Breed effects on semen traits of dairy and beef artificial insemination bulls

I Boujenane and K Boussaq*

Department of Animal Production and Biotechnology, Institut Agronomique et Vétérinaire Hassan II, Rabat, Morocco
i.boujenane@iav.ac.ma
* Association Nationale des Producteurs de Viandes Rouges, Avenue Annakhil, Rabat, Morocco
b_khouloud@hotmail.fr

Abstract

The objective of this study was to evaluate the effect of breed on semen traits of 38 Holstein (HO), Charolais (CH), Piedmontese (PM), Belgian Blue (BB) and Oulmès-Zaer (OZ) artificial insemination (AI) bulls. A total of 4050 ejaculates collected from January 2012 to May 2013 were analysed using a mixed model that included the random effect of bull within breed and fixed effects of breed, age at collection, season of collection, year of collection, interval between two collections and ejaculate order.

The analysis of variance showed that the breed of bulls had significant effects on semen traits, except on ejaculate volume on which the effect of breed was not significant. The PM bulls had the highest sperm concentration (1.12±0.05x10⁹/ml) and mass motility (3.51±0.11), the CH bulls had the greatest number spermatozoa per ejaculate (6.41±0.55x10⁹) and the HO bulls had the highest individual motility (76.7±0.71%) and post-thawing motility 58.3±0.81%). In addition, the BB bulls had the lowest sperm concentration, mass motility, individual motility and post-thawing motility, whereas the OZ bulls had the lowest number of spermatozoa per ejaculate (3.00±0.95x10⁹). On the basis of total AI doses produced monthly, the CH and BB bulls ranked first and last, respectively. However, due to the low number of bulls for some breeds, there is a need of further studies to establish breed differences.

Keywords: AI, Belgian Blue, Charolais, Holstein, Morocco, Oulmès-Zaer, Piedmontese

Introduction

Due to the rapid increase of Moroccan population, the national milk and meat production does not cover the human protein needs. Thus, in order to meet the increasing demand of the growing human population for these products by 2020, the government set up programmes for developing milk and meat production. Among the axes for promoting faster genetic improvement and increasing profitability of herds, the introduction of genetically superior dairy breeds and the use of crossbreeding with productive exotic dairy and beef breeds by the use of artificial insemination (AI) were envisaged. Two AI centres managed by the government exist in the country. However, their production does not cover the increased AI demand; consequently, thousands of frozen doses are imported annually from European and North-American countries. Recently, one AI centre was transferred to a breeders’ association, which hopes to increase the local production in order to satisfy the breeders’ AI demand (Boujenane and Boussaq 2013). Therefore, a wide variety of breeds with different genetic make up have been imported in this centre from European countries, i.e. from temperate areas, for semen production. However, breed differences in semen characteristics were reported in several studies (Fields et al 1979; Brito et al 2002a). Thus, it is useful to have extensive information on semen characteristics obtained from these different breeds raised under Moroccan management conditions, in order to increase the productivity and profitability of the AI centre. Moreover, semen characteristics of the Moroccan local Oulmès-Zaer were never studied. This is a good opportunity to evaluate its semen characteristics and to compare it with other exotic breeds.

The present study was undertaken to evaluate the genetic variation of semen characteristics among different breeds of bulls managed under the same conditions in Morocco in order to improve their production potential.

Material and methods

Animals and management

Semen data from a Moroccan AI centre, CRIA Fouarat, collected from January 2012 to May 2013 were evaluated. Average daily ambient temperature during the collection period was 16.3°C with a minimum of -3.7°C and a maximum of 42.8°C. Average humidity was 77%.

A total of 4050 ejaculates were analysed. They were obtained from 21, 6, 5, 4 and 2 Holstein (HO), Charolais (CH), Piedmontese (PM), Belgian Blue (BB) and Oulmès-Zaer (OZ) AI bulls, respectively (Table 1). The HO is a dairy breed, CH, PM and BB are beef breeds and OZ is a Moroccan local breed. Age of bulls at collection averaged 41.0 month old, varying from 19 to 93 months. The bulls were managed uniformly. They were individually housed and maintained on a diet of mixed alfalfa and oat hay, approximately 5 kg of concentrate and vitamins and minerals mix. All the bulls are periodically vaccinated against foot and mouth disease.

Semen collection

In general, semen was routinely collected in the centre early morning. Semen collection was preceded by a controlled sexual preparation. Thus, after arrival on the collection floor, bulls are tied in the waiting stall from which they observe the collection of the other bulls. When their libido was stimulated, they were allowed a short walk and two false mounts with a 2-min interval. At the third mount using a teaser animal (a bull known for it docility and robustness), the ejaculate was obtained with an artificial vagina (37° C). One or two ejaculates were collected from each bull on each collection day. The interval between two consecutive collections varied from 2 to 36 days, with an average of 2.98 days.

Semen exam

Immediately after collection, the tube of semen was placed in a water bath at 32 to 34° C. Each ejaculate was evaluated for volume, sperm concentration and motility traits. Some ejaculates were discarded by the technician on either established standards or judgment (colour, presence of blood or dirt…). Volume was measured in the graduated collection tube (ml). Sperm concentration (spermatozoa number per ml) was estimated by using a photometer (Reference 1203, IMV Technologie, France). Mass motility score was subjectively assessed for undiluted unstained semen using a scale from 0 (no activity) to 5 (rapid swirling motion). Individual ejaculates were then diluted with egg yolk citrate-glycerol extender to give a concentration of 24 million total spermatozoa per 0.25 ml straw. Individual motility or percent progressive motility, expressed by the percent of mobile spermatozoa per ejaculate, was estimated in 5% steps on a subjective scale of 0% to 100% by examining unstained diluted semen under microscope (Nikon Eclipse 50i, IMV Technologie, France) using a 100x magnification. After gradually cooling to 4°C, the semen was packaged in 0.25 ml straws (24 million motile spermatozoa before freezing per straw) and frozen to -196° C. Post-thawing motility was measured 24 hours after storage in liquid nitrogen. For post-thaw semen evaluation, two straws from each bull at each collection were thawed in a water bath of 37° C for 30 seconds and evaluated individually for the percentage of progressively motile spermatozoa. Ejaculates with less than 35% of post-thawing progressively motile spermatozoa were eliminated. Valid straws were stored in large containers containing liquid nitrogen.

Statistical analyses

The traits studied were ejaculate volume, sperm concentration, mass motility score, individual motility, post-thawing progressive individual motility and total number of spermatozoa per ejaculate, which was calculated as the product of ejaculate volume and sperm concentration. After editing, the file analysed included 4050 ejaculates corresponding to 38 bulls of different breeds. The number of ejaculates averaged 145 per bull, varying from 7 to 349 ejaculates. Except mass motility score that was analysed using the GLIMMIX procedure (SAS 2002), since it is multinomially distributed, the other semen traits (ejaculate volume, sperm concentration, total number of spermatozoa per ejaculate, individual motility and post-thawing individual motility), which are normally distributed, were analysed using the MIXED procedure (SAS 2002). The mixed model used to analyse all variables included the random effect of bull within breed (38 bulls) and the fixed effects of bull’s breed (5 levels: HO, CH, PM, BB and OZ), age at collection (7 levels: age ≤ 24 mo., 24 < age ≤ 30 mo., 30 < age ≤ 36 mo., 36 < age ≤ 42 mo., 42 < age ≤ 48 mo., 48 < age ≤ 54 mo., age > 54 mo.), season of collection (4 levels: winter: January - March, spring: April - June, summer: July - September, autumn: October - December), year of collection (2 levels: 2012 and 2013), interval between two successive collections (5 levels: 2, 3, …, 6 days or greater) and ejaculate order (2 levels: 1 ^st and 2^nd). Interactions between effects were assumed negligible and hence were not tested. When the effect was determined to be significant (P < 0.05), differences among least-squares means were examined by the Tukey method for multiple comparisons.

Furthermore, to compare semen traits of the Holstein dairy breed with CH, PM and BB beef breeds and the Oulmès-Zaer local breed with beef breeds, the following linear contrasts were computed:

Results and discussion

Descriptive statistics

Arithmetic means, standard deviations and coefficients of variation for sperm characteristics of HO, CH, PM, BB and OZ bulls are presented in Table 2. The means are in general similar to those found in other studies for different breeds (Fields et al 1979; Everett and Bean 1982; Taylor et al 1985; Mathevon et al 1998; Brito et al 2002a).

Breed effects

The objective of this study was to evaluate the effect of breeds on semen characteristics. Therefore, the influence of other effects will not be discussed. Nevertheless, the results showed that age at collection, season of collection, year of collection, interval between two successive collections and ejaculate order had significant effects on the studied variables. Semen production and sperm quality increased as the bulls became older and when collections occurred in winter and spring seasons. Additionally, increasing collection intervals resulted in higher semen characteristics, and higher semen quantity and quality were observed for first ejaculates. These results are in agreement with those of several studies (Everett and Bean 1982; Taylor et al 1985; Mathevon et al 1998; Brito et al 2002a; Fuerst-Waltl et al 2006; Karoui et al 2011; Boujenane and Boussaq 2013).

Least-squares means and standard errors for semen traits of HO, CH, PM, BB and OZ bulls are presented in Table 3. In most cases, the semen characteristics were significantly different among the breeds of bulls.

Sperm concentration varied significantly among breeds of bulls. Ejaculates of BB bulls had the lowest sperm concentration (0.74±0.06x10⁹ /ml), those of PM bulls had the highest concentration (1.12±0.06x10⁹/ml) and those of OZ, CH and HO bulls were intermediate. This result confirms the existence of genetic variation on semen concentration as supported by many researchers (Fields et al 1979; Brito et al 2002a; Asad et al 2004; Adamczyk et al 2013). Fields et al (1979) reported that the Hereford and Angus bulls from Florida showed the highest concentrations, the Herefords from Montana had intermediate concentrations, and the Brahman and Santa Gertrudis bulls had the lowest sperm concentrations; however, their study involved only young bulls. They explained this difference by the pubertal processes in the Santa Gertrudis that occurred over a longer period of time than in the other breeds studied. Asad et al (2004) found that the highest concentration of semen was obtained in Local x Friesian x Friesian and the lowest in Sahiwal x Friesian x Friesian. Likewise, Simmental bulls were characterized by a higher sperm concentration compared to Holstein-Friesian bulls (Adamczyk et al 2013). Moreover, Brito et al (2002a) found that Bos indicus bulls had higher sperm concentration than Bos taurus bulls, with intermediate values for crossbred bulls. Furthermore, there was no significant differences between dairy and beef breeds, between local and beef breeds and between dairy and local breeds for sperm concentration (P>0.05).

The total number of spermatozoa per ejaculate was also different among the bulls of different breeds. The CH bulls had the highest total number of spermatozoa per ejaculate (6.41±0.55x10⁹) owing to their higher ejaculate volume. The total sperm number of CH bulls was 20.7%, 29.0% 87% and 114% higher than those of HO, PM, BB and OZ bulls, respectively. Brito et al (2002a) reported that Bos indicus bulls had higher total number of spermatozoa than Bos taurus bulls, with intermediate values for crossbred bulls. They explained the superiority of Bos indicus bulls by the higher sperm concentration, since no significant differences among genetic groups for ejaculate volume were observed. Moreover, the number of spermatozoa per ejaculate was not significantly different between dairy and beef breeds, but it was higher in dairy and beef breeds than in local OZ breed (P<0.05).

The mass motility of sperm was significantly influenced by the breed of bulls. Mass motility score of BB and OZ bulls was the lowest (2.91±0.10 and 3.06±0.16, respectively), those of PM and HO bulls was the highest (3.51±0.11 and 3.42±0.05, respectively) and that of CH bulls was intermediate (3.26±0.08). Nevertheless, least-squares means of BB and OZ on one hand and those of HO and PM on the other hand are not different (P>0.05). Similar studies were made by Asad et al (2004), who found a mass movement of semen as 3.98 grade in Local x Friesian, 2.58 in Friesian and 2.49 in Sahiwal x Friesian bulls. Moreover, studying the interaction between breed of bulls and season, Fiaz et al (2009) reported that the mass motility of semen in Friesian and Jersey breeds was significantly lower (P<0.05) during wet summer than other seasons. Additionally, mass motility of local OZ breed was not significantly different from that of beef breeds, whereas it was superior for dairy HO breed than beef breeds and than the local breed (P<0.05).

The breed of bulls had a significant influence on individual motility of sperm. The highest individual motility was recorded in HO and PM bulls (76.7±0.71% and 75.6±1.55%, respectively), the lowest in BB bulls (67.2±1.80%), whereas CH and OZ bulls were intermediate (71.9±1.19% and 71.6±2.40%, respectively). The significant effect of breed is supported by Fields et al (1979) who found that sperm motility was significantly lower for Santa Gertrudis and Brahman bulls than for Angus and the Florida line Hereford bulls; breed averages were 83, 69, 69, 58 and 48% for the Florida Hereford, Montana Hereford, Angus, Santa Gertrudis and Brahman between 16 and 20 months of age, respectively. Likewise, Asad et al (2004) observed that the highest individual motility was obtained in Friesian bulls (62.3%) and the lowest in Sahiwal x F2 Friesian bulls (53.7%). However, the significant effect of breed on individual motility is not in agreement with that of Brito et al (2002b), who concluded that sperm motility was not significantly different between Bos Taurus and Bos indicus bulls (mean 59%). In addition, the comparison among dairy, beef and local breeds showed an advantage of the dairy HO breed for the individual motility.

Breed of bulls had a significant effect on post-thawing motility. Bulls of BB breed had the lowest post-thawing motility (47.6±1.80%) compared to those of HO, PM and OZ bulls, but not significantly different from that of CH bulls. Moreover, HO dairy bulls were superior to beef bulls (P<0.001), whereas the differences were not significant between local and beef breeds and between dairy and local breeds.

Although the ejaculate volume varied from 3.31±0.81 ml for OZ bulls to 5.76±0.45 ml for CH bulls, the breed of bulls did not have a significant effect on this trait (P>0.05). The present result is in agreement with those of Brito et al (2002a) and Beran et al (2011), who did not find a significant difference in ejaculate volume among Bos indicus, Bos taurus and crossbred bulls and between Holstein and Czech Fleckvieh bulls, respectively. However, it is not consistent to the findings of Fields et al (1979) (Hereford, Angus, Santa Gertrudis and Brahman bulls at average ages of 16 and 20 months), Haque et al (2001) (Friesian, Local x Friesian and Sahiwal x Friesian bulls), Brito et al (2002b) (Bos taurus and Bos indicus bulls), Asad et al (2004) (Friesian, Sahiwal and their crossbred bulls) and Atikuzzaman et al (2007) (Local, Sahiwal, Friesian and their crossbred bulls), who found a significant effect of genotype of bulls on volume of ejaculates. In addition, Fiaz et al (2009) observed an interaction between breed of bulls and season, showing that ejaculate volume was significantly lower during dry summer in Holstein-Friesian bulls, whereas, it was higher during wet summer in Jersey bulls compared to other seasons.

In general, although the age of bulls was fitted in the statistical model, some age effect may explain a part of differences among breeds for semen characteristics. Several studies reported an increase of sperm production and semen quality with age of bulls (Everett and Bean 1982; Taylor et al 1985; Mathevon et al 1998; Brito et al 2002b; Fuerst-Waltl et al 2006; Boujenane and Boussaq 2013). In the present study, the age of HO, CH, PM, BB and OZ bulls averaged 41, 55, 21, 44 and 22 months, respectively. Thus, the lower semen traits, especially the volume, the sperm concentration and the mobility of sperm of PM and OZ bulls may be due to their young age. However, the low semen production of BB bulls, despite their mature age, may be explained by their worse adaptation to environmental conditions under which they were managed.

To compare the breeds of bulls on the basis of number of AI straws produced monthly, the number of motile spermatozoa produced per month was calculated (ejaculate volume x sperm concentration x individual motility x number of collections per month allowed by a given interval between collections). It was assumed that when the interval between two successive collections was 2, 3, 4, 5 and 6 days, the numbers of collections allowed within 5 working days per week were 13, 9, 7, 5 and 5 collections during a month period, respectively. Thus, the analysis of number of motile spermatozoa produced per month, by adding the breed x interval between two collections x ejaculate order interaction to the mixed model used previously, showed that CH bulls collected once a day at 2 days interval produced per month 2%, 79%, 93% and 95% more motile spermatozoa than HO, PM, BB and OZ bulls, respectively (Table 4). When they were collected twice a day (sum of motile spermatozoa obtained at the 1^st and 2^nd collections) at 3 days interval, the CH bulls produced per month 15%, 21%, 116% and 54% more than HO, PM, BB and OZ bulls, respectively. Under conditions of this study and on the basis of number of AI doses produced per month, the ranking of breeds of bulls was CH, HO, PM, OZ then BB, whatever the interval between two successive collections. Also, the comparison among dairy, beef and local breeds did not show any significant difference with regard to the number of AI doses produced per month. However, it would be prudent to take with caution the ranking of breeds found in this study.

Conclusion

• These results indicated that except the volume of ejaculate, semen traits characteristics are influenced by the breed of bulls. It seems that the HO and CH bulls produced better semen and the BB bulls produced worse semen than the other breeds. Thus, in order to satisfy the high demand of farmers for BB semen, it might be necessary to increase the number of collections per day and to reduce the interval between two successive collections. However, because of the low number of bulls for some breeds, further studies are needed to establish breed differences.

Acknowledgments

The authors would like to thank the Director, the technical staff and workers of the CRIA of Fouarat for the help they provided.

References

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Received 20 April 2014; Accepted 2 May 2014; Published 1 June 2014

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