Live weight changes during lactation in Montbéliarde cows

© Slovak University of Agriculture in Nitra Faculty of Agrobiology and Food Resources

The data (milk yield, live weight) was obtained through AMS (Lely Astronaut). For the sake of our analysis, data from the 4 th to 7 th lactation cycles were merged into one group (Table 1). For the assessment of changes during lactation, data about live weight was divided into 10 sections, 30 days each (Table 4). Collected data was statistically analysed. The dataset was analysed by the SAS statistical software. Significance of effects and differences between means were tested via the analysis of variance procedure PROC ANOVA (post hoc analysis using Tukey test). Statistical significance was tested at level of significance α = 0.05. Procedure PROC REG was used for estimating of regressions coefficients.

Results and discussion
Our data, as presented in  Chládek et al. (2001). The live weight of 699.94 kg is very similar to the number reported by Gruber et al. (2018) for the Fleckvieh breed -702 kg. A lower average live weight of 654.9 kg is reported in the Holstein Friesian cattle by Toshniwal et al. (2008) and even lower live weight of around 540 kg was reported by Mlynek and Glowinska (2020) in the same breed in different stages of the lactation cycle. The changes in live weight and milk yield are depicted in detail in Figures 1-4. From the data collected we can observe that in all Figures an expected rapid increase of milk production takes place at the beginning of the lactation cycle, which is also accompanied by a distinct decrease in live weight. This happens regardless of the number of lactation cycle. This finding is in order with the findings stated by Soyeurt et al. (2019) and Alawneh et al. (2011). In their cases the decrease of live weight also culminated during the first two months of lactation.
Each of the Figures also shows a constant increase of live weight after the 60 th day of lactation. This increase is more distinct mainly during the first, eventually the second lactation cycle, being the period in which the cow completes the physical development. This tendency is confirmed by Soyeurt et al. (2019) and Alawneh et al. (2011). Figures 1-4 also show that the development of live weight during lactation in first-calf heifers is distinctively different (both the increase and the decrease are more abrupt) from that in cows after more lactation cycles. Similar trends are described by Toshniwal et al. (2008) as well and they are similar to the trends in milk yield (Kopec et al., 2013).   Course of milk yield and body weight during third lactation

Figure 4
Course of milk yield and body weight during fourth and higher lactation The data also show (  The numbers on live weigh minimum and maximum found out in this research correspond to the numbers described by other authors, for example Toshniwal et al. (2008), Soyeurt et al. (2019) or Alawneh et al. (2011).  Table 4 shows the average data on cattle live weight during different stages of the lactation cycle. Through this data we can observe a statistically significant decrease of live weight in the dairy cattle up until day 60 of lactation. On the contrary, the changes in live weight during the last 60 days of standardized lactation proved to be inconclusive. Between days 60 and 240 of the lactation, an increase of live weight of varying intensities was observed, mainly in cows who had undergone less lactation cycles in the past. An initial decrease along with the subsequent increase of live weight in different stages of lactation, similar to the data collected in this research, is observed by Mlynek and Glowinska (2020). Similar trend was also documented by Toshniwal et al. (2008) and Soyeurt et al. (2019). This research has observed a conclusive impact of the number of lactation cycle on the dairy cattle live weight (Table  5), mainly during the first, second and third lactation (645.21 kg, 700.35 kg and 752.10 kg respectively). However, no significant change in live weight was measured between the third and further lactation cycles. The trend of live weight increasing with every lactation cycle was, according to Ledinek et al. (2019), apparent from the 649 kg during first lactation to the 744 kg during the fifth and further lactations.

Conclusions
The changes in live weight during lactation can be used in dairy management. To observe the development in live weight, this research used automatic data collection via AMS. The observed herd of dairy cattle had the average live weight of 699.94 kg per cow, the average daily milk yield of 33.67 kg of milk per cow and the average day of lactation was 111.75. Based on the data collected, we can state that we observed a significant decrease of live weight up until the 60 th day of the lactation cycle. On the contrary, the changes in live weight in the last 60 days of lactation proved to be always statistically inconclusive. Between days 60 and 240 of the lactation, an increase of live weight of varying intensities was observed, mainly in cows who had undergone less lactation cycles in the past. Similarly, the research proved an influence of the number of lactation cycles the cow had undergone in the past on its live weight. In cows going through the first three lactation cycles, the overall live weight increased with each new lactation cycle. No significant increase of live weight has been proven between the third and further lactation cycles. The data collected shows that the physical development in high-production dairy cattle continues even during the third lactation, which we propose should be taken into consideration during optimisation of their breeding management.