Modeling for determining the superiority of Holstein bulls as frozen semen producer and genetic source for milk production

The objective of this study was to develop models for determination the superiority of Holstein bulls as a producer of frozen semen and inheritance of the genetic traits of milk production. The ability of the bull to produce frozen semen per years was analyzed descriptively. Reproductive efficiency of frozen semen in artificial insemination was calculated by service per conception (S/C). Estimation sire breeding value for milk production was calculated by contemporary comparison (CC) method. Model of superiority bulls was analyzed by Structural Equation Model with Partial Least Square method (SEMPLS). Total average production of frozen semen was 23,109±14,970 doses/year. The average S/C was 2.83. The CC value ranged from -1,865.7 until +1,636.3. Potency of milk production resulted from lactation cow offspring per bulls ranged from 951,749.2 to 52,347,822.9 liters per year. The economic value of bulls based on the potency milk production of offspring ranges from IDR 4,758,745,999 to IDR 261,739,114,505. The superiority of bulls was affected significantly (P<0.05) by frozen semen production, reproductive efficiency and average milk production of daughter cows (DC) as much as 0.59, -0.53 and 0.33, respectively. In conclusion, the superiority of bull can be explained about 78.3% by the production of frozen semen production, reproductive efficiency and milk production of offspring.


INTRODUCTION
The superiority of Holstein bulls in terms of economic traits are the ability of bull to produce frozen semen, reproductive efficiency and genetic traits of milk production measured simultaneously.This statement was in accordance with Fuerst-Waltl et al. (2016) who stated that economical traits should be considered in the breeding objective, included production and functional traits in order to get qualified bull.
Study on the superiority of bulls have been conducted separately based on economic traits like bull breeding soundness evaluation (BBSE) and semen quality (Purwantara et al., 2010;Chenoweth and McPherson, 2016;Penitente-Filho et al., 2018); reproductive efficiency (Pecsok et al., 1994;Plaizier et al., 1996;Fernando et al., 2016); breeding value (Wilder and Van Vleck, 1988;Groen and Steine, 1997;El-Bayoumi et al., 2015).Chenoweth and McPherson (2016) stated that bull breeding soundness evaluation (BBSE) is able to describe the superiority of bulls based on their ability to produce frozen semen by 65-85%.Quality semen is one of four factors (25%) affecting successful service of insemination such as skill of inseminator, timing of insemination and status reproduction cows (Fernando et al., 2016).Heritability of milk production was medium, being 0.34±0.02(scale 0-1), so that it has little effect on the measurement of bull superiority (El-Bayoumi et al., 2015).The problem is if the evaluation of superiority bull was limited on one trait separately, then it would unable to describe and measure interactions among traits and would have an impact in the mistaken decision in the bull selection.To obtain more accurate overview, it was important to evaluate the economic traits affecting the bull superiority thoroughly and simultaneously by using more comprehensive model.The objective of this study was to develop model for determination the superiority of Holstein's bull as a producer of frozen semen and inheritance of the genetic traits of milk production.

The Ability of the Holstein Bull to Produce Frozen Semen
The study was conducted at Lembang and Singosari Artificial Insemination Center (AIC), Indonesia.Data used in this study were 24,634 data of frozen semen production from 67 Holsteins bulls (2-9 years old) as producer of frozen semen during the production period from 2008 to 2016.Data were analyzed descriptively.

Determination of Reproductive Efficiency of Frozen Semen of Holstein Bull in AI Activities
Reproductive efficiency of frozen semen in artificial insemination (AI) was used service per conception (S/C) value calculated from reproduction record of AI acceptor at the dairy farmer located in Java Island that used frozen semen produced by Lembang and Singosari AIC.The Java Island was selected as the location of the study based on a report of Anggraeni (2012) which stated that the Java Island has 97.2% of the Holstein population s in Indonesia.The S/C was calculated by formula of Atabany et al. (2011).

Determination of Genetic Superiority
The observed data were milk production record of daughter cows (DC) of Lembang and Singosari bulls and milk production records of contemporary cows at the same location and age at period 2011-2017.The full milk production per lactation was estimated using test-day method, standardized to 305 days milk production, milking twice daily and mature age based on DHIA-USDA correction factors (Hardjosubroto, 1994).Estimation of sire breeding value for milk production was calculated by Contemporary Comparison (CC) method described by Kurnianto (2012)  The potency of milk production per bulls was calculated based on the potency of the number of the lactation DC multiplied by average of milk production from DC of bull's offspring tested.The economic value of bull was calculated based on milk price assumption of IDR 5,000/liter.

Statistical Methods
Effect of age and bulls in frozen semen production were analyzed by nested design.Statistical model was: i = 1,2,3,..,a j = 1,2,3,..b k = 1,2,3,..cWhere Y ijkl : The k th observation, the j th age factor and the i th bull factor µ : Overall mean A i : Effect of i th bull B j(i) : Effect of j th age factor of i th bull The model of superiority bulls was analyzed by SEM-PLS 3.0.According to Sholihin and Ratmono (2013), partial least square (PLS) was a variance-based structural equation analysis (SEM) that can simultaneously perform testing of measurement models as well as structural model testing.SEM-PLS can estimate p values for path coefficients and can provide an indicator criteria of fit model in the form of average R-squared (ARS), average path coefficient (APC) and average variance inflation factor (AVIF).The statistical model is:

Ability of the Holstein Bull to Produce Frozen Semen
The average total production of frozen semen per bull per years is presented in Table 1.The total production of frozen semen per bull ranged from 1,270±1,124 until 70,577±2,492 doses/year.Total average production of frozen semen was 23,109±14,970 doses/year.The production of frozen semen per year was varying greatly due to the bull's condition, the frequency of semen collection, the quality of fresh semen and the frozen semen processing.The average production of frozen semen per year is lower than that reported by Tiwari et al. (2012) amounting to 39,536 doses/year on Sahiwal bulls but higher than the report of Bhosrekar et al. (1980) 10,458 doses/year of Holstein bulls in Sri Lanka.This low amount of frozen semen production was caused by poor health conditions of bulls, which affected the frequency of collection and quality of semen produced.The high variation coefficient showed that the average production of frozen semen per year was influenced by the age of bull (P<0.01).It is in accordance with Fuerst-Waltl et al. (2016) which stated that the age had a significant influence on semen traits of semen Simmental bulls in Austria.

Determination of reproductive efficiency of frozen semen of Holstein bulls in AI activities
Qualified frozen semen improves the reproductive efficiency of AI activities.The reproductive efficiency data per bulls is presented in Table 2 low enough from all acceptors who received AI services.The average S/C value was 2.83.The average S/C value (2.83) showed there was still inefficiency reproduction performance in Indonesia.Nuryadi and Wahjuningsih (2011) reported the normal S/C value was ranged at 1.6-  (Ghasemi and Ghorbani, 2014).Potential number of lactation cow per sire is presented in Table 3.The average number of lactation cows that resulted from 52 sires was 2,863 daughter cows (DC) per bull, it ranged from 296 to 12,228 daughter cows.A smaller value of S/C and greater ability bulls to produce frozen semen affected higher potential numbers of lactation cow per bull's produced with the assumption of the other technical coefficients were constant.This is in accordance with Ferguson and Skidmore (2013) who stated that reproductive efficiency was an outcome of S/C values tthat can be combined with a variable determining pregnancy rate.Decreasing the number of insemination has a positive effect on the profitability and one of the most economically important traits in dairy cattle industry (Ghiasi and Honarvar, 2016;Ghiasi et al., 2016).Improvements in reproductive performance can potentially yield remarkable economic benefits (Fodor et al., 2018).Further, Villa-Arcila et al.
(2018) stated that reproductive performance has also an impact on the economic results of the dairy business, as low reproductive efficiency may cause a decrease in milk production and the number of calves born per year.

Determination of Genetic Superiority
The average milk production and CC estimation is presented in Table 4.The numbers of milk production records that suffice the requirements for use were 1,006 records of DC milk production from 36 bulls tested and 1,019 milk production records of cows as comparative.The average population of milk production was 4,068 liters per lactation or 13.34 liters/day.The average milk production of DC from sires tested was 4,258.7 liters/lactation or 13.96 liters/day with a ranged from 2,320.1 to 7,128.6 liters/lactation.The CC value ranged from -1,865.7 to +1,636.3;these showed that the lowest average milk production per lactation was 1,865.7 liters below the average milk production of Model of Holstein Bull Superiority for Milk Yield (A.Argiris et al.) 51 population tested while the highest production was 1,636.3liters above the population.The number of bulls with a positive CC score was 20 bulls or 56% of the total bulls tested and recommended as the bulls donors for the genetic traits of milk production.The difference in CC value was influenced by the average production and the number of DC per sire.The different amount of DC was caused by poor awareness of farmers to record milk production, so it was difficult to obtain a lot of milk production data.Milk production can be increased through genetic and environmental factors.Efforts to increased milk production could be achieved by selecting bulls whose have positive CC values.
Identification sire with high genetic potential is a challenge for animal breeding (Rotar et al., 2016).Genetic improvement is one of the main factors responsible for the large increase in milk yield of dairy cow; this success is mainly attributable to the efficient application of AI with semen from proven sire was selected by progeny test (Yang et al., 2018).The potency of milk production and economic value per bull is presented in Table 5.The potency of milk production resulted from lactation cow offspring per bulls ranged from 951,749.2 to 52,347,822.9 liter/years.The economic value of bulls based on the potency milk production of offspring ranges from IDR 4,758,745,999 to IDR 261,739,114,505.The greater potential for milk production and economic value of the bulls tested will be obtained if the ability of bulls to produce frozen semen was high, the S/C value was low and the milk production of DC was high.The result discussion confirmed the statement of DeJarnette et al. (2004) who stated that the AI industry must supply the genetic resources for the dairy industry's with specific breeding objectives; including the emphasis placed on production, type and reproduction in AI sire programs which largely directed to dairy producers through their semen purchasing options.

Model of superiority bulls
The model obtained was declared fit based on the value of average path coefficient (APC), average R-squared (ARS) and average variance inflation factor (AVIF) were 0.481, 0.783, 1.225, which fit the requirements according to Sholihin and Ratmono (2013), being less than 0.05 (P<0.001),0.05 (P<0.001), 5, respectively.The ARS value showed the variance of the superiority  1.The superiority of bulls was affected significantly (P<0.05) by coefficient of frozen semen production, reproductive efficiency and average milk production of DC which found 0.59, -0.53 and 0.33, respectively.The model equation obtained was Y = 0.59X i -0.53X 2 + 0.33X 3 + ε.These path coefficients values showed the ability of bulls to produce frozen semen (0.59) and the reproductive efficiency (-0.53) have more considerable value than the genetic potential of milk production (0.33).Therefore, the ability of Holstein bulls to produce qualified frozen semen maximally in an effort to increase reproductive efficiency in AI activities must take the high priority on selection bull in the AIC.This result confirmed the statement of Naha et al. (2016) that the primary goal of the AIC is to produce the   *) it was assumed that the price of milk/Lt : IDR 5,000 largest quantity of the highest quality semen in a shortest possible time.The path value of genetic potential of milk production (representing heritability value) in this study was found 0.33; it confirmed the statement of Hardjosubroto (1994) that heritability value has a moderate criterion while environmental factors and management have a dominant influence in the milk production process of dairy cattle.Despite milk production has a moderate heritability value; the genetic trait of milk production in Holstein bull has an important role in efforts to improve the genetic quality of their offsprings.Breeders will choose the frozen semen of bull with a higher estimation breeding value (EBV) than a lower one.Kumari and Coudhary (2018) stated that detailed knowledge about raising the bulls was important for better management to support the needs of the AI industry.

CONCLUSION
Frozen semen production, reproductive efficiency and milk production of daughter cows determined the superiority of bulls.The equation of the superiority of bull = 0.59 (semen production) -0.55 (reproductive efficiency) + 0.33 (milk production) + error.The superiority of bull could be explained about 78.3% by the production of frozen semen production, reproductive efficiency and milk production of offspring.
which fit to smallholder farmer with ownership of less than 5 cows.The formula of CC was

Figure 1 .
Figure 1.Structural Equation Model of Superiority Bulls

Table 2 .
Reproductive Efficiency per Bull

Table 1 .
The Average Production of Frozen Semen per Bull per Years

Table 4 .
Average Milk Production and Contemporary Comparison of Holstein Bull

Table 5 .
The Potency of Milk Production and Economic Value per Bull