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The effect of the light period on milk yield and fertility of dairy cows
 VRBOVÁ, Aneta
The main objective of the study was to ascertain fertility and milk productivity of dairy cows raised under the conditions of modern technology in the context of micro-climactic features and the quality of housing. The observation occurred from 1. 1. 2013 to 31. 12. 2014 in Cooperative Farm Pluhův Žďár and 150 dairy cows of the Holstein cattle were observed. The program Statistica 12 (StatSoft?) was used to evaluate observed values. Data characterisation was conducted through the use of descriptive statistics, and, furthermore, a correlation analysis and a chi-square test were used. During the evaluation of the micro-climate of the stables, it was detected that the average temperatures of the environment shifted from 7.90 °C to 27.03 °C. Relative humidity was measured in the range of 73.44 % and 86.84 %. THI achieved values from 45,11 to 68.93. The milk yield correlated negatively with the temperature during autumn months (r = - 0.377) and a negative correlation was also found in relation to the relative humidity (r = - 0.356) and a similar relation existed between the THI and the milk yield (r = - 0.409). The influence of the length of the photoperiod on milk productivity showed itself to be positive in the cases of all groups of observed dairy cows. The group of cows at the 1st lactation increased milk productivity by 4.7 % the cows at the 2nd lactation showed an increase of milk productivity by 12.6 % and the dairy cows at the 3rd and further lactations provided an increase of milk yield of 18 %. The influence of the length of the photoperiod on conception was not statistically conclusive (p = 0.100), but there was a tendency pointing to worse conception results when automatic lighting was used as opposed to when the natural photoperiod was used. With the temperature on the day of conception taken into consideration, the rate of conception ranged between 27 % and 51 % in the periods of 24 and 48 hours before insemination. There was a tendency of a better conception in the group of primiparous cows in the temperature range over 15.1 °C in comparison with the group of cows at the 2nd and further lactations. The influence of the temperature of the environment on conception after first insemination 24 and 48 hours before the insemination itself was statistically conclusive (p < 0.05). A positive influence of an extended photoperiod on rumination was found among all groups of observed dairy cows. The dairy cows at the 1st lactation increased their ruminative activity by 42 minutes and the group of older cows by 25 minutes in 24 hours. The greatest difference between these two groups was observed during the winter months (XII-II), during which time the dairy cows ruminated longer by 21.7 % on average in comparison with the natural photoperiod (p < 0.001).
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