Abstract: The present research, was carried out to determine reproductive traits and effects of environmental factors on these traits in Holstein cows raised at polatli state farm located in Ankara province. A total of 2177 reproduction records between 1997 and 2006 were constituted the research material. Environmental factors were analyzed by least squares method. The least square means of gestation duration, first servicing period service period, NIPC and calving were 274.971±0.524, 111.55±3.73, 149.60±4.36, 1.72±0.05 and 427.88±4.36 days, respectively. On gestation duration, effects of breeding year, breeding age, birth type and sex of calf were significant (p<0.001). However, effect of breeding season on gestation duration was non-significant (p>0.05). Effects of breeding age on all reproductive traits (service period, first servicing period, Number of Insemination for Per Conception (NIPC) and calving interval) were significant (p<0.001). Effect of breeding season on service period and on calving interval was significant (p<0.05). However, effect of breeding season on first servicing period and on NIPC was non-significant (p>0.05). As effect of breeding year on all reproductive traits was significant first servicing period, management was the most important factor in this study.

INTRODUCTION

Holstein cows were considered the most dairy cows in world. Holstein-friesians become more prevalent day by day, as is generally the case in most of the countries of the world, due to their high milk and meat production and good adaptation to different climates under good management (Grothe, 1995; Kaya et al., 2003). As number of Holstein cows in Turkey is more than other breeds, breeding of Holstein cows is very important in Turkey. In breeding of dairy cows, the most important aims are to obtain a calf in a year and high milk yield from cows. To obtain a calf in a year from cows dependents on some parameters in ideal limits (60 day dry period, 305 day lactation duration etc.). For these aims, good management in herd of dairy cows is very important. Profitable breeding could be achieved by keeping lactation duration, dry period and service period between optimal limits (Alpan, 1994; Kumuk et al., 1999; Cilek and Tekin, 2005; Kocak et al., 2007). Getting cows pregnant is the major goal in any dairy farm’s reproductive program. There has been a lot of research done to determine the cost of number of days open after a cow’s voluntary waiting period following calving. The range varies from $3.00-6.00 per day open per cow (Tahmasbi et al., 2004).

The yields of farm animals are the result of the combined effects of genotype and environmental conditions. In order to increase the yield level, it is necessary to optimise the environmental conditions and to improve the genetic structure of the animals. Environmental factors can be classified as factors with measurable effects (age, year, season, milking frequency, etc.) and factors with un-measurable effects (infectious diseases, parasitic infestations, etc.). The amounts of effects of factors with measurable effects can be determined and they can be used in the planning of management in farm (Yalcin, 1975; Yaylak and Kumlu, 2005; Cilek and Tekin, 2007). In this study, reliable information regarding environmental factors effecting fertility traits of Holstein cows have been gathered.

Average gestation length of Holstein was reported between 278.5 and 280 days (Zambrano et al., 2006; Erdem et al., 2007; Kocak et al., 2007; Kopuzlu et al., 2008). It was reported that the longest gestation length in those who calves in spring and the shortest in those who calves in summer (Tilki et al., 2003; Cilek and Tekin, 2007). It was reported that the gestation duration for male births was longer than famela births (Pelister, 1999; Cilek and Tekin, 2005, 2007). Twin births were reported shorter than single births (Pelister, 1999; Cilek and Tekin, 2005, 2007).

First servicing period of Holstein cows was reported between 72.8 and 90.2 days in previous researches (Berry et al., 2003; Ajili et al., 2007; Melendez and Pinedo, 2007). Service period of Holstein cows was reported between 100.7 and 163.34 days (Olds et al., 1979; Kumlu and Akman, 1999; Kaya et al., 2003; Ajili et al., 2007; Erdem et al., 2007; Kocak et al., 2007; Melendez and Pinedo, 2007; Kopuzlu et al., 2008). Effect of calving season on service period and on calving interval was reported significant (Kocak et al., 2007; Kopuzlu et al., 2008). However, it was reported non-significant (Cilek and Tekin, 2005, 2007).

Calving interval was found between 393 and 402.4 days by Kumlu and Akman (1999), Erdem et al. (2007), Kocak et al. (2007), Melendez and Pinedo (2007) and Kopuzlu et al. (2008). It was reported that service period and calving interval decreased till 4 years of age and then increased after this age (Inal and Alphan, 1989; Ogan, 2000; Cilek and Tekin, 2007). It was reported that effects of calving age on calving interval was significant in previous researches. However, Cilek and Tekin (2005), Erdem et al. (2007) and Kocak et al. (2007) reported that effect of calving age on calving interval was non-significant.

Number of Insemination for Per Conception (NIPC) was reported between 1.4 and 1.8 (Berry et al., 2003; Zambrano et al., 2006; Erdem et al., 2007; Melendez and Pinedo, 2007). Effects calving age and year on NIPC were reported significant in pervious study (Erdem et al., 2007). Effect of calving season was reported non significant by Cilek and Tekin (2005) and Erdem et al. (2007).

This study was conducted to investigate the environmental factors affecting reproductive traits of Holstein cows reared at the polatli state farm between 1997 and 2006.

MATERIALS AND METHODS

At the polatli state farm located in Ankara province, a total of 2177 reproductive records of Holstein cows raised between 1997 and 2006 were used. Seven age groups were formed beginning from 2 years and ending at 8 years and older for calving age; 4 groups for calving season (Spring, Summer, Autumn and Winter) and 10 groups for calving year, between 1997 and 2006.

All gestations ending with a live birth were used in calculation of gestation length. Environmental factors, which were effective on first servicing period, service period, NIPC, calving interval and gestation length were investigated. General Linear Model (GLM) was used for variance analyses of fertility traits. Duncan’s multiple range test was used as multiple comparison test. For gestation length, the statistical model was:

For first servicing period, service period, NIPC and calving interval, the statistical model was:

RESULTS AND DISCUSSION

The least square means for gestation length were presented in Table 1. Average gestation length was found as 274.97 days. Effects of sex of calf, calving age, calving year, on gestation length were found statistically significant (p<0.001). However, effect of calving season was non significant (p>0.05).

The least square means for first servicing period, service period, calving interval and NIPC were presented in Table 2. Effects of calving year and calving age on these traits were found significant (p<0.001). Average first servicing period was estimated as 111.55 days. First servicing period was the shortest at 94.41 days in 2 age of year, the longest at 140.70 days in 8 and older age of years. First servicing period was the shortest at 97.18 days in 1999, the longest at 150.38 days in 2004.

Average service period was estimated as 149.60 days. Service period changed between 117.87 days in 1998 and 224.04 days in 2006. Service period was the shortest at 118.68 days in 2 age of year, the longest at 182 days in 7 age of years.

Average calving interval was found as 427.88 days. Calving interval changed between 396.99 days in 1999 and 501.54 days in 2006. Calving interval was the shortest at 396.76 days in 2 age of year, the longest at 436.70 days in 7 age of years.

Average of Number of Insemination for Per Conception (NIPC) in the herd was found as 1.7 NIPC was found the shortest in 2 age of years at 1.45, the highest in 8 age of years at 2.18.

In this study, means of gestation duration was 274.97 days. This value was nearly between limits of previous researches (Zambrano et al., 2006; Erdem et al., 2007; Kocak et al., 2007; Kopuzlu et al., 2008). That effect of breeding season was non-significant was not in agreement with literature (Tilki et al., 2003; Cilek and Tekin, 2007). The gestation duration for single and male births was longer than that for twins and female births, this result agreed with those of previous researches (Pelister, 1999; Cilek and Tekin, 2005, 2007). Effect of breeding year on gestation duration was significant. Gestation duration changed between 274.1 days in 2005 and 276 days in 2004. This may have influenced the nutrition quality of rations, which might have become deficient and irregular, leading to a later end of gestation as an mechanism for adjusting to adverse climatic and nutrition conditions.

In this study, average first servicing period was estimated as 111.55 days. This value was higher ideal value and literature values (Berry et al., 2003; Ajili et al., 2007; Melendez and Pinedo, 2007). In this farm, oestrus detection was not performed at the right way. In this farm, accurate oestrus detection in cows will decrease in first servicing period. The most important factors were breeding age and breeding year. First servicing period in the youngest cows was shorter than value in oldest cows. Differences of first servicing period among breeding years may be related to the management differences.

Table 1:	The least square means of gestation length (day)

Table 2:	The least square means of service period, calving interval, first servicing period (day) and NIPC
*:p<0.05; ***: p<0.001; ns: non-significant and a,b,c: Means without a common superscript within each variable and each factor differ (p<0.05)

Oestrus detection was carefully performed early time in this farm. Furthermore, accurate techniques may be used for oestrus detection.

The average calving interval was higher than ideal value (365 days) and literature (Kumlu and Akman, 1999; Erdem et al., 2007; Kocak et al., 2007; Melendez and Pinedo, 2007; Kopuzlu et al., 2008). Similarly, as service period, except for 6 years cattle, service period with age of cows increased.

Several methods are considered for oestrus detection such as, calendar method, observation method, vaginal examination, conductive meter, progestrone test of milk, measurement of vaginal pH, measurement of boby temperature, searching bull, ultrasonography (Coyan and Tekeli, 1996). These methods can be used in this farm for shorter service period. In cows with lactation, synthesis osterogene from interstitial cells stops, GnRH secretion is inhibited and increased cortisone level inhibites secretion of LH. This situation is postpartum anoestrus (Coyan and Tekeli, 1996).

Although, 305 days milk yields and parity are generally adversely associated with fertility, service period may be significantly reduced by the use of a GnRH injection. Injection of GnRH during artificial insemination under this dairy farm conditions should improve reproductive performance (Tahmasbi et al., 2004).

Service period of Holstein cows was reported 149.6 days. This value is higher than ideal value (60-90 days) and at top of limits in literature (Olds et al., 1979; Kumlu and Akman, 1999; Kaya et al., 2003; Ajili et al., 2007; Erdem et al., 2007; Kocak et al., 2007; Melendez and Pinedo, 2007; Kopuzlu et al., 2008). That effect of calving season on service period was significant was in agreement with previous researches (Kocak et al., 2007; Kopuzlu et al., 2008). As reported by Cilek and Tekin (2005), the fact that the service period and NIPC were shorter in cows calving in Winter may result from the effects of temperature and humidity and the availability of green fodder during the spring, which might favour the physiological functioning of different systems. Service period generally increased with breeding age in this study. This result was not in agreement with literature (Inal and Alphan, 1989; Ogan, 2000; Cilek and Tekin, 2007). Except for 6 years cattle, increasing of service period with age of cows may be associated with degenerative endometrial changes. Decrease in service period in 8 years and older, may result from keeping with good fertility in the herd. After 1999, increase value reported in milk yield by Cilek (2008) in this farm may be the reason for the extension of the service period. As reported by Kaya et al. (2003), higher yield is associated with reduced reproductive performance in lactating cows and one of the most common causes of low fertility in dairy cows is negative energy balance in early lactation.

Number of Insemination for Per Conception (NIPC) was found as 1.72. This value was top of limits in literature (Berry et al., 2003; Zamrano et al., 2006; Erdem et al, 2007; Melendez and Pinedo, 2007). That effects calving age and year on NIPC were found was in agreement in previous study (Erdem et al., 2007). Similarly, after 1999, the increase in milk yield (Cilek, 2008) could have caused an increase in NIPC, service period and calving interval. It may also, be relate to the endocrine system. Oestrus detection in cows with high milk yield was carefully performed. Furthermore, accurate techniques may be used for oestrus detection.

Dry period was higher than the ideal value (80 days). However, the dry period increased with calving age, a result of increase of milk yield level with age in the herd. It can be said that if milk yield increases with calving age, dry period will decrease. Effect of calving age on all milk yield traits was significant. Differences among years may be related to management. It can be said that differences of management among years was the most important factor affecting milk yield traits.

CONCLUSION

In this study, service period and calving interval and NIPC was higher than ideal levels. As factor of effect on all reproductive traits was breeding year, management is the most important factor in this farm. Management was done carefully. Oestrus detection and artificial insemination should be performed at the right time and in an appropriate way. In order to make animals more profitable, it is essential, they be made pregnant as soon as possible during the service period in order to shorten the dry period. It can be concluded that Holstein cattle are raised unsuccessfully for reproductive yield on polatli state farm and under Turkish conditions. Service period may be significantly reduced by the use of a GnRH injection. Injection of GnRH during artificial insemination under this dairy farm conditions may improve reproductive performance of cows with high milk yield.