samples from the ram lambs in each breed group were used to evaluate the physical properties of semen at first ejaculation. Semen motility was examined weekly until it reached a score of 80% of the age of the ram lambs' and other physical properties of the semen were also recorded.

Results

Ewe lambs

Puberty performance

The breed of the ewe lambs had a highly significant effect on age and weight at puberty (P<0.01). O ewe lambs reached puberty at younger ages and heavier weights (P<0.05) than A ewes (Table 1). C ewe lambs, however, reached puberty at a younger age than both O and A ewe lambs (P<0.01). CO ewe lambs exhibited their first oestrus significantly earlier than the O ewes (P<0.01), but at a similar weight. The CA ewe lambs reached puberty significantly younger than A ewes (P<0.01) and at slightly heavier weights.

Single and triplet ewes lambed at a slightly older age than twins, but the differences were not statistically significant (Table 1).

Ewe lambs born in May/June reached puberty a few days later than those born in January/February, and were slightly heavier (Table 1).

Table 1. Mean age in days and body weight in kg at first oestrus for ewe lambs in the breed groups.

Classification	No.	Age		Body weight
		Cons. (day)	± SE	Cons. (kg)	± SE
Overall means	138	275.3	17.2	32.0	1.3
Breed groups
Ossimi (O)	28	12.9	0.4d	1.3	0.0
Awassi (A)	25	40.2	2.0b	1.4	0.2
Chios (C)	27	-45.0	3 8a	-1.8	0.7
CO	26	-7.8	1.3c	1.2	0.1
CA	32	-0.0	0.1d	1.0	0.0
Type of birth
Singles	117	5.1	12.3a	1.1	0.9
Twins	19	-10.8	1.2b	-1.0	0.1
Triplets	2	-5.8	19.8a	-0.0	1.4
Seasons
May-June	75	19.4	1.9	1.0	0.1
Jan-Feb	63	-6.6	2.4	-1.0	0.2

Values within the same column with different superscripts differ significantly (P<0.50).

Yearling fertility

Conception rate was highest amongst yearlings, lowest amongst A, and O yearlings were intermediate (Table 2). C ewe lambs had a better performance than either O or A ewe lambs (P<0.01). The crossbred yearling ewes had significantly (P<0.05) higher conception rates than O and A, but lower conception rates than their parent (C). The difference between C and CO crosses was not statistically significant.

Table 2. Conception rate and body weight of yearling ewe lambs in the breed groups.

Breed group	No. of ewe lambs	Conception rate %	Body weight
			x (kg)	± SE
Ossimi (O)	28	77.1b	37.5	1.6
Awassi (A)	25	44.0c	34.7	1.7
Chios (C)	27	74.1a	38.2	1.4
CO	26	65.4a	39.2	1.6
CA	32	59.3b	37.4	1.5

Values within the same column with different superscripts differ significantly (P<0.05).

Ram lambs

First ejaculation

The two CO and CA crossbred ram lambs performed their first ejaculation at a slightly older age and heavier weight than their A and O parents (P<0.05). They showed better performances in pubertal weight and age than C ram lambs (Table 3). C ram lambs reached their fist ejaculation at the oldest age and lightest weight of all the groups studied, possibly due to slow growth rates. Variations in pubertal age within each group were high, except for C ram lambs.

Table 3. Age and body weight of ram lambs at first ejaculation.

Breed group	No.	Age at puberty		Weight at puberty
		(day)	± SD	mean (kg)	± SE
Ossimi (O)	14	296.8	35.4a1	41.1	6.6a
Awassi (A)	14	284.6	48.5a	38.7	5.9a
Chios (C)	17	334.9	45.3b	35.4	1.9b
CO	15	318.5	39.7ab	51.7	5.3d
CA	16	286.9	24.4a	44.7	5.5d

Estimates followed by the same letter in any column do not differ significantly (P>0.05).

Semen physical properties

Table 4 shows the analysis of semen samples from first ejaculation at puberty. C rams showed the lowest motility score while CA rams had the highest. The other breeds had intermediate scores. Most of the other properties followed the same trend as the motility scores. Both CO and CA crossbreeds had high values for semen volt/me, percentage of live sperm and total number of sperms per ejaculation. C ram lambs had the poorest semen quality.

Performance at 80% semen motility

As the age of the ram advanced, semen motility increased to 80%. The crossbred ram lambs reached 80% semen motility at a younger age than purebred parents (Table 5 and Figure 1) and were also heavier. Most of the semen samples were creamy or whole milk in appearance. The pH values at first ejaculation were high, and gradually declined in alkalinity. Differences in percentage of dead sperms between breeds were not significant. Variations in the percentage of abnormal spermatozoa were generally insignificant, except for CA ram lambs (P>0.05). Sperm cell concentration per ejaculation was high in C, CA and CO ram lambs (Table 5), probably due to their high semen volumes.

Table 4. Physical properties of semen at first ejaculation.

Breed group	No.	Volume (ml)	Motility %	pH (%)	Dead sperm	Abnormality %	Sperm Con. x 106/mm3
Ossimi (O)	5	0.6	50a	7.5a	28.0a	11.6a	2.0
Awassi (A)	5	0.8b	50a	7.3a	34.0a	12.8a	1.5
Chios (C)	5	0.8b	45a	7.5a	24.0a	9.8a	1.3
CO	5	0.8ab	50a	7.2a	25.0a	8.0a	1.9
CA	5	0.9b	55a	6.9a	21.0a	7.5a	1.9

ab = Estimates followed by the same letter in any column do not differ significantly (P>0.05).

Table 5. Semen physical properties, age and body weigh at 80% semen motility score.

Figure 1. Semen motility changes from puberty up to score of 80% for different breed groups.

Discussion and conclusions

Most subtropical breeds reach puberty late (Osman, 1985), possibly due to low growth rates (Aboul-Ela and Chemineau, 1989). However, C ewe lambs attain their puberty at about 225 days (Fox et al, 1971), which agrees with the present study. The results of this study show that crossbreeds between C and O and C and A reached puberty earlier than purebred O and A sheep. Similar reports have showed that heterosis may contribute to earlier sexual development (Land, 1978; McMillan and McDonald, 1983; Lahlou-Kassi and Marie, 1985). However, season of birth seems to have less influence on age at puberty of subtropical breeds, compared to its effect on their body weight. Results obtained by Younis et al (1978) support these findings.

Early breeding of subtropical sheep can result in lower conception and twinning rates and higher lamb losses (Younis et al, 1978; Aboul-Naga et al, 1987). This showed that C, CO and CA yearling ewes had better early breeding performances than the O and A yearling ewes (Table 2). C sheep are expected to infuse the advantage of early breeding to their crosses.

The two crossbred ram lambs reached puberty at younger ages and heavier weights than C ram lambs. C ram lambs seem to be adversely affected by the environment in Upper Egypt, resulting in slower growth rates than those reported in their home country (Lysandrides, 1981). The evidence does not show crossbreeds having better semen properties at puberty. However, by the time the sperm had reached 80% motility, ejaculation volumes in the two crossbreeds and C ram lambs were significantly higher (P<0.05) than in both O and A ram lambs. These differences may be due to the variation in testicular size (Mann, 1964). This study shows that crossbreeding with the highly fertile Chios subtropical breed can considerably improve the early breeding performances.

References

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Lahlou-Kassi A and Marie M. 1985. Sexual and ovarian function of the D'man ewe. In: Land R B and Robinson D W (eds), Genetics of reproduction in sheep. Butterworths, London, UK. pp. 245-260.

Land R B. 1978. Reproduction in young sheep: some genetic and environmental sources of variation. Journal of Reproduction and Fertility 52:427-436.

Lysandrides P. 1981. The Chios sheep in Cyprus. World Animal Review 39: 12-16.

Mann T. 1964. In the biochemistry of semen and of the male reproductive tract. Methuen and O. hid., London; John Willy and Sons Inc., New York.

McMillan W H and McDonald M F. 1983. Reproduction in ewe lambs and its effect on 2-year-old performance. New Zealand Journal of Agricultural Research 26:437-442.

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Osman H A. 1985. Near East sheep breeding and improvement. World Animal Review 54:2-15.

Younis A A, El-Gaboory I A, El-Tawil E A and El-Shobokshy A S.-1978. Age at puberty and possibility of early breeding in Awassi ewes. Journal of Agricultural Science (Cambridge) 90:225-260.