Relationships between production and fertility traits in first lactation and life time performances of Holstein cows under subtropical condition

The objective of this study was to determine the relationships between milk yield and calving interval in first lactation and breeding efficiency, herd life and length of productive life of 1 293 Holstein cows maintained at Ceylanpinar State Farm in Southeast Anatolia from 1990 to 2002. The least-squares means of first lactation milk yield, lactation length and calving interval were 5 620.1 ± 76.6 kg, 315.5 ± 2.0 and 386.9 ± 2.6 days. The values for breeding efficiency, herd life and length of productive life were 94.9 %, 2 095.9 ± 34.7 and 1 257.2 ± 34.4 days. The year of first lactation had significant effect (P<0.05) on all traits except for calving interval and lactation length, and breeding efficiency was only affected by age at first insemination and age at first calving (P<0.05). Heritabilities were 0.27 ± 0.08 for milk yield, 0.02 ± 0.05 for lactation length, 0.06 ± 0.05 for calving interval, 0.05 ± 0.05 for breeding efficiency, 0.30 ± 0.08 for herd life and 0.29 ± 0.08 for length of productive life. Genetic and phenotypic correlations between different traits ranged from −0.49 to 0.99 and −0.37 to 0.99 respectively.


Introduction
High milk yield, regular fertility, and improved herd and length of productive lives are desired traits for dairy animals.Latter two ones have significant effect on economic advantage by reducing replacement and increasing the number of cows producing at mature levels in a herd (SZAJKO 1987, KALM 2002).These characters are influenced by several factors such as inheritance, year, season, parity, feeding, management and age at first calving.Lower age at first calving and the ability to produce longer years are charming for high yielding cows.VUKASINOVIC et al. (2001) reported that age at first calving did not have a significant influence on the length of productive life.However, some researchers (PIRLO et al. 2000, MARTINEZ et al. 1983) emphasized that the reduced age at first calving decrease the generation interval and feed costs, but may also reduce calf liveability at the same time because of dystocia.
The purpose of this investigation was to determine relationships of first lactation milk yield and calving interval with breeding efficiency, herd and length of productive lives of Holsteins in subtropical conditions.

Material and methods
Records of 1 293 Holstein cows maintained at Ceylanpınar State Farm from 1990 to 2002 were used in this study.The area has subtropical climate conditions and geographical coordinates are 36.84°N and 40.02 °E.The climate of area is characterized by hot summers.The meteorological data are given in Figure 1.
Milk yield, lactation length and calving interval in first lactation, and breeding efficiency, herd life and length of productive life were examined.
The breeding efficiency (BE) (WILCOX et al. 1957) was estimated as where is N the total number of parturitions and D the number of days from first to last parturition.
Herd life was defined as the number of days from date of birth to date of culling.Length of productive life was defined as the number of days from first calving to date of culling.(1) 15-17th month, (2) 18-19th month and (3) 20-25th month, and AFC were subdivided into three groups viz.(1) 24-26th month, (2) 27-28th month and (3) 29-34th month.Only 82 sires with greater than or equal to 5 cows were included in the analysis.Heritabilities (h 2 ), genetic (rG) and phenotypic (rP) correlations by paternal half-sib method were computed by LSMLMW program of Harvey's (HARVEY 1987).

Least-squares analysis of different traits
The least-squares means are presented in Table 1.Calving year had significant effect (P<0.05) on all traits except for lactation length and calving interval.The effect of season on milk yield, lactation length and breeding efficiency were significant (P<0.05).Age at first calving were significant (P<0.05) for only breeding efficiency.The over all means for milk yield, lactation length, calving interval, breeding efficiency, herd life and length of productive life were 5 620.1 ± 76.6 kg, 315.5 ± 2.0, 386.9 ± 2.6, 94.9 ± 0.5 %, 2 095.9 ± 34.7, and 1 257.2 ± 34.4 days, respectively.

Heritabilities, genetic and phenotypic correlations
Heritabilities, genetic and phenotypic correlations among investigated traits are shown in Table 2.

Discussion
Least-squares analysis of different traits Significant (P<0.05)effects of calving year and least-squares means showed that while the milk yields increased breeding efficiency, herd life and length of productive life decreased with the advancing years.The fact that the fertility and longevity may be depressed while trying to boost milk production by changing feeding and management conditions throughout the years may explain this phenomenon.First lactation milk yield and breeding efficiency were found to be higher in relatively cool season calvers.In addition to green fodder and first-cut silage, low ambient temperatures during these seasons may result in improved performance.Heifers that freshened at younger ages had better herd life and length of productive life.The average for first lactation milk yield was between the values of OJANGO andPOLLOT (2001) andJAIRATH et al. (1995) for Holsteins.The mean for breeding efficiency (94.87 %) was higher than the values reported by AGEEB and HAYES (2000), GOSHU (2005), andWILCOX et al. (1957) in dairy herds.Different breeds, feeding, management, climatic conditions and calculation methods might cause this.

Heritabilities, genetic and phenotypic correlations
The heritabilities were moderate for milk yield (0.27 ± 0.08), and low for lactation length (0.02 ± 0.05) and calving interval (0.06 ± 0.05).This is in agreement with the findings of various workers (HOEKSTRA et al. 1994, OJANGO and POLLOT 2001, HAILE-MARIAM et al. 2003a, DEMATAWEWA and BERGER 1998, CAMPOS et al. 1994, JAIRATH et al. 1995).Heritability for breeding efficiency (0.05) was lower than that of WILCOX et al. (1957).This could be due to the influence of some non-tangible environmental factors that may be specific to each animal besides the factors included in the least squares model.The moderate heritabilities were also estimated 0.30 and 0.29 for herd life and length of productive life.These findings were higher than the values announced by several researchers ( VAN DOORMAL et al. 1985, HARRIS et al. 1992, JAIRATH et al. 1995, VOLLEMA and GROEN 1996, SETTAR and WELLER 1999, ROXSTRÖM and STRANDBERG 2002, NILFOROOSHAN and EDRISS 2004, TSURUTA et al. 2005, MESZAROS et al. 2008) except WILCOX et al. (1957).Correlations of first lactation production and fertility traits with longevity were relatively lower than the findings of several researchers ( VAN DOORMAL et al. 1985, HARRIS et al. 1992, JAIRATH et al. 1995, VOLLEMA and GROEN 1996, SETTAR and WELLER 1999, ROXSTRÖM and STRANDBERG 2002, NILFOROOSHAN and EDRISS 2004, TSURUTA et al. 2005).This may be from the methods of estimation.
In conclusion, some environmental factors had significant effects (P<0.05)influence on life long performance in this study.This must be considered when breeding values are computed.First lactation milk yield, herd life and length of productive life were found to be more heritable.Therefore, these traits may be preferred by breeders as selection criteria.Although correlations of the first lactation production and reproduction with longevity traits were non-significant, larger investigations would be useful due to undesirable way correlations of calving interval with milk yield, breeding efficiency, herd life and length of productive life.
Figure 1 Temperatures and rainfall for Ceylanpınar State Farm Temperaturen und Regenmenge im Untersuchungsbetrieb

Table 1
Least squares means and standards errors for different traits Mittelwerte nach der Methode der kleinsten Quadrate und Standardfehler der untersuchten Merkmale