Radica Djedovic

Involuntary reduction in vigour of calves born from sexed semen

The objective of this study was to compare the reproductive traits of heifers and the development characteristics of their calves following artificial insemination (AI) with sexed and non-sexed semen. The analysed characteristics included conception rate, gestation length, calf birth weight, calf vigour, stillbirth rate, and twinning rate. Data of 530 calves produced with sexed and 1,163 calves produced with non-sexed semen were analysed. The General Linear Model (GLM) was applied to assess the influence of semen type, farm, season of insemination, the calfs sex and the inseminating sire on gestation length and calf birth weight. With the exception of gestation length (P > 0.05), all other traits studied were significantly (P < 0.01) influenced by the type of semen. The conception rate was 55% for conventional and 44% for sexed semen, and the average gestation length was 274.6 and 274.9 days, respectively. The mean calf birth weight was 37.47 kg for non-sexed and 36.75 kg for sexed semen. The stillbirth rate was 6.19% for conventional and 7.54% for sexed semen, while the twinning rate was 3.78% for conventional and 1.13% for sexed semen. The calves produced with non-sexed and sexed semen differed significantly in viability (P < 0.001), the latter having a lower calf vigour score. The use of conventional semen did not affect the ratio of female and male calves (52.7:47.3%; P > 0.05); however, artificial insemination with X-sorted sexed semen significantly altered the sex ratio of calves (85.1:14.9%, P < 0.01). The results obtained in this investigation are in agreement with the majority of studies which compared the fertility traits, sex ratio and calf characteristics depending on the application of artificial insemination with sexed or conventional semen.

THE EFFECT OF THE LEVEL OF MILK YIELD ON THE REPRODUCTION TRAITS IN BLACK AND WHITE COWS

In this study a relationship between the milk yield and following reproduction traits: number of inseminations per conception (AIS), service period (SP), age at calving (AC), calving interval (CI) and birth weight (BW) is studied. The research involved dairy cows of European type of Black and White cattle which are being intensively improved by the genes of Holstein - Friesian breed. Mean values of general average for number of inseminations per conception, service period, age at calving, calving interval and birth weight are: 2.00; 98.78; 1088.08; 376.70 and 36.40, respectively. In general, the estimated phenotypic correlations (rp) between the milk yield over standard lactations and fertility traits were positive and unfavorable, and ranged from 0.24 for the relationship between milk yield and birth weight to 0.70 for relationship between milk yield and age at calving.

Systems of cattle housing

In intensive milk production particular attention is given to genetic improvement of cattle for high milk production and high quality of milk. Such trend should be followed by improvement of non genetic factors through technology and management. This is related to up to date solutions for high milk production, better cow reproduction, increase of productivity, better working conditions, better housing, efficient health protection and hygienic conditions, better technology of cow feeding, etc. It is known that two systems of cattle housing are present: free stalls and station barn with a number of modifications, among which the frequently mentioned one is semi-free stall as a combination of the two basic ones. Some variations within two systems are due to farm, climate and other differences. Based on a number of investigations, it is found that station barns have some advantage when milk yield is considered, while free stalls have preference when the reproduction of cows, productivity of labor, health protection and longevity of cows are considered.