The effect of non-genetic factors on reproduction traits of primiparous Polish Holstein-Friesian cows

The aim of this research was to estimate the influence of environmental factors, such as air temperature and milk production, on reproduction traits of primiparous Polish Holstein-Friesian cows. The following reproduction traits were considered: interval from calving to first insemination, interval from first to last insemination, interval from calving to conception, number of inseminations per conception, first insemination conception rate and first insemination non-return rate. The impact of several measures describing the level of milk production and climate on fertility was examined using linear models. The model for each trait contained fixed effects of herd-year, month-year, age at calving and a random additive genetic effect. Deterioration of fertility due to an increase in peak milk yield was observed, e.g. elongation of the interval from the first to last insemination by 6 days as peak milk yield increased by 10 kg. It was found that temperature strongly affected reproduction. However, the results concerning the direction of that influence were inconsistent. An increase in temperature during the month of insemination had a negative effect on the length of the interval from the first to last insemination: elongation by 13 days along with an increase in temperature by 10°C. The opposite influence of an increase in temperature during the month of calving on the length of the interval from calving to the first insemination and on the length of the interval from calving to conception was observed: reduction by 8 days along with an increase in temperature by 10°C in both traits. The relationship of fertility with temperature and milk yield suggests the need to include these factors in the model used for genetic analysis of reproduction traits.