Abstract: The research was performed to determine the effect of non-genetic factors on milkability characteristics and to estimate genetic parameters and relationships among Milk Flow Rate (MFR), Milking Time (MT) and milk yields of Holstein Friesian cows reared in Eastern Region of Turkey. The data used in this study consisted of 1267 observations of MT and MFR on 177 lactations of 91 Holstein Friesian cows. The least squares means for MFR, MT and Total Test Day Milk Yield (TTDMY) were 1.049 kg min^-1, 5.83 min and 12.31 kg, respectively. Parity, stage of lactation and calving season affected (p<0.01) on the MFR, MT and TTDMY. Multiparous cows had higher MT and TTDMY (p<0.01) than primiparous cows. Calving season affected (p<0.01) on MT, MFR and TTDMY. The heritability coefficients for MFR, MT and TTDMY were 0.21, 0.23 and 0.23, respectively. The positive genetic correlations of MFR with TTDMY, actual milk yield and 305 days milk yield were 0.62, 0.49 and 0.48, respectively, while genetic correlations between MT and TTDMY, actual milk yield and 305 days milk yield were 0.20, 0.28, 0.34, respectively. Phenotypic and genetic correlations between MFR and MT were -0.49 and -0.63, respectively.

INTRODUCTION

Milkability in dairy cattle is one of the traits which belongs to the group of functional, cost saving characteristics in addition to health, feed efficiency, fertility and calving ease (Gade et al., 2006). Common characteristics in the milkability trait are average Milk Flow Rate (MFR), Milking Time (MT) and maximum milk flow rate.

Milkability traits are important economic factors in dairy cattle practice. They are used for animal selection (Bruckmaier et al., 1995), animal breeding and monitoring of udder health (Duda, 1995; Naumann et al., 1998), evaluation and development of milking machines and in setting parameters for their use (Rasmussen, 1993). Milkability evaluation also helps to improve labour efficiency.

Many researchers have obtained moderate estimates of heritability for milkability characteristics (Sekerden and Kuran, 1991; Povinelli et al., 2003; Gade et al., 2006). The estimates of heritability for average MFR and MT varied from 0.17-0.49 and from 0.16-0.38, respectively. Regarding the results of the literature (Santus and Bagnato, 1998; Mijic et al., 2003; Cho et al., 2004; Juozaitiene and Japertiene, 2005), there were positive genetic and phenotypic correlations between milk yield and MFR and MT.

Average altitude of Erzurum Province located in Eastern Region of Turkey is about 1950 m. Cold season in this region is longer than rest of the country and it snows a lot. In recent years, number of Holstein Friesian cattle brought to this area considerably increased. However, there is no information about milkability characteristics of Holstein Friesian cows reared in such high altitude conditions. Therefore, the study was undertaken to investigate effects of non-genetic factors on the milkability traits and to estimate genetic parameters as well as relationships among milk yield, MFR and MT of Holstein Friesian.

MATERIALS AND METHODS

The study was carried out in Research Farm of College of Agriculture at Ataturk University, Erzurum, Turkey. Data used in this research consisted of 1267 observations of MFR and MT on 177 lactations of 91 Holstein Friesian cows. The cows were milked in the same milking parlour in order to collect data. On each sampling day, the milking and pulsation vacuum was adjusted to 50 kPa and pulsation ratio was 60:40 at a rate of 60 cycles min^-1. Each, stall of the milking parlour contained a milk-o-meter. Observations were made once a month during the lactation period and data were collected for 3 years. All observations on MT and MFR were determined by the same researchers at evening control milking. The observers stationed around the milking parlour and recorded MT of each cow by using chronometers. MT was determined as the interval from the attachment of the milking unit to the udder until it was completely removed. MFR was calculated as the ratio between milk yield and MT. Amounts of milk from morning and evening milking were also measured and recorded. Total Test Day Milk Yield (TTDMY) resulted from adding up the respective milk yields from all single milking per day. Three hundred and five days milk and actual milk yields were also calculated for each cow.

Statistical analysis was carried out by a least squares and maximum likelihood general program for mixed models (Harvey, 1987). A general linear model with fixed effects of parity, calving season, stage of lactation and their interactions with each other was used to identify the main sources of variation for studied traits in preliminary statistical analyses. Interactions were excluded from final statistical model, since they were not statistically significant.

The statistical model was following as:

Significant differences between the levels of the effects were tested by Duncan’s multiple range test for studied traits. Heritability estimates as well as genetic and phenotypic correlations were also calculated (Harvey, 1987).

RESULTS AND DISCUSSION

Least square means with standard error for MT, MFR and TTDMY are tabulated in Table 1. The average MT of Holstein Friesian cows reared in Eastern Turkey was 5.83 min (Table 1). The finding is in accordance with results of Petersen et al. (1986), Arave et al. (1987), Povinelli et al. (2003) and Gade et al. (2006). Shorter total MT values (1.54 and 3.30 min) were obtained respectively by Tripathi et al. (1991) and Bhivasankar et al. (2003). On the other hand, the average MT reported by Pandey et al. (1990), Tancin et al. (2005) and Lee and Choudhary (2006) were higher (6.63, 7.43 and 8.23 min, respectively) than results of the present study. Major factors which affect on MT reported by other researchers could be due to differences in the milk production levels, age of cows as well as pre-milking preparations.

The average MFR for Holstein Friesian cows was 1.049 kg min^-1. The result is in agreement with findings of Pandey et al. (1990) and Kuran and Sekerden (1992). On the other hand, the mean MFR observed in the present study was lower than results of Arave et al. (1987) (1.61 kg min^-1), Mijic et al. (2003) (1.61-3.60 kg min^-1), Gade et al. (2006) (2.21-2.75 kg min^-1) and Lee and Choudhary (2006) (2.30 kg min^-1) for Holstein Friesian cows. However, the average MFR of crossbred and Shavial cows were 0.467 kg min^-1 and 0.597 kg min^-1, respectively (Bhivasankar et al., 2003). Corresponding values were 0.81 and 0.57 kg min^-1 for crossbred and Desi cows in mid lactation (Tripathi et al., 1991). Singh et al. (1999) also noted that average MFR of crossbred cows in the range of 0.691-0.920 kg min^-1 and all these findings were lower than results of the present study.

Parity affected (p<0.01) all milkability traits (Table 1). Multiparous cows had higher MT and TTDMY than primiparous cows. Increased MT with parity corroborates previous studies (Petersen et al., 1986; Aydin et al., 2008). Naumann and Fahr (2000) observed that increasing parity was associated with decreasing average MFR and the result is in accordance with our finding.

Stage of lactation had significant effect on MT, MFR and TTDMY (Table 1). Peak milk yield was attained at the first month of the lactation and later, milk production declined gradually. Similar results were also reported by Sekerden and Erdem (1996) and Aydin et al. (2008). The values of MT corresponded TTDMY changes during the lactation. As a result of that fact, MT was the greatest at the beginning of the lactation and diminished as long as lactation advanced.

Table 1:	Least squares means with standard errors for milk flow rate, milking time and total test day milk yield
**p<0.01

Table 2:	Heritabilities on diagonal, genetic correlations below diagonal and phenotypic correlations above diagonal of milking and milk yield traits
*p<0.05; **p<0.01; MY-am: Milk Yield from Morning Milking; 2 MY-pm: Milk Yield from Evening Milking; 3 MFR: Milk Flow Rate; 4 MT: Milking Time; 5 TTDMY: Total Test Day Milk Yield; 6AMY: Actual Milk Yield; 7305 DMY: 305 Days Milk Yield; 8Standard Error of Heritability Estimates

The result is in agreement with findings of Povinelli et al. (2003) and Tancin et al. (2006). MFR decreased gradually with increasing stages of lactation. Similarly, Tancin et al. (2005) and Gade et al. (2006) reported that MFR of the dairy cows gradually reduced during the lactation.

The effect of calving season on all studied parameters were statistically significant (p<0.01) (Table 1). MT was the longest during winter and fall milking while the greatest MFR and TTDMY were measured from cows calved in spring. Significant influence of calving season on MFR was also observed by Jomeh and Pakdel (2000), Cho et al. (2004). Significant effect of the calving season on the TTDMY of cows was also supported by findings of Kurt et al. (2005) and Nagawade et al. (2008).

Heritability estimates for MFR and MT are presented in Table 2 and the values for MFR and MT were at moderate level with 0.21 and 0.23 respectively. Similar results were calculated by Sekerden and Kuran (1991) who estimated heritability coefficients for MFR, MT and TTDMY as 0.172, 0.204 and 0.221, respectively. However, the findings of the present study were lower than results of Gade et al. (2006).

Genetic and phenotypic correlations among milkability and milk yield traits are given in Table 2. Significant positive correlations of MFR with TDMY, actual and 305 day milk yield were obtained. The results are in agreement with findings of Sekerden and Erdem (1996), Mijic et al. (2003), Cho et al. (2004), Lee and Choudhary (2006). MT had also positive genetic and phenotypic correlations with TDMY, actual and 305 day milk yield, but they were not significant. The higher milk yield traits were associated with higher MFR. The results indicate that further selection for higher milk yield could cause in deterioration of udder health since higher MFR was associated with increased udder health problems (Lacky-Hulbert and Hillerton, 1995; Boettcher et al., 1998; Zwald et al., 2005). Therefore, Holstein cows with extremely low or high MFR should be tried to exclude from breeding due to the interrelation to labour efficiency and udder health and to avoid a worsening of the udder health and to attain more uniform milking duration among cows simultaneously.

CONCLUSION

The results of this study demonstrated that non-genetic factors such as parity, stage of lactation and calving season had significant (p<0.01) effect on the MFR, MT and TTDMY. Moderate heritability coefficients for MFR and MT and significant genetic and phenotypic correlations among MFR, MT and milk yield traits were also obtained.