Live Weight Changes, Feed Consumption, Milk Yield and Energy Balance in Dairy Cattle during the First Period of Lactation

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Abstract
The purpose of this study was to estimate any breed differences and to investigate the interrelationships between live weight changes, feed consumption, milk production in kg energy corrected milk (kg ECM) and the therefrom calculated energy balance with emphasis on the first part of lactation. Altogether 508 lactations were studied for 153 cows from the same herd in first to fifth lactation of the following Swedish dairy cattle breeds: Swedish Red and White (SRB), Swedish Friesian (SLB), reciprocal F1-crosses of the two breeds, and Swedish Jersey (SJB). The gamma function (Y n=an b·ecn) was fitted to each animal's records in order to derive secondary traits from the functions. A Mixed Model Procedure was used to estimate breed and parity effects and variance components. The average goodness of fit to the function, as assessed by the R 2 value, was best for milk production data, followed by feed consumption, while lower R 2 values were obtained for live weight changes and especially for energy balance data. The frequency of atypical curves was also greatest for the latter two traits. On average, minimum body weight was reached about 2 months after calving, the average weight loss being 15 kg. About 75% of the weight loss was regained around 4 months after calving. Average maximum yield in kg ECM was at about 3–4 weeks after calving. A large variation in accumulated energy deficit after calving (x=269 MJ, SD 409 MJ) was obtained, and accordingly a large variation in days after calving for energy balance. On average, however, cows were in balance 3–4 weeks after calving. Breed differences were statistically significant for most traits and parity significantly affected all traits. The highest repeatabilities (0.46–0.57) were obtained for 120 and 305 days ECM, maximum milk yield and max. feed consumption, while repeatability estimates for days until minimum weight and max. ECM production were the lowest (0.05–0.09). The phenotypic correlations followed an expected pattern. The sizes of the correlations between weight losses and energy balance and other measures were so low however (-0.12–0.26) that there was considerable scope for factors other than those studied to influence the relations. In general, there was a closer relationship between energy balance parameters and milk production than with weight changes and feed intake. Correlations between different time variables, e.g. days after calving for max. feed consumption, max. production etc., were low, as a rule. The observed relationships could have been influenced by the feeding regime. The cows were fed concentrate according to milk yield and a constant but live weight dependent amount of roughage.