Estimation of the breeding value and ranking of holstein-friesian bulls for milk production traits

The aim of this research was to estimate breeding value and rank of Holstein – Friesian bulls for milk production traits. The analysis included 433 daughters of 10 bulls, calving for the first time in the period from 2007 to 2014, on 6 dairy farms of the Agricultural Corporation Belgrade AD. Fixed factors included in the model were the effects of the farm, genetic groups and calving season, and as a random factor the impact of the bull sire. The observed milk traits on the basis of which the breeding values were calculated were the milk yield (kg), the 4% fat-corrected milk yield (kg), the fat content (%), the fat yield (kg), the protein content (%) and the protein yield (kg). Sires were ranked according to abovementioned milk traits and Spearman’s Rank correlation was used to determine association between the ranks of the sires. According to the breeding values calculated by using the Best Linear Unbiased Prediction (BLUP) method, the sire 1676 was best ranked for the traits: milk yield (+363,88 kg), fat yield (+13,57 kg) and protein yield (+15,55 kg), relative to the average of daughters. The effect of the calving season showed a high significance (p<0.01) for the following traits: milk yield, 4% fat-corrected milk yield, fat yield and protein yield while there was no significant effect for other traits (p>0.05). Statistically very significant correlations between sire estimated breeding values for fat content and the protein content of 0,84 (p <0,01) and between the fat yield and the protein yield of 0,96 (p<0,01) was determined by the Spearman coefficient of correlation.


Introduction
Western corn rootworm (D. virgifera virgifera LeConte) is the most destructive insect species in all regions under maize cultivation worldwide. It is believed that D. virgifera virgifera and the plant host have been evolved together in subtropical regions of Mexico and Central and Northern America (Meinke et al., 2009). The rapid distribution of WCR and the formation of the continuous population have resulted in intensive attacks, which affected the maize production throughout Europe. The WCR was probably introduced in the second half of the 1970s (Edwards et al., 1994;1998).
Since the moment of its appearance in Serbia (1992), this polyphagous pest has been populating the main production regions of maize cultivated in continuous cropping and its territorial expansion was faster than the spread of areas of harmfulness/destruction. In a short period of time, this pest has spread in as many as 13 European countries, including Austria, Bosnia and Herzegovina, Bulgaria, Czech Republic, France, Hungary, Italy, Romania, Slovak Republic, Switzerland and Ukraine.
This insect species has one generation per year and overwinters as eggs in soil (diapausing eggs). Larva hatching varies over years, but it is usually performed at the end of May and the beginning of June. Their presence is observable up to the beginning of August, and maximum of their emergence occurs at the end of July and the beginning of August (Komaromi and Kiss, 2004;Pierce and Gray, 2007;Bača et al., 2002;Borzykh et al., 2013;Voineac et al., 2015;Igrc-Balćić et al., 2004). Male adults occur a bit earlier than female adults, because the development of males is faster than the development of females, while the population peak of males (50%) occurs before a cumulative occurrence of females.
It is generally accepted that the presence of one or more adults per plant at the time of their maximum abundance, can result in economically significant damages by larvae during the following year in fields under maize continuous cultivation. In order to avoid further spread and development of the population, as well as a possibility of economic and ecological impacts, a timely forecast is necessary to regulate the level of the abundance of the insect population of both sexes. The forecast of the intensity of a WCR attack is based on the number of hatched larvae after sowing, the number of captured individuals on yellow and green sticky and pheromone traps. The effectiveness of different trap types is based on their attractiveness for adults, which is reflected in deviations of the population abundance and the sexual index as main parameters of dynamic changes. The differences in the population abundance over years were present on all locations. The maximum number of the population and oviposition did not overlap in all years. The comparison of the total number of adults overall years, locations and trap types showed that the pheromone Pal Csalomon trap, then green Multigard and yellow Pherocon AM sticky traps were the most efficient.
Environmental factors significantly affect the occurrence, development and reproductive ability of WCR. A precipitation sum must be taken into account when forecasting the WCR occurrence. The more frequent precipitation during overwintering of eggs the lower percentage of their destruction. The lack of moisture in the soil significantly reduces the number of WCRs and, consequently, damage to corn is lower .
The aim of this study was to monitor and manage the WCR population to prevent invasion of this economically damaging insect species. Monitoring requires comprehensive knowledge of biological traits of the pest, its life cycle and the economic threshold of harmfulness so that the response could welltimed and efficient plant protection could be implemented.

Material and Methods
The WCR flight dynamics was visually monitored by the application of pheromone Csalomon, yellow (Pherocon AM®) and green sticky traps (Multigard) in the period from the beginning of July to the end of September.
Visual inspection of plants was based on the determination of the density of insect abundance by counting and expressing the average number per plant. A hundred plants were examined (10 plants sampled in 10 randomly selected spots) during silking (June 25 th -July 2 nd , depending on the location and the year) for 2-3 days. The presence of adults was established on leaves, stalks and ears of maize in early morning hours (7 30 -8 30 ), when the activity of adults is greatest since high temperatures do not suit them. The total number of insects was determined in 100 plants in Zemun Polje and Crepaja during the three-year period (2005)(2006)(2007) in the field crops on corn hybrid ZP 434.
The presence of WCR adults was monitored by yellow (Pherocon AM®) and green (Multigard) rectangle traps (28 x 22.5 cm), with a sticky surface facing outward when it was wrapped around the maize plant at the ear height. These traps were made of waterproofed cardboard, and applied glue was of exceptional thermal and hydrostatic properties. Traps were set up in early July, and replaced every two weeks, while the trap inspection was done every third day.
At the same time, Pheromone panel Csalomon traps were randomly set at the ear height. These traps had a sexual pheromone as an attractant, stored within the small capsule hanged in the middle of the trap. Individuals attracted by pheromone were glued to a colourless external sticky surface (36 x 23 cm) of the trap. Capsules and sticky panels were replaced every 28 and 15 days, respectively. The number of captured females and males was regularly recorded.
A total of 45 traps, 15 of each type, were placed during the monitoring season of flight dynamics of WCR adults. In Zemun Polje, traps were inspected 11 times during the fiveyear investigation (from July 10 to August 18). On the other hand, the three-year investigation (2005)(2006)(2007) was carried out in Crepaja and inspections were performed on the following dates: July 10, 13, 17, 20 and 27 and August 3.

Results and Discussion
In the investigated period (2005)(2006)(2007), on two locations, variations in the abundance and density of the adult population of D. virgifera virgifera were established by the application of the absolute sampling method. During the stated period, in July, in the period of maize silking, adult insects were detected in analysed locations. Similar results have been recorded in other European countries. WCR adults have been present in the maize growing regions of Poland, Bulgaria, Ukraine and Croatia form the second half of July to the end of September and the beginning of October (Bereš andSionek, 2010, 2012;Toshova et. al., 2017;Borzykh et al., 2013;Voineac et al., 2015;Igrc -Balćić et al., 2004).
The differences between locations were determined by monitoring the WCR distribution by the application of the visual methods. Out of total 1.007 registered adults, 591 (58.68 %) and 416 (41.31%) were detected on the locations of Crepaja and the experimental field of the Maize Research Institute, Zemun Polje, re-spectively. Based on 100 examined plants, the average number of adults ranged from 1 to 9. On the location Crepaja, the number of adult insects per plant was 10-12 individuals, or 7-9 insects, on average.
The WCR flight dynamics was monitored using the pheromone, yellow Pherocon AM and green Multigard sticky traps in the period from July 7 th to August 18 th . In Zemun Polje, the maximum abundance of adults was recorded on yellow and pheromone traps in 2005. The drastic drop in the number of adults was noted in 2006, while only pheromone traps were efficient enough to register WCR individuals in 2007. In the succeeding period (2008)(2009), the reduction in the abundance of this harmful species was recorded in all three trap types.
Monitoring the abundance of WCR adults in the three-year continuous maize cropping, started by setting traps in Crepaja on July 5, 2005. The high population level of adults in this location was recorded in all three years, particularly in 2005. In the 2005-2007 period, the total of 8,550, 12,101 and 24,028 adults were registered on yellow, green sticky traps and pheromone trap, respectively ( Figure 1).
The beginning of the WCR flight was registered in Zemun Polje on July 17th 2005 (Table  1). Out of the total number of registered individuals, there were 240 males and 42 females on pheromone traps, 363 males and 35 females on yellow traps, while only 12 males were captured on the green traps ( Figure 2).  The abundance and dynamics of the WCR population were completely altered in Zemun Polje during 2006 when a low number of adults was recorded in all trap types: only 19 males and two females on yellow traps and two males with no females on pheromone and green traps ( Figure 2).
Favourable climatic conditions during 2007, the beginning of the summer on July 10 th , as well as the presence of adults until the end of the growing season, affected the flight duration. Comparing to the previous year, in Zemun Polje, a significant increase in the number of males and females were observed on pheromone traps.
The tendency of the decline in the number of adults was observed during 2008 and 2009. Extremely high temperatures during the growing season and low air humidity, alongside with the shortage of high-quality food, resulted in either sporadic catches in August or an absolute absence of flights. The confirmation of our results of an extremely strong impact of climatic conditions on stoppage of the distribution and the reduction in the adult abundance has been provided by the results obtained in other countries infested by this pest. The dry period with a shortened maize growing season can directly affect the population's dynamics (Mahmoud et al., 2017;. According to the Serbian authors (Sivčev and Galo, 2002;Sivčev, 2004;Sivčev and Tomašev, 1999), an exceptionally dry spell can cause the great mortality of adults. Unfavourable climatic conditions identically affected the distribution and the abundance of WCR in Croatia (Igrc- Barčić and Bažok, 2004). Long-term studies of this phenomenon, distribution and abundance of this pest confirm dominant effects of climatic changes on the reduction of levels of WCR populations (Karić et al., 2010;Grozeet al., 2011;Kereši et al., 2005;Cean, 2005;Borzykh et al., 2013). The oscillation in the number of adults of both sexes was recorded in 2008 and 2009 when their number was enormously low (Figure 2). In the five-year studies in Zemun Polje, trap readings were done in the period from July 10 to August 18. Out of the total number of registered adults (978), there were 467 or 47.8% on phero-mone traps, 444 or 45.4% on yellow sticky traps and just 67 or 6.8% on green Multigard sticky traps (Tables 1 and 3). The maximum number of insects captured on pheromone traps was recorded on July 23 rd . Out of the total number of registered adults (467) on this trap type, 4.13 adults per trap were recorded on average, which was a maximum value for the stated period. As far as 2006 is concerned, the flight of adult insects almost completely failed, except on August 3 rd , where there were 0.13 adults per trap. The average number of adults per plant amounted to 0.739 in 2007.
The total number of captured WCR adults on the Pherocon AM yellow sticky traps varied over years and the maximum abundance was on July 27. The highest number of 4.20 adults per trap on average was observed on the same date in 2005 (Table 1). The drop in the number of adults in 2008 and 2009 resulted in a very low presence of the population (111 adults or 11.3%) in relation to the total number of adults registered in the five-year period on all trap types. It is important to emphasise that the efficiency of yellow traps was low in the years with the lowest number of WCR population (Table 3).
The analysis of variance for the total number of adults in 2008 and 2009 pointed out to highly significant values for years, trap types and their interactions (Table 4).
Results obtained on the monitoring of WCR flight dynamics in Crepaja are presented in Figure 3. Data obtained on the total number of registered individuals of both sexes on all three trap types in Crepaja in the [2005][2006][2007] period indicate the high abundance and migration of WCR adults during July and August. During the 25-day trap reading in the stated period, a total of 4,679 adults were registered out of which 24,028 or 53.8% were detected on pheromone traps, 8,550 or 19.1 % on yellow traps and 12,101 or 27.1 % on green sticky traps. The maximum abundance, 9,746 captured adults of both sexes, was registered on the Pheromone Pal trap in 2005, with the average number of 16.7 adults per day. The maximum, daily recorded number of adults per trap in Crepaja was detected on both yellow (4.8) and green (8.1) sticky traps, which was above the critical number limit of 6 to 7 adults per trap for the climatic conditions of the USA (Tollefson, 2007). Karić et al. (2010)  In the succeeding years, the highest abundance of captured adults of both sexes was recorded on pheromone traps, but the numbers were lower than in the previous year. The first reading was performed on July 10 th in all three years and the following numbers were recorded: 5,346 (22.2%), 2,235 (26.1%) and 1,967 (16.3%) on pheromone, yellow and green traps, respectively. Based on the obtained number it is observable that the highest number of captured adults was detected on pheromone and yellow traps. The total number of captured adults in this period varied over reading dates from 2,324 to 5,346 on pheromone traps, from 732 to 2,235 on yellow traps and from 1,340 to 2,558 on green traps. In the three-year period of investigation, the abundance of adults on pheromone traps was higher by 2.81 and 1.98 than on yellow and green traps, respectively ( Table 5).

monitored
The analysis of variance of the sum of captured adults showed significance for the following factors: Trap (T), and year (Y), and their interaction (Y×T), at almost all reading dates. Significant impact on the total number of adults was established for both factors and their interaction (Table 6).