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Reproductive traits in boars

By Dr Stanley Janyk, Irene Animal Production Institute
Breeding practice and research have shown that the response to selection can be improved if some of the sex related traits of the boars could be used as predictors of reproductive efficiency of genetically related sows.(7) (See references at end of article.). A positive correlation between testis size and sperm concentration, as well as a superior mating ability, were found in large white boars by Hauser (3), Wilson (9) and Neely (6). Esbenshade (2) established that the libido scores in boars of both Duroc and Yorkshire breeds increased quadratically with testis volume. The largest increase occurred after testis volume had reached 1 900 cm3. Shinkel (7) and Toelle (8) have presented evidence of a favorable relationship between reproductive traits in males with those of females. They reported that boar lines selected for increased ovulation rates in their offspring had larger testes compared to the boars of the control group with small testes.
Land (5), Islam (4) and Carr (1) established a positive correlation between testis size and ovulation rate in offspring from males with larger testes. According to Young (10), direct selection for increased in situ testis volume of boars would not be antagonistic to the improvement of growth rate or back fat thickness. They also suggested that selection for boars with large testes would decrease the age of puberty as well as litter size in their offspring.
Practical application
Measurement of the scrotal circumference in young bulls is one of the basic selection criterions. In boars testis size can only be determined by the assessment of testis volume using a formula described by Esbenshade (2). Testis width (TW) and length (TL) can be easily measured using a commercially available caliper. Using the Esbenshade formula:
nr_h, where “r” equals one/half of the width of both testes and “h” is equal to the testis height.
Breeding performance traits
A total number of 118 young randomly selected Large White boars (age 80 days, body weight 35 kg) were assessed. Testis sizes were measured every 14 days using a standard caliper and testis volume was calculated according to the formula proposed by Esbenshade. Of 118 boars, 20 animals (10 with largest/1000 cm and 10 with smallest/432 cm testis volume) were selected at the age of 145 days for assessment of the breeding performance traits. The results are presented in Tables 1, 2 and 3. Boars with the average testis volume of 1 000 cm showed a higher daily gain, superior performance index, as well as higher eye muscle depth and higher body mass at the end of the performance test ( 840.8 g/day, 207,66.6 mm, and 84.8 kg respectively). In comparison, boars with small testis volume have lower average performance parameters (daily gain, performance index, eye muscle depth, and body mass: 786 g/day, 199, 64.3 and 80.8 kg respectively).
Only eye muscles were significantly different (P < 0.05).
Libido and semen quality
Selected boars with large and small testes (10 in each group) were kept till the age of 230 days when semen collection started. A total number of 212 ejaculates (106 of each group) were collected and evaluated. The semen evaluation results and libido score are presented in Table 4. Semen obtained from boars with large testes showed a significantly greater number of live sperm and progressive motile sperm (P <0.01), and a significantly lower percentage of sperm with major morphological abnormalities (P<0.05). No significant differences were found between groups of boars concerning the other semen parameters. However, all the semen quality parameters were greater in boars with large testes.
Litter size
Assessment of ovulation rate in daughters from two groups of boars (large and small testis) was based on the litter size obtained from 37 sows (all 4th parity), the daughters of experimental boars (2 of large and 2 of small testis). Semen from one, non-related boar were used to AI the daughters of experimental boars. The total number of piglet born/litter (11.9 and 10.0 of large and small testis boars respectively) differs significantly between the daughters from large and small testis boars (P<0.05).

Conclusion

This research indicated that selection of boars for breeding should consider the measurement of testis volume as an important selection factor.
References
1. CARR, R.W., LAND, R.B. J.Reprod.Fert. v.42,p.325,1973
2. ESBENSHADE, K.L. et al. J.Animal Sci. v.48,n.2,p.246-250, 1979
3. HAUSER E.R. et al. Missouri Agric.Res. Bulletin. N 503, 1952
4. ISLAM, A.B.M. et al. Genetic.Res. n. 27, p 23, 1976
5. LAND, R.B. Nature. n.241,p.208, 1973
6. NELLY, J.D. et al. Proc.Southern Agric.Workers.n.10
7. SCHINKEL, A. et al. J.Animal Sci. v.56.n.5,p.1065 – 1076, 1983
8. TOELLE, V.D., ROBINSON, O.W. Z.Tierz.Zuchtungsbiol..n.102, p.125, 1985
9. WILSON, E.R. et al. J.Animal Sci. v.44, p.939, 1977
10. YOUNG, L.D. et al. J.Animal Sci. v.63, p.17 – 26, 1986

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