Comparative evaluation of the impact growing heifers and feeding cows on milk yields

The results of studies on the influences of heifers growing intensity and the level of feeding cows on milk yields in the highly productive herd of Alfa farm are presented. The mechanisms and patterns of this influence have been clarified. The data for the research were given on milk yields, feed consumption and heifers growing during different periods of farm functioning. In particular, these indicators were monitored in two three-year periods: the previous one - from 2007 to 2009; and the next one - from 2012 to 2014. The dynamics of milking and the main indicators of feeding and growing of young animals for the previous and next periods were analyzed. Using the analysis of variance, the significance of differences between milk yields, the level of growing and feeding in different controlled periods was established, as well as the degree and characteristics of the effects of the period on these indicators. A stepwise multiple regression analysis was used to develop a model for estimating milk yield on cows' feeding rates and heifers' growing intensities, using as a dependent variable annual milk yields, and as independent variables, different feeding and growing indices. It has been found that milk yields for feed cows in Alfa increase over time. Thus, with average milk yields in the previous period (2007-2009) 6062 kg, in the next period (2012-2014 years) they increased to 7838 kg, ie by 1776 kg. The degree of influence of the period on milk yields is η2 = 88.2% (p = 0.005). The impact of the considered periods on the average daily increase in heifers is η2 = 72.3%. At the same time, the average daily increase of heifers' live weight changes from 640 g in the previous to 817 g in the next period, or by 27.7% at the significance of difference between the periods (p = 0.032). The dynamics of feed consumption for feeding cows during the analyzed period had a positive trend. In particular, at 2012-2014, the level of cows' feeding averaged 80.4 centner feed unit per cow per year, and compared to the previous period it increased by 17.2 centner feed unit (27.2%). However, this difference is not significant (p = 0.083). Another important controlled indicator of feeding is the amount of concentrated feed consumed. It was found that the percentage of concentrated feed in the structure of ration increased from 32.6% in the previous to 36.9% in the next period, although this difference (4.6%) is not significant (p = 0.267). An accurate (R2 = 0.999) and significant (p = 0.001) regression model for predicting milk yields has been developed based on live weight of heifers at the age of 18-month and proportion of concentrated feeds in rations. The live weight of heifers at age of 18 months has a much greater impact on predicted milk yields than the proportion of concentrated feeds, as recorded by differences in the standardized regression coefficients β for these indicators (0.885 σmilk yield / σlive weight versus 0.230 σmilk yield / σ% concentrates, respectively).