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Figure 1: The relationship between scrotal circumference and volume of semen in two breeds |
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| Livestock Research for Rural Development 24 (7) 2012 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The relationship between scrotal circumference and semen volume, sperm motility, sperm concentration and number of motile sperm per ejaculate of 30 Holstein Friesian and 22 Brahman breeding bulls was studied. Scrotal circumference and semen of two consecutive collections at seven day intervals was evaluated. After collecting, semen volume, sperm motility, sperm concentration and number of motile spermatozoa of fresh semen were immediately measured.
The result showed that scrotal circumference was highly correlated with semen volume and number of motile sperm per ejaculate in both breeds while the correlation between scrotal circumference and sperm motility, sperm concentration were found at medium and weak levels in this research.
Key words: correlation, scrotum size, semen production
Sires contribute 50% of the genetic of the offspring. A bull has a larger impact on herd productivity than a single female: a common saying is that the bull is half of the herd. When AI is applied, each bull can serve thousands of females per year. It, therefore, is extremely important to do the selection of breeding bulls in order to improve their offspring. Using bulls with good genetic potential for producing features will play an important role in improving productivity, quality and economic efficiency for the cattle industry.
Breeding bulls raised for making frozen semen were selected through many characteristic included scrotal circumference. That is one of the most important features represented for the reproduction of bulls.
It is said that crossbred bulls having bigger scrotum and earlier puberty could produce better semen (Siddiqui et al 2008), but there is little reliable information on scrotal circumference and quality of semen. The present study was conducted to evaluate the relationship between scrotal circumference and volume of semen, sperm motility, sperm concentration and number of sperms per ejaculate of Holstein Friesian and Brahman breeding bulls raising in Moncada Station of Vietnam.
The study was conducted in Moncada Station - Vietnam Ruminant Breeding Center, Tan Linh commune, Ba Vi districts, Ha noi, Vietnam, from December 2010 to September 2011.
A total of 30 Holstein Friesian (HF) breeding bulls and 22 Brahman breeding bulls, 24 to 36 months of age were selected in Moncada Station.
These breeding bulls were taken care and nurturing by the same mode for frozen semen making bulls. Ejection interval of these bulls was twice a week.
Breeding bulls were restrained in a squeeze chute and the scrotal content was held in the ventral scrotum from the cranial side of the scrotum. Scrotal circumference was measured in centimeters using measuring tape (Lane Manufacturing Co., Denver, CO, USA) as described by Foote (1969).
Semen was collected in graduated tubes at homosexual mount using artificial vagina (AV). Two ejaculates from each bull were collected at 7-day intervals for 9 months and 75 times of collection were recorded and analyzed. The collection tube was sent to the laboratory immediately for semen evaluation.
The volume, sperm concentration and initial motility of spermatozoa were recorded immediately after collection.
The volume of semen (V) was recorded by reading the graduation marks on the receptacle.
To evaluate sperm motility (A), 10 µl of semen was placed on a pre-warmed (37oC) slide, covered with a cover slip and examined under phase-contrast microscope (400×).
The concentration of spermatozoa (C) was determined by using Density Spectrophotometer (SDM-5, Minitüb, Germany). Semen was diluted in glassware with 0.9% sodium chloride solution at the ratio of 1:100. The reading was recorded from the Density Spectrophotometer in million/ml.
Total number of motile spermatozoa per ejaculate (VAC) was determined by multiplying the V, A and C values of that ejaculate.
Data were subjected to one-way analysis of variance (ANOVA) and pair wise comparisons of means were performed using the Turkey test in Minitab 14. The relationship between scrotal circumference and each semen parameter were determined by using correlation test (Microsoft Excel 2007).
Semen volume, sperm concentration and number of motile spermatozoa per ejaculate of Holstein Friesian bulls were significantly higher than those of Brahman bulls while there is no significant difference in sperm motility between two breeds (Table 1).
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Table 1: Semen parameters of Holstein Friesian and Brahman bulls |
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Semen trait |
HF |
Brahman |
SEM |
P |
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Volume (ml) |
6.78 |
6.23 |
0.045 |
0.000 |
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Motility (%) |
66.43 |
66.55 |
0.27 |
0.764 |
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Concentration (Billions/ml) |
1.20 |
1.15 |
0.007 |
0.000 |
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Total number of motile sperms per ejaculate (Billions/ejaculate) |
5.54 |
4.84 |
0.054 |
0.000 |
In Holstein Friesian and Brahman breeding bulls raised in Moncada Station, the scrotal circumference varied from 32 to 44 centimeters. The volume of semen varied from 4.63 to 8.01 ml . The sperm motility varied from 58.67 to 70.90 %. The sperm concentration fluctuated between 1.06 to 1.34 billions/ml. The total number of motile sperm per one ejaculate varied from 3.47 to 7.29 billions/ejaculate (Table 2).
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Table 2: Semen parameters of bulls with different scrotal circumference |
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Scrotal circumference (cm) |
Volume (ml) |
Motility (%) |
Concentration (billions/ml) |
Total number of motile sperms per ejaculate (billions) |
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32 |
4.63 |
58.67 |
1.20 |
3.47 |
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33 |
5.14 |
63.17 |
1.19 |
3.96 |
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34 |
5.72 |
64.52 |
1.21 |
4.54 |
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35 |
6.14 |
66.25 |
1.14 |
4.70 |
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36 |
6.54 |
64.78 |
1.14 |
5.09 |
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37 |
6.65 |
64.09 |
1.06 |
4.60 |
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38 |
6.63 |
66.65 |
1.17 |
5.21 |
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39 |
6.78 |
68.03 |
1.15 |
5.30 |
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40 |
7.35 |
69.43 |
1.14 |
5.88 |
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41 |
7.27 |
70.90 |
1.34 |
6.89 |
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42 |
7.40 |
70.13 |
1.26 |
6.50 |
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43 |
7.59 |
69.63 |
1.16 |
6.10 |
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44 |
8.01 |
70.73 |
1.29 |
7.29 |
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SEM |
0.092 |
0.600 |
0.016 |
0.11 |
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P |
0.000 |
0.000 |
0.000 |
0.000 |
In this study, most bulls can be regarded as normal based on their scrotal circumference and fresh semen quality. Bulls had varied scrotal circumference and significantly differed with respect to all four studied semen indicators. However, semen volume and number of motile sperm per ejaculate seemed to higher in bulls with bigger scrotal circumference while sperm motility and sperm concentration did not show clearly trend.
The differences in semen parameters among bulls may be due to variations in secretary activities of the sex glands, scrotal circumference, breed, age, body size and body weight (Graves 1978; Leon et al 1991; Sharma et al 1991). Moreover, collection frequency, pre-collection stimulation, feeding regime and weather can also influence the semen parameters (Graves 1978; Al-Hakim et al 1986).
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Figure 1: The relationship between scrotal circumference and volume of semen in two breeds |
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The scrotal circumference had positive correlations with semen volume and the determination coefficients were 0.92 and 0.91 in Holstein Friesian and Brahman breeds respectively (Figure.1)
The results of this study are consistent with the research of Latif et al (2009) in crossbred Sahiwal, who found a high correlation between the scrotal circumference and ejaculate volume (P <0.05, r = 0.72). Thus, the perimeters of the testicles have a great influence to the semen parameters of bulls. Those crossbred cattle aged between 18 to 18.5 months, the scrotal circumference must be larger than 30 cm are eligible for producing frozen semen (Siddiqui et al 2008). The circumference of the testicles is a trait which has average heritability and it is an important indicator of selecting breeding bulls at the age of sexual maturity (Bourdon and Brinks 1986, Smith et al 1989). Ball et al (1983) argued that the perimeter of the testicles in semen production in bulls of any breed should always reach over 31cm in 15-18 months, and 32 cm at over 18 months old. Testes size of the Holstein Friesian and Brahman bulls in our study were achieved from 33 and 32cm respectively. The young bulls with large scrotal circumference could have semen volume and total number of sperm greater than those with small scrotal circumference in the first ejaculate (Randel et al 1994; Sundararaman et al 2002). The bulls have small testes will produce sperm with lower quality and lower conception rates even nature mating (Randel et al 1994). These studies demonstrated that determining the scrotal circumference in selecting bulls to serve the artificial insemination is very important.
Besides affecting the ejaculate volume of bulls, scrotal circumference also had certain influence to the sperm motility. However, the effect on sperm motility was not as high as that on semen volume.
Scrotal circumference and sperm motility of Holstein Friesian and Brahman bulls in this research were positively correlated but correlation levels were both at medium degrees with R2 = 0.51 and 0.72 respectively. This is clearly illustrated in Figure 2.
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Figure 2: The relationship between scrotal circumference and sperm motility (A) in two breeds |
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When it came to sperm concentration, very low level of correlations were found in both Holstein Friesian and Brahman breeds with determination coefficients were 0.20 and 0.06 respectively (Figure 3).
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Figure 3: The relationship between scrotal circumference and sperm concentration (C) in two breeds |
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In contrast to the loosely correlation between scrotal circumference with sperm concentration, the indicator total number of motile sperm (VAC) correlated quite closely with the perimeter of the testicles. This correlation is shown in figure 4.
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Figure
4: The relationship between scrotal
circumference and total number of motile sperm |
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Research results showed that the correlation between circumference of the testicles and total number of motile sperm (VAC) were at medium level in Holstein Friesian (R2 = 0.78) and at high level in Brahman bulls (R2 = 0.94).
VAC indicator is an important index to evaluate the semen production ability of bulls. This index depends on many factors such as age, nutrition, crop and because VAC is a combination of three indicators: the volume of semen, the sperm motility and the sperm concentration, thus any factor that affects 1 in 3 indexes also affects the VAC.
In this study, Holstein Friesian and Brahman bulls with different scrotal circumference had ejaculated volume, sperm motility and sperm concentration varied. However, these differences are due to many other reasons that also affect the quantity and quality of individual bulls of different breeds. According to Graves (1978); Leon et al (1991) and Sharma et al (1991), the difference in semen parameters between bulls may be due to difference in level of activity of the gonads, the perimeter of the testicles, breed, age, size and body mass. In addition, ejaculated interval, pre-collected stimulation, nutrition and climatic conditions also affect semen indices (Graves 1978; Al-Hakim et al 1986).
Scrotal circumference influenced quite clearly to some indicators of semen quantity and quality of Holstein Friesian and Brahman breeding bulls adopted in Moncada Station. In particular, the correlation between scrotal circumference with ejaculate volume was found pretty close with the determination coefficients R2 = 0.92 and 0.91 in Holstein Friesian and Brahman breeds respectively; The correlations with total number of motile sperms per ejaculate (VAC) were at medium levels in Holstein Friesian bulls with the determination coefficient R2 = 0.79 and at quite high level in Brahman bulls with determination coefficient R2 = 0.94.
The relationships between scrotal circumference with sperm motility in Holstein Friesian and Brahman breeds were found at medium levels with determination coefficients were 0.51 and 0.72 respectively.
The correlation between scrotal circumference and sperm concentration were low in both breeds with determination coefficients of 0.20 and 0.06 in Holstein Friesian and Brahman respectively
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Received 11 May 2012; Accepted 2 June 2012; Published 1 July 2012
