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Factors influencing conception rates of Arab mares in Tunisia
Animal Reproduction Science 117 (2010) 106–110
Contents lists available at ScienceDirect
Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci
Factors influencing conception rates of Arab mares in Tunisia Haifa Benhajali a,c , Marie-Annick Richard-Yris a , Mohammed Ezzaouia b , Faouzia Charfi c , Martine Hausberger a,∗ a b c
Université de Rennes I, «Ethologie animale et humaine», UMR CNRS 6552, Campus de Beaulieu, 263 av. Général Leclerc, 35042 Rennes Cedex, France Haras national de Sidi Thabet 2020, Tunisia Université Tunis-ElManar, «Unité de biologie animale et de systématique évolutive», Campus universitaire, 2060 Tunis, Tunisia
a r t i c l e
i n f o
Article history: Received 21 January 2008 Received in revised form 25 March 2009 Accepted 27 April 2009 Available online 3 May 2009 Keywords: Horse Breeding Reproduction efficiency Multivariate analysis
a b s t r a c t In order to investigate the factors affecting the reproduction efficiency of Arab breeding mares in Tunisia, breeding data corresponding to 2340 mated cycles, over 5 years (from 2000 to 2004), from 555 mares offspring of 50 sires and bred with 17 stallions were analysed using a multivariate logistic regression. We chose logit link function and binomial distribution and we used log-likelihood-ratio (LL) and Wald tests (X2 Wald) to test the mean values. The factors of variation included in the model were the year, the stallion, the age of the mare at mating, the sire and the category of the mare. Logistic regression results showed that age and sire affected both the overall conception rate and the first-cycle conception rate of the mares whilst category and stallion influenced only the overall conception rate. To our knowledge, this is the first study showing that the sire of the mare can affect both the first-cycle conception rate and the overall conception rate of the mares. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Very limited information is available on the breeding performance of the Arabian horses (Demirci, 1987) and studies that examined factors that influence reproductive efficiency in the horse have two main limitations (Bruck et al., 1993). First, the relationship between reproductive efficiency and each of the factors of interest are examined individually. This method of analysis does not take into account the influence of variables that are related to both the factor being examined and reproductive efficiency on the results. Second they put an emphasis on three general categories: mare, stallion, and management factors, genetic parameters (dam and sire effects) are rarely explored. The sire has been shown to influence daughter’s fertility in several species such as bovine (Humblot and Denis, 1986; Kadarmideen et al., 2003), porcine (Varona and Noguera, 2001) and ovine (Olivier et al., 1998). A sire effect on the
∗ Corresponding author. Tel.: +33 299 28 69 28. E-mail address: [email protected] (M. Hausberger). 0378-4320/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2009.04.010
volume, motility and sperm concentration of the stallion was reported by Parlevliet et al. (1994). In the mare, Sevinga et al. (2004) found that the sire affects the offspring of the daughters’ gestational length. Mahon and Cunningham (1982) found significant differences in fertility between paternal half-sib group of thoroughbred mares in Britain and Ireland. However in their study, fertility of the mare was summarised as the proportion of her successful years at stud, adjusted for the decline in fertility with age. This measure of fertility depends on the number of years in the stud and does not take into account the number of matings per conception nor the per-cycle conception rate which are better able to illustrate the influences of the stallion and management on reproductive efficiency. The aim of this study was to investigate the factors that influence the reproductive efficiency of Arab breeding mares, determined by two parameters: the per-season conception rate and the first-cycle conception rate. The results will provide information regarding management at the farm and mare level that significantly influence reproductive efficiency. Such information may also create a starting point for a breeding programme.
H. Benhajali et al. / Animal Reproduction Science 117 (2010) 106–110
2. Materials and methods 2.1. Housing conditions Studied horses were at the national breeding facility of Sidi Thabet, located 20 km from Tunis, Tunisia. Mares are brought to this facility every year in order (between February and June) to be bred with the stallions housed there. They were housed in individual boxes where they received barely grains (4 kg/day) and hay every morning and evening and some freshly cut grass once a day. Boxes (5 m × 3 m) were straw bedded. Mares belonged to three different reproductive status: maiden mares (had never been bred and were in this facility for the first time), barren mares (were not pregnant the last season but had been in the stud at least for once) and foaling mares (mares with foal at foot that had been bred in this same stud). 2.2. Reproduction management Estrus was detected once every 48 h by teasing with a stallion in early morning. Two veterinarians detected estrus in mares by rectal palpation and ultrasound to verify the follicular status of the mare. Mares were mated then in hand with one of the stallions housed in this same facility according to the owner decision. The mare was restrained with a lip twitch and a foreleg lifted to ensure immobility before the stallion was brought to the mare. Handlers directed the stallion to approach the mare directly to the hindquarters limiting the stallion’s access to the head and fore body of the mare and thus limiting the pre-copulatory contact with mares. Matings were performed at 48-h-intervals until ovulation was detected by ultrasound. The same 2 veterinarians performed pregnancy detection by ultrasound examination at days 15 and 30 post-ovulation. 2.3. Statistical analysis For each mare mated in a year, three dependant variables were created: - A bimodal variable which takes the value 1 if it was diagnosed pregnant at the end of the breeding season and 0 if no pregnancy was detected. - A bimodal variable which takes the value 1 if it was diagnosed pregnant (at day 30) at the first cycle (post-foaling cycle for foaling mares) and 0 if it was barren. The factors of variation were studied by a multivariate logistic regression using the software Statistica (v. 6.1, Statsoft, Tulsa, Oklahoma, USA) which is the appropriate method for such a bimodal variable. We chose logit link function and binomial distribution and we used log-likelihood-ratio (LL) and Wald tests (X2 Wald) to test the mean values. The factors of variation included in the model were the year, the stallion, the age of the mare at mating, the sire and the category of the mare. The category of the mare is described as being one of the three levels: barren for the preceding season; foaling; maiden (not mated before). Interactions between these factors were tried in the models but excluded if not statistically significant (p > 0.05).
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The correlation between variables was determined using the Spearman rank order test (r). The confidence interval was 95% (p < 0.05). We excluded from statistical analysis data corresponding to: - Stallions which covered less than five mares during the five seasons. - Sires which have less than five offspring. - Mated mares which left the stud before being diagnosed for pregnancy. Breeding data corresponding to 2340 mated cycles, 5 years (from 2000 to 2004), 555 Arab mares offspring of 50 sires and bred with 17 stallions were analysed. The mean proportions of maiden, barren and foaling mares were respectively 13.54%, 26.71% and 59.74%. The age of mares at mating was from 2 to 26 years at mating (9.34 ± 4.6). Barren and foaling mares had almost the same mean age (barren: 10.82 ± 6.87; foaling: 10.03 ± 5.30) and no correlation was found between age and category of the mare (p > 0.05). 3. Results 3.1. Overall conception rate The overall conception rate was of 84%. The logistic regression results revealed that age and category of the mare, stallion and sire affect significantly the overall conception rates of the mated mares (all p-values < 0.05, Table 1). The effect of the age on the overall conception rate was observed only in older mares (>20 years, Fig. 1). Foaling mares had the better overall conception rate with 87% followed by maiden, 84% and barren 77%. The overall conception rates ranged from 57% to 100% per sire (Fig. 2) and from 72% to 93% per stallion (Fig. 3). 3.2. First-cycle conception rate The first-cycle conception rate was of 51%. Factors that affected the first-cycle conception rate were year, sire and the age of the mare (Table 1). The first-cycle conception rate varied over years from 45% to 61% and ranged per sire from 29% to 79% (Fig. 4). Like for the overall conception rate, Table 1 Logistic regression results for the overall conception rate and the firstcycle conception rate of all the studied mares (N = 555). X2 -value
p-value
Overall conception rate Sire −541.606 Category −512.206 Stallion −512.206 Age (mare) −516.144 Year −496.482
91.17 11.60 32.37 40.25 0.93
0.0002 0.003 0.009 0.01 0.92
First-cycle conception rate Sire −878.842 Category −844.590 Stallion −854.867 Age (mare) −867.905 Year −852.362
69.98 1.48 22.03 48.11 17.02
0.026 0.48 0.14 0.001 0.001
Log-likelihood-value
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H. Benhajali et al. / Animal Reproduction Science 117 (2010) 106–110
Fig. 1. Overall conception rate (number of pregnant mares at the end of season/number of mated mares) according to the mare’s age (mean ± SE). Note that the lower number (44 mares) of mares above 22 years may explain the large error bars observed for them.
Fig. 2. Variations of mares’ overall conception (number of pregnant mares at the end of season/number of mated mares) according to these mares’ sire. 1, 2, . . ., 49 = different individual stallions (ranked randomly); means ± SE for these sires’ daughters.
Fig. 3. Overall conception rate (number of pregnant mares at the end of season/number of mated mares) according to the stallion they are bred to. 1, 2, . . ., 17 = individual stallions (ranked randomly).
H. Benhajali et al. / Animal Reproduction Science 117 (2010) 106–110
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Fig. 4. Overall conception rate (number of pregnant mares at the first cycle/number of mated mares) according to the stallion they are bred to. 1, 2, . . ., 17 = individual stallions (ranked randomly).
the age affected the first-cycle conception rate only in older mares (>20 years). It is also worth noting that the fertility of the sire (estimated by the number of pregnant mares/the number of mares bred) was not correlated with the fertility of its daughters (r = −0.43, p > 0.05). 4. Discussion According to our results, age and sire affected both the overall conception rate and the first-cycle conception rate of the mares whilst category and stallion influenced only the overall conception rate. To our knowledge, the present study is the first to show that particular parameters are affected by paternal origin of the mares, such as the first-cycle conception rate and the overall conception rate. Whilst one earlier study (Mahon and Cunningham, 1982) reported significant differences in fertility (the proportion of successful years at stud) between paternal half-sib group of thoroughbred mares in Britain and Ireland and bring more accuracy to the effect of the sire on daughters’ fertility. The first-cycle and the overall conception rates found in this study (84% and 51%, respectively) were comparable to those reported by Demirci (1987) for Arab horses in Turkey (80.1% and 60%) and therefore suggest that overall reproductive efficiency for this breed did not differ in this facility from usual records. Similarly to the findings of Samper et al. (2002), the category of the mare affected only its overall conception rate. Mares that were barren during the previous breeding season were less likely to become pregnant at the end of the season than maiden or foaling mares. The same results were reported by Sullivan et al. (1975), Samper (2001), Hemberg et al., 2004 and Schideler, 1993. No correlation was found between age and category of the mare (p > 0.05) which does not support the conclusion of Ricketts and Alonso (1991), Morris and Allen (2002) and Hemberg et al. (2004) who speculated that the main reason for the lower fertility in barren mares would be the age of the mares. Foaling mares had the best overall conception rate which is in accordance
with the findings of Langlois and Blouin (2004) and on contrary to the supposed negative effect of lactation on fertility (Gibbs and Davison, 1992; Bruck et al., 1993). This supports the idea that to have declared a foal for the preceding mating season may be a good marker of the reproductive aptitude (Langlois and Blouin, 2004). It is not surprising that stallion affects the fertility of the mare. The stallion was shown to affect the overall conception rate (Davis Morel and Gunnarsson, 2000) and the first-cycle conception rate (Dowsett and Pattie, 1982; Samper et al., 1991; Hellander, 1992; Buiten et al., 1994). Large variations in semen quality exist both between breeds and between individual stallions (Parlevliet et al., 1994; Jasko et al., 1990). The quality and quantity of semen of stallions mating naturally is not checked before mating. If many mares are mated in a short time, sperm production by the stallion can become a limiting factor (Buiten et al., 2003). However we found no correlation between the number of mated mares per stallion and stallion fertility. According to Merkt et al. (1979) such effect of the number of mated mares on the fertility of the stallion is detectable only when the number of mares covered/stallion rose above 80 per breeding season. The age of the mare affected its overall conception rate as well as its first-cycle conception rate. The effect of the age of the mare on its fertility is generally accepted in all studies (Wesson and Ginther, 1981; Bruck et al., 1993; Garrot et al., 1991; Davis Morel and Gunnarsson, 2000; Morris and Allen, 2002; Hemberg et al., 2004; Heilkenbrinker et al., 1997; Samper et al., 2002; Morehead et al., 2002; Langlois and Blouin, 2004). Breeding stallions are generally selected on the basis of their racing performances. The present study shows that these stallions even if they may be good breeders may disseminate a low fertility to many thousands of daughters. This could have serious economic implications for producers and implications on the future of the species as fertility is essential to spread any genetic performances. As it was not statistically possible in this study to investigate the effect of sire of the stallion on fertility parameters, further
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research is needed to elucidate this factor. These results suggest including the sire of the mare as a criterion in brood mare selection. References Bruck, I., Anderson, G.A., Hyland, J.H., 1993. Reproductive performance of thoroughbred mares on six commercial stud farms. Aust. Vet. J. 70, 299–303. Buiten, A.V., Bruin, G., Parlevliet, J.M., Colenbrander, B., 1994. Factors influencing fertility in the horse. In: Proceedings of the 45th Annual Meeting of the European Association for Animal Production, Edinburgh, UK, p. 366. Buiten, A.V., Westers, P., Colenbrander, B., 2003. Male, female and management risk factors for non-return to service in Dutch mares. Prev. Vet. Med. 61, 17–26. Davis Morel, M.C., Gunnarsson, V., 2000. A survey of the fertility of Icelandic stallions. Anim. Reprod. Sci. 64, 49–64. Demirci, E., 1987. Fertility in purebred Arab horses in Turkey. Anim. Reprod. Sci. 15, 265–271. Dowsett, K.F., Pattie, W.A., 1982. Characteristics and fertility of stallion semen. J. Reprod. Fertil. Suppl. 32, 1–8. Garrot, R.A., Eagle, T.C., Plotka, E.D., 1991. Age-specific reproduction in feral horses. The highest foaling rate was found among animals aged 6–15 years. Can. J. Zool. 69, 738–743. Gibbs, P.G., Davison, K.E., 1992. A field study on reproductive efficiency of mares maintained pre-dominantly on native pasture. J. Equine Vet. Sci. 12, 219–222. Heilkenbrinker, T., Kossin, C., Scherbarth, R., Frerking, H., 1997. Examination of the appropriateness of anamnestic and clinical parameters for the prediction of the course of pregnancy under field conditions. Dtsch. Tierarztl. Wochenschr. 104, 313–319. Hellander, J.C., 1992. Current practical use of a glasswool/sephadex filtration technique of frozen stallion semen. Acta Vet. Scand. (Suppl. 88), 67–70. Hemberg, E., Lundeheim, N., Einarsson, S., 2004. Reproductive performance of thoroughbred mares in Sweden. Reprod. Domest. Anim. 39, 81–86. Humblot, P., Denis, J.B., 1986. Sire effects on cow fertility and late embryonic mortality in the montbeliard breed. Livest. Prod. Sci. 14 (2), 139–148. Jasko, D.J., Lein, D.H., Foote, R.H., 1990. Determination of the relationship between sperm morphologic classification and fertility in stallions: 66 cases (1987–1988). J. Am. Vet. Med. Assoc. 197, 389–393. Kadarmideen, H.N., Thompson, R., Coffey, M.P., Kossaibati, M.A., 2003. Genetic parameters and evaluations from single- and multiple-trait
analysis of dairy cow fertility and milk production. Livest. Prod. Sci. 81 (2–3), 183–195. Langlois, B., Blouin, C., 2004. Statistical analysis of some factors affecting the number of horse births in France. Reprod. Nutr. Dev. 44, 583–595. Mahon, G.A.T., Cunningham, E.P., 1982. Inbreeding and the inheritance of fertility in the thoroughbred mare. Livest. Prod. Sci. 9 (6), 743–754. Merkt, H., Jacobs, K.O., Klug, E., Aukes, E., 1979. An analysis of stallion fertility rates (foals born alive) from the breeding documents of the Landgestut Celle over a 158-year period. J. Reprod. Fertil. Suppl. 27, 73–77. Morehead, J.P., Blanchard, T.L., Thompson, J.A., Brinsko, S.P., 2002. Evaluation of early fetal losses on four equine farms in central Kentucky: 73 cases. J. Am. Vet. Med. Assoc. 220, 1828–1858. Morris, L.H., Allen, W.R., 2002. Reproductive efficiency of intensively managed thoroughbred mares in Newmarket. Equine Vet. J. 34, 51–60. Olivier, W.J., Snyman, M.A., van Wyk, J.B., Erasmus, G.J., 1998. Genetic parameter estimates for fitness traits in South African Merino sheep. Livest. Prod. Sci. 56 (1), 71–77. Parlevliet, J.M., Kemp, B., Colenbrander, B., 1994. Reproductive characteristics and semen quality in maiden Dutch Warmblood stallions. J. Reprod. Fertil. 101, 183–187. Ricketts, S.W., Alonso, S., 1991. The effect of age and parity on the development of equine chronic endometrial disease. Equine Vet. J. 23, 189–192. Samper, J.C., 2001. Management and fertility of mares bred with frozen semen. Anim. Reprod. Sci. 68, 219–247. Samper, J.C., Hellander, J.C., Crabo, B.G., 1991. Relationship between the fertility of fresh and frozen stallion semen and semen quality. J. Reprod. Fertil. Suppl. 44, 107–114. Samper, J.C., Vidament, M., Katila, T., Newcombe, J., Estrada, A., Sargeant, J., 2002. Analysis of some factors associated with pregnancy rates of frozen semen: a multi-centre study. Theriogenology 58, 647–650. Sevinga, M., Barkema, H.W., Stryhn, H., Hesselink, J.W., 2004. Retained placenta in Friesian mares: incidence, and potential risk factors with special emphasis on gestational length. Theriogenology 61 (5), 851–859. Schideler, R.K., 1993. History. In: McKinnon, A.O., Voss, J.L. (Eds.), Equine Reproduction. Lea and Febiger, Philadelphia, pp. 196–203. Sullivan, J.J., Turner, P.C., Self, L.C., Gutteridge, H.B., Bartlett, D.E., 1975. Survey of reproductive efficiency in the Quarter-horse and Thoroughbred. J. Reprod. Fertil. Suppl. 23, 315–323. Varona, L., Noguera, J.L., 2001. Variance components of fertility in Spanish Landrace pigs. Livest. Prod. Sci. 67 (3), 217–221. Wesson, J.A., Ginther, O.J., 1981. Influence of season and age on reproductive activity in pony mares on the basis of a slaughterhouse survey. J. Anim. Sci. 52, 119–129.
Contents lists available at ScienceDirect
Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci
Factors influencing conception rates of Arab mares in Tunisia Haifa Benhajali a,c , Marie-Annick Richard-Yris a , Mohammed Ezzaouia b , Faouzia Charfi c , Martine Hausberger a,∗ a b c
Université de Rennes I, «Ethologie animale et humaine», UMR CNRS 6552, Campus de Beaulieu, 263 av. Général Leclerc, 35042 Rennes Cedex, France Haras national de Sidi Thabet 2020, Tunisia Université Tunis-ElManar, «Unité de biologie animale et de systématique évolutive», Campus universitaire, 2060 Tunis, Tunisia
a r t i c l e
i n f o
Article history: Received 21 January 2008 Received in revised form 25 March 2009 Accepted 27 April 2009 Available online 3 May 2009 Keywords: Horse Breeding Reproduction efficiency Multivariate analysis
a b s t r a c t In order to investigate the factors affecting the reproduction efficiency of Arab breeding mares in Tunisia, breeding data corresponding to 2340 mated cycles, over 5 years (from 2000 to 2004), from 555 mares offspring of 50 sires and bred with 17 stallions were analysed using a multivariate logistic regression. We chose logit link function and binomial distribution and we used log-likelihood-ratio (LL) and Wald tests (X2 Wald) to test the mean values. The factors of variation included in the model were the year, the stallion, the age of the mare at mating, the sire and the category of the mare. Logistic regression results showed that age and sire affected both the overall conception rate and the first-cycle conception rate of the mares whilst category and stallion influenced only the overall conception rate. To our knowledge, this is the first study showing that the sire of the mare can affect both the first-cycle conception rate and the overall conception rate of the mares. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Very limited information is available on the breeding performance of the Arabian horses (Demirci, 1987) and studies that examined factors that influence reproductive efficiency in the horse have two main limitations (Bruck et al., 1993). First, the relationship between reproductive efficiency and each of the factors of interest are examined individually. This method of analysis does not take into account the influence of variables that are related to both the factor being examined and reproductive efficiency on the results. Second they put an emphasis on three general categories: mare, stallion, and management factors, genetic parameters (dam and sire effects) are rarely explored. The sire has been shown to influence daughter’s fertility in several species such as bovine (Humblot and Denis, 1986; Kadarmideen et al., 2003), porcine (Varona and Noguera, 2001) and ovine (Olivier et al., 1998). A sire effect on the
∗ Corresponding author. Tel.: +33 299 28 69 28. E-mail address: [email protected] (M. Hausberger). 0378-4320/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2009.04.010
volume, motility and sperm concentration of the stallion was reported by Parlevliet et al. (1994). In the mare, Sevinga et al. (2004) found that the sire affects the offspring of the daughters’ gestational length. Mahon and Cunningham (1982) found significant differences in fertility between paternal half-sib group of thoroughbred mares in Britain and Ireland. However in their study, fertility of the mare was summarised as the proportion of her successful years at stud, adjusted for the decline in fertility with age. This measure of fertility depends on the number of years in the stud and does not take into account the number of matings per conception nor the per-cycle conception rate which are better able to illustrate the influences of the stallion and management on reproductive efficiency. The aim of this study was to investigate the factors that influence the reproductive efficiency of Arab breeding mares, determined by two parameters: the per-season conception rate and the first-cycle conception rate. The results will provide information regarding management at the farm and mare level that significantly influence reproductive efficiency. Such information may also create a starting point for a breeding programme.
H. Benhajali et al. / Animal Reproduction Science 117 (2010) 106–110
2. Materials and methods 2.1. Housing conditions Studied horses were at the national breeding facility of Sidi Thabet, located 20 km from Tunis, Tunisia. Mares are brought to this facility every year in order (between February and June) to be bred with the stallions housed there. They were housed in individual boxes where they received barely grains (4 kg/day) and hay every morning and evening and some freshly cut grass once a day. Boxes (5 m × 3 m) were straw bedded. Mares belonged to three different reproductive status: maiden mares (had never been bred and were in this facility for the first time), barren mares (were not pregnant the last season but had been in the stud at least for once) and foaling mares (mares with foal at foot that had been bred in this same stud). 2.2. Reproduction management Estrus was detected once every 48 h by teasing with a stallion in early morning. Two veterinarians detected estrus in mares by rectal palpation and ultrasound to verify the follicular status of the mare. Mares were mated then in hand with one of the stallions housed in this same facility according to the owner decision. The mare was restrained with a lip twitch and a foreleg lifted to ensure immobility before the stallion was brought to the mare. Handlers directed the stallion to approach the mare directly to the hindquarters limiting the stallion’s access to the head and fore body of the mare and thus limiting the pre-copulatory contact with mares. Matings were performed at 48-h-intervals until ovulation was detected by ultrasound. The same 2 veterinarians performed pregnancy detection by ultrasound examination at days 15 and 30 post-ovulation. 2.3. Statistical analysis For each mare mated in a year, three dependant variables were created: - A bimodal variable which takes the value 1 if it was diagnosed pregnant at the end of the breeding season and 0 if no pregnancy was detected. - A bimodal variable which takes the value 1 if it was diagnosed pregnant (at day 30) at the first cycle (post-foaling cycle for foaling mares) and 0 if it was barren. The factors of variation were studied by a multivariate logistic regression using the software Statistica (v. 6.1, Statsoft, Tulsa, Oklahoma, USA) which is the appropriate method for such a bimodal variable. We chose logit link function and binomial distribution and we used log-likelihood-ratio (LL) and Wald tests (X2 Wald) to test the mean values. The factors of variation included in the model were the year, the stallion, the age of the mare at mating, the sire and the category of the mare. The category of the mare is described as being one of the three levels: barren for the preceding season; foaling; maiden (not mated before). Interactions between these factors were tried in the models but excluded if not statistically significant (p > 0.05).
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The correlation between variables was determined using the Spearman rank order test (r). The confidence interval was 95% (p < 0.05). We excluded from statistical analysis data corresponding to: - Stallions which covered less than five mares during the five seasons. - Sires which have less than five offspring. - Mated mares which left the stud before being diagnosed for pregnancy. Breeding data corresponding to 2340 mated cycles, 5 years (from 2000 to 2004), 555 Arab mares offspring of 50 sires and bred with 17 stallions were analysed. The mean proportions of maiden, barren and foaling mares were respectively 13.54%, 26.71% and 59.74%. The age of mares at mating was from 2 to 26 years at mating (9.34 ± 4.6). Barren and foaling mares had almost the same mean age (barren: 10.82 ± 6.87; foaling: 10.03 ± 5.30) and no correlation was found between age and category of the mare (p > 0.05). 3. Results 3.1. Overall conception rate The overall conception rate was of 84%. The logistic regression results revealed that age and category of the mare, stallion and sire affect significantly the overall conception rates of the mated mares (all p-values < 0.05, Table 1). The effect of the age on the overall conception rate was observed only in older mares (>20 years, Fig. 1). Foaling mares had the better overall conception rate with 87% followed by maiden, 84% and barren 77%. The overall conception rates ranged from 57% to 100% per sire (Fig. 2) and from 72% to 93% per stallion (Fig. 3). 3.2. First-cycle conception rate The first-cycle conception rate was of 51%. Factors that affected the first-cycle conception rate were year, sire and the age of the mare (Table 1). The first-cycle conception rate varied over years from 45% to 61% and ranged per sire from 29% to 79% (Fig. 4). Like for the overall conception rate, Table 1 Logistic regression results for the overall conception rate and the firstcycle conception rate of all the studied mares (N = 555). X2 -value
p-value
Overall conception rate Sire −541.606 Category −512.206 Stallion −512.206 Age (mare) −516.144 Year −496.482
91.17 11.60 32.37 40.25 0.93
0.0002 0.003 0.009 0.01 0.92
First-cycle conception rate Sire −878.842 Category −844.590 Stallion −854.867 Age (mare) −867.905 Year −852.362
69.98 1.48 22.03 48.11 17.02
0.026 0.48 0.14 0.001 0.001
Log-likelihood-value
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H. Benhajali et al. / Animal Reproduction Science 117 (2010) 106–110
Fig. 1. Overall conception rate (number of pregnant mares at the end of season/number of mated mares) according to the mare’s age (mean ± SE). Note that the lower number (44 mares) of mares above 22 years may explain the large error bars observed for them.
Fig. 2. Variations of mares’ overall conception (number of pregnant mares at the end of season/number of mated mares) according to these mares’ sire. 1, 2, . . ., 49 = different individual stallions (ranked randomly); means ± SE for these sires’ daughters.
Fig. 3. Overall conception rate (number of pregnant mares at the end of season/number of mated mares) according to the stallion they are bred to. 1, 2, . . ., 17 = individual stallions (ranked randomly).
H. Benhajali et al. / Animal Reproduction Science 117 (2010) 106–110
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Fig. 4. Overall conception rate (number of pregnant mares at the first cycle/number of mated mares) according to the stallion they are bred to. 1, 2, . . ., 17 = individual stallions (ranked randomly).
the age affected the first-cycle conception rate only in older mares (>20 years). It is also worth noting that the fertility of the sire (estimated by the number of pregnant mares/the number of mares bred) was not correlated with the fertility of its daughters (r = −0.43, p > 0.05). 4. Discussion According to our results, age and sire affected both the overall conception rate and the first-cycle conception rate of the mares whilst category and stallion influenced only the overall conception rate. To our knowledge, the present study is the first to show that particular parameters are affected by paternal origin of the mares, such as the first-cycle conception rate and the overall conception rate. Whilst one earlier study (Mahon and Cunningham, 1982) reported significant differences in fertility (the proportion of successful years at stud) between paternal half-sib group of thoroughbred mares in Britain and Ireland and bring more accuracy to the effect of the sire on daughters’ fertility. The first-cycle and the overall conception rates found in this study (84% and 51%, respectively) were comparable to those reported by Demirci (1987) for Arab horses in Turkey (80.1% and 60%) and therefore suggest that overall reproductive efficiency for this breed did not differ in this facility from usual records. Similarly to the findings of Samper et al. (2002), the category of the mare affected only its overall conception rate. Mares that were barren during the previous breeding season were less likely to become pregnant at the end of the season than maiden or foaling mares. The same results were reported by Sullivan et al. (1975), Samper (2001), Hemberg et al., 2004 and Schideler, 1993. No correlation was found between age and category of the mare (p > 0.05) which does not support the conclusion of Ricketts and Alonso (1991), Morris and Allen (2002) and Hemberg et al. (2004) who speculated that the main reason for the lower fertility in barren mares would be the age of the mares. Foaling mares had the best overall conception rate which is in accordance
with the findings of Langlois and Blouin (2004) and on contrary to the supposed negative effect of lactation on fertility (Gibbs and Davison, 1992; Bruck et al., 1993). This supports the idea that to have declared a foal for the preceding mating season may be a good marker of the reproductive aptitude (Langlois and Blouin, 2004). It is not surprising that stallion affects the fertility of the mare. The stallion was shown to affect the overall conception rate (Davis Morel and Gunnarsson, 2000) and the first-cycle conception rate (Dowsett and Pattie, 1982; Samper et al., 1991; Hellander, 1992; Buiten et al., 1994). Large variations in semen quality exist both between breeds and between individual stallions (Parlevliet et al., 1994; Jasko et al., 1990). The quality and quantity of semen of stallions mating naturally is not checked before mating. If many mares are mated in a short time, sperm production by the stallion can become a limiting factor (Buiten et al., 2003). However we found no correlation between the number of mated mares per stallion and stallion fertility. According to Merkt et al. (1979) such effect of the number of mated mares on the fertility of the stallion is detectable only when the number of mares covered/stallion rose above 80 per breeding season. The age of the mare affected its overall conception rate as well as its first-cycle conception rate. The effect of the age of the mare on its fertility is generally accepted in all studies (Wesson and Ginther, 1981; Bruck et al., 1993; Garrot et al., 1991; Davis Morel and Gunnarsson, 2000; Morris and Allen, 2002; Hemberg et al., 2004; Heilkenbrinker et al., 1997; Samper et al., 2002; Morehead et al., 2002; Langlois and Blouin, 2004). Breeding stallions are generally selected on the basis of their racing performances. The present study shows that these stallions even if they may be good breeders may disseminate a low fertility to many thousands of daughters. This could have serious economic implications for producers and implications on the future of the species as fertility is essential to spread any genetic performances. As it was not statistically possible in this study to investigate the effect of sire of the stallion on fertility parameters, further
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