Influence of Lactation Number, Year and Season of Calving on Milk Productivity of Cows

Abstract

The main characteristics of the milk productivity of Holstein dairy cattle differ in different countries due to differences in terrain, management and breeding objectives. At the same time, the manifestation of non-genetic (that is, environmental) factors during milk production, as a rule, mask the real breeding value of animals. The main goal of this study was to analyze the influence of lactation number, year and season of calving on the milk productivity of 238 Holstein cows during a 4-year period (2014-2017). The study was conducted using primary data on the dairy productivity of livestock in the conditions of PJSC Plemzavod Stepnoi of the Kamian-Dnipro district of the Zaporizhia region.The following characteristics were evaluated for each animal: duration of lactation, hope for 305 days of lactation, hope for the entire lactation, fat content and protein content in milk. P. Wood's model was used to approximate lactation curves within each subgroup. All signs of milk productivity were analyzed based on the algorithm of one- or two-factor analysis of variance with fixed factors using the statistical package STATISTICA v. 6.0 (Statsoft Inc.).Lactation number was found to have a significant effect on all milk yield traits that were examined (in all cases: p<0.001). Hope for 305 days of lactation increased with the growth of lactation number. The highest values of this characteristic were noted during the 2nd and 3rd lactations. The lowest estimate of milk yield for 305 days of lactation of dairy cows of this farm was obtained in 2014, and the highest in 2016. The calving season probably influenced the indicators of milk productivity (primarily, the content of fat and protein in milk) of firstborns. In addition, the milk yield score at 305 days of lactation was lower among winter- or spring-calved gilts compared to fall-calved animals. No influence of the calving season was noted among adult cows. Lactation number and year of calving probably influenced the estimates of the coefficients and parameters of P. Wood's model. The shape of the lactation curves of firstborns was flatter compared to mature cows. Estimates of peak milk yield were lower, but the index of constancy of the lactation curve was higher during the 1st lactation. Thus, we found that obtaining real (unbiased) estimates of milk productivity traits of Holstein cattle requires preliminary adjustment of data regarding the influence of lactation number, year and season of calving