Random regression models (RRM) have recently been used not only in the analysis of milk traits such as milk, fat and protein yield, but also somatic cell score (SCS), lactose yield and milk urea nitrogen (MUN), and very seldom they have been applied to analyze milk dry matter (DM) yield. RRM have many advantages over lactation models: 1) they account more accurately for environmental factors affecting the performance of cows in each day in milk (DIM) throughout the lactation, 2) they allow ABSTRACT: The objective of this research was to examine heritabilities and genetic, phenotypic and permanent environmental relationships between milk dry matter (DM) and milk traits such as milk, fat, protein and lactose yields, milk urea nitrogen (MUN) and somatic cell score (SCS) in extended (to 395 days) lactations of Holstein cows from a big farm in Poland. The data set consisted of 78 059 test day records from the first, second and third lactations of 3 792 cows, daughters of 210 sires and 1 677 dams. Single-or two-trait random regression models were used with fixed effects of calving year, calving month, dry period and calving interval and random additive genetic and permanent environmental effects. The last two fixed effects were not included in the analysis of first lactation data. The highest values of heritabilities for all traits, except DM, were observed in the second lactation. First lactation heritabilities for all traits -except milk yield and SCS -were smaller than those in the third lactation. Lactose yield was highly heritable, with average h 2 equal to 0.25, 0.29 and 0.28 in lactations 1, 2 and 3, respectively. Heritability for DM was slightly lower than that for lactose (0.22, 0.26 and 0.28 for lactations 1, 2 and 3, respectively). In all lactations heritabilities for SCS were below 0.1. Genetic correlations between DM and milk yield (0.64-0.74) were lower than those between MUN and milk yield (0.67-0.79) as well as between lactose and milk yield (0.72-0.82). In general, DM was much more closely correlated with fat or protein yield (0.55-0.79) than with MUN or lactose (0.38-0.76). Only in the third lactation the correlation between DM and protein (0.72) was lower than between lactose and protein (0.76). For all lactations there were very high genetic correlations between DM and lactose (0.96-0.98) and high correlations between ) and between lactose and MUN (0.70-0.85). The results suggest that further research is needed, focused on DM and its relationship with other traits in larger populations.

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The objective of this study was to detect the relationship between weather information, obtained from nearest public weather station, and milk productions of Holstein cows breeding in Sanliurfa province of Turkey. Data used in this study comprised 711,968 first-five parity individual daily milk and live weight records of 939 Holstein cows. Results from this study indicated that using combination of minimum ambient temperature and relative humidity values one day earlier from daily milk yield in temperature – humidity index (THI) formula can be good alternative for determining heat stress in Holstein dairy cows under climatological conditions in Sanliurfa province of Turkey. As a result, this study confirmed that for quantifying heat stress in dairy cows valuable information can obtained from public weather stations.

The aim of this study is to investigate the possibilities of using the meteorological data obtained from the public meteorology station in determining the effect of air temperature and relative humidity on milk yield in Black and White dairy cattle raised in Diyarbakır province of Turkey. Records on daily milk yield obtained from a commercial farm in Diyarbakır province were used in the study. Meteorological records containing daily maximum and minimum temperature and daily maximum and minimum humidity data were obtained from nearest public weather station in Diyarbakır province. Data set related to milk yields includes 46 438 daily records during five different lactations of 185 healthy Black and White dairy cattle and information of some environmental factors of the animals. In the study, five different temperature-humidity index (THI) types consisting of different combinations of daily maximum, minimum and average temperature and humidity values were considered to evaluate the effect of heat stress on milk production. This study confirmed that weather stations located away from the farms contain useful information for research on heat stress in dairy cows. Using the combination of maximum daily air temperature and minimum daily humidity in THI formula performed better than other THI types in quantifying the heat stress in this study. This combination was less affected by other environmental factors and the results obtained from this combination seems to be more biologically meaningful. According to this, dairy cattle were exposed to heat stress for 160 days between May and October in a year. In this period, the losses of milk production were 1518.85 and 0.73 kg for per cow per year and per unit THI increase, respectively.